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Design of a Composite Link for the Freedom-7 Haptic Hand Controuer

by

John McDougall

Department of Mechanical Enginee~g

McGiU University, Montreal

A Thesis Submitted to the Facaiîty of Gtaduate Studies and Research

in Partial Fulnllment of the Requirements of the De- of

Master of Engineering

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A bstract

The Fnedom-7 Haptic H h d Ccmtroiicr is a high pafbmmœ hapic device &velopd

jointly bctween McG'ï and MPB Tcchnologies. This thesis diScusses previous wœk in

the field of haptic devices. the rrsearch into the bcmâing of mctils to Compdsites,

optimization procedures f a Composite hmhtcs, snd iiiclucks a bief ovav*w of human

haptic capabilities. The disassicm imludes the anal* procas d to design a

composite box-kem structure to replace one linL of tbe translation stage of tbc head

controlier, and to &termine the opcimil bond chatacteristics fa tbe joining of a smaU

diameter composite tube to a mail end fitting. Iterative finite element anaiysis as welï as

failure and vibration testing wae u d to dttcrmine tbc efficicncy of the designs. and to

measure the improvemcnts in the dynamic propcrties of the haptic device's structure.

Though certain clifficultics w a e eacountcred during tbe manufktwhg of the prototype

that lead to disappointing physical test d t s . th simulations p v e that a haptic device

such as the Frtedom-7 cuuid grcaîiy benefit !km the inclusion of composite materials

into the structure.

Résumé

Le contrôleur haptique Eieadam-7 est un aispositif de haute @OC~B~MX dévelappé

conjointement entre l'Université McGiU et MPB tachnologit~. Cette Ceac tbtse les

travaux existants sur les dispositif& haptiqucs, les mCthodcs d'dhaaia entre lu

matériaux composés et les métaux, les proddiins pour optimiser la structure des laminés

ainsi que les recherches sur les capacités du système haptique humain. L. discussion fait

part de l'analyse d'une sa~cbrie mcmocoque en fibre de carbanc utilisée pour remplacer

un joint d'alruninium dans k dispositif. De plus, l'opthhtion de la géométrie d'un

joint adhésif entre un tube ai fibre de a&mc et une garniture m aluminium est

expérimentée. L'efficacité du design a Cté Cvaluée par une analyse empirique ainsi que

differents tests mesurant la résistance et la vibration. C a demiers sement aussi a Cvaluer

les am6liorations des amcté&icpes dynamiques dc la stn~cture du dispositif. Cer<ams

problèmes de fabrication nuisent L 1. paf~rmzt~lce du dispositif lm des tests physiques,

mais les simulations par adinatau prouvent qw la possibiiité existe d'accroître

considérablement la penormance avec l'utilisation de matériaux avancés.

This work is dedicated to sevaal p p s ofpeop1e, without wh- SU- it neva

wouid have ban completed To my parmts, fa @ng me hat. To my fiends for

supporting me. To Rof. Lamy Lessard fœ ptting up with m. And to Emilie fa king

them for me.

Thanks must also p to Rof. V i t ILyward fa initiating the Freedom- 7

project. Also, to the peopie at MPB Tdmolqks, Dr. Ln Sinciair, Smdcr Boclm, a d

Jean Pouiin for ali thtir help in the initiai stages of the projcct. S@d thanlu must a h

go to Dr. Diao Xiaoxue for his invaluable help at th end of the pmjcct-

Table of Contents ............................................................................................... 1 . I.ntroduction to M o m - 7 1

1.1 Haptic Devices .......................................................................................................... 1

1.2 Requircmcnts for Haptic Devices . ................. ............................................................ 2

1.3 Advanced Matcrial Advantages .................... ............................................................ 4

1.4 F d ~ m - 7 ................................................................................................................. 5

. 1 5 Objectives of this thesis ........................................................................................... 11

. ....................*....*......*..*.*......................................................*............. 2 Litcrame Review 12

....................................................................................................... 2.1 General Haptics 12

........................................................................ 2.2 Literaûuc Review of Bonded Joints 17 . . . 2.3 fiterature Review of Iamhate Optimur mm. ......................................................... 23

............................................................................................... . 3 Design of Bonded ni- 29

3.1 Introduction ............................................................................................................. 29

3.2 Material Survey of Composite Tbbes ...................................................................... 29

3.3 Geometry and Parameter Variation of B4aded Inscrt~ .......................O...................e 33

3.4 Axisymmetric Fmite Element Modcls .................................................................... 34

............................................................................... 3.5 Results of Parameter Variath 36

3.6 Three Dimensional Finite Element Mode1 ............................................................ 43

4 . Bonding Tests .............. ..................................................................... ................. 4 9

4.1 Three-Point Bend Test ................... ....................................................... 49

4.2 Calcuiaîions for Bending Moment Load Case ........................................................ 51

4.3 Test R d t s ............................................................................................................. 53

5 . Design of Box Beam ..................................................................................................... 56

5.1 Introduction ............................................................................................................. 56

5.2 Dimensionai Requirrments f a the Box Bcrm .................................................... 56

5.3 Finite Element Mode1 of the Disral Stage Lhkage ............................................... 58

5.4 Results of Fite Eletnent Modd ............................................................................. 60 6 . Box Beam Prototype ..................................................................................................... 61

.......................................................................................... 6.1 Carbon Fiber Box Bcam 61

6.2 End Fittings ........................................................................................................... 65

.......................................................................................... 6.3 Bondhg of End Fittings 66

................................................................................ 6.4 TCSU an Fnedam-7 67

6.5 Frequtncy Respawc ofTransiatio(1 Stage .............................................................. 68 6.6 Refied Fite Element Mode1 of Distal Style Linkagc ......................................... 71

6.7 Maximum Acctlaati011 test^^^^^^.^^^.^^.^^^^^^^^^^^^^^^^^^^^^^^^^^^ 76

6.8 Summary for Box Berm Protdyping and Testing .................................................. 77

7 . CO~C~US~OLIS and R ~ C O ~ T T I S ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - ~ ~ ~ * ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ * ~ * ~ ~ ~ ~ ~ ~ ~ * ~ ~ ~ ~ * ~ ~ ~ ~ * 79

7.1 Rccommendaticms fbr Futme W d . . ...................................................................... 80

8 . Bibliogxaphy ............. ..................................................................................................... 81

1 . Appendix A ................................................................................................................... 9-i

2 . Appendix B ............................................................................................................... 10-ix

McGiii University Depamxms of MacbraicJ h g b u h g

Table of Figures Rgun 1.4.1 . PHANTOM .................................................................................................. 5

......................................................................................... Figure 1.4.2 O PER-Force device 6

Figure 1.4.3 O SARCOS dcxtcrais mn ................................................................... 6

Figurt 1.4.4 . Large W- IIud m&ok (LWHC) ................................................ 7

............................................................................ Figure 1.4.5 O S W S Hand Controller 8

Figure 1.4.6 . Frredom-7 Translation Stage ........................................................................ 9

. fi gui^ 1.4.7 O M m - 7 Distd St-6 ........................................................................ 10

...................................................... Figure 1.4.8 . The Frecdom-7 Haptic Hand conar~Uet 10

.............................................................................. Figure 3.2.1 O High-tech Arrow Shifts 30

Figure 3.3.1 . Bond Geometry for Parameter V a 0 1 1 .. ............................................ 33

Figure 3.4.1 . Axisymmtnc Fuite Elcmcnt Mode1 of Baided Geometry ....................... 34

Figure 3.4.2 . Rcfercnce Locations on Bond Geometry .................................................... 35

Figure 3.5.1 . Variation of Peak Rincipai Stress with Ad- Wail Thiclmess ............ 37

........................ Figure 3.5.2. Variation of Peak Rincipal Stress with Axial Engagement 37

Figure 3.5.3. Variation of Peak Principal Stress due to Bood Linc 'Ihickness ................. 38

Figure 3.5.4 . Maximum Principal Stress Contours in Epoxy Matairil fol

Test 1.4 (Bond AD Broken) ..................................................................................... 38

Figure 3.5.5 . Maximum Rincipal Stress Contours in Epxy Materhl for

Test 1.1 (Bond AD Exists) ...................................................................................... 39

Figure 3.5.6 . Maximum Rincipal Stress Contours in Epoxy Material with

Epoxy Fiet for Test 1.3 (Bond BAD Exists) .......................................................... 39

Figure 3.5.7 . Variation of Rincipal Sûes Along Bond due to Adberend

Thickncss (a) ................... ......................... .............................................................. 4 0 Figure 3-58 . Variation of Rincipai Stress Along Bond due to Bond Lise

Thichess (i) ................................. ....... ...................................................................... 41

Figure 3.6.1 . Three Dimens id Fite Element Mode1 of Bonded Tube

Geometry ................................................................................................................... 43

McGiii University Deputment of Mtchnicrl pjimmcnnr . .

Figure 3.62 . Maximum Rmcqioi S c r ~ Ccmtaars in Compaitc Tiibe

Close to Bondcd Region *..............**.~.....~.*~.......*.*~.*.....................*...*......................... 45

Figure 3.6.3 . Maximum Phcipal S m Coafouft fa B o d d F~ce of

....................................................................................................... Aluminm IIISCrt 46

Fiw 3.6.4 - Maxim- Principal Stress Con- in Epoxy Bond M.rcri.l .................. 47

Figure 4.1.1 - Sketch of thme-point buxi test wtup .......................................................... 49

Figure 4.1.2 . The-point bcnding test sprçimen ............................................................. 50

Figure 4.1.3. Variation of dimensions f a t h point bcnding tests ................................ 51 Figure 4.2.1- Shear and bading mmicnt diagrmm fa ibrrapoint kadmg tests ............ 5 1

Figure 4.3.1 . Graph of piston f a a va centexpoint displaccmcnt .................................. 54

Figure 4.3.2 O Broken thte~point bad rprcimm ............................................................ 54

Fi- 5.2.1 . Clearance area foi the distal stage driving Sazags ................... ... ............ 57

Figure 5.2.2 . Exploded view of cabon f i k distal stage assembly ................................. 57 Figure 6.1.1 . Time-tempcraturie Profile fa LTM25 Cure Cycle .................................... 62

Figure 6.1.2 . Lay-up Rocedurt for Composite Box-Sectim ........................................... 64

Figure 6.6.1 . Rcfined modcl of dist.l iinkagt for vibration simulati 011 ........................... 71

Figure 6.6.2 . Renned finite elemait modcl of distai linlrage with addd

cover for vibration simulah'011 ........................... ........... ........................................ 72

Figure 6.6.3 . Normal mode vibration in x direction of disîai stage with an

added cover ..................... ... ............................................................................... 73

Figure 6.6.4 œ Normal mode vibration in x direction fa u n c o v d distal stage .............. 73

Figure 6.6.5 . Stress contours in u n c o v d pilky btock base ...................................... 75

Fi- 6.6.6 . Stress contours in covasd puilcy block base .................... .................... 75

McGiU University Dcpucmnt ofbfdmid- . .

active DOF - eny DOF that can ex- r face or tmpc cm tbe usa's haad / body

uctuation dime1csio114Jity - tbc n u m k of active &pcs-of-- in the &via

adherend - the part of a bonded joint thaî b bejag glued

adhesive - the glue holdmg the two adhemds togetber

actzutor - any systcm to c01lvty torQuc a fcrce to a part of th mbatic device

buckdn'veuble - the abiLity to move a M c structpre by applying fara to tbe end

effector without any aiding joint torques

bucklash - small movcments in btMngs aad otba joints

bi-directional - a &ta Stream that fiows in two directions, i.t. rcad and w r i ~

bond Iine thickss - the distance betwccn two a d h d that is fillexi with adhesive

construined impedrutce - innnitc stifhess contact

crispness - subjective tam m f e g to the quality of a sensation felt through a haptic

interface

cure - the process of hcating, prrsourizing ancl then cooling an cpoxy to change the stnte

fkom liquid to soiid

degrees-of-fieedom (DOFI - the numbcr of dircctiolls in which a device is fkcc to move in

either translation or rotation

device intrusion - physical prcscnce of the haptic device in the operator's W-

engagement - the length of the adbesive bonâ

fidelity - the ability of a haptic intcdkc to accurately rrprerient a vlla>al aivuomSnent

fiber ~ r i e ~ o n - the direction almg which the fibcrs in the composite matcrial arc

aligned

haptics - the branch of study derLUig with tbe human sense of touch

marter robot - a robotic structure that controis through teieopcraticm motha robot

m o u - a rigid tool used to fam the imaMd composite rmPBii1 into a useabk sbripc

siàve robot - a robotic structure that is controiied by anotba robot or hand amtroUcr

teleoperution - action transmittcd ova a distance by an electronic signal

1. Introduction to Freedom-7

1.1 Haptic Devices

In the short span of twenty yr03, the computcr has gone fran an expensive.

novelty item to an essential tool that can be famd in ail walks of lifc. 'Lbe gains in

computing powcr have ban aiormous: early gcnerations of cornputers wcrc the sizc of a

r o o m a n c o u l d d o l e s s t h a n w b a t m o s t ~ a f c h c a l ~ d o ~ y . Thisquantum

Ieap in speed and capability. as weU as an mcrtrsmg danand foc hi@ s p d pcass to

idonnation, has contributcd to the incursion of the cornputer into every aspect of our

lives.

With the inCrrascd spssd of compufas. users can exist and interrt witû virtual

environments that woald have aai impossible to imagine only a dccde rgo. A viiai91

environment is a amputer quivalent of the reai world It can bc anything from a flight

simulation to a museum, w h m the user can browse thraugh thmszl~lds of rare painthgs.

The one thing about the vutual environment that remains constant is that it does not

physically exist anywherc except as a coiiection of 1's and 0's in the b ' i memory of a

computer.

Where btfote p p l e couid d y expaiare th*re m a l environmcnts ihrough

sight and sound, with the intmcluction of a varicty of haptic devices they c m now explore

with the sense of touch also. Hhptics is th branch of psych010gy that deals with the

cutaneous sense data, in otha words the data tbat is transmitted to the brai. by the

pressure receptors in the skin. 'Ibmfm, a @tic device is a &vice that will translate

cornputer signals into prwsun a face on the usa. The slan prwwirr that the user feeLp

fkom the device, wmbined with the visuaï and auditory inputs fmm the vir&uai

environment, crcate a -ter sense of bcing inside the envinrnmcat gc11eratcd by the

cornputer.

The haptic device is a bi-dircctional interface [l] between the human user and the

computer. It has to k able to accept usa @ut as welï as deliva its own àata output

back to the user. Ibe &CC~~VCIICSS oftfiU delivay % what udl dintraia'str! a "good"

haptic &vice h m a "badn au. HOWCVQ, detumining the qculity of this delRmy is not

assirnpleasitseems. T h c ~ t s f a h r p i c & ~ r r r d i t f i a e D t ~ o t h a

robotic applications. For clarity, a set of texms wiii be urtd to describe the gencrai

attributcd of ai i hand ~~~~trol îcrs:

DOF - & m f - f i e e d ~ m

hand controller - MY &vice thit â~ ui htafsce the US^ rnd

virtud enviranmcnt that is htcnded to be uscd by an operator's hand

a ~~~riveDOF-&~f-fi.eedomaiwbichthachfaaaatsdbythW

controller

a octuam - my focce or toque applicator

end-ejJiector - point at which the interfact bttwcc~l hwnan operator and hand

controilcr occurs

FFB - force ftedback

1.2 Requirernents for Haptic Devices

The earliest &tic devices wac designcd to give i a f d o n to the usas about

force states in the rai environment that they wert conttolling. Thcse k t FFB devices

were connectai physidy ta the remdt environmcnts by mechanical IinJcagcs such as

wires. For instance, in the bippluvs of Wodd War I, the pilots d d feel the faces on

their control surfaces tnulsmitted tbrough Qu flight control sticks, making the wntrol

stick into a haptic dtvicc [2]. The first genaiPon of -tic d e v i a ~onneard

electronidy to a nmote cnvvOnment t a c deviscd fa use in the nuclcar industry, to

enable operations to be carricd out in extttmtly hazadous enviraamcnts [1,2]. TheSe

devices consisted of dymmicaiiy identicai nuaster and s h robots, since the comp~ting

power at the time was not mfficicnt to calcuiatc extensive trandormatio~ls bctwœn the

two. The master =fers to the contmiihg device, and the slave refcts ta the mate

device.

In a virtual d t y application, the most important conccm is whctûcr th opnta

fbels lilre hdshe is r d i y inside tbe enviraimmt [3-'11. Ifthe virtuai cnviromneiit sccms

resolution of the device Cl], due to the limitai capacity of the human scnsory sygan to

absolutely locate a given point in space. Resolution is the maximm defiection about a

stationary point that the &vice genartes at an upilibrium statc. A vibratory dcflcction

caused by the conml systcm, irtuua ined#luacies or structurai Wts kreascs the

transparcncy of the hand colltroilcr.

To achieve transparency in a haptic device like a hand cuntrollet, tbae arc several

key requirements that need to be met. Fust, the structure of the hand contdler mua have

a very low inertia If the opaata is moving h g h h c s p x h i d e the cornputer, they

should not feel a large mass of the hrad cunaolla rcsisting h i . rnotiolls. Tbe low

inertia of the coatro11cr must k couplal with an almost constant and diagonal inertia

tensor. Achieving an inat* tcnsor that is constant and d i a g d wil l aiiow the inertia felt

by the operator to be equd in alï configurations of the hand controller mechanism. 1t wiîi

not seem heavier or lighter towards the edgcs of the wodcppw than it does in the middle.

Furthermore, a low linlt inertia will incrase the crispllcss of such FFB sensations as

impact with an immovblc wall- Minimizing the link inatia wil l incruise the maximum

acceleration that a given actuators can aeate at the end effcctorr. The s a m d requircrnent

of the structure of the hand controiler W link stiffiiess. The sti&r the links, the grtater

the dynamic benefits. The ramant iutursl fiequcncy of a sûuctun is depmdmt on its

stiffiiess: the higher the stiffiress the gMta the naairal fiqucncy. With stifftr links

comprising the structure of the hand conîmiier, hi* frcqucncy phcnomcnon such as

working a drill or scratchhg a mugh surface Mth a pencil can k simulrtcd without the

danger of rcaching a nsaiant frcquency of the stmcturc and inducing vihtion- As the

vimial pointer wmcs into contact with a solid wali, tbe cornputer QC&S to sample the

pointer location and calculate a joint face consistent with the proximity to the walL To

achieve thefidelity of such a simulation, the rrspaisc of the controller must be at a vay

high frcquency, on the order of #)O Hz.

McGill University Deputmcnt of Mechrnicrl- 3

1.3 Advanced Material Advantages

ïhge arc -y advmtagcs to the incapoiriion of dvmced Compogite mmeruls

into the dcsign and COIlSfNctioa of a haptic hand controiicr. Whm designers rcstrict

themselvestotraditidmstn;als,tbaeisaIunittoth~gnc~~ttUtc~ibermide

to op* lhk stifnie9p to wcight d o s . Fbr ( n d i t i d mrta.lr such u rtrel rid

duminum, the stinness and dcnsity aze constant. liaevitaôly, c o m p m k h a hu be made

in one of the design arcas.

With the in- utic of dvraced composite muaiils in mauy areas of

industry, the design toob fot applying Uvst matcri& arc becoming m a c avulrble. As

designers becorne more dortab le w&g with tkoc materiais, mon advantages

btcome apparent The ability to tailor the mataiai m e s of a laminate f a a spccific

task is unique to this type of matairl. A designer a n optimize the rmtcri.l in a iobotic

link for tcnsile moddus a d damping [8-141, two propcrties which are arasslrily nxed

in traditional matenalS. Designers are no longer rcstricted to madifications in the 1uiL

cross sections to obtain dcsmd results fa l ia dynamics.

1.4 Freedom-7 mm alnady e* scvctal makis of h;ipic &vice5 that are u!Bd specifically fa

vilaial nality applicaticms. Thy cm be divided into thcc categdcs- Tbe &st is the low

W F (dtp-of-frieed~m) dence$. 'Lbcse ae haptic devices thubm bi-diractid data

flow on three DOF's or less. They includt th PHANTOM (13.S. 15.1q &via

1.4. l), which is active in the thme trauslatid modcs aad has a thriee DOF rotationai

gimbai attached to a thimble that can k woni on tht user's index tinger. The Pantograph

[1,16,17] hasonlytwoactivettanslatidmades. WorkhaskcndcmeatUBCto

include a third active rotational mode to the Pantogmph [l]. As weU, severai haptic

applications have used muiitple Pantogmph uni& simdtancously to obtain mcrecised

active DOFs [lq. Th- arc scvcxal FFB joysticks on the market such as the immersion

Corporation's line of Irnpuise Sticks [18]- Tbtoe devices can d y provide an eshate of

the cask that the operator @onas in the vixtuai mvllanmcnt. Tbey am not sufficieat to

fully simuiate a reai system.

Figure 1.4.2 - PER-Force &vice

McGill University De- of Mechrnicrl E q m a m g . .

in the case of tbe PHANTOM &vice, the simuhW eavirainrent j8 siniilm to a

point probe. The user can invcstigatc the vimul mvinrmuiit in the thcc C M c s h

directions, but hPS w active rototicmai DOFs. This limits th vrricty and b of tbc

interactions that the user can have witb tbc mmote mvirarment,

The high DOF devices have enough compiexity to M y .imulra an interaction

with a virbal environnacnt. lhey do nut nœd to appmximate a ta& but cm rcpmcnt it

Mly . Examples of these high DOF devices am the Texas 9-string and the SPIDAR-I&

both stringed haptic i n t e r f ~ [lq. the PER-Fm joystick h m Cybcrntt Systcms Co.

[lq (figure 1.4.2). mt SARCOS tkxtawis a m masta (figure 1.4.3). and the FREFLEX

Figure 1.4.4 - Large Worksptace H4nd C ~ o l k r (LWHC)

McGiU University Deputment of Mechrnicrl Engmemg . . 7

exoskeleton mastem, among many others. T'hcsc FFB devices ail have several

drawbacks, the most cornmon of which is high complexity anâ inmision into the user's

workspace [la. Revious work by MPB anci Maiill d t e d in two high DOF hand contmiiers.

Tht first was a large worlcPprce h a d wntroller (LWHC) [6,19]. It comistd of a 3-DûF

rotational wrist mounted on a 3-WF translational stage (sec figwe 1.4.4). Large fiction

loads consistent with cxtrrmely ovcr1CIIYlCA bearings war dctrimcntal to the patimnance

of the LWHC. Another device caosc~cted at McGiîi was the cantilevd HC d e d the

STYLUS 119 1. The distal stage of this mode1 was surpendcd from the end of a jointed

aiutilever arm(figurt 1.4.5). The major drawback to this coz~troiîa was the static load on

the driving strings gentratecl by the gravity vecta. nie high moduius polymeric strings

required to drive the force feedback of the ccmtroiîa are prone to CL~CCQ. 'Ihis

configuration would themfoct k macccpW1e foi a production model

e 'TbeFreedom-7~~0lltro~irtbrlaerrhi~DOFhnd~odlatoemage

from the coqmation ktwœm MPB d Maiill [l9]. Xt has si% active DOF in the

translation and r o t a î ï d modes as weU as an o p t i d active scvmth DOF at the d

effcctor to simulate a plimgcr a a pir of sehom. 'Lht ttat paaypc, which exists in

an aii aluminum forni, solves the p b l c ~ l l s with th previous two prototypes.

The paraiiel design of the ttruislatim stsge (fi- 1.4.6) d œ ~ not rsquirc the hi&

modulus fibers for actuation, and they arc d c t e d to the ricbidtim of the distal stage

only. Low fiction, bush-1ess DC matcm m used as dinctLdiive acmitas on the

translation stage and aiiow fa -g of the grivicy f- vectar. An Mpn,ved

design of the distai stage ( f i p 1.4.7) IC~UCCS the incrtia felt by the opera-. Simple

tendon paths make assemb1y easiet md d o w for zero faa on the fibas at a@i'btium.

eliminating any creq d e f d m . A schematic of thc ursmibly of tht Fntdom-7

hand conttroiicr can bc sœn in figure 1.4.8.

1.5 Objectives of this thesis

niere exists two avauer f a improvcmcnt to this design thrt will be imdaraLen

in this work The f h t h to replact tbe stage 3 hbgc (figure 1.4.6) by a srmll diameter,

commerciaiiy avaiiable carbon f i k tube with boidcd mail insats. Second, the distaï

stage linlrage (figure 1.4.6) udi be rrplwd by 8 composite box-btam stnicbre. ?he

purpose of both these hclusions is to hcmaw the stühcss of tbe d t i n g sûucture while

decreasing the iink mas and inatu Howevcr, incranentai impovements of the

dynamic chanictenstics of hsptic devices need to be mcppurrd bascd <ni Specinc

pe~ormance criterion that do not correspoad neccssarily to those used fot traditional

robotic applications. As mch, propet mawmmmts have to be made to detam.int the

overall efféct the incorporation of advmced mstaiils hto the structure has on the

performance of the haptic device.

The foiiowing nsurch topics arc assocbd with the design and inclusion of

these two parts in the F d o m - 7 hsptic hanci controllcc

nieory and application of pmpcr end fixtures, i.e. propa design of composite

metal interfaces wiU k addrcssad. The design of the mral imerts wiU k optimjzcd fa

several basic geometric crittr ia

ïay-up choicc far the opthhtion of a bax. beam stnicturc will bc examined.

The choice of a lay-up fot composite parts can be @y af5cctcd by the applied loed

conditiolls.

optimization of composite parts for hi@ natunl frcquency and high damping

wiU be performed. The haptic hand controlk iaquins a vay high bandwidth, likc many

other potential applications for composite materials.

,Testhg of bonded joint strengîhs in bending wii l bc @annad. This testing is

m l y scen in the literaturc, whac the most cornmon foms of losding for a c m cross

section joint art torsion and axial.

Application of pmpcr test methods to dctcrmine prfamance characteristics of

haptic devices wii l be performcd. Thae is vay litilc in the way of serious pafbmmce

criterion for heptic devices, a d this topic shouid be ddrrsscd in ada to simpiify fiuther

work in this field.

M a University De-& Mecbrnicrl- . . 11

2. Literature Review

Before any action h taken to optimize the construction of a haptic devia, several

questions nttd to be auswctcd, F i of di, what factars wil l contri'butc most to the

improvcment of the devia? In [Il, Hayward md Strmg plnpose s c v d d i m t

performance muwns that can k usai to qyantitativcly detamirie the sUndard of a

haptic device. These measurcs include degrces of fieedom associated with the device

(actuated and non-actuatd), the type of device-body intcniiot, the range of motion of the

device. peaL force, incrtia and damping d pcak acce1eraticm. Howevcr, many of meSc

characteristics can be subject to M i t inttrpretatio~ls; ffa hstancc shodd the incrtia be

measured h m the point of view of the actuatars a the user, a d does the peak fora

mean the maximum actuator fofct, the hi- transient foife that can felt by the user, or

the maximum continuous fonx that can be applicd by the end efféctor? 1t becornes vay

important to &termine which factor wiU most af5ect the cvcntuai ~~a of a device

because expensive incremcntal improvcmcnts to nmdt ica i factors wili not serve to

increast the feel of the device.

The authors of [l]. H a y w d and Astley, suggest that the most important

characteristic of a haptic interface is bidimctiomlity. Tbe haptic chamel, as a human

sense, wiii both rcccive input fnnn and give output to the cnviranmcnt, Thercfort, any

device that sceks to use this sensory c h e l mua k b i d i r c c t i d as weU Achieving

both re!ading and writing of haptic M ' i o n by a mechanid dena rrquircs a design

that accounts for the inhacnt Limitations and capabbilies of the human haptic organs such

as the fïngertips, han&, and arms. In [2]. Durlach and Mavor d e w a p a t d d of woaE

that has been done to measme the sc~lsing capabilitics and limits of the human saisc of

touch, including both the hand and the arm. Though a full c-cm of the humui

sense of touch is weil beyond the scope of this work, certain clcments of prcviais wark

can be used to help detexmine rneaningfbi criterion fa the pafbrmmce muuns and

design goals of aie haptic inftnace. The human haad has 22 de- of fiaedom of

McGili University Deputmnt of M d m k d Eqummg - . 12

locatcd under the surfsce of the aLia Haptk opaatiocls arc divided into two ategorics.

ezphation and muùprrcetion. Exploration is dominrted by thc scmmy systcm located in

the skin, and serves to detamine the rmtcrkl and texturai pr0Peatic.s of the objea king

exploreci. Manipulation is a motor d o m h t d aperation tbat c01lsiscs of modifying the

environment thmugh the exa<im of faccs ai an objcct, and quires bi-directcmality of

the data seeam for succcssM ta& completion. Iae haptk data strecim itself can à

transmittcd by the neme endings under the skin and dominat#l the exploration ta&. The

kinesthetic data refas to the positionhg sauie derived by the I~CNOUS systcm from

information on joint angles and tendon faaa This data strcam wji l obviously dominate

the manipulation tasls. and is the most inîeresthg f a tbe purposes of this w& Any

mechanical design of a haptic intuface wii i be bavily dcpen&nt on the limitaticms of tbe

kinesthetic data nsolution. Of the w& that the authora [2] revicwed, the foiiowhg data

was providd for the ltinestbctic data rcsolution fa the average human:

1. It is possible to dctect joint rotatio~ls of a fiaction of a degree over the time

interval of seconds 121.

2. The kinesthetic saise had a bandwidth on the ada of 20-30 Hz. but goa up to

1 kHz for the tactual data stream [2].

3. The fartber the joint is 6rom the -ter of the body (th more distai the joint)

the lower the sensitivity to absolute joint rotations. 'Ibe methad for dctcrmining this is

caiied the jwt-mticeuûk-differcllce (JND). The JND for the fingcr joints is 2.5

degrees, for the wrist and elbow joint is 2 &grce and f a the shdder joint is 0.8

desces VI* 4. The Liaesthetic sense can detenaine to within 8 patent the différences in

position of a fixai point in space or a repeattcd movement [2].

5. A stiffness of at ltrst 25 N/mm h n c d d for a surface to be paoeived as rigid

Pl

--

McGill University Depurnrent of Mrcbrnicrl bguwamg . . 13

h [ 2 O ] , H a y w a r d ~ p ~ e v i 0 ~ w ~ t h a t w a s d a n e t o ~ t b t e n ~ ~ t o f

these haptic parameters an an eventuai design of a haptic i a t d b . ?be tests w a r

performed in a s u DOF simutrta on various subjacts- The conclusions of these tests

w m that the sensitivity of the subjbns to dUcrctc motions vaKd much 6 t h tbe subjoft's

training. A surgeon had tbc best s a m q discretization. ' I ky .Ira ccmcIuded tht, as the

most demancihg senses wac involved with high fhquency mations, the actuation of the

haptic &vice is much more hportant than its o v d pxecision in absolutt positionïng.

This conclusion is contrary to ~~~tvcntional robotic practice where the end e f f m

positioning is normally of the utmost h p t a m x , evca mae m thm avaiïable joint

toques and Linlc specds. Thus hi@ frcqucncy nsolutioa kfanes an important design

criteria for haptic &vices.

Other rt~earchers in the haptic design a m have come up with rcquirements for

haptic devices. In [3], Massic defiaes the ultimate feedback &vice as a "device . . . able

to apply forces, toques and dermai stimulation to m y part of the hnd" This is

obviously an imwnscly complu ta&. JU81 tbc degrces of hedom of mechanical motion

in the hand, 22 in all, w d d malrc this kmd of haptic &vice ptohibitively cornplex.

Massie goes on to list thrœ s u b m v e munas of a potcntiaiïy z d h b l t haptic device.

They are device intrusion, actuution dimc~lswnuiity andjMeiity. Device intrusion is

simpiy an ergonomic fiuiction of the design. and mliy has littie to do with the dynamic

behavior of the haptic &vice. Actuation dimcnsiOIllility refers to the active numbcr of

DOF's in the &vice. Fidelity is the ability of the haptic device to accurately simulate the

vittual event. To achieve sufncient fidclity in a dcvice, it should ncccwdy k ground

refercnd. If the device is mountcd to a fixed winace such as the floa or a rigid

tabletop, the forces that it will excrt on the operator will cause a teaction farçe on the

ground, not on anothcr part of the aperato~'s body as would k felt fa a body rcfcrenccd

device. This will allow fa a mat nalistic impression of the viraul environment.

However, Massie States thrit a gn>uad based device with long linlrages to a i l w f a a

greater range of motion WU duce the fidelity of the sirnufah'n.

In [21], Lawrence and Chape1 de- the ideai hand umtrolk in terms of

mechanical impbdance, and use this to detcmllae a range within which a non-idcal hand

McGill University Dcparmmt ofhkhmial Enpinacnnp - . 14

controllercanfunctionasanidcllhradccm~Ila. ' ï h c y ~ u e t û a î . ~ t h t h c i d a l ~

controlIer, whtn thcre is no contact crcaîcd in the virtual environment, the user should

feel no force, and that when in contact with 8 v i a w u a ob#r immovab1e obw the

stiffiiess should be infinite. 'Ibey SU- that t h ~ t r m s p i c l l ~ y of th^ tynnn will bê

improved by incrcasing structural stifnwsr rad toqse output of the h.ad ~tro l i cr , while

decreasing link stifhess. Lawrence d Chspel propose two mechanical hpdmces, the

constrained impedunce and the ~~~:onstraillCd inipcdonce, which coaespoad to infinite

stifbess contact and fkœ motion respectively, as two muair# of pdbnmxe for the

hand controllcr. Th unwmtmhd impedaiwr U afimctioa of thc f a a senshg

threshold of the human haptic syJtcm, md the mU-off frcquency above which a human

operator is unable to foilow a sinusoidal input to the h.ad coatrollc~, as well as the

amplitude of this input. 'Ibe simple sinusmidal input b a method of mwwcmcnt that can

be constant for alI haptic &vice$. The value for th imptdrnce required by

any haptic device wiil thcrefoct be vay sensitive the abilitics and training of individual

operators. nie constraincd impedancc for a low kqyency antact situation is a fbncticm

of the maximum masonable f- exerted by the user divided by the kineshetic nsoluticm

of the human operator. At high ficquency, the low hpency f k U x into a mae

complex equation including the same 20Ui)ff fiquency and amplitude for the sinusoida1

input to the human operator. nicrcfm, the constrainad irnpedana for the ideal heptic

device is also very dcpcndent on the Qualitits rad tnining of th aperatat, exoept in ihe

low Çcquency case. A device that bas enough fidelity fa use by a -do11 wodra

would not necessarily f e l good to a surgc011. ït Q possible to detetmint genaally the

haptic scnsing abilitics of the targeted usa population, but to do so Mth ciny &&LEC of

accuracy is almost impossible. Howevcr, we cm assurne fa the p p ê ~ of the Fradom-

7 pmject that, as the target user population for this devia is surgical training [22], the

structurai impedances on the mcchanism wili be v e y demanding.

In [23], Fasse and Hogan a#cmpted to measurc tbe hriptic paaption of a group of

subjects in a methodical statistical way. lbeir rrailts show that thzc is much marc work

to bc done in orda to modcl and mepsure the @tic prception of hunrsns. Two

experimcnts w e n pafcmncd to gage the subjects' ability to ducmmak . . . betwœn

McGili University Depurmmt of Mechrnrrl h g b m b g 15

lengths and angles in virmil rectangles and trhglcs rtspectively. The abjects all M

similar- . . . 'ai ptcms, kit th patterns tbemselves did not fit into a physid

Reimannian rcpre~c~ltation of sprc 'Ibac cicans to bc liak quantifiable l i e between

the traditional methuds of mechanics and human hrptic peEcepti011, and a ~~t

approach is rcquircd if detcrministic CntCrja are to be introduccd into this facet of

engineering.

In gentral, the design gorls of the @tic hanci controUer fa control and stability

in an interface with a hurmm operrtor are summed up by Kucrwai and Snydcr in [24].

The haptic &vice must be h ~ C 4 6 k . the opaua miut k able to mwe the systcm's

end effaiun M t h t any aiding toques applied to the actuators. Thc joints shouM have

very iow friction and b a c b h 1221. The structure must be v a y rigid, and designal with

the minimum numba of stia lightweight components.

nie industry leader for haptic hand controî.ias, the PHANTOM [3.4.6,8.16]

device (sec figure 1.4.1) h m SensAble devices, addtesses some but not al1 of the

requkrnents set out in this d o n . Accading to [SI, th designers of the PHANTOM

device consider that the most hportant haptic interactions involve ody the positioning

and forcing of a virtuaî point in thrcc dimensions. The PHANTOM &vice provides thme

active DOFs in the translation of a fingcr thimble rnountad on a univasal joint. The

thimble allows the user's fïnger to assume any orientation, but has no &ve DOFs to

provide haptic simulation. The translation stage is designcd out of lightweight aluminwn

tubing with the direct-drive actuators providing f a the WC mterbalancing. The

translation structure tbenfon aiiows for the low inaiio and low friction, rrqulltd of a

haptic device. 1 e . g to a v e y low free mechanical impedance. Howeva, the

Lightweight structure of aluminum t u b and the light actwtom do not provide a very high

level of constrained mechanical impcdanct. The incorporation of composite matcrials

into the structure of a haptic device ha9 the obvious aâvrntage of simultancously meeting

the design goals of stiffiness and light weight while inmeashg structurai dampinp. as weil

as providing for imaginative uscs of matdais to pmtect sensitive COmpoLlents while

acting as primary structural members.

McGill Ukrsity Dtpirtmcat of Mscbrnicrl Eagb&ng 16

2.2 Literature Review of Bonded Joints

nK arca of study of aühesivclybadedjoiuts is vayimparfint to the

development of the use of composite muniils in mechanid structures. 'Lbe adhesively

bonded joint comprises th most effective methd ofjoining compo~ite nuteriais to

met& and to other materials. The field of study of the bondeci joint includes matahi

selection for both the uàken&, a the boadcd entities, anâ the a k s i v e , or the glue

mattrial that bonds the adbuxb to@crt Aaotha area of infaiest is the stress in the

bonded joint, and the effect that the joint gcometry has on the stress distribution. It is this

second field within the grieatet study of boaded joints that wilï be of patest interest to

this work, as the mstnisii selccîion far the nrihcimuin (Md adhcrcnt arc somewhat m m

limited by other factors, includmg availability and compzttibility with aha mua*ls in

the F d o m - 7 stmcairt.

Th- arc several design problems zlssocia!ed with adhcsively bcmdcû joints that

are unlilre other types of mechanical joints. kr [25], k sctb to acqunint mgineas

unfamiiiar to adhesively bonded joints with the particular mquiremcnts of this type of

fastening. Lees lists seven problem arcas with dbcsivcs in joints thu mua be addrcsscd

in the final choice of a joint dcsign:

adhesives tend to have poor impact behavioz

O failurc ocaus easily f a a peel a cleaving face

material properties are very sensitive to surr0ulldi.g mvircmmmtd conditions

there exists liak accurate a usefal design data

a there is Little data n f d g to environmcntal cffects

a k k of codes fa implemmtation of standad & s i p

a poor communication b a n manufktwus and engbœm

Of these sevai factors, th most impatmt for the eventuai choie of the joint gtomctry

are the h t two, those that dcterminc the zlcccptable loading d o s of the adhesive

joint Lees goes on to say tbat the design of the joint s h d d be made such that the

adhesive is not exposed to high tcnsile lodk The prcfmed l o d case f a a ôondedjoiat

is in shcar. For a lap joint, the m m impatiint gaometry detail waitd have to be the

design of the dgc. with ôcmd fillets and tapacd dbaeods amtributhg patïy to the

overaii sîrcngth of the bonded &in.

The typicai joint gcomeûy that bcs examines in [25] is the single lap jomt This

can give several good indications about p f d desi@ aiterion f a otbcr types of

bonded joints. Fmt, the maximum l o d supportcd by a pint is dcbmiined by the sbear

ana of the adhesive. Howeva, as the majority of the adhtsives rire polymcric, they can

be subjected to ~t rep &formation. As such, at lcast part of the joint should be essc~ltiaüy

unstressedfortbatmbtnoaeepdefdanmidaa~ca~lod. Ibe

thickness of the adhercnds a f k t the distn'bution of stresses almg the adhcsive bon6 By

reducing the thicknss of the adh-d near to the adge of the bond arcs, there is a

reduction in the stress wncentration near the exige of the bond. Howevcr, by rcûucing the

adherend thichess in a s i a g k lap joint, then exists the pasii'biiity of inducing plastic

deformation in the a d h t t ~ ~ ~ d s , rcsulting in peel and fensile sûesses applied to the

adhesive. Adhesives should, at ail timcs, be k c from thesc peel Jtnsses. At worst. any

non-shear stresses expcricnccd by the adhesive s h d d be compressive in nature, and

certain design changes in the bond geomefiy could casily allow this to occur.

The final recommc11dation by Lets coma in the choice of the adhaive. A ductile

adhesive allows for the stress in the joint to be more cvenly distributcd ovcr the bond

area. For this reason, a more ductile adhcsive will o h d t in a stmnger bond than the

use of a vexy stiff? britîie adhesive.

in [2q. Adams and Hams examine in detaiî tbe double hp joint for the h d i n g

of unidirectional carbon film reinforccd plastic (CFRP) to a steel adhaend. The ovcrall

recommendation is that the failurc in an -1y dcsigntd joint should occur in the

adhesive and not in the adhaend. Adams and Hauis use finite dement methods ta

accuratcly determine the locations of the stressa in the joint, and the effacts that the

different geometry parameters have on the joint strength. The thickness of the adhesive.

caiied the bond line thickicss, is not modifi4 ncitber is the tbickncss of eithcr adhercnd.

The parameters that are examined arc: the effècts of the bond fillet at the edge of the

joint, and the effkct of the tapcring of the steel dbacad. Using the finite elemat mcthod

to examine both the sliear and tmmv~gt strwses in tbe amponents of the joint, Adams

andHarrisdrawsevdcoircllusi~aboutt&naaldesignofabondedjamt Fust,the

pcak traamerst stresses in the adbcsive, which would cause peeling Mure in the

adhesive, occur near the conier of tbe steel cdhgends. Tbey also canclude that tbc

tapering of the steel dhamds has v a y little effect cm this uadesllablt loading of the

adhesive whcn the adhesive mitmil ends rbniptly at tbe d g e of the steel dhamd The

reduction in the tranmetsc stress in the &esive is obtahd by adding a fillet to the

adhesivc bcyond the steel adherend. Furthermart. the introduction of an intemal taper to

tht steel adhercnd in combination with the dbcoive fillet gocg evcn Emba towards

reducing the peehg stress in the idhesive matcriaL F d y , the two modes of failue

predicted by Adams and Harris with the fiaite elcmcnt model shown in [26] h the inter-

Iaminar failurc of the CFRP due to the increased transverse - in the adbesive cl-

to the material bounciary, and cobesivc Wure in the adhtsive due to the ~ ~ ( ~ ~ t l t r a t i o n of

s t r e s s a in the adhcsive mrtaial almg the h c edge of the adbesive fillet. Fa a q a k

situation, the f b t failme mode is undesirab1e. as an inter-laminat fiiilure of the CFRP is

not easy to sec or to fix.

Much of the work associateci Mth the bonding of mctal composites is in the

field of composite aircran wing rcpair [17,27,28]. In [27. Xi0118 a d Raizenne dcvelop

an analytical model to &tcrm.int the strcngth of a compositdmetal patch joint. The

overall geometry of the joint considncd is that of a composite matcrial patch, adhesively

bonded to a metal s u b s a a or base matcrial, f a patching and fitigue tnhancing of the

metal par^ The model is capable of takhg into account the tapering of tbe composite

patchcs and calculates the adhesive &car strrsscs as weli as the interface p l stresses

between the composite and the sdhsive marerial, and the inter-laminat transverse

stresses in the composite. The model takes into account tbe differential thermal

coefficients of expansion of the differing matcrhb that rrwùt in thamally induccd

stresses and is used to prtdict joint failm.

Xiong and Raizcnae draw five ~ ~ I u s i o i w about the joint geomctry and matcrial

propertics for this type of patch joint:

McGill University Depumwit of Mtchrnid 19

T h e m o s t d t i d r i r e a f a t h e W ~ ~ t o f ~ m c t a l ~ b 9 a . s t e u n d e r

compression is the taperhg of the composite pich, which cui cause miaix shcaring in

the patch.

The pmiictions of the Mure I d and mode arc heavily depeadent an the

choice of matcrial pmpcrtits f a the différent amqmmts of the joints, so mataial choice

and envin,nmcntal f w arc a vay impatint consideration in the design of a composite

patch joint.

The most critical area of the bonded joint far a tcnsile load case is near the

center of the patch, by the edge of the crack in the mP1 wibsoate-

The tapering of the composite patch is uscfhi to &ce the stress in the adhesive

near the cdge of the patch, but am r d t in excessive omosts building up in the plies of

the composite material ncar to the adhaive boundary.

AU stresses necd to be collsidcred, rather than just the shcar area for the

adhesive as is cornmon, for proper design of a patch joint

Further work suggested by the authors is the investigation of the plrrticity eff-

of the bond matcrial, the bcnding effects an the joint due to I d ecccntricity and the

effect of de-bonding at the exa~mitics of the j o k

In [28], Charalambides e t PL use finite elanent anaiysis and physical testing

methods to determ.int failwc Cntena on enviranmentally trcatd patch joints- The main

conclusions werc that the environmental trtamient of the patch joints, cach test specimcn

was immcrsed in a 50° C wata bath for 16 maths, had vay îittle effkct on the s t m g t h

of the joint in tension or fatigue. Howeva, th fuiguc @ormance of the patchcd

specimens is much worse than thet of the whole. untouchecl specimens. Joint failw

criteria bascd on maximum aiticai stress a strain did not producc rcSuIts consistent with

the test specimens- It is their cociclusion that this methd of prcdicting th strcngth of the

joint is not adcquate due to the edge effets of the finite elcment mesh, and instcad

propose a fracturc-mechanics bwd mcthod that yielâs bettcr results.

In [29], Ricc and Moulds &der the variables govcming the design of a boodcd

interface between a composite pmpshaft and a mtal end fitting fa the p q of

transmitting toque. The goals of this design arc the reductim of o v d weight rad mst,

reàuction of whirling prob1ems causcû ôy tbe unbahces genenued by mechanimi

fasteners, the potcntial eIimirintion of an inmmahtc beaning, the rcdllctin of noise and

vibration and a lower part count fm the assembly. Ria and M d d s use an anaiytical

program based on continuum mechanics to evduatc the eEkt of proghssively modifyiag

certain joint geomcûy variables such as d k m d wall thickness, bond line tbichiess and

matenal properties. 'Ibe program determines the stress àistri'bution h g a single lap

joint and compares it to an elastic limit f a the cpoxy mrmiaL The c&a of dissimila+

materials in the joint with a hcat curcd adhesive is vay high, and not rmmmadd The

choice of a cold currd adhcsive is beneficïai to thejoint wlaietb, m that it does not rcsuit

in high residual su esse^ in the bond that wiil aggravate any m e r loading on the joint.

The cffect of changhg one adheread to GRP (glass reinforcd plastic) causes an Uicrease

in the stress in the bond ncar the dgc due to the difféxmtiai d e f d c m of the

adherends. To d u c c the stress concentration, the thicknss of the composite adhcrad

must be inctcased, to king the stiffiiess close to that of the duminum. and the h d line

thickness must be incrtased to ailow far mort m a t d in which to distrifite the stress.

The final joint mafiguration for the single lap joint is a 5 mm thick aluminum adhaend, a

3 mm thick GRP adhaend and a 0.2 mm bond line thickness of a two part, ductile, cold

cured epoxy. These amclusions arc used in the design of the bonded intcrf' between a

metal end fitting and a composite tube. The first geometry considercd is a simple plug-

tube joint, that causes exccs~ively high loads near the end of the plu& whüe the -ter of

bnded area is unloaded. A bore hole added to the center of the plug, mnlring a partiai

nght cylinder of the insert sucacds in Kstcibuting the more of the stress towards the

inner part of the bond fhxn the dg=, but docs not s u d in lowering the stress in the

adhesive bclow the elastic lirnit everywhcrc. Therie still txists a stress concentration near

the edges of the bondcd arek By -ring the dgcs of the insert, the stress in the bond

can be reduad fiirthcr ncar the tapend edge, but it rcmains high at the o<ha end of the

bonded region, near the end of the fuk. This stress concentration can be redud by

increasing the bond iinc thickncss, nt the ri& of causing a#p deformatcm in the bond.

The final conclusion by Ria and Mouids is that, if it is possible to bond both the inside

and the outside of the tube to the metal end fitfing, the iaaerse in the ovedi strength of

A wedrer, but dude &haive is prefcrable to strcmger yct brittle m.

Twghened adbtsives will work bcst.

The joint design must take into recamt eirviranmeatal degracW011 of the

adhsive mrtcn;il propeities.

'Ibemgaganrntoftbeboad,tbc~oftbc~vebocd,shddbcLept

assho~aspo~~~1e i fah~cwdadhes ive i sused . Thiswillrcducetùe

diffmtial expansion ww~er m mntti-matcrilll joint*

The bond line thickness s h d d as gmat as possible without allowing the joint

to expericnce awp fatigue.

Thcrc must k no con m o n of the composite part by mold reIcasc agents.

Composite s u r f i cari bc prcpand by chernical solvent wiping, foiiowd by

light abrasion end dust rcmovlil A h , ôcmbg prc-treatnments cm k used to

reduce wmsion and inciuise the wetting of a surface by the adhesive.

The use of bondcd joints in various h of design has a g m t potcntial f01

growth. The bonded tu- joint has the kaefit of rcâucing parts count by eliminathg

mechanical fastcners, and by incolpaating mstaial tûat b alrcady available in industcy, it

has thc potential of nducing manufktwhg costs as weL Tbae L somc difncuity

inherent in the bonding prauss, but 4 t h propa jig design in an n b l y liii. pmduction

method, thtsc problems are easily surmantable.

2.3 Literature Review of Laminate Optimization

One of the most attmctive rraums f a using composite nucaiain in a robotic

smicturc is the ability to precisely Pila matairil Propercics such as S i f f b s and muai.l

damping. The material propenies of a part made h m a cOmpOQitt miiai.l ut highly

dependent on the sequcnce that tbe individuai plies cire laid-up. and on the orientation of

the fibers embedded in the plies By varying tk n u m k of pl*s in a lay-up, md the f i k

orientation9 a base matcrial such as unidiribctioaal carbon fibers embcddd in an p x y

matrix uin exhibit mataiPl Propcrtics o v e a vecy large range. 'Lbac hm bccn much work

donc on meth& of optimizing the lay-up fa various Ptoparics. includhg severai linea

progmmming schemcs fot determining the optimum iay-up f a muimituig a parti&

material property such as damping. T1iW section wi l i se& to ovcntiew S O ~ C of the WC&

already done in implcmenting composite compo~c~lts far robutic systcms, as weli as

detailing some of the existiag lay-up optimi7ntion mcthods.

In [8], Lee et. ai. dcvelop an antfvopomorpbic robot using composite matcripls to

construct the Linlrs. ïhey state that the specific siifnrtss of the links has to be high and

the materid damping has to be. in any robotic structure. high aiough to ~ I O W fot hi-

positional accuracy and dynamic @&mance. Ibe high specific stiffiicss of the linLs

will d o w lighter links to carry the same payload. IIence the Pcaiaton can be made

comspondingly SrnaUcr and less expensive. Tbe high mataial damping of the links wiU

allow for the daqing out of vi'brations induced in the st~~ctum by high acaleratio~ls. and

create a grrater end point accuracy fm the manipuiator. Lee ea ai. show that the

longitudinal stiffiiess of an mrgk pl& individuai plies that are placed with the f i k

direction at an angle to the part direction, deops off sharply at 15'. and they ch006e a lay-

up stacking sequaice of i1S0 for the composite nn with a box-type scctim. The robot

in [8] also used filament wound drive transmissicm dm&, ma& h m carbcm-fiber

matcrial. The interfaces betwecn the links and betwœn the drive iphllftp and the motars

were made using bonded end fittings on the composite m. A choice of bond line

thickness of 0.lmm was made. with an engagement length of lWmm fa the box-bcam

forcarm, and Sûmm for the drive trarismissian shsfts. Tbt shear erw ribquùed by the logd

case expected for the robot would dictate a minimum bond engagement of Uhnm, but L#

et. al. suggest that the longer bond lengths makc f a an euia joining process, anâ the

forearm joint might became unstable in baiding if a shortcc bond engagement w a e

chosen. The end fittmgs ae msehinrA as a double-lap joint Both th inside and the

outside of the composite parts are bcmded to the mtai sdberends. Hybrid jomts ue ustd

for the pivots on the composite fmcann. The joints ccmsist of a metal plate bonded oa the

outside of the box section, with P bolted reinfimcing plate on the Wde. Such a joint can

b t t x p t c t e d t o p c r f ~ n n w e U i n s h u r r ~ w e U a s h ~ o n d c o m p n # s s i ~ ~ ~ Tht

composite ami was cornparcd to an quivalent steel a m f a a variety of static anci

dynamic Cntcna The nindsmentai natural neqUency of the composite arm was mare

than twice that of the steel a m , anci the inhrrnt damping ratio was s e v a times as much

for the composite arm than for the stccl atm. The mass of the composite arm was lcss

than one quartet that of the steel ann. Overaii, the inclusion of the composite materials in

the robotic stmcture, while involving some complicstrA boading techniques. S C C ~ S to k

very advantageous to the dynamic perf6muncc of the device.

For accurate control of robots including composite matcri& in the structure.

accurate modeling of the dynamic charact&stics of the composite matcrial has to k

perfonned In [30], Gordaninejad et aL tak as a base assumpticm for the dynamic model

of a composite robot arm that ait rigid and flexible motions of the um must k couplai.

The basis of this assumption is that, for modem high s p d robot manipulatas, the

vibrations inducad in the structure arc not sa small as to be ntgiigible in the d-c

modeling of the robot structure, as is traditiodly the case fm large, low speed

manipulators. By applying their model of coupled dynamic tams to a simul.trd

composite box bcam made of ande plies, they show tht an inacasc in defldcticm for

angle plies up to about lSO of ply angle is negligible cornparcd to th unidirectional plies

(the highest obtainable spccif~c stiffiiess). Howeva, the marrimm nonnal bcnding stress

in the part shows P minimum fot the angle plies at lSO. This wiggtsts a masonable fimt

assumption for an ideal ply angk for the mata*l of the box bcam. Gordaninejad e t al.

show conclusively that the couphg of the dynamic tams in the caiculation of end point

defltction is rcquired f a accurate modehg of a ro&tîc systnn. BI (311, Gordaninejad e t

al. dcvelop a similat coup1ed dynamic modehg of a rcvo1ute-prismatic beam mrde of

composite matcrialS.

To design for specific matmial c-CS such as matai.l -hg, a methad

for predicting the value of the propaty is riequiricd, Ni and Adams, in [9], attcmpt to

formulate a predictive damping equati011 ôascd on the stmin encrgy in a symmctricaiiy

laminated composite bcam vibrating at a natuai fbqyency in fret flemrc. The damping

calcuiations arc functions of thr# measuted paramctcrs of the base material, the

longitudinal. txansvase and &car spccific damphg crpacity. The values fa the thnt

specific h p i n g coefficients f a the laminatad kam are calculated as s u m ~ of the

material properties and orientatins ovcr the tbiclmess of the iaminatca. The results of the

theoretical calculations arc vcry close to the values thai Ni and Adams meunirrd f a the

f?cc flexural damping of the symmetridy laminated bcams.

In [13], Adams and Bacon alsa attcmpt ta evaluatc both thcofcticaiiy and

experimentally the dpmpiag asociated with a composite mucri.l iay-up. Specifîcaiîy,

they evaiuatc the effect of the fiba orientation and the laminate gcometry on the damping

produced in a composite specimen. In general, the darnping in an mgic ply i4minritc

reaches its maximum at a fiber orientation of 3S0, and the dominant dissipation term is

the shear stress term. The majority of the damping that can k associateci with a

composite part is due t4 the rcsin systern use& more so than the fibers. This is shown by

the in- in the damping for a decrcast in the fiber moduius, The lowcr the fiber

moduius. the grrater tbe s t n i n mergy in the miau matcriaï, and the hi* th dampimg

wil l be for the laminate.

The same authors as [13] suggcst in [IO] somc mthodp f a increasing the

damping in a multi-laycr, unidirectional laminate specimen. Adams and Bacon show that

the prtsence of imperfections in a laminatr?, such as min poor amas, voids a even smaü

cracks can lead to grcater values of Asmping in the laminate. ' Ihy a h say that the

majority of the damping occurs with the strain aiasy in the mMix in the longitudinal, or

fiber, direction. The strain enagy s t o n d in the mmix mamiaï as a diîation will

contribute linle to the o v d damping of th lamime. Finally, as the modulus of the

f i k r s i s r e d ~ c c d , t h m c r g y s t m d h t b e r m r r i x ~ ~ TbtdamphgurociiodMth

the &car deformatim of an off-axis iaiiiun is esscntially unchangai, bit the

longitudinal damping incrrrres. Tkrefort the ovaaU dimping rorociPted wiih the

laminate wiU show an incIieasc. Whik the prrrare of voidr d cracks c;ia bc v a y

detrimental to the life of a irminatr, a similsr &kt of increaSing th Iiminitc damping

beyond the p d c t e d leveIs can be obtained by a slight deviation in the straighbness of the

fibers during manufiicturingœ For parts made unidirectid rna<airl, this caild k

very helpfil in improving the dynamic charactcristics of the composite parti

Extensive imowlcûgc of the rsquaed @amuice criterion f a any mnipulator is

needed to be able to acaurtely specify the mataiil pararncters that will be obaiaed with

the optimization of the iziminntE. In [ll], Lee et. al. constmct a SCARA type direct drive

robot with composite mrtcri.l linlrnpcs. A SCARA robot is a saudy. pick-and phcc

robot. Two revolute ihkagts fam a two dimcnsid pianar workspacc, through which a

prismatic k h g e can be moved in orda to @am the rrquvcd task~. Tbc hy-up of the

composite materiais was detennined by the static deflcction caldations of the end

effector. The oum a m of the SCARA robot is subjected to vay littk torsion l d , so a

filament winding angle boundary of betwt~~l S0 and lSO was chosen for this îinkage. nie

end effector deflection was calcuIated ova the wodrspacc joint angles fa a range of

winding angles for the inner a m . The winding angies choscn were 2ûO for the inna arm

and 10° for the outcr ann, while the matimum deflection of the end effectot ovcr the

entire workspace did not excecd 30 microns for 10 N of p a y l d Only the stifhess

material parameter was chosen for the o p ~ t i o n of these parts. and no cauideratians

other than the static load dcfîcction wert takcn into accuunt.

h [14], Sung a d Thompson propose a systcmatic mcthod foi optimizing the lay-

up of a robotic structure for maximum wonnance bcnefits. They show the influence

that material propcrtics of a laminatc can have ova the pdormancc of a robot with a

simple schematic. The fiber orientations and cbanrctaistics combineci with the matrix

characteristics, lay-up and stacmg scquencc have a dirrct effcct on the dcnsity. the

strength and the damping of the matcrial. The mataial density combined with the Iuik

gcometry detenaines the maap of the structure. The saagth of the mita*l and the linL

gcometry determine the Itifnuar of the structure. Howeva. the muairl damping b the

only f ~ r that contn'butes to th strucûd damping if the dculatedpints err

anisiderd ideal. F i y , the the ancl s t i f b a of the tbecûne i n b w iatdth tk

damping propercies of the matainl wii l detumine the aamacy, tbe wlt W. tbc

workspacc, payload and repeatability of the robotic xmnipulaîcx. ki m m y the Iinlr

geometry will bc fixed for rt.sans of interfkmcc, a drive syDtcm muting. For thh

m o n , it becornes neces~vy to provide a means to oprimiot .11 thsec materhi propcrties,

density, strength and âamping. simultaneously to obt.in a fully optiaiirrrt robotic

structure. The iinw programmïng techniques usrd m th* rrriclcr~t d e r i p d to

optirnue the properties of thin lamhatc bcamsT tht wül subsupcntly be boadrd togethcr

to form a box-section stnicturc. The opthhtion mutine dclaminer th hy-up tbt

obtains the maximum metcriai dmiping subjeacd to catam wmstmhts on the fiber

angle, maximum laminatlr tbickncss and knce ïink weight, fi- volume fiaction and

bending stiffiiess terms for the Carttsian diredions x and z (the axis of the link is

consideml to be the y direction). Ilie laminate gcometry obtained h m the optimizing

routine showed significantly improved dampiag over tbe arbittarily chosen initial design

for the composite part . The optimization mutine propooed in (141 is fiirthcr nfïned by Sung aad Shyl in

[12] to determine the optimum lay-up for a cornpletc box-section, rathcr than a box-

section made h m bonded i.minete plates. The pmposd optimizcd box bc8m could be

manufacture by bag molding cmwmd an intcrml mold as a single part. Sung a d Shyl

propose severiii iiiustrative exampks to show the fltxibiïity of the opbhatian mutine.

The first is a simple saial manipuiator. whrr the magnitude of th mdpoint viôraîion is

to be minimiird. The resuits of the opthh ion routine show that the waU thickness of

the laminates incrrase to the maximum vilue pumittad by the comtrahts as the routine is

dependent mon upon the &ess of the links than the o v d linlr weight. The secund

example. using the same manipuiatorT sœks to have the shortest settïing tim for a

pTeScribed maneuver. The same m t s on the box-section wae imposai as f a the

first example, but the optimum hy-up wrs @te dine~~~lt. For the shortest sctthg time,

the fiber-volume fiaction tcndcd to be minunilrA . t . .astbedrmpingoftbcmuairlwrs

heavily dcpendcnt on the mmix content of the iay-up. The potential fa ôphmmg . . . the

matcrial ptopeaies is extensive* 'Lbe pins mde iu thme two simple txamplcs arc

testimony to the impartanœ of a carefbi choice of all the mrtcn'ai chsnictenstics fot

optimuing a laminatc* Howeva, detailad critenon are q u i r d fa a opthbtion

to be possible. The srme manipuiator, subjcctcd to two slightly di&rrnt opthhtion

criteria rchinied two very din~~tnt Iiyspa 'Ibt breaw in the rmtrix W o n

for the second opthkation of the manipdator would k contrary to tht requihments of

the first optimization of the manipuiator* A h , ncitber case multed in a minimum

wtight far the manipulator lintrn. Bottr Optimizptiolls ~ ~ w e ~ t t o t h e b g i c f i t

of the material properties ofthe hminatc.

Unfortunatdy, the &tailed daaminrton of the performance cxitcaia fa a haptic

device is beyond the scape of this w a l c Subsequciltly, a fuii w o n of the i a m i ~ ~

for the box-section linkagcs carmot k prformd. As a p r r h h r y ophhaticm

technique, an iterative finite elexnent modtling of the lay-up in question will be usai

instead of the more rigorous non-lincar p r o ~ ~ g c o v d in this sccticm.

McGill University Deputment of- - . 28

3. Design of Bonded Tubes

3.1 Introduction

Small diameter commacislly availAhIe composite tubhg wu considercd as a

bais for the constniction of the h b g e s of the tninslation stage kfuue it pamits

several intmsting options. For an load scenario, such as that faiad in the

links of the translation stage of the hrrptic -, the most enicmt cross section fot

dealing with multi-axis I d is circulnr. A h , rclativcly inexpensive commctcially

available cylindncal tubes made nOm cacbau-fibcr rmtai.l pmmt a viable altemative to

the heavy machining costs usoCi.tai with compltx aluminum parts.

3.2 Material Survey of Composite Tubes

Anextcilsivesurchwumadctonnddequucmtcrialintbef~~fsrmll

diameter carbon-fiber mbcs rtadily availaôle fhm the commercial scctor. The choice of

puitruded carbon-fibcr tubes was made basai on üie design gmîs f a the Freedom-7

project: decrtasc the linL weight and incrcasc the link stiffness. Unidirectid carbon-

fiber tubing provides the highest stifniws to weight d o f a any materid. Howevcr, it

tumed out to k no easy ta& to find this mataiil cm the maLet Puitrusioa of carbon

fibers r e q u k special dies and vay expensive setups. The qoxy matrix matmcil

cornmonly uscd in conjunction with carbon fibers does not lend itself casily to the

pulltnision proass, as the cure tim f a this matenpl is normally quite long.

Several market s~nar wac targetbd as potcatial suppliers: the COIIStnrCtion

industry, the amonautics hdustry .nd î k sprts equîpment h c h s t ~ ~ . It was discovercd

thar,in thc~~~l~t~ctiiai~,th~jorifyofihe~ttmitai.ltnbhgUmrdeof

glass fibers. nK diameter of this tubhg was llso too large to k uscfiil in the translation

stage of the Fradom-7. A seirch in the acmmutics uidustry turned up s c v d candidates

for the Li& matcrial. 'Lbe most promlnig came from tbe Aa0Sp.a Composite Roducts

[32] a Company in rafironiia Th muairil obtainui b m thcm was originaily intendcd

for the construction of spars and contml aufre puah rods in mode1 ahplanes. 'Ik tubes

wcrcpar~carbcmfiibcr,partgîasafibcrrratcrial. 'Lhrtw~sonetypoftubingmadeof

w o v e n c a r b o n f i b e r ~ t h c R H - 2 . 'Lbtspatsindustryhsümanymaematairrl

options avaüable. The hunting industry manubures carbon f i k (vltows for high tcch

sport huntm, and composite ski poles can be found aU ova îhc market. 'Ihra spmples

of arrows w m obtained h m varias hunting stores in the Montrd uea. Thcsc arc

show in figure 3.2.1. 'Iëc top arrow, an aü aluminum shafk, is the XX75. the middle

shaft is the all-composite unidirectionai shaft, the V-Max, anà the boaom is the Easton

ACC. an a l h u m shaft sumwdcd by a wovm crrbon f i k shcath. F l y , the aoss

country sk i pole industry turned up the most ptomising materid in the form of

unidirectional pultruded csrban-fiber polyester ski pole bianks, bought fmn Top Sports

[33], a sports equipment man- in Mmtrcal.

In order to &termine the bcst d d a t e foc the iinlr matMial from all the available

tubes, a thrte-point knd test was pafomwd to &tamine the effketivt longitudinal

moduius of the material. The effectve mryiUtus was divided by the density of the tube to

determine the cffcctive speQfic lcmgihldilllt modulus ofthe tub. This wu done

according to the following caicuiatio~ls:

EIais the effective longitudinal moduius times the moment of inertia of the

tube (flexural stiffhcss)

El, is the e f f d v e speçific lungitudinal modilus times tbe mament of jncrtia of

the tube (specific flexurai stiffIicss)

A summary of the d t s of the three-point beidiag tests an the dBércnt tubes

can be found in table 3.2.1. The desircd propaty fot the optimizaticm of the structure is

the maximm E&, as that dctcrmines th f i e x ~ y stïf5est tube mamiaï and geometry foi

the lightest weight. The ski pole matMial, the unîâircctid carbon-fi& polyester, is

therefore the prcferrcü matcrial for the constmctioo of the stage 3 Linltage.

T d k 3.2.1 - Swnmaty of Composite T h Propcrn0es

McGill University Depumncnt of h&&nial . . 32

1

0.006

0.00384

0.00618

0.0058

0.00864

RH-2

Vmax

ACC

TU06

XX7S

TU-07 1 0.148 1 0.00384

0.768

0.838

0.870

0.287

0.850

0.008

0.00644

0.0076

0.0071

0.00956

0.0074

0.0218

0.0246

0.0203

0.0059

0.û294

0.0152

1.247~10'~

9.278~10'~

8.036x10"j

3.997~10-'

7 . 0 8 7 ~ 1 ~ ~

9.662~ 106

6.635~10"

5.293~10~

2.561~10"

2.531~10~

7.145x10-~ 2.186~10~

3 3 Geometry and Parameter Varintion of Bonded IiiseftS

The composite tubes raquirr baaded mul hsczts to aUow fa bcaring fitîhgs. A

choice was made to use extaior cylinAiid fittings. Ibe tube cnws d a n did n a aUow

for the more acsthetic intanrl fittings duc to SIMU b e r tube diametm. The extemal

fittings wue &Cr to ïmplemc~~t

As show prtviously, tbis type of boildtd joint hr bcm studiaï fa

loading, such as is f d in mqmite püp-sbaff design [29]. HOWCVC~~ littlt aûdysis

had becn done on this type of joint fa threcdhmsicmai beading and taisile Io& that

are consistent with the hand controilcr I d cases.

For the mode1 consi- in thW wod. s e v d pammctczs wae ch- rad

varied in diffcrcnt finite elemnt modcis to gaugt tbek eff- on the ccmcmtration of

principal stresses in the bond mrtaiil Figure 3.3.1 shows a scbernatic chgram of the

bonded geomeûy, with the parameters a. e, and 1 am. rcspcctivcly. the dbaead

thichess, the axial engagement anci the bond linc thiclaiess. In edi model, the

diameter of the composite tube. the aâhesive f'iilet and the fillet an the inside adherend

surface remain constant.

Figure 33.1 - Band Geowutry for Pcvamctc~ Vorirrtion

- -

McGill University Dep~rtmnt of h k d d c d . . 33

3.4 AxSsgmmetric Finite Element ModeIs

ThefinitcelaaentmOdclsdtodctamiaethe&cooftbe~

parametcrs on the k m d saaigtâ w a r comtmcW using uioymmeaic elcxtmts. nie fht

i~mtionofthettsting~~doae~mcsberrimilPtothu~hfi~3.4~1. 'Ibe

Figure 3.4.1 - Axisymmctn*~ Finite E k n t M& of Bondcd Geonutry

elements composing the composite tube arc of an orthotropic muaial having the

propertis of unidirectional carbon fiber material [34]. The matcrbl axis for these

elements was set to be the same as the axiai direction of the tube. 'Ibe matcrial Properties

of the isotropie epoxy bond were dctcmiined frrnn fiterature. The elements of the

metallic insert w a e assignai isotmpic mntai.l propercies umsistent with duminuma061

PSI *

The elcments of the tube ut jomed (they have coincident nodes) with the

elements of the epoxy bond dong the bottom fkc (CW in fi- 3.3.2). nK elements of

epoxy and aluminum are wnnected h g the entire intahce fa test 1 and 2 for each

model, and the bond DAB in figure 5.3.2 is bmlaa in tests # 3 and #.4 in cach modd

This discontinuity is consistent with a bond th.t is going to be lodtd purcly in shear. As

the results will show in th next sections. the brt.lr is rlpo consistent with a pottntial first

failure mode.

Tests 3.1-3.4

Tests 4.14.4

Ttsts 5.1-5.4 2.0 0.05 5.0

Test Number r

Tests 1.1-1.4

A total of scven finite ekment m&ls wac cunstructed to anaiyze the of

the dinerent parametcm on the maximum principai stress in the bonci . E r h of the sevcn

models had four tests paf~~med. The fht and fair(h test w a c w i t b t the bcmd fillet at

the extreme end of the composite tub (lïnc PB in figure 3.4.2). The second and third

tests both have this fiilet. As mentioncd befort, the fbt and second tests have a bond

between the aluminum and the cpoxy on 1 . DAB in figure 3.4.2 whcrt in the third and

fourth tests, this bond has been broka. Table 3.4.1 shows the test numbers and the

patameter variations for each m a l . Tests 1.1-1.4 arc the arbitrarily choscn bw tests.

Tests 2.1-2.4 and 3.1-3.4 vary the adherend thickness u h m 0.5 mm to 4.0 mm. Tests

Figute 3.4.2 - Rcfe~encc Loc4tion.s on Bond Geomctry

a (mm)

2.0

1 (mm)

0.25

e (mm)

5.0

4.1-44and5.1-5.4varythebandlincthi- lfiam0.05 mmto 1.Omm. Tbeiasttwo

sets of tests, namc1y 6.1-6.4 and 7.1-7.4, v w the axial engagement e from 3.0 mm to 10

mm.

3.5 Results of Parameter Variation

To propcrly interprct the d t s that will be shown in this Secfion, the purpose of

the optimization must be msde clcar. As was staîd prcviou~ly, the design goal of the

Freedom-7 is to provide 8 h a d ccmtroUcr structure thit WU d n i m b the link weight and

inertia fclt by the opcrator, whik at the sam time meeting aii the design aiterion such as

minimum rcquircd smmgth and lowest mmant nrninl fkqcncy. To obcim this goal,

the links, and s u b s e q d y the boaded inserts, have to k designai with tbc following

purpose in mind: minimize the weight and muaial witbait sacrificing minimum strcngth

requirements. In our case, ifrcmoving maraiai fnni the intaf.ce inmeases the

maximum principal stress in the bond, then this b a desirable effect, so long as th final

geometry is able to withstand a minimum nquircd loaci. Howevcr, if incrcasing the

materiai in the bonded interface (such as incrcasing bond liae thickntss and adhercnd

thickncss) ingeases the maximum principal s~CSS in the bond, thn this ôaomcs a very

undesirable effecf countcring both design goals of minimum weight and minimum

required strength. Figure 3.5.1 shows the variation of the pcak maximum principal stress

with respect to the variation of a, th adbermd waü thickaess. Ibe maximum priacipi

stress concentration in the epoxy bond darrates Mth an iacrrape in the adhcrcnd wdl

thickness. F i e 3.5.2 shows the variaîiop of the peak maximum principaï stress Mth

the variation of e, the axial engagement of the tube hto the metil h c r ~ The stress

concentration dccmscs with the incrase of the axial engagement of the b d c d aitities.

Figure 3.5.3 shows the variation of the pcak maximum principal stress in the epoxy bond

material with the variation of the bond line thicknes 1. Tbac is a minimum fa the p&

principal stress in the bond mstn;al near a bond line thichiess of 0.25 mm.

~ c G i I l univmity Deparment of ~echriiicrl ~aghœhg 36

Figure 35.1- Vorlolon of P d P n n c i ' Stress with &Uaerd

W d mckrcss

Figure 3.5.2- Viwùation of Peak Principal Stress wirh AxhL

Engagement

Figure 35.3- VàrMon of P d Principal Stress dur to Bond fine

mckuss

Figure 3.5.4 - Màxiwuun Principal

Sacss Contents in E , M '

for Test 1.4 (Bond AD Broken)

Figure 3.5.5 - Maximum Pn'mipul Figwe 35.6 - M m Principal Stress

Sîress Contours in E'q Material Contours in E ' M W with E m

for Test I .l (Bond AD Ekists) Fillèt for Test 1.3 (Bond BAD Exwts)

Figures 3.5.4 and 3.5.5 show the effcct of brcaking th W h g the DA

interface. The stresses become much mozc distributed throughout tbe ôond lke

thickncss, and the pcak principai s t m s is also reducd. This situation is advantagcous, as

more of the bond is now loaded. As weli, ri& of &ieminat;on in the carbon fiber

material is reduccd, as the stress concentration is movcd to the ngian of the bond in

contact with the metal. Ibe e f f a of ddmg a fïiict in the Compogite tube is hÜly small.

Figure 3.5.6 shows the stress umtours of th 1.2 test, whcrc a band exists ktwan the

epoxy and the metai dong DAB and a met is dded in the composite tube to hacase the

bond line near the end of the joint (PB in figure 3.4.2). lbae is a lrge stxess

concentration at point B on figure 35.6 and thrr is little decrase in the maximum

principal stress betwccn test 1.1 and 1.2. The diaerc~lce in the band sîrcngth due to the

fiilet is considcred negligible ancl, fot mmufktming mamus, it wil i k lefk out of the

final geametry. L grnetal, the e f f a of kaoag the bond dcmg lise DB in figure 3.5.5

has the effcct of ducing the kge stress concentration in the epoxy at eitbcr A a B

dependhg on whethcr the epmy fillet exists a not.

Figure 3.5.7 - Variation of Priacipal Sirus Abng Bond due to Adhcrend TAIckss (a)

Figure 3.5.8 - VCUiQtion of Principal Stress Along Bond Civr to Bond Line Tliickness ( I )

McGiU University DcputnrwtofkCbcbrnicrlEagummg . . 41

The variation of the priaciple stress with tbc parameteft a and 1 b show11 in

figures 3.5.7 and 3.5.8 respeçtively. Figure 35.7 shows the variation of the priacipai

stress in the bond dong the s d h œ of the arbon fikr aibe (AC) due to the variation of

the adhercnd thickncss, a. As the adhermd decrieescs in thicbiess, the maximum

principal stress in the h d inncases. Thcrtf~~it, vrading to the design gorls stotcd

previously. to optimh the bond f a this geomctcy parameter involves decrtasing the

adherend thickness to the limit of sûuctural strcngth. The aptimizcû mode1 wiLt use a

value of a of 1.0 mm. Figure 3.5.7 shows tblt thC mainmm principal stxcmcs in the

bond are only weakly deperdcnt on a.

Figure 3 5.8 shows the variation of th maximum principal stress due to boad line

thicknss, 2. As the bond line t h i c b iacrtascs, ~~ICSS is distributed more e v d y ova

the bond. 'Ihe optimum line thickness &aiM be somewhat in ktwem 0.05 mm and

0.25 mm. According to the literaSutt [3q, tbe bond line thiclaiess should rcmain

between 0.01 and O. 1 mm for stabiity rrrisans. As such. a bond Line thiclaiess of O. 1 mm

was chosen for the optimized model

Obviously, in the interest of wcight savings cm the part, the &ai engagement

should be as short as possible. This factor wiU not be as critical in a puely tcnsile

application. However, as the stage thrre iinkagc can be subjocted to high trausvcrse

bending loads, the length of the uial engagement WU be critical in the rcsulting strcngth

of the bondcd joint 181. This f a ~ o r M11 kcam vay apparcnt lata cm during the testing

phase of the optimized joint As such, the value of e chosen for the optimizcd bond

geometry is 10.0 mm.

Appendix A shows the maximum principle stress contours for the whole range of

parameter variations. A 1 shows the maximum principal strcss contours fa the epoxy

material of the base instance, namcly test 1.4. A2 shows the effect of the band betwec~l

the aluniinum and the cpoxy dong DB in figure 3.4.2 cm the entire bcmd rcgicm, showing

the maximum principal stress contours in the epoxy material fa test 1.1. A.3 shows th

effet of the adhcrend thickncss on the maximum principai stress umtours and iacludes

the stress contours for the epoxy muairl fa tests 2.4 md 3.4. A 4 shows tk e f fa of

the bond line thickness on tbe muimum principal ;md incl* the stress contaas fa the

epoxy matcrial for tests 5.4 Md 4.4. Finally, A5 shows the effact of the axial

engagement on the maximum pincipal stress caîtouft. and ~ C ~ U ~ C S th stnac c01ltours

for the epoxy material for tests 6.4 and 74.

Thus fot optimum weight and aâupmtc st i f fhs. th o~mmuy of the d t s of the

study art:

makc a as small as possible within the sbnictural stability

malrc e as short as possible within the sîn~ctural stability

makc 1 such that it lies betwan 0.05 and 0.25 mm

3.6 Three Dimensional Finite Element Mode1

The strucbrt of the ~rnslation stage expaiemes two d imens id beading loads

as weli as Ioads in tension and compression. Therefw, we can not assume the bond

geometry is properly dtsigned without subjectllig it to off axis loads. ACCOCdiLlgly, a

th- dimensional M t e elemmt mode1 wu, ccmstructed to evaluak the design safety of

the optimized bond geometry. Values fa a, e. d 2. w a e obtaincd by the axisymmctric

parameter variation perfonncd in th prcvious scdoa: 1 .O mm, 10.0 mm. and O. 1 mm

respectively. Because of symmetry. only one haif of thé îube I insat was modeled,

significanùy rcducing computaticm tirne. Tht tbree dimensionai finite eicmcnt mode1 can

be seen in figure 3.6.1. 'Lbe blue composite tube elemcnts are thin sheiï elcments. with

Figure 3.6.1 - l k e e Diwaenswd Fink EkiKnt Modrl of Bondcd Tube Geometty

- - - - --

McGill University Deputmcnt of 43

a the mataial proPatics of unidireciid clrboi, nba mrterirL The yeilow aluminum

elements arc linear brick ekmmts and have tbe mrtairl -CS of botrupic

aluminum. The light blue cpoxy elcments have rmter*l propaties of isotqic cpoxy and

arc also linear bnck elcmcnîs. The load is M b u t e d ova seven nodes on the fhcc of the

aluminum insert, and the baiadry coaditions arc ruch tht the eid of tbc t u b is clamped

while the symmetric &&ce is rcstrictcd to move dong the phne of symmetry.

According to [SI, the typical maximum lard applicable by a h g e r is 40 N. If we

consider a hand grasping the end effkctor, mon than one fhga will k in a position to

apply force to the M m - 7 stnicturt. Thus, it is mmzmblt to assume a worst load case

scenario of 80 N on the end effectot. This l d is obvious1y b e y d the limits of the

actuators, but can be obtauied whn the sûuctaue cnc0~11tcrs a physicai limit stop ncar the

edge of the workspace. For the stage 3 Jinkage, thc mommt am is 150 mm. Ibe total

bending moment on the interface is therefm 12x1d N-mm. The offkt f a the eid of the

duminum insert is 10 mm, thcreforc, the rcquircù face fa the womt l d case scenario,

distributcd over sevai nodes. is 85.714 N pcr node. The units for IDMS-Mucr's Series

V. 2.0 [31] is mN, thertfort. the load rppiicd to cach node W 85 714 mN.

Figures 3.6.2.3.6.3 anâ 3.6.4 show the maximum principal stress amtours in the

various components of the bond gcometry. Figure 3.6.2 shows th maximum principal

stress contours in the composite tube, Mth the bonded region outlinal. Figure 3.6.3

shows the maximum principai stress contours on the bonded fke of the aluminwn imea

Figure 3.6.4 shows the maximum principai stress contours in the epoxy bond m a W .

The locations for the stress mncentrations en not in the same place on the txmd for cach

of the entities. The maximum stnss comtration fa the composite tube occurs near the

edge of the bonded region. The fibers in this ana arc in tension due to the kadiiig load

The stress concentration for the aluminum end fitting, howevcr, seans to be an lrrtifaa of

themesh,asitdoesnotcamspoad~,mydsoeasri~. 'Ibepcakprincipplstxessinthe

epoxy matcrial is on the fLict face of the band fillet, which is one of the Mure modes thaî

was observed in [W. As the stress is not conccntrated near the intdllct with the

composite tub, WC can wume that thae wiil be no delamination in the composite tube

due to the bond.

McGiii University Deputmmt of Macbrnical J h g h d a g 44

Boaded ~itgim

Outer surface of composite tube

Badedhgifnl

Iana swfacc of composite tube

Figure 3.6.2 - Maximum P n ' n c i ' Stress Contours in Composite Tùbe Close îo Bonded

Region

McGill University De- of Mbchrnicrl- . . 45

Figure 3-63 - Muxirmun Principal Stress Contows for Bondcd Face of Aluminwn

Insert

Figure 3.6.4 - M i h u m P r i n c i ' Sirus Co- in E ' Bond Mat&

McGiiï University Dcputn#it of Mecbrnicrl- . . 47

In figure 3.6.2, the maximum stxcm in tbe amp&c tube occ~rs m tcnsim mar

the end of the bondcd ricgiom niir stress ccmcentration is due to the transfa of the

~ i o n s ~ s e s g ~ b y t b e ~ o d t h e c p b e f r o m ~ b e U m i n u m a a d e p o x y t o c b e

composite tube, and is unavoidablt. Howevcr, the stressa kgin befw the end of the

cpoxy bond, which co~ltriôutts to a gradwl m a of the 1 4 aad rcduces the ovcraii

stress concentration. This graâual trrilisfi is thercason fa designhg the metil eiid

fitting with a fillet, and fa d g a Wt with the epony rmitairl nie composite tube

is not in danger of f&iling from this peak principal stress.

Figure 3.63 shows the imvr aima of the aluminum mSar The pcak principal

stress is locatcd right at the camer of the metal insat This stress at this point is fat

below the yield stress of aluminum, so tbac is no danger of M u e in thh part.

Figure 3.6.4 shows the epoxy m0tCri.l. 'Ibe maximum principal stxess is locatcd

near the top of the fillet on the metil insert. The maximum prhcipai stress is 16.7 MPa.

The value of the stress at this point is close to th yidd stxcngth of the cpoxy. The yield

strcngth of the epoxy is 20.3 MPa [38]. The factor of safety for the opcEnurd lxmd

subjected to the worst case l d scenario described above is b r e f - 1.22. The actual

hand load on the end effcctor could be 1.22 times greatcr, or 97.2 N, btfm a Wm

would occur at the bonded joint. It would wt be advisable to try to fiirther optimi7r! the

geometry of the bond, as this w d d jeoperdue the safcty of the bond fa the postulatcd

worst case loading scenario. W e can assume that the bond, as it stands, is optimbd for

this application.

McGiU University Depument of Mechaid . . 48

4. Bonding Tests

4.1 Three-Point Bend Test

It was proposed to @orm a tbra-point bend test to ev.hua the thrce

Composite tube

\

Figwc 4.1.1 - SActcR of thne-pint bend e s t se-

dimensional finite elment mode1 and the chosen optimai ~ g u r i t i o n of the boaded

interface. The thrcc-point bend test was paformed accordkg to Figure 4.1.1. A thr#-

point bend test, rather than a fouf-point bend test, was chosen for feat that the composite

materiai might fail localiy due to the applied pressme. 'Ibe thrcc-point *fixain above

d o w s loading on the duminwn inoar. 'Ibe aluminum irurar rsqiiirrd a double bond

configuration, with the load applied in the enter, to aIiow fa the maximum beading load

applied during the test ta be in the region of intacst, and ta allaw far the test to be

performed in a symmetric fashion.

The test was paformed on tbe MT'S machine 1391. Four simples w a e usai

(figure 4.1.2), tach with a diffcrc~lt bond gmmebry. The ccmsûuction of the samples went

as folIows:

. . McGiii University Deputnvnt OTMcchnicJ 49

1. Aluminum inacit?9 w a c machird with two bond in-

according to the dimmsicms shown in pble 4.1.1. (mfinaad

dimensions arc rccading to fi- 3.2.1)

2. Unidirectid cartxm-fiber / polyester tubing was ait into eight

loomm lcngths.

3. The inside bcmding s&bœ of the aluminum inrat was

roughcnd with a small file to iecreart the shcaring stmgth of the

bond.

Figure 4. I .2 - TIvee-point brnding tut spcciwaen

4. As suggested in [3q. the surfnce of the c ~ m p ~ s i t e tube thpt was

to be bondcd was a h sanded with cmery cl& to remove any

rclcast agent and extra min that might have bœn pmsat b the

manufacairing process.

5. The duminum iwrts w e n clampai in such a way as to be

vertical and couial with th composite tubes.

6. nie bond volume was fully filleci with Mbcmd epoxy [4û] md a

bond fillet was &a@ by heid to approximately 45 degras.

7. The set-up was leh 24 hours at m m temperaturr to nue.

McGill University Depsrcnwnt of Medunid &@e&g 50

Design of a Compogtie Link fa dw PIssQat7 Hirpric H a d

Test # The sampks were mounted in a

&me-point testins jig that ailowed fa

0.1 10.0 3.0 simp1y suppcxtcü conditions. 'Lbe l od F wu atppiicd by a cyiinâricai appliclltoc ai a

daBtsurfkcmachinadintothc

aluminum in!wrts at C an figure 4.1.1 to Figure 4.13- Variation of diwunswu

assure a point 1d conditicm. The for three point bmding ~ c s t s horizontal distances AC and CB art the

displacement rate for the position control was chosen to k 0.095 mmlsec, d t i n g in a

quasi-static loading case.

4.2 Calcuiations for Bending Moment Load Case

The ideal shear force (V) and bcnding mommt (M) &gram for the simply

Figure 4.2.1- S k and bedng inoment diograms for thme-point

benàïng tesu

supported threc-point knd test is show in fi- 4.Z 1. Tbe maximum bndbg moment

on the sample is at point C. The maxjmum kadiag moment on tk boided mgion is at

D e s i g n o f a C o m p o J i t e L i a L f d t t h t ~ 7 5 @ ~ ~ ~

pointsDandE. nrstfailurcwjllawthacductothefmsi011coDIcdb~thb~0f

the sample. Due to the na -honqpmw nature of the test samples, the pure bending

formula for the caiculation of tbe ItSUltant stress in tbe sdlllple dœs not hold 'Iae

individual wmponcnts have MCICII~ moduli ofclasticity a d dinirient rdii for

the same load. The ideai caldations f a the stress in a prismatic beam unda pue

bending qui re that the riuiius of curvature for the bcam is constant and that the cross

sections of the kam remain udefOllILtd and papendicular to the laigitudinai pris. an

assumption that d a s not hold hem.

To provide a design der ion fa the bondcd gcomcîry, th remrl l d canditicms

have bcen repmduccd as closcly as possible. 'Ibe bcnding mode is the load case that wïli

bcsecnintheactualpn>tot~pehriid~~~ltrollet,sadamuimum~~ldcmbe

calculated as follows:

M- is maximum ômding moment expeaed in h c e (case of usct hitting a

physical limit stop)

Fiihmd is maximum user hand force. In out case we take this to bc 40 N [3]

23 is the Iength of the stage 3 iinkage (sec figure 1.4.3). 1H)mm.

EB is the distance fmn the simply supportai sdge to the end of the bondeci

area (sec figure 4.1. 1). 90mm.

F , is the maximum f a a the sample is requirrd to withstand without failurc

Applyhg the nimnt values to the above equatim, we gct a minimum Mure load

of 133.33 N of force to be applied to the sample befae finit Mure If we takc a

minimum safety factor of 2.0. thc load that wiii need to be suppatcd by the sample is

266.67 N,

McGill University Departmcnt of Mechrnicrl- . . 52

The piston fixce vs. dispiaccment curves fœ the fam samples a shown in figm

4.3.1. The curvts for tests 1.2 .nd 3 show two definite filllult modes. Figure 4.3.2 shows

a failcd speciwn. niese a causcd by cracking in the epoxy bond. h the third ~gim cm

the curve, the bond is nùly M e 4 and the to the bcnding of the uaiplê hi due

entirely to the friction bctwecn the aluminum intchœ and the epoxy bond. The cur~e

for test 4 shows d y one Um. the -C MIKC. foiîowed by a simila Woii dominated by the fiction fora ktwœn the bond end th ioughencü dumin- insert.

The initiac f 0 Z w (IF) is what wïii be dealt with in thc campariscm bttwœn the bond

geometnts.

ceaterpoht dîspJaaHnent [mm]

Figure 4.3.I - Gr@ of pismn fom vs. cmtmpoint displrutement

Figure 43.2 - Broken the-point knd specimcn --

McGilï University Deputnrnt of Mocbraicrt . .

The sccond -le, with an .dbmnd waU thiclurnn of 3.0 mm, shows the highest

value of piston force for the IF. nie IF occurs at 600 N. The third sample shows a IF at

560 N. The fïrst sample's IF occurs at 540 N. Finally the fouah samp1e's IF occurs at

220 N.

Fmmthecurvcs, wecanseetheffktthatcachpuimctabas aitbeIiCSUIting

strength of the bonded joint. As prcdicted in the axiSymmetnc model in chaptcr 3,

incrtasing the bond line thickncss and increasing the adhacnd thickncss in effect

strengthen the joint. Howeva, it is obvious that the inaease in saiength is vay slight

cornparcd to the hacase in mamial in the joint. I k m s b g the axial engagement of the

joint decreastd the o v d strcngth of the joint. This coincides with the conclusions

drawn h m the finite elacmt modeling p a f d in chaptcr 3. Howeva. the e f f ' on

the overall strcngth of the joint is very pst. Thc lod thet the joint can su- befolt

catastrophic failurc is 4.7% of the nominil specimcn (test sample #1). The joint in this

case does not meet the safcty requircments f a use in structure.

It is intcrcsting to note that the physical specimens showcd a much higha failme

load than predicted by the finite clement model. 'Ibc maximum piston facc that should

have b e n sustainable by the nRt sample, bascd ai the fînïtc elment analysis, is 292.8 N.

The actual value for the piston force at IF for the first sample was 1.91 times this

theoretical value. However? the finite elcmcnt model did not nccessady predict

catastrophic failurc. The physical test of the bonded sample may not have measund

some initial cracking in the bond marcnpl that marc closcly matchcd the filllurc critcrion

obtained h m aie £initc elemcnt model of the h d e d joint The physical test provides a

factor of safety for the bond in bending of 2.33 o v a the worst load case scenario

considemi for a haptic devia.

Rom these tests, WC can see that the nominal joint COIIfiguration is vay close to

the optimizcd value. No gzat gains would k made in inmeashg the adhercnd wall

thickness or the bond liae thickncss, and decrrasing the axhi engagement of the

composite tube would jeopardLc the o v d streagth of the bondecl joint.

5. Design of Box Beam

The construction of a composite box bcam to bc usaï both as a stnictural member

and as a wver for the dista1 stage strings wu> made f a production and marketing rasons.

A less expensive structure w d d ccmsists entrly of the btmded composite tubCs as

describeci in the prrceding chpcas. Howmver, the polymaic Piriag that m usai to

actuate the distal stage of the hand controila arc fairly deliate. and shaild not bc left

exposed in a marketable product. Iastcd of usîng a tu- structure as the structural

entity, and fixing a protective covering over if tbacby grcatiy iwumg the link weight,

the carbon fiber box-section was pmposd as bot. a structural m c m k .ad a cover to

pro- the distal stage strings.

5.2 Dimensional Requirements for the Box Beam

The cross sectional dimensions of the box section fa use as the distal linhge and

the cover for the distal stage strings w a e detcrmined by the intcrfkcnce rcquirtments of

the pulleys caqhg the distal stage strings. The puiieys at dK intersection of the stage 2

linkage and the distal stage h h g e and the puiïeys out at tbe distnl stage arc 23.75 mm in

diameter and 6 mm in height. The puiieys at the distai stage rlso rotate k45" about an

axis that is 3.25 mm bclow the centcr of the N e y . The centers of rotation of the distal

stage puileys arc 32 mm .part, vcrticaliy. nirough simple trigcmometqr, the clcamnce

area for the box bcam c m k detennined as 23.75 mm widc and 53.5 mm high. A

cushion ne& to be added aiound this minimum clearance to pvent intcrfbcnce

between the bondcd inserts that WU be rcqumd for mounting the box-section u> the other

links in the translation stage and the dWal strings. Figure 5.2.1 shows the cl-a a m

for the strings at the distal stage end of the box section.

The box section rsquirrs a methoci of m g to the rrst of the translation stage

stmcnirt. As with the bonded tubes, it was chosen to machine aluminum ïma%s to bc

McGiU University Deportnwit of Mecbrnicrl- - . 56

Figure 5.2.1 - CIccuollce orea for the dis@ stage driving stdngs

adhwively bonded to the cadnm maicrial îhaî waild thcn bamme attacbment points foc

the other aluminum parts requirrd for tbt structure.

Figure 5.2.2 shows an explodtd view of the assembly of thc new crubon f i k

distal stage assembly. Ibe pullcy block base mecl as a mounting point f a tbc h f b

connectingthedistallinltapetothcstageZd3liolages. Thediralstagemamt

providcd the interface with the h c a a a i direil stage.

5.3 Finite Element Mode1 of the Distal Stage Linkage

The design criterion for the tmwIati011 stage of the hmd mtroUer is not kxd

upon a traditional failme critaion, a even a displacemnt &criai as is ofta the case in

robotics applications. The humsn haptic kinesthetic sense is not fine tuneci en- to

accurately disaiminatc kwai two points m spre. hstead the lowcst nmml structural

fkquency of the assembly is the design g d .

To simulate a viriual contact with a soiid wall with acceptable fidelity. th rate at

which the signal is modifled during the simulation is ncar 200 &. If the structurai

natural fiequency is nau or below 2ûû HZ, tben nsomnces can be set up in tbe structurit.

rcducing the fidclity of the sirnuiation.

Threc finite element modeh wae consaucted using 1-DEAS Miicn Series V2.O

of thne separate distal lintsge assemblies. 'Ibe first h i t e elemait mode1 was of the

composite box-bernn structure discussrd hue (figure 5.3.1). Th second modd

corresponded b the proposed shcct-mctai c o v d linlrngc (figure 5.3.2). An itcrative

process was used to determine the lay-up requited fa the composite part f a it to have an

quivalent defltction stifhess to the duminum c o v d linlrage. A iay-up of thme woven

layers (0/9û) was chosen. for a lay-up of [(0/90h Ir. Unfortuoately. due to the excessive

cost associatcd with a filament winding machine. the d y option f a fabncating the box

beam was hand lay-up. For this reason a more rigo~ous ophhation of the hlhatc.

hcluding prccise angle plies to in~rt8se mrrtciial damping. was not possible within the

=ope of this work. Such an optimhtion proccss, howeva. is a suggestion fot fbturc

work on this project.

- - --

McGill University Departnmt of Mcchrnicrl . . 58

Aluminum brick

Figure 53.1 - Fin& riement mesh of conpositc box-section ünbge

Aluminum elements

Aluminum brick elements

5.4 ResuIts of Finite Element Mode1

The finite elemcnt modeh wert solved far a test I d case of 10 N in static

bending to detexmine the e f f i v e s t i f b s s of th Linlcape. Ibc makis wac citso solved

ushg a normal mode dynamiccs iterative solva to dotermine the lowest rescrnant natural

frequencies for the first thrcc modes. Thrc w a e no bouodricy conditions placaï on the

models for planar motion during th normal mode dynamics solution because it vas

1 Max. Deflection

Table 5.4.1 S- of Coniplrrion Between Box B a Finite E k n t Modcls

Vetticaîly Vertical Natural Frq.

, Horizontal Naturaï Frcq. Total Estima- Weight

desircd to h d the rcwnant fiequencies in dl thrrc primPy directions.

Table 5.4.1 summarizes the most impaaat rrsults of the modehg. h m table

5.4.1, it is obvious that the composite h b g e cnnperrs fivorably to the aluminum

covered linkage. Then is a gain in vatical bcnding stifniess of the hkage of 8.67% for

the composite linlcage over the duminum mercd linkage. The vertical natural fnrluaicy of the composite linkage hacrises 31.89% ovcr the aiuminum c o v d linlrage. The

horizontal naturai fhpency of the aluminum linirage does not mœt the design critaion

of 200 Hz, while the composite Iinlrage does. F i y , it is expe*ed that a deatuc in

total weight of the lintage hm the aluminum covercd to thc composite of 35.43% wii i

occur. From these d t s , it is obvious that a composite box-secticm in p h of an

a1uminu.m sheet-metd cova is a vcry advmtagcous design choice.

AhmiinmCovcrcd

15h10-2 mm

McGill University Deparînmt of i k b a i d 60

' Composite Lkkagc

I

1.37xlû-2 mm

552 Hz [l86R'zJ

127 g

l

728 Hz 221 Hz

82 R

6. Box Beam Protoope

6.1 Carbon Fiber Box Beam

The actual co~~~truction of the box beam prototype rcqpbd s e v d steps. The

fint step was the constnicticm of an extcmal mold f a the carban fiber matdal. The

mold was d e in two halves. The stock mstniat for the mold was exbruded aluminuxu

channel. The use of the cbaaael allowed for conrers with Cansistent cumature of M y

large radius. It is important to avoid sharp COWR whcn w&g with an extemol mold

The channel sizc was chosen to have the same intenial dimmsians as the extemal

dimensions of the composite box-beam sbnictme. Ibe inncr mfke of the mold WU

polished to provide for a good surface finish for the composite picce. Holes wem drillecl

and tapptd in the w& of the channe1 to provide clamping points f a the two halva of

the mold. The purpose of the mold is to ptoviâc a rigid surf.ee on which to pbce the

carbon-fiber material to give it shape. The mw carbon-fiber materiai cornes in the farm

of long sheets of woven or unidirectid fibers pre-imprcgnated with an epoxy resin.

The epoxy resin holds the nbeR together in the finished piea while the fibers, being

much stronger than the epoxy, arc respoasible fot caxrying the l& applied to the part.

The @-up refers to the procas by whkh loyers of the cadxm f i k material rue placcd in

succession, one on top of the other, to neatt a waU t h i c b f a the composite part. The

materid for the layers can bc cut dinctcllt wiys to obtriii diffhntfibcr orientcrtions.

ailowing customizaticm of laya propaiies as explaineci in Chaptcr 2.

The choice of an extemai mold was ma& fa tum L~CBSOIIS: first, the cross-section

had to be hoiiow to allow the passing of the distd stage strings, and second, a marketable

product would nquire a superior s u a finish to be acceptable. Whik the fht condition

could bc met with an internai. rcmovable mol& the SeCoad rrquind the extcrnal mold to

prevent material wrinlüag during the c m .

To cure a composite part, the carbnnkr muai.l has to k subjectcd to

prolonged periods of hest and prrssuit in ada to hrrdm th^ epxy miin. l k sue cycle

BkGiU University Depattme~t of ~ c c h r n i ~ r l ~nghmkg 61

refers to the controlied changes in pssme and a ~ ~ l i t d to tk pt

duringthehardeningprocessoftbeepoxyresin. AUcOmpOSitemrta.lrrrgiiircanne

cycle. However, some resmS cure at much lowa tcaiparturw than otbas. Ibe cure

cycle that is used for the rmtmcil chosai [37] foe the cumpo&c box-section is the

Revious attempts at a lay-up with the split mold wen unsuccesJful b- of the

choice of a thin tefion sheet as a reieuscfih. 'Lbe rcleasc film is nquirrd so that the

epoxy min does not stick to the mold during the cure cycle- S e v d pr0bl.m~ ocaimd

with this technique. Fust, the mold had to be closed fimm the start of the iay-up process

to d o w for the insertion of the tcflon film. Not only did this mak the lay-up technique

more difficult but didn't aUow SuffiCient pressure to be applied to the corners of tk box

beam during curing. The teflcm film had a tmchcy to strctch away Ibn the corners of

the molci, causing gaps bctwccn the pazt and th mold mufkc thai, afta -8, d t e d

in excessive dry spots on the outer SUrf~ce.

Amisol. a Company that produces Fretkote liquid nlares, aras approached and

they provided a combination of BIS liquid seahnt and Ftetkde 7ûûNC releuv agent to

treat the inside of the mold [42]. This solution wodrtd v a y well. Application of the

seaiant and release agent took 20 minutes plus po1yrileriPng tim (24 h m ) and the

dtingSUrfacefinishwa9muchbaia~thtori~ypropoecdttfl0~tnIm. The

McGiU University Departmnt of Mecbinicrl Engmœnog . . 62

release agent on the mold riirnce .Ilowed thc lay-up to k stazted with the mold rpa.

which made the lay-up techaique much d e r .

'Lhe first laya of the carôm-fiber matcriai wu put in phcc with the mold spart.

Two picces of the (W9û) woven carbcm nba maîdal4Smm x 175mm werc pisceci inside

one half of the mold with the cùgcs flush with th split edga of the mol& %O otba

pieces 60mm x 175 mm wcrc placcd in the ocha h.lf with m ovahrng of approxUnately

15mrn. The layers also ovaiap on the middlt of the large face of the box b m by

approximately Smm. Part of the second layg of woven niritaipl is addcd kfae to mold

is joined to ailow for beücr placement and cornplesai011 ofthe layem. 'NO picces of

60mm x 175mm are cut of the [W90] wovcp mntmal and arc p W f i t the lege

surf'acc of the mold, with a small overhp of a p p r o ~ t t l y 5mm k y d the midpoint of

the corner cwaturc. This mail overlap is essential fa goai bonding of tbe full laya to

the srnalier 30mm x 175mm pieces thrt arc addcd aice tbe mold b c l d A cornpletc

third layer consisting of two pieoc9 of 6ûmm x 175 mm. and two of 3<)mm x 175 mm are

put in place with the mold closcd nie f h i nsult is a loyYp comisthg of threc layen,

[(0/9ûhlr, where the (W90) grwp repmsats the woven graphite matuiai. In the mgions

of overlap near the corners, the lay-up is actually [(0/9û)SJT, and h g the middlt of the

large fafe of the box-beam, [(W90)4]r. The Iiy-up is show step by step in figure

6.1.2.

Two pieces of the teflon rcIease film were applied to the insi& of the composite

part, foUowed by a layer of brcather motenPl fa the even application of the vacuum to the

whole piece. The teflon film in this case pvents the brcather mptmel hm sticking to

the cured epoxy. The vucuwn h g is a seaicd plastic shea that wmpktely covers the

part By drawing a vacuum inside this bg. the composite mataial is presscd up against

the waii of the mold, cornpressing the layas togethcr and faming a much stmnger p i e .

The reason it is necessary to avoid sharp wmas in an extanal mol& as was mentioncd

above, is that the vacuum ôag cannot i n f i l m a shup radius to qply an evai prrsauc on

the composite material. It is the leck of vacuum pmsurc cm the mamiaï that causa dry

spots to occur.

~ c ~ i l l University ~cpertmnt of Mecbrnicrl ~ n g b e h g 63

layer 1 Aluminum mold

layer 2

1

1

Figue 6.12 - Luy-up P10ccdrve for Coni;posi& Box-Section

McGiU University Dcputmcnt OdMechrnicrl Piiarrwrnp . . 64

Design of a Composite Liuk for bit -7 Haptk Hlir;r-

The vacuum brgging t~chnique was slightly diffiicnnt tht is t m d i t ï d fa an

extcrnal mold applicaîiom The oven to be used did rmt hm a prtraimbag pump, d y a

vacuum pump attachmmt Thcrcfm, instcad of an innarshle i n t d b l d d a tù tpply

pressure to the part, a cyiindricai arrangement of tbc vacuum bag was dtvised. Two

cyhders of vacuum bagging mrtaipl, sedeci h g the side, wat piaced inside and

outside the mold. The ends w u c tha, d e d to each athcr aicmg the c v c u m f ~ c e . Th*

allowed for aîmospheric pressure to bc applied to the ni1l intemai sufbx of the molcl,

without the added expense of an Maiable bladdcr.

'I%ecurcdpiecehadgaodsurface~0ilb03hthcoutsjrlr!andinffiALsun8ces.

There was no wrinLling on the inside SULf'acc of the box bcam k a u s c the motaiPl WU,

slightly under tension. It was difficult to gct evcn p s s u c into the ~ ~ ~ Q C X S , anâ &y

ended up slightly min rich. It was obvious by looking u the thicbress of the waUs

throughout the cross section. me best comprtssion occuucd on the lPpe hct of the box

beam. This leads to a slight prob1em with dimensionai to1eranœs. It is diîflcuit to

control the final interior dimensions of the box kam since tbey pe v a y depeadent the

compression that could be obtained on the f&cs of the part d the guality of the vacuum

pressure in the corners. For the casc of the Ereedom-7 projcct, good dimensional canml

was quired on the inside d a c e of the box beam siafe machincd md fiüings an to be

bonded to this inside SUfact.

6.2 End Fittings

The nnai design of the end fittings was detcmhcd aRer siflcant pro-s had

a l d y bcen made on the consûuction of the box beam. Onginilly, small plPtes fixed cm

the exterior surface of the box bcam w a c inttnded u> bt uscd as mounting points fa th

various aluminum parts nquirrd for the ksriag mounts and joint shafts of the hand

wntroller. Last minute design cimages led to a modification of this i d u to d o w for

precisely machined, end fittings to be bonded to the inside waiî of the box section. As

discusseù in the previous section, the intcrior dimensions of the box bcam are not weli

controlled and can seriously affect the bond lim thiclaiess and, co~lsc~uently, the tbesemgth

of the bonded joint As weU, due to the close clcarance seleeted f a the distai stape

McGill University Depararuot of Mechinicrl- 65

strings, the wall thiclwss of the mctal inoar miut neccssdy be v a y rmrll. which pores

machining difficulties- A ampmmhe was mde betwecn thsc vdous -ts,

and the piece was designcd

The material selection for the end fitiiog was rnotba problem area. One of the

design goals of the Frcedom-7 was d u c c d link inatia. To achieve this goal, parts of

minimum weight werc rcqumd fot alî amas. Th existing metal pmtotyp it made

entkly of aluminum-6061. To avoid using two di&rmt mctals and mcoiinging gaivanic

wmsion among the metallic parts, it would k logicai to choolie aluminm 6061 as the

material for the bonded insgts. Howcver, almninum f m an &de v g y d y in au and

this aluminum oxide is highly anodic. In the pnsence of an eleca~lyte such as sca water,

there can be signincant corrosion of the contact surfaces bttwccll aiuminum and a

cathodic material such as graphite. As a resuit, the aluminum d fittings rcquire etchmg

to remove the aluminum oxide iaycr on the baading sudacc befoft the bonding opcrati011,

The West-Systcm's aiuminum etching kit (431 wu uscd to pnpsn tûe boading

surface of the aluminum hscrts. The portions of the bat not subjea to dhesive

bonding were maskd with tapc, and the etching process was Camed out accordhg to the

directions on the etching Lit. With the carcful ptcpatatim of the aluminum and

composite surfaces the galvanic corrosion of these purp should be kcpt to a minimum-

6.3 Bonding of End Fittings

The bonding of the aluminum end fittings roquirrd the collsf~cticm of a jig to

keep the two planes of the end fittings paraIlel. The jig coasisted of two acaratcly

machined right angle L's mounted on magnetic bases. The mgnetic bvles k themselves

to the top of a metai level table. nie right angk maire use of the mounting holes on the

end-fiaings to hold the end-fitthgs in p h . A dial-gauge wu, uscd to mepsun the

deviation of the end-fittings and the box-section from parallcl.

As sated before. the internai dimensions of the box-section wcm poaly contn,iied

with the rnanufacbg me- Thc min rich arcas in the comas of tk box-section hd

to be filed d o m to aliow the end-firtings to fit inside.

McGiil University Depatmitot of Mecbrnicrl- - . 66

One standard pmdurc f a casuriag evm boncl liiu thickncss ova a iargc

bonduigaruiistoursmrll~gearireembeddadhchcboadmaa*ltortuaspra

during the adhesive bonding [36]. nieSe wires normrlly ovc~Iap the bondcd region md

are cut flush with the adge once the adhcsive is curcd, Tbese wirw arc not necded in this

case to maintain the bond line thicloless as the corners of the metal insats art in contact

with the resin rich areas in the comas of the box-section. The mah &car camying amas

of the bonded interface, the 5 t fhccs of the boadtd region. have a gcmd, u d o m i bond

line thickness without the discontinuities and potential stress concentration points that

could bc caused by the incluskm of the sPndsrd wirc m tbc boadcd region.

Due to the long cure time (24 hours) of the Adbond epoxy [W. thac was ~ome

seepage around the interface with the end fittiag and the composite maîcd. Ibe

strength of the bond was not comproaiised. as the bonci lcngth was dcsigncd with a iarge

factor of safety. However, for friture production, an epoxy with a much lowa cure timc

should be considemi.

6.4 Structural Tests on Fkedom-7

The existing aluminum prototype at MPB Technologies was COIlfigurcd in such a

way as to be able to accept bath a distai stage linlcage and a stage tbrse linluge in the

form of a box beam. nienfore, a second box bum was constructed using ihe J I M ~

technique as for the ht, and substituted for the stage thrce linkage (inrttsd of using the

bonded composite tubes). This was a marketing design change. and will not the

continuhg research inta the propcr design of bonded intufbces fbr smaU diaiiaetcr

composite tubing that continues in the next chptns.

-

Table 6.4.1- Weight Dmbwion for BOX-Bccun Ports

Distal Stage Link

Stage 3 Link

McGill University Depattmcnt of hkhmid 67

Fittings 17.5 g x 2

17.5 g x 2

Flber 23.7 g

28.0 g

Composite 101.5 g

106.6 g

luluumiaumuminum 103.2 g

98.2 g

The weights of the iadividiial parts of thc box krm assemblics arc shown in pble

6.4.1. as weii as the overail weights of the asanbled mes md the aarespoidiiig

duminum linlrages. They do not match with thc dmaîcd weights fiom tabic 5.4-1. It is

obvious fkom the weight brtakdown that the aluminum bats f a the comp0site box

beams arc significantly ovadcsigned. As mentioncd kfae. the machin*tr have

difficulties working with aluminum of vay thin wall thichicrs. Thcrcf-, to facilitate

the machinhg process, the wail thicknesses were increased and more matujaî was lefk in

the center for mounting of the intcrface parts- The weights of the enâ fittings s~count f a

34.4% and 32.8% of the overail weights of the dïstd .nd stage 3 linlrnges rcspd.ve1y. It

is by no means unreasonable to consider that a design of the ad fittings could d u c e

their weight by 50%. malaiig the overail weight of the link assembiics 84s fa the distai

stage linkage and 89.1 g for the stage 3 bkage, which w d d be much closa to the

original estimateci weights. This des ign wodd COIlStitute a weight savings of 19.2

grams, or 18.6%. in the distd stage, wbich is the major contributor to the o v d inertia

of the translation stage.

6.5 Frequency Response of Translation Stage Two dynamic rcspoase tests wae pcrfamed on the translation stage of the

Freedom-7 hand controiier. 'Lhc first consistecl of sading a fiequency varying sine wave

individually to each of the thrte motors and mtasuring the end tffcctot accelledon in the

nominal direction g o v e d by each motor. Tht pur- of this test was to determint the

resonant frequencies of the structure in each direction. If we consider the translation

stage to be planar, with the positive xdirection paralle1 to the stage 1 and 3 iinkagcs

pointing towards the motor mounts 6Rnn the distd stage, the positive ydirccticm paralle1

to the distal stage linkage pointing out towards the usa. the right hanà ruic gives us the

positive z-dirrction as downwards perpendidar to the plrae of the brsnslation stage (sec

figure 1 A.6). A small magnitude rotation of the stage 3 motor about the centcd

position provides an instantancous movcmmt dong the x-axis. 'Lbe sznail mapitude

rotation of the stage 2 motor provides movemmt dong the y-axis. The smaU magnitude

rotation of the stage 1 motm govcms the disphcement a h g the the-axis. It is imparmt to

note that, as the stage 1 and 3 motors arc co-plmir, their effkts ai the disphœmcnt of

McGiII University Dep~rcme~lt of MechrnicJ Equrumg - . 68

Dtsign of a Composite Link fa dK Frtuîom-7 HIptic W rrribakr

the distal stage are coupled. Thrrfoee, the hdcpmdmt axes d y M d for smaU

magnitudes of joint displacement around tbe neutraï position. 'Ihc neutd position has ail

the joint angies at 9û0. The second SCLics of dynamic tests to be pcrformed on the

translation stage consisted of inducing an impulse in the motas ofa set amplitude auci

duration and measuring the maximum aac1eration of the end effcctot. This test was

perfonned in order to mcasurt the overail inertia of the stnicîurc in each of the three

motor directions.

Ideally, the resonant 6nquency for the structure in cach of the thee directions

should be greater that 200 Hz. This is an adequate mIution to simUlnlr_ contact with a

solid surf'ace in a virtual environment, The maximum acœleratïon at the end e f f w far

the motor impuise test should be as hïgh as possible, yct alupl ia aU directions. The

higher the maximum a~cclaation at the end effanoi, the greatcr the Mispness of tbe

device. Haptic sensations wiil fccl more rtaliStic and 1- sluggish. Howevcr, if tùe

maximum acceieration is not the same for each link, the apaata may acnac a change in

the response of the device bascd upon the devices orientation. 'Ih* is undesirable, as the

Freedom-7 is intended to be able to bc orientad in any direction.

For convenience, the fhquency rrspoase NVCS have becn gtouped in Appcndix

B. Figures B 1 through B5 show the acceleromcter output vs. the excitation frcquency of

the stage 1 motor (z-dirrction) for the five configurations of tbe translation stage links.

B1 shows the response of the aluminum st~~caire af<er a very carcfbl assembly, wiîh

proper pre-tensionhg of the bcarings and alignment of the shafts. B2 shows the nspoase

of the aluminum structure aAct a somcwhat lcss colltrolled, less expaicnced asscmbly

procedure. B3 shows the ~cspomc for the translation stage wich the two carbon f i k

links included in the structure. B4 shows the rrspanse with only the carbon fiber distal

stage hkage and BS, with only the stage 3 linkage. Similsr tests wae p a f ~ ~ n e d for

each of the other two motors, with figures B6 through BI0 nf-g to the stage 2 motors

@-direction) and figures BI1 through B15 rrfcning to the stage 3 (x-direction) motor. A

summary of the first nsonant fresuency for the translation stage in each Connguration can

be found in table 6.5.1.

-

~ c G i l l University ~cpartmnt of ~ac l iu i i~r l E n g k u h g 69

Second Aluminum Assembbly 103.9 Hz 95.6 Hz 94.2 Hz 1

Two Carban Lïnkagcs 128.0 Hz 127.8 Hz 102.9 Hz

Carbon Distal Stage Lïnkage 115.9 Eh 91.9 Hz 91.9 Hz

Original Aluminum Assembly

Table 65.1- Svnv~ly of First Reso~nt Ftequenciw for the Fretdom-7

Transhtion Stage

Several concIusions may drawn frwi these tests about the fkequmcy rrspaise of

the translation stage. First, the fkquency rcsponse of the translation stage is hcavily

dependent on the assembly proctdurc. F a the stage 1 mode, the aluminum pmiotype

experienced a drop of the naairal fkpency of 7.75% ôctwecn the cucful and

inexperienced assemblies. Second, the stage 1 mode was not afkckd by the inclusion of

tbe carbon linkages, as the frtqucncy rcspomc is dependent on the stifniess in bcnding of

the stage 2 linkage (which was not modined) and the mars of the distai stage, which as

discussed before, suEercd h m ciifTicultics in the mrchhing of the end fittings. 'ïbird,

the incorporation of the carbon linlrs improved the h p c ~ l c y f a the stage 2

mode. With the inclusion of the two composite linltp the naturai fiequency rose 12.2%

over the original assembly and 20.6% ovcr the incxpaiend asscmbly. Tbe stage 3

linkage was the greatest contributor to this impmvement, and f a the test with it slow. the

natural fkequency was 22.4% higher than the iaexperienccd assembly of tbe aluminum

prototype. Fourth, the inexperienct of the asembly contributai to the damping of the

translation stage. In every case th magnitude of the signai from the accelerometct was

higher for the original assembly of the aiuminum structure than fm the inexpcxienced

assembly of the aluminum structure Finally, th- was a problem with the design of the

puiiey block base (sec figure 5.2.2). 'Ibe inclusion of tbe carbcm distal stage was v a y

detrimental to the penormanct of the stage 3 mode. The naturrl fhquency dropped by

34.0% and the magnitude of the signai was vcry high. The rsoembly with only the stage 3

x ~ c m

189.9 Hz

McGill University Departmcnt of MechPniccil- . . 70

y-dllaction

1 15.0 IIz

zdirection

100.1 Hz

linlrage out of carbon ôehaved similady to tbe ahimmum prototype. lu, it's co(1~'kitim to

this m d e is cotlsidered limitai

6.6 Refbed Finite Element Mode1 of Distai Stage Linkage FurthcrinvcstigationwasrcquircdtodaecmMtbeaurtofthtpoa

pafomance. Mon refïncd finitc elaium mOdeIs than tbt one ccmstcuctcd m chiper 5

were uscd to detcrmine specifïcaiiy the rn0d.l v i i a m in the xdirectim fathe displ

stage linkage. 'Lbt author was wispicious of the strmgth in kiding of the pulley block

base. as the weight rcducing atouts wuld significantly compromise the stiffiiess of the

par^ For tbis m. two models w a t usai. The fht mode1ed distal stage iinkagc as

it was for the physicai tests (figure 6.6.1). The d dded a miaforculg cova tbst

exwided h m the carbon fiber nmtdai brk over the piiiey block base (figue 6.6.2).

simiiar to the configuration sem in the sketch in figure 1.4.6-

Figure 6.6.1 - Rrfned &l of d i s d linAuge for vibration simUlCJtiOn

Figure 6.6.2 - Rcfinedjîmk elanrnt d l of distal linkage with a d cmer

for vibran'on simulan'on

The two modcls werr sulved using the itcrative namrl mode vibration solva in

1-DEAS Masters Saies V2.0. Thcy w a c constdned to move dong the x-z plane, in

order to simulate the vibrationai modes that would occur for the stage 3 excitation. The

shafts were considemi as pin connections with the axis of rotation dong the y-axis. The

fïrst normal mode vibration d t fa rbc uncovcmî distal stage is shown in figure 6.6.3.

The biack outline shows the vibration mo&, which is about the stage 2 linkagt

axis. The fkqutncy of vibration is shown at 127.93 Hz. which is very close to the

measured frtquency of the vibratian in the x-directiou with d y the carbon distai stage

shown in Appendix B. figure BI4 of 139 Hz. Tht mode1 seems to be a littïe less stiff

than the physical structure, anâ tends to vibrate at a slightly lowcr fLequ~~~cy. 'Ibis might

&O be accounted for by the lack of matcrial damping in the h i t e elexnent modcl as well

as the inaccuracy of modcling the bcarbg and 0 t h intafre khaviors as describeci in

section 6.5. The iack of matenil dampiag d d cause emws up to 5% and the intanice

effects wuld m u n t for an a d d i t i d lm ema in the naturaï fhpencics, based on the

vibration tests pafomied cm the duminum prototype.

Figure 6.6.4 - Normal d vibroiion in x direction for wu:overed distol stogc

Figure 6.6.3 - Norrrml ww& vibration in x direction of dis@ stage with M cddcd cmer

McGill University De- of Mecbiiricrl Eapmamg . . 73

The solution of the c o v d madcl fa the modal n i o n s is sbown in figure

6.6.4. The fkquency of vi'bration is 202.28 Hz fa tbc fmt rn0d.l frrqueacy in the x-

direction. Even if we do not take into ucomit the slightly lowcr value f a the naîurai

frtquency of vibration in th hite ctmem modcl, h m p m t h g thïs design mto the

translation stage structure would rcsult in an inatpoe in îbc naturai mmcy of 5.9%

over the aluminum box kam prototype. Obviously, the assumptim thir the iack of

stifhess in the pulley block base was the d t of the poor mmcy mponsc is Corna,

and the inclusion of a composite cova ova the Wey block base is an exallent solution.

In order to&tcnninctbcp~jb1eminthepiilley blockûascthatcauscdtbe

wealrness in the x-direction w'btation, the two modeis wcre soLved fa the static l d case

where a load of 10 N was applied to the stage 3 lïnkage SM in the xdircctiun and the

distal stage mount was ciamped in place. The maximum principle stress contours in the

puilcy block base for this load case are displaymi in fi- 6.65 for the u~lcovercd distai

linkage and in figure 6.6.6 f a the w v d distal lhWge.

h m the contours, it is obvious that the weak point in the pilley block base

cornes form the weight reduction cutouts around the shaft that j o b the distal d the

stage 2 linltages. The cutouts create non-rigid sections in thut arcas becau= thcy arc tut

right through instead of having a small flange as would an 1-bcam. F a th covercd distal

stage Linkage, the magnitude of the stress in the wealra region around the shaft holcs is

much less than for the unwvcred case. It is also apparent thu some of the l a d is

transfemd through the standoff bctwecn the two shpA holes to the wmposite covcr.

This rrdistribution of the l d explains the gains in structurai stiffiicss obtained by rddirig

a composite cover to this piece.

--

McGiii University Departmcnt of Mechrnicrl Equsmag . . 74

Figurc 6.6.6 - Stress contours in covcredpul@ b l d &se

McGill University DeprrÉment of MachiMcil . . 75

6.7 Maximum Acceleration Test In orâer to muwnthehecti~~~inlinkmatir. atcstwaspaiOLmddtomcasurc

the maximum acceleratim of the end e&da f a a givm impulse fiinctiaa It is &sirable

to have the highest end enaCtor acceleration possible. A higher end e&cta acœleratîon

capability wiU d o w a grriter aiqmcss of the haptic ~ 0 ~ 1 s féd bak to tbe user

through the device-

The physical test for the maximum üaL rceleration oonsirtcd of sending a single

10 ms pulse of 10 V peak to each of the motors in tum, and measuring the instantantous

output of the acce1erometcr rnouned at the end e f f i pogiticm on the translation stage

in each case. This test will be r e f d to as the k e p test, as the signal sent ta the motors

is a short voltage beep. The signal was gencratcd by a polynomial wavrfam synthesizer,

mode1 20U) by ANALOGIC. The wavcfam synthesiza was to a sq-

wave of pend 10 seconds, amplitude 10 V peak and a duty cycle of 0.1%. The pulse

was used to trigger a single sampling display f a a digitai OSCiUoscopt, which mu3 the

output of the accelemmttcr.

The beep test was pcrformed on each configuration of the translation stage (except

for the original alumùium assembly) for each motor direction. 'Ih output of th

acce1erometer had becn calibrate- to 10.20 mVfg accordbg to [44]. Table 6.7.1

summarizes the resuits of the maximum accelcration tests.

I Composite stage 3 linkage 1 3.43 g 1 2.54 g 1 2.94g 1

Alilminiim assembly

Two composite 1 i . c ~

Composite distal stage iïnkage

The results of this test show tht. fa the mcst part, the inc1usion of the composite

links have a beneficial e&ct on thc maximum ad e f f î a c c e l d o n Ibc giuast

3.43 g

3.92 g

3.92 g

2.94 g

2-94 g

3.92 g

2.94 g

3.92 g

3.92 g

gains are made in the x md z directicms fa the inc1usi01~ of boch CampoBite links.

However, with the design of the metailïc end fittings? the gains in maximum

acceleration shouid be highcr, as the linL weights rad t h d m t b ~ C O U H ~ ~

weights should dtcrcasc dong with the structurai iriertia.

6.8 Summary for Box Beam Rototyping and Testing The hand Lay-up method for fkbricating a composite box h m is time consamhg

and inappropriate for a pioductiou mode1 of the haptic hand controlier. A m a t suicable

manufacniring method would be filamait winding. Accurate f ï k orientations, almg

with good dimensional tolerances could be obtamed fot a much longer box section, that

couid thcn be cut to the rrquirrd lcngths for the linlugcr. Howevcr, fa pmtatyping

purposa, the hand lay-up in the extemal mold providcd a good sdhcc finish and wur

l a s expensive than obtaining a filament winding machine.

The design of the metal end fitiings was not carricd out rigaaisly mou@. An

overly cautious design couplcd with the iaberent difEiculties in machiiriiig duminum parts

with small waU thiclmcss crcatcd a part that was too hcavy fa the design rrquiricments.

By simply revising the part to be have one half the bond engagement would decruise the

weight of the end fitting by 50% and approach the rcquired design critaion.

The bonding of the aluminum end fiühgs to the composite box bcam was

accomplished without difficulty using a bondhg jig to hold the parts in place during the

epoxy cure. A s h o w cure epoxy could be substituted to allow for a quicker acsmibly

timc for the linkage.

The inclusion of composite mataials has koefits kyond w h t wu mersurrd in

the physical tests on the translation stage. The vibration charactcristics of the translation

stage are very heavily dcpcndent on the asscmbly pmccss. and the inexpience of the

author resulted in assembly dominated vaiues f a the lowest naturai hquency of

vibration in some modes for the translation stage.

The vibration modes tbat took advantage of the composite matcr*l showd sow

improvement over the alumulum prototype. Then was little gain in the maximum

acceleration of the end effcctor due to the ovcrdcsign of tbe bondcd bats thit

the weight of the composite links. Roblems assxiatcü with thc design of the alumin~m

Design of a Composite T,inC fa the Fxœdom7 H@c Hami rmkrJtr

interface parts such as tbe puiiey block base fa the disPl stage .Ir0 ccmtributed to the

poor penormance of the composite iinkages. niaha f i t e elcmnt analysis mnfhed

the wealmess of the pulley block base part, and showd that the simple inclusicm of a

composite cover to reinfo~ict this part wouid @y imPn,vt the dynimic respoase of tbe

composite distal stage ïinkage.

It is clear that the composite mataials show bcnefitr fa the dypanic

performance, however more carc has ta be t aka with the corMnaction of the metal

interface parts that are needed for the incorporation of the advanceci mataiils hto the

structure.

McGill University Deparmnent of Mtchirnicll- . . 78

7. Conclusions and Recommendations

This thesis has undatalrcn to r e h e and improve the design of the Rrcdom-7

haptic hand controkr f a dynamic and structurai rcpmse. Analysis was p a f d to

determine the optimum rncthod for incluskm of c011lpositc muaials in the translation

stage of îhe hand wntrok. Improvements hpve kai made in the 8nalysis and design of

composite parts for robotic applications:

An optimized bond geometry is proposcd fa the joining of smrll diameter mmposite

tubes to metallic W. Thc finite element modeling predicts a fiUlm that b slightly

lower than the muisurcd fail- of the test specimens. lhis d g u W a n ir ppd

as a repiacement for machineci aluminum iinkagges in the ûmdati011 stage of the had

controlier, such as the stage 3 iinkage.

Physical testing of the optimized bondcd gcometry cOIlfilmed the d y t i d e&cg

obtained through finitc element analysis. T b strength of tbe bond in bcnding is d y

weakly dependent on the adhercnd wali thichss and the bond Line thiclaiess, but is

very dependent on the axial engagement of the t u b and the duminum insaL The

overall strength of the physid spccimen was hi* than that of the finite el-t

model. suggesting an overly cowrvative modcling of the joint.

The distal stage linkage of the translation stage of the Frdom-7 is replsccd by a box

beam structure that is at once a structural elemeat of the translation stage and a

protective covering for the distai stage strings. 'Ibe iay-up lad box-bePm structure of

the carbon fiber is beneficial to the dy-c pdonnaiice of the translation stage.

However, insufficient sangth in the machincû duminum inscrts arc rwpoasible for a

drop in the lowest n a d resonant frcqucncy of the translatjon stage.

Swept sine tests were pcrformed on the translation stage, ushg an 8ccclcromta to

measure the resonant pcak w'brations at the end effcctot. This aiiowcd fa a separaticm

of the modal vibrations for the excitation of cach motor individdy.

- -

McGill University Dcpartmcnt of Mechanid Engbc&q 79

a Maximum link accelerations weric masurcd wing an acœlerometer maunted at the

end cffcctor for a voltage pulse to e r h motor. 'Ih rcspnsê of tbe translation stage to

this excitation depends on the link weighto rad inatirr â~ m ~ c h â~ W rcautor

capabilities.

7.1 Recommendations for Future Work The Freedom-7 haptic hand contr011cr could -y -fit hm the inclusion of

composite materials in the strucau~ of the translation stage. Howevu, more wodE is

requcd to narrow the design rtQuircments to d o w for prapa exploitation of the

potentials of the composite material pacts. The foliowing att samt suggestions f a fiiture

work on the Freedom-7 projcct, based on the obsemations and conclusions drawn fmm

this work:

hplement the addition of a reinforcing cuver over the puiiey block base. The addition

of a reinforcing covcr of carbon f ikr matcriai o v a the pulley block bPse of the duul

stage has bcen shown, by M t c element analysis to i m p v e the dynamic @'ce of the distal stage linkage.

Redesign the bondcd aluminwn insais on the distal stage box barn f a r e d u d

weighî.

Perfonn an extensive analysis on the human haptic systcm to determine Specinc

requirements of a haptic manipulator, such as maximum allowable end point

deflection, sensory bandwidth. etc..

Perfom a complete lay-up optimization routine on the linlrages of the translation stage

to detcnnine the optimum fiber orientations foi the opegfic haptic rcqhments and

proâuce filament wound box sections ushg this layiip.

McGili University Departmcnt of Mechrnid E n g b e i q 80

Design of a Composite Li& fœ bw Frrsdoat7 Hkptk Had

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Research: the 7L Intematid SympaSium, Springs Vctlag, pp.195-Un.

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McGill University Departumt of Mechanid 81

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12. Sung, C.K. 6 Shyl, S.S., "A Composite raminatui BoxSection Beam Wgn for

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the ASME, VoL109, Mar. 1987, pp-74-86-

15. Rosenberg et al., '4ElectromecMd Human-Computer Iiiterf- Mth Facc

Feedback", United States Patent # 5 576 727, Nov. 19,1996.

16. Burdea, Gngore C., "Force and Touch Fdhack for V i Reality", John W i y and

Sons, NY, 1996.

17. Laschet, G., "Numerical Strength Prcdictions of Adbcsively Boaded Multinratcrial

Joints", AGARD-CP-590, No. 12, Jan. 1997.

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McGilI University Deparment of Mechauid E n g h h n g 82

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29. Rice, A. & Molds, J., "Bondecl Ropshnftr: design and Asscmbty of Com@te I'ubes

and Metal End Fittings", Matcriaïs Science and Tcchnoloey, VoL9, June 1993,

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McGiii University Department of Mccbrnicrl- - * 83

Design of a Composite Link fa the Fr#dom-7 H@c Hhad C m î m k

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McGifl University Departnmt of hidmaid E- - . 84

Figure A 1 - Test 1.4

l

Figure A 2 - Test I . 1

, University Departmnt of Mechanid 9-ii

Figure A 3- Test 2.4

Figure A 4 - Test 3.4

pue A 5 - Test 4.4

ity Departmnt of Mechanid Eo@eubg 9-v

Figure A 6 - Tcst 5.4

- . McGiU University Depertnient of M c d m ï d 9 4

iof aCompositeLmkfordreh#dom-7

1

Figure A 8 - Test 7.4

IO. Appendk B

Vibration in z-àirecüon (Stage 1) - Alnminiim prototype orblnil-b

Figure B 1

McGïU University Departmnt of Mechrnicrl . * 10-ix

Figure B 2

McGiïï University Depiutment of Mechrnicrl- S . Io-x

Design of a Composite Link for the -7 &rptic Had

Vibration in z-dlrraion (Stage 1) - two fubon Jhbges lodudd

Figure B 3

McGiIl University Departmat of hhhaa id Enpmrimnp * .

Vibration in z-dirrction (Stage 1) - carbon disfPl stage

Figure B 4

Figure B 5

McGill University Dep~rrmnt of Macbaaicll- . . 1exiii

Figure B 6

McGill University De- of M d a n i d Engummg . - 10lxiv

Figure B 7

Vibration in y-direcüoa (Stage 2) - fwMmbIy with two carboa -

Figure B 8

McGill University De- of Mcdmaid WXV~

Figure B 9

McGill University Deputnient of bkhmid l & d

Vibration in y-direcüon (Stage 2) - arbon stage 3 k h g e

Figure B 10

McGili University De- of Ibkdmid Engmumg . . 10-xviii

Vibration in s-diroetion (Stage 3) - aiaminom prototype o r i g i d -Y

Figure B I I

McGill University Deputment of Mechrnicrl- . .

Vibration in xldirection (Stage 3) - .Inminom praotJpc 2ad asmnbly

Figure B 12

M O University Depmmnt of Mechinicrl - . 10-xx

Vibration in x-âûecüon (Stage 3) - assembly with two arbm -

Figure B 13

McGill University Deputment of I u k h i d b g m c m g . .

Design of a Composite Li& fol tbc F e 7 HIptic RMA Coatrollca

Figure B 14

Vibraüon in s -dhdon (Stages) - carbon a#age 3 Wmge

350E-02 -

3.ûûE-02 - -

Figure B I S

McGill University Department of Mechraicrl- . -