16th IEEE International Conference on Robot & Human Interactive Communication WC4-4August 26 - 29, 2007 / Jeju, Korea

A wireless Bluetooth Dataglove based on a novel goniometric sensors

0. Portillo-Rodriguez , C.A. AvizzanoI, E. Sotgiu , S. Pabon', A. Frisolil, J. Ortiz2 and M. BergamascoI'Perceptual Robotics Laboratory (PERCRO), Scuola Superiore Sant'Anna, Pisa, Italy2Instituto Tecnologico de Estudios Superiores de Monterrey, Campus Toluca, Mexico

e-mail: (otniel, carlo, bergamasco)g sssup.it

Abstract- In this paper the design and construction of anovel wireless Dataglove based on new flexible goniometricsensor technology is described. The device is characterized bya low cost and rugged construction and no requires calibrationbefore its use. Indeed, the sensors used are purely goniometric,so they are not sensible to dimensions of the user's hand. TheDataglove can measure the angular displacement of the fingershand using 11 sensors, each sensor has a resolution of 0.2 de-grees, with 3 degree of accuracy in the worst case. The com-munication between the Dataglove and its computer Host iscarried out using a 2,4 Gigahertz Wireless Bluetooth radioprotocol, in a guaranteed range up to 10 meters with a refreshrate of 100 Hz.

I. INTRODUCTION

Dataglove is a glove fitted with sensors to measure the rela-tive angular displacement of the finger limbs. Datagloveshave been of high interest since the beginning of virtualreality, telerobotics and biomechanics. Datagloves may useseveral technologies: fiber optics, strain gauges, potenti-ometers, accelerometers or Hall effect sensors [1].

The fiber optics technology relies on polymeric lightguides with a photo emitter and receiver at one end and areflector at the other. The light beam is reflected at the end,the measured intensity returned to the base depends on thecurvature of the beam. The optic fibers are mounted on aDataglove and allow the detection of the fingers' move-ments. Zimmerman [2] presents a commercial example ofthis technology: the Dataglove, which is a neoprene fabricglove with two fiber optic loops on each finger. If a user hasextra large or small hands, the loops will not correspond verywell to the actual knuckle position and the user will not beable to produce very accurate gestures, in consequence theDataglove requires recalibration for each user. Fifth Di-mension Technologies (5DT, Irvine, CA) produces aDataglove that measures two joints per finger using fiberoptic sensors. Two versions (5-sensor and 14-sensor) of thisexpensive wireless sensor Dataglove are available [3].Sama et al [4] presented other technology to construct

Datagloves based on resistive strain gauges insertedin-between plastic slices. By curving the component, theresistance of the bend sensor changes and the angle can beestimated. These devices are placed on a glove for the ac-quisition. The devices based on this technology are preciseand not encumbering, but their cost is high (10000 15000USD) and they suffer reliability problems in the long timedue to the high level of deformation. The Cyber Glove [5]

(Immersion Corporation, San Jose, CA) is the most signifi-cant example of this technology; it contains 5 to 22 straingauges to measure individual joint movements. Anotherexample is the P5 Dataglove (Essential Reality) [6], thischeap device -approximately 50 USD- uses one bend sensorper finger and transmits its position and rotation measure-ments to desktop mounted receiver using infrared emitters,its receiver range is limited to 3-4 foot.

Potentiometers have been used to construct Datagloves inapplications where easy and fast implementations are re-quired [7]. The main advantages of potentiometers are thelow cost and the small size, its main drawbacks are firstly itstendency to capture electrical noise, secondly the contactbetween the wiper and the resistive element that reduces thelife of the device and thirdly the thermal drift of the trans-ducer.Hand gestures are typically captured with alternative

sensors, for instance, accelerometers integrate motion ac-celeration cues and filtering drifting errors for finger mo-tions. Pergn et al. [8] presented a system interface dedicatedto hand movement recognition to enable mouse-like inputusing the Acceleration Sensing Glove, the Dataglove isequipped with six 2-axis accelerometers on the finger tipsand back of the hand, it has also an RF transmitter to senddata to a personal computer, thus acting a wireless glovedevice.

Hall effect sensors measure slow changes in magneticfield. The name Hall-effect refers to the physics process ofbending the flow of electrons through a semiconductor,perpendicular to the magnetic field lines. This bending oftheflow results in a displacement of electron concentrations andtherefore a voltage difference. The Humanglove [9] is asensorized elastic fabric Dataglove designed and commer-cialized by Humanware, it is equipped with 20 Hall effectsensors, each sensor measures data related to a DOF of thehand. The Exos Dexterous Hand Master is not really aDataglove but a mechanical hand exoskeleton system. TheExos Hand Master measures the position for all fourjoints ofeach finger using Hall effect sensors [10].

People have different length, thickness oftheir fingers andsize of their hands' palm, so it is necessary a calibra-tion/normalization procedure to match the sensor outputspans with the specific user range of motion. For all Datag-loves previously mentioned, quantitative assessment of rigidrange of motion (ROM) is required and a calibration meas-uring procedure must be done [11]. Calibration it is neces-sary when the Dataglove is made with sensors that measure

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the deformations ofthe Dataglove itself, including those dueto the variations of length occurring to a different user eachtime that wears the Dataglove.

In this paper we propose a Dataglove characterized by alow cost and rugged construction that does not require cali-bration before its use. PERCRO Dataglove (Fig. 1) is basedon absolute goniometric sensors [12] that measure the rela-tive angular displacement between its transduncig bulb andits tail (Fig.2), independently ofthe specific deformed elasticline of each sensor.

fiber around the hole by acquiring the displacement of thecable free end. This quantity can be measured attaching amagnet to the cable free end and acquiring the intensity of itsmagnetic field by means of a low-cost Hall effect sensor.

Tralisdilu'r ilt13

\ ~~~~~HallEffrtSenlsort

77

f,7~=J~/1"&0S/

7~~~~~i( ofCal Niagn__

End

B~Flexuilg Bar

Fig. 2 The Goniometric Sensor

This paper describes the design, construction and char-acterization of a wireless Dataglove based on these novelgoniometric sensors. The objective was to produce aDataglove that would allow multiple angular finger jointpositions to be recorded in static grip postures and in dy-namic manipulative task using wireless technology.

The structure ofthis paper is described next. In the secondsection, we will give a brief description of the goniometricsensor. In the third section we will describe more deeply thecharacterization ofthe goniometric sensors. In the fourth andfifth sections, the hardware and software ofthis Dataglove ispresented and then in the sixth section an evaluation of thisdevice is presented. Finally, in the seventh section we willpresent the conclusions and the future of this work.

L-NKLAO

vFiFig. 3 The Working Principle of the Sensor

The resulting sensor is very rugged, it is not sensible to ex-ternal magnetic fields, it has a low cost, and it provides asignal that does not require amplification.The following block-diagram presents a schema of thetransformations involved in the goniometric sensor.

II. THE GONIOMETRIC SENSOR

The sensor (Fig. 2) consists in a transducing bulb and asensing flexing bar, with respective dimensions of (5 x 8 x21) mm and (2.4 x 2.4 x L) mm where L is a variable length.Its support material is polyurethane and is therefore veryrugged. The sensor comprehends very few components: asteel wire, a steel cable, a magnet, and one Hall effect sensor.

The working principle of the sensor relies on the fact thata flexible bar subject only to pure flexion has the propertythat the longitudinal elongation AL of the fibers is propor-tional to the bending angle AO and the distance of the fiberfrom the neutral axis w, see Figs. 2 and 3.

AL= wAO (1)

Ao AL AB AV

e H

AL=-eAOBIeani witheccentlic hole

AB-HALLinearmovement ofthe ihmanet

AV-SABHall effectsefnsor

Fig. 4 Principle of measuring

Where

e= eccentricityH= magnetic field variation per unit of linear displacementS= Hall effect sensor sensibilityV= Goniometric sensor output

A flexible but axially rigid cable inserted in a hole runningparallel to the neutral axis of the bar, with one end fixed tothe end of the hole, allows measure the elongation of the

We have assumed that the overall relationship that rulesthe sensing system is described by the following linearizatedequation [13]:

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--l11 cl CAW

111%-

of'Hole 15.;.9

7.1-...

i--

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AV= SH e -AO =Ko(rad)A0A

where

KO(rad)=S He

inverting the relation (2) we obtain:

AO = AV=KV(radAVwhere

KV(rad) 1KK(rad)

connected to an ADC of 16 bits of resolution of a commer-(2) cial acquisition card (dSPACE 1103). A rotatory base is

used to measure the bend angles using a quadrature encoder(2000 pulses per revolution) that is also to the acquisitioncard connected. Manually the rotatory base is moved while

(3) the output voltage and bend angle of the goniometric sensorare simultaneously sampled, then a Matlab script is used toobtain KV(rad) and 00 optimally interpolated from the ex-

(4) perimental data.

(5)

KV(rad) is the slope coefficient of the theoretical charac-

teristic tension-angle of the sensor. Finally, the relationshiptension-angle of the goniometric sensor is given by (6),where 00 is the angle measured when V = 2.5 volts.

0 = KV(rad)V + 00 (6)

To assure proper functioning it is necessary that the sens-ing bar is flexed only in one plane containing the cable andthe neutral axis (as seen in Fig. 2), although small deflectionsoutside this plane will cause only minor errors. Experimentalresults have shown also that errors due to shear forces areneglect able. The electric signals generated by the Hall Ef-fect sensors ranges from 0 to 5V and are acquired by a mi-crocontroller's ADC converter with 12 bit of resolution.

The resulting sensor performances are the following:* Range of measure: (0-180) degrees* Resolution: 0.05 degrees / Typically 0.2 degrees* Accuracy: 3 degrees in the worst case* Output span: 0-5V

Due to its flexible body, the sensor can be adapted to anyexternal kinematics; in particular, it can be easily attached tothe human body without exerting constraints. Resuming, themain advantages of the sensor are: the relation An-gle-Voltage is linear, characterization is "for life", the ac-quisition electronics is simple and its construction is veryrugged.

III. SENSOR CHARACTERIZATION

To convert correctly the analog output of the Hall effectsensor into an angular format, each goniometric sensor it hadto be characterized previously. In order to make it, it is nec-essary to take samples of its output voltage at known bendangles to generate a regression curve and obtain the slopecoefficient of the theoretical characteristic tension-angle ofthe sensor KV(rad) and the curve's offset. With these pa-

rameters, a given bend angle can be estimated from a givendigital output.

In order to automate the characterization process, a cus-tom hardware was built (Fig. 5); it is constituted principallyoftwo bases; in a fixed base where the goniometric sensor isconnected to external source of voltage and its output is

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IV. SYSTEM HARDWARE OVERVIEW

A. The Dataglove

The Dataglove measures each finger with two sensors ofdifferent lengths for each finger; the sensors measure theangular displacement ofproximal and medial phalanxes withrespect to the back of the hand. The difference between thetwo signals is implemented in software in order to obtain therelative angular displacement between the two phalanxes.The flexo-extension of the distal phalanx with respect to themedial is considered equal to the medial with respect to theproximal; therefore just two sensors are enough to describethe flexo-extension of each finger.The adduction-abduction movement of each finger is not

measured, except for the thumb where a third sensor bendsin a plane normal to the flexo-extension of the other twosensors. The sensors are mounted on the Dataglove with thebulbs fixed to the back ofthe hand, while the thin parts oftheflexible beam are guided by sewn slots in order the bendadherent with the fingers. The sewn slots allow free axialmovement of the sensor; this way, no axial force occurs andthe sensor can measure an absolute angle (Fig. 1).

B. EmbeddedAcquisition Electronics

An electronic acquisition unit has been built in order toacquire the analogical signals coming from the goniometricsensors, convert them to digital signals, and to send them tothe computer using a Bluetooth protocol (Fig. 6).We have used the microcontroller (uC) PIC18LF4423

operated with an external oscillator of 40 MVlhz, 11 analoginputs have been used to read the output signals of theDataglove's goniometric sensors using its internal ADC of

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12 bits. Ten general digital input/output have been used inorder to read/control external circuitry.The communication between the uC and the class 2 Blue-

tooth device (F2MO3AC2) is through its USART ports. TheBluetooth device enables a full duplex asynchronous trans-parent communication between the uC and the controlcomputer; the communication between them is at 115,200bits per second.

+5VBluetooth

+3,3V RadioProtocol

V. SYSTEM AND APPLICATION SOFTWARE

A. Embedded Software

The Dataglove embedded software is divided in two mainmodules, uC software module and Bluetooth Stack. The uCmodule is responsible of the data acquisition and packing ofthe Dataglove's signals, also it implements a quantizationnoise reduction algorithm that over samples and averages thesensor' readings, codifying each reading into a 16 bits ofdata.

The F2MO3AC2's Bluetooth vl.1 stack module imple-ments the software services required for the communicationwith the Host computer, enabling a virtual serial port con-nection between them (Fig. 7).

USB DongleDevice

BluetooRadio

Protoc

Windows

C i Q" 11 5200bps

Fig. 7 Virtual Serial Port Connection with the Dataglove

When the uC receives a request command (2 bytes long),it responds with a frame of 26 bytes, the composition of thisframe is described in Table I. Each component frame can beinterpreted as an unsigned integer of two bytes of length;first the low byte is sent and then the high byte.

Table I. Composition of the Dataglove's Response Data Frame

Fig.6 Dataglove ElectronicsArchitecture and its Implementation

The Bluetooth technology implements the wireless linkbetween the Dataglove and the host PC, it is the most suit-able method compared to other wireless alternatives like the802.11 and the HiperLAN/2 [14]. Bluetooth is a radiostandard and communications protocol primarily designedfor low power consumption, with a short range (power classdependent: 1/10/100 meters) based around low-cost trans-ceiver microchips in each device. Bluetooth differs from802.11 in that the latter provides higher throughput andcovers greater distances but requires more expensive hard-ware and higher power consumption. They use the samefrequency range, but employ different multiplexingschemes. While Bluetooth is a cable replacement for a vari-ety of applications, 802.11 is a cable replacement only forlocal area network access.

NamePacket HeadThumb 1Thumb 2Thumb 3Index 1Index 2Middle 1Middle 2Ring 1Ring 2Little 1Little 2CRCTotal

Usablebits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits16 bits

Data typeUnsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)Unsigned integer (2 bytes)26 bytes

The packet's cyclic redundancy check (CRC) is calculated11

with the following relation: CRC = E sensori Independ-0

ently if the result of this summatory is greater than OxFFFF(maximum value that can be saved in a two bytes variable),only the 2 two less significative bytes are saved in CRC.When the Bluetooth communication link is working, a

virtual full duplex 115,200 bps baud rate is guaranteed in therange of 10 meters. With this baud rate, a maximum of 492frame packets per second could be transmitted. In normaloperation the PC host application request to the Dataglove tosend frames at rate of 100 per second.

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Request Packet(2 bytes)

GLOVE B uetoothPC

ResponsePacket (Frame

26 bytes)

Fig 8. Communication Process between Dataglove and Host PC

B. Applications Software

Two applications were developed in order to displaygraphically the measurements made by the Dataglove. Thefirst application is a simulink S-function that displays nu-merically the value of the angles of the Dataglove (Fig. 9).The second, it is a graphical application that animates in realtime an avatar ofthe user's hand. The graphic representationof the hand (Fig. 10) was developed by Graphics and Hy-permedia Lab at the University of Cyprus, it has been im-plemented in a virtual 3D environment called XVR [15, 16],which is an advanced and lightweight system for the de-velopment of Virtual Reality applications both for the Weband for 3D Immersive systems. For this application, theangular positions of the skeletal joints are associated to theobtained angles, and then 3D hand meshes are deformedapplying skeletal motions applying geometrical transforma-tions to the point ofthe mesh associated to the correspondingpoint of the skeletal.

VI. SYSTEM EVALUATION

The performance of PERCRO's Dataglove has been as-sessed from a variety of perspectives including its ergo-nomics and feasibility as finger motion monitoring. Table IIsummarizes the technical characteristics of PERCRO'sDataglove used in the initial trials.

Table II. Dataglove SpecificationsParameter Value

Number of sensor 11Tracking update rate Up to 492 Hz, 100 Hz guaranteedTracking Resolution 12 bits (0.05 degrees)Accuracy 1 degreeCommunication Physi- Wireless Bluetooth 2.0cal Interface 2,4 GigahertzOperation Range 10 meters

A. Power Consumption

The Dataglove power consumption at 100 Hz acquisitionrate and 115200 bps of throughput is divided as follows:

Table III. Power consumption of single componentsCOMPONENTS Average Power

Consumption (mW)Power Stabilizers 0.4Microcontroller 32

Goniometric Sensors 550Bluetooth Transceiver 23

Total 605.4

868 PoliceVR

--Io-~~ 4.S4l3

Vndice4VR

606|eiSOei MhedioVR

Anulare AIR || 4.12

Mignolo VR

Reedy AiM del

Fig. 9 A Sfunction developed in Simulink in order to estimate the sensor'sangles of the Glove

Considering values in Table III, the four 1.5 volts AArechargeable batteries of 2400 mAh provides to the Datag-love a continue operation of 24 hours. With the intention ofexpand the batteries time life, a watchdog and polling strat-egy have been programmed in the uC to reduce power con-sumption when reading are not needed, resulting an ex-panding factor of 30.

B. Wireless Performance Analysis

To evaluate the system we tested the performance of theDataglove in terms of packet loss. We measured how thedistance between Dataglove and Host PC's Bluetooth don-gle affect the correct reception of packets. The test consistedin counting packets correctly received based in the numberof solicited packets.

Table IV. Percentage of packet lossDistance (meters) Packet Loss (%)

0.05 01 05 18 510 2012 4515 65

Fig. 10 A graphical application where the Dataglove's measurements aredisplayed graphically in the Hand Avatar

Table IV, shows that almost all the packets are receivedcorrectly in a distance range of 10 meters. In the range of10-12 meters, the system decreases its performance but it is

guanto

S-Function

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still usable. For distances greater than 12 meter the system IEEE International Workshop on Robot andHuman Interaction, 1999,packet loss exceeds 40°0 . Thus our Dataglove usability is 219-224.

[14] Chatschik, B. (2001), "An overview of the Bluetooth wireless tech-guaranteed within 10 meters, which is suitable for typical nology", IEEE Communications Magazine 39(12), 86-94.usage of this device. [15] Carrozzino, M.; Tecchia, F.; Bacinelli, S.; Cappelletti, C. & Ber-

gamasco, M. (2005), "Lowering the development time of multimodalinteractive application: the real-life experience of the XVR project",Proceedings of the 2005 ACM SIGCHI International Conference on

VII. CONCLUSIONS AND FUTURE WORK Advances in computer entertainment technology, 270-273.[16] VRMedia Web Site. http://www.vrmedia.it

The results are promising, PERCRO's Dataglove couldhave a wide commercial diffusion due to its low cost androbustness compared with its measuring qualities. Actuallywe are studying how to improve the overall perfornance ofthe Dataglove: 1) putting sensors for the adduc-tion-abduction movements ofthe fingers, 2) putting a sensorto the back of the hand in order to acquire its movements, 3)developing a finite element model of the Dataglove in orderto estimate the relative movements between the fingers andthe sensors guides.

Future research will be aimed at reducing the overall di-mensions of the sensor, also investigating similar goniom-etric sensors (i.e., substituting the steel cable with an in-compressible fluid and the Hall effect sensor with a pressuresensor).

VIII. ACKNOWLEDGMENTS

This work is supported in part by Enactive EuropeanExcellence Network and SKILLS European IntegratedProject.

IX. REFERENCES

[1] Sturman, D.; Zeltzer, D. (1994), "A survey of glove-based input",IEEE Computer Graphics and Applications 14(1), 30-39.

[2] Zimmerman, T.; Lanier, J.; Blanchard, C.; Bryson, S. & Harvill, Y.(1986), "A hand gesture interface device", Proceedings of theSIGCHIIGI conference on Human factors in computing systems andgraphics interface, 189-192.

[3] 5DT Fifth Dimension Technologies, 5DT Data Glove 14. Available:http: /www.5dt.com/products/pdataglove 14.html

[4] Sama, M.; Pacella, V.; Farella, E.; Benini, L. & Ricco, B. (2006),"3dID: a low-power, low-cost hand motion capture device", Pro-ceedings ofthe conference on Design, automation and test in Europe,136-141.

[5] Immersion Corporation, "CyberGlove", Available:http://www.immersion.com/3d/products/cyber_glove.php

[6] Essential Reality, available at: http://www.essentialreality.com/ andhttp:/www.vrealities.com/P5.html

[7] Zurbrugg, T. (2003), "Dynamic Grasp Assessment for Smart Elec-trodes (GRASSY)", Semester Thesis. ETH Zurich (Swiss Federal In-stitute of Technology), Department of Information Technology andElectrical Engineering.

[8] Perng, J.; Fisher, B.; Hollar, S. & Pister, K. (1999), "Accelerationsensing glove (ASG)", Digest of Papers of the Third InternationalSymposium on Wearable Computers, 1999, 178-180.

[9] Humanware S..R.L. Humanglove developers manual; Pisa, Italy;1998.

[10] Jacobsen, S.; Iversen, E.; Knutti, D.; Johnson, R. & Biggers, K.(1986), "Design of the Utah/MIT Dextrous Hand", Proceedings ofIEEE International Conference on Robotics andAutomation 1986.

[11] Simone, L. & Kamper, D. (2005), "Design considerations for a wear-able monitor to measure finger posture", Journal ofNeuroEngineeringand Rehabilitation 2(1), 5.

[12] PCT WO 2004 059249 A1 "Goniometric Sensor", International Pat-ent Application, Publication Date 15 July 2004, International FillingDate 30 December 2002.

[13] Ferrazzin, D.; di Domizio, G.; Salsedo, F.; Avizzano, C.; Tecchia, F.;Bergamasco (1999), "Hall effect sensor-based linear transducer", 8th

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