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Kinematic Modelling for Glenohumeral Shoulder of Humanoid Robot AHMAD TAYBAhmad Tayba University of Paris Saclay LISV laboratory 10, 12 avenue de l’Europe Velizy-Villacoublay FRANCE [email protected] SAMR ALFAYADamer Alfayad University of Paris Saclay LISV laboratory 10, 12 avenue de l’Europe Velizy-Villacoublay FRANCE [email protected] FETHI B. OUEZDOUethi B. Ouezdou University of Paris Saclay LISV laboratory 10, 12 avenue de l’Europe Velizy-Villacoublay FRANCE [email protected] FAYCAL NAMOUNaycal Namoun President of BIA Institute of Mechanical Engineering ZA Les Noutries, 8 rue de lHautil, Conflans fin dOise FRANCE [email protected] Abstract: This paper aims to develop the kinematic model for a hybrid structure proposed for the Glenohumeral shoulder of humanoid robot. A detailed description for the three Degree Of Freedom (DOF) model has been presented and then, a detailed geometrical model has been carried out in order to be used as a powerful tool for the optimization process. Key–Words: Humanoid Robots, Shoulder Complex, Glenohumeral and Girdle shoulder. 1 Introduction The development of a humanoid robot has recently received an important attention, especially when it entrusted with the task of space discovering, human save and other medical jobs. Hence, there were differ- ent ways of thinking according to the design of these robots. Some wanted to get a humanoid robot with high degree of intelligence with no caring about the morphology and human being. Other, they focused on the degree of anthropomorphism in order to emulate the motion of human for medical and rehabilitation purposes. Therefore, the design constraints grows up, due to the scarcity and lack of anatomy information about human kinematic ,and also due to mechanical, design space and manufacturing constraints. Shoulder complex is one of the complex mecha- nism in human body. Therefore, an exact kinematic model that describes this mechanism is difficulty ob- tained. In general, it is composed from Inner and Outer joint. The Sterno-Clavicular (SC) joint oc- curs between the proximal end of the clavicle and the sternum. It allows a 3 DOF, Elevation and Depres- sion, Protraction and Retraction, and axial rotation. Thus, it can be modelled as a ball and socket joint with a predefined range of motion. The Acromio- Clavicular (AC) joint exist between the acromion of the scapula and the distal end of the clavicle. All movements at this joint are passive; there is no muscle present which produce an active movement between the bones[12]. The Scapulo-Thoracic (ST) joint is a gliding joint which allows the scapula to glide over the thoracic[15][16]. Different model assumed that the ST joint can be modeled as 4 or 5 DOF [13][14]. All the presented joints are including in the inner joint of the shoulder complex and its called the Shoulder Gir- dle. The outer joint of the shoulder complex is called the Glenohumeral joint which occurs as a ball and socket joint between the humerus and glenoid fossa of the Scapula[12]. This large number of degree of free- dom are associated with each other to offer the most mobile kinematic system in human body. The figure 1 present the different bones and joint for the shoulder complex. Since decades, many researches have been in- vested to get a kinematic model for the Shoulder Com- plex to use it even for humanoid robot or other med- ical devices. HRP4[1], Asimo[2], H7[3], Qrio[9], WSEAS TRANSACTIONS on SYSTEMS Ahmad Tayba, Samer Alfayad, Fethi B. Ouezdou, Faycal Namoun E-ISSN: 2224-2678 218 Volume 16, 2017

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Page 1: Kinematic Modelling for Glenohumeral Shoulder of … · Kinematic Modelling for Glenohumeral Shoulder of ... for a hybrid structure proposed for the Glenohumeral shoulder of humanoid

Kinematic Modelling for Glenohumeral Shoulder of HumanoidRobot

AHMAD TAYBAhmad TaybaUniversity of Paris Saclay

LISV laboratory10, 12 avenue de l’Europe Velizy-Villacoublay

[email protected]

SAMR ALFAYADamer AlfayadUniversity of Paris Saclay

LISV laboratory10, 12 avenue de l’Europe Velizy-Villacoublay

[email protected]

FETHI B. OUEZDOUethi B. OuezdouUniversity of Paris Saclay

LISV laboratory10, 12 avenue de l’Europe Velizy-Villacoublay

[email protected]

FAYCAL NAMOUNaycal NamounPresident of BIA

Institute of Mechanical EngineeringZA Les Noutries, 8 rue de lHautil, Conflans fin dOise

[email protected]

Abstract: This paper aims to develop the kinematic model for a hybrid structure proposed for the Glenohumeralshoulder of humanoid robot. A detailed description for the three Degree Of Freedom (DOF) model has beenpresented and then, a detailed geometrical model has been carried out in order to be used as a powerful tool for theoptimization process.

Key–Words: Humanoid Robots, Shoulder Complex, Glenohumeral and Girdle shoulder.

1 Introduction

The development of a humanoid robot has recentlyreceived an important attention, especially when itentrusted with the task of space discovering, humansave and other medical jobs. Hence, there were differ-ent ways of thinking according to the design of theserobots. Some wanted to get a humanoid robot withhigh degree of intelligence with no caring about themorphology and human being. Other, they focused onthe degree of anthropomorphism in order to emulatethe motion of human for medical and rehabilitationpurposes. Therefore, the design constraints grows up,due to the scarcity and lack of anatomy informationabout human kinematic ,and also due to mechanical,design space and manufacturing constraints.

Shoulder complex is one of the complex mecha-nism in human body. Therefore, an exact kinematicmodel that describes this mechanism is difficulty ob-tained. In general, it is composed from Inner andOuter joint. The Sterno-Clavicular (SC) joint oc-curs between the proximal end of the clavicle and thesternum. It allows a 3 DOF, Elevation and Depres-sion, Protraction and Retraction, and axial rotation.

Thus, it can be modelled as a ball and socket jointwith a predefined range of motion. The Acromio-Clavicular (AC) joint exist between the acromion ofthe scapula and the distal end of the clavicle. Allmovements at this joint are passive; there is no musclepresent which produce an active movement betweenthe bones[12]. The Scapulo-Thoracic (ST) joint is agliding joint which allows the scapula to glide over thethoracic[15][16]. Different model assumed that theST joint can be modeled as 4 or 5 DOF [13][14]. Allthe presented joints are including in the inner joint ofthe shoulder complex and its called the Shoulder Gir-dle. The outer joint of the shoulder complex is calledthe Glenohumeral joint which occurs as a ball andsocket joint between the humerus and glenoid fossa ofthe Scapula[12]. This large number of degree of free-dom are associated with each other to offer the mostmobile kinematic system in human body. The figure 1present the different bones and joint for the shouldercomplex.

Since decades, many researches have been in-vested to get a kinematic model for the Shoulder Com-plex to use it even for humanoid robot or other med-ical devices. HRP4[1], Asimo[2], H7[3], Qrio[9],

WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

E-ISSN: 2224-2678 218 Volume 16, 2017

Page 2: Kinematic Modelling for Glenohumeral Shoulder of … · Kinematic Modelling for Glenohumeral Shoulder of ... for a hybrid structure proposed for the Glenohumeral shoulder of humanoid

Figure 1: Bones and joints of the Shoulder Complex[12]

Wabian[10], and CB[11] are using a simple serialmechanism to model the shoulder glenohumeral jointto provide more simplicity in the manufacturing pro-cess. However , the serial configuration suffer fromheavy weight and bulky mechanism since that eachactuator has to support the weight of its followers.Nevertheless, this configuration can be easily mod-elled using the conventional method for direct or in-verse geometrical, kinematic and dynamic models,and therefore the way to control such mechanism be-come more simple and easy. As far as we know, asmall number of biped robot use a parallel mechanismfor the shoulder, due to the limited range of motionthat can be offered such mechanism. however, andthanks to the rigidity of paralell mechanisms, it can bean ideal solution for shoulder kinematic to ensure thestability and the rigidty during motion. OKADA et al.have introduces the mechanical softness in the designof shoulder :”The mehanical Softness include such re-quirement as human-like high mobility and human-like sensitive compliance”. [8]. Nevertheless they usea parallel mechanism , its actuators use a large spacefrom the chest to locate the actuators preventing theability to develop an active torso inside the robot.

In this paper, we will present the kinematic struc-ture proposed for the first part of the shoulder complex(Glenohumeral). Our proposed solution consist of us-ing a hybrid mechanism which combine the benefit ofserial (large range of motion) and parallel mechanism(stability and rigidity). This mechanism should be

integrated to the underdevelopment humanoid robotHYDROı̈D [6][7][17]. The HYDROı̈D will have thesize of 1.6 m and a weight of almost 120 Kg and has1.2 m/s as a nominal speed. All the HYDROı̈D bodyjoint are actuated hydraulically [18],while it head isactuated electrically [19].

The first part will describe the proposed kinematicstructure to get the three DOF of the glenohumeralshoulder, then, a generalized analytical model for theinverse geometrical model will be presented in orderto get a powerful tool for the optimization processsuch as design, shape and geometrical optimization.In addition to this, this model will be used as a feed-back for the control algorithm of such mechanism.

2 Structure Description

According to the anatomy study, the outer joint ofthe shoulder complex is called the Shoulder Gleno-humeral joint (SG) which occurs as a ball and socketjoint between the humerus and glenoid fossa of theScapula. Therefore, it can be modeled as a sphericaljoint with 3 intersecting axes.

The hybrid solution proposed for the SG joint ofHYDROD is depicted in Figure 2. It consists of a 3-DoF mechanism that has 17 joints arranged in threekinematic chains leading to two independent closedloops. Starting with a serial chain with a rotary jointallows us to have a large range of motion around the

WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

E-ISSN: 2224-2678 219 Volume 16, 2017

Page 3: Kinematic Modelling for Glenohumeral Shoulder of … · Kinematic Modelling for Glenohumeral Shoulder of ... for a hybrid structure proposed for the Glenohumeral shoulder of humanoid

pitch axis, reaching almost 180◦. For the 2 other DOF

, rotation arround Roll and Yaw axis are obtained from

2 linear actuators (A2 and A3) in the input to produce

a large motion at the output and to decrease the singu-

larity positions. Each of linear actuator are located

in 3D space between 2 spherical joints (A and D),

(B and E), F and G . The Whole description for the

choice of such mechanism can be found in the follow-

ing reference[5].

X0

Z0

Y0

A

D

BE

F

G

Pitch

Roll

Yaw

End Effector

A1

A2

A3

Figure 2: General Kinematic Model for Glenohumeral

Shoulder

3 Parameter Description

The parameter description based on the Khalil et

al. notation [4] of the new solution is given in

Table 1, Where the main parameters are defined

as follow: αj is the angle between Zj−1 and Zj

with respect to the rotation around Xj−1, dj is the

distance between Zj−1 and Zj along Xj−1, θj is

the angle between Xj−1 and Xj with respect to the

rotation around Zj , rj is the distance between Xj−1

and Xj along Zj . All limbs and all joint axes of

the fully-parallel chains are respectively noted jCi

and Zij with j = 1, 2 indicating the kinematic chain

index the frame belongs to and 1 ≤ i ≤ 9 as given

in Figure 3, where (A, B, D, E, F & G) are the

centers of the links (C13, C2

3, C1

4, C2

4, C1

6& C2

6)

respectively. The relative coordinates for these

centers with respect to the previous link are de-

fined as A(XfA, Y

fA , Z

fA), B(Xf

B, YfB , Z

fB),

D(X3,1D , 0, Z3,1

D ), E(X3,2E , 0, Z3,2

E ),F (X0

F , Y0

F , Z0

F ) and G(X0

G, Y0

G, Z0

G) respec-

tively. Since the new hybrid mechanism is generic,

Broken joint

Broken joint

Cf

Cv

Cs

C31

C41

C51

C91

C61

C71

C81

C32

C42

C52

C92

C82

C62

C72

Z0,ZVX0Y0

Zf

Zs

Z31

Z41

Z51

Z91

Z61

Z71

Z81

Z32

Z42

Z52

Z92

Z82

Z62

Z72

1

2

A(XAf,YA

f,ZA

f)

B(XBf,YB

f,ZB

f)

D(XD3,1,0,ZD

3,1)

E(XE3,2,0,ZE

3,2)

F(XF0,YF

0,ZF

0)

G(XG0,YG

0,ZG

0)

1

2

1left

1right

2left

2right

RC1,left

RC1,right

RC2,left

RC2,right

Pitch

Roll

Yaw

Figure 3: Detailed Kinematic Model for Gleno-

humeral Shoulder

some parameters have to be set to particular values

(see Figure ?? for the definition of these param-

eters),in order to get the complete description of

the hybrid hip solution. These conditions can be

summarized in the following set of equations:

XfA = X

fB, Y

fA = −Y f

B , ZfA = Z

fB (1)

X3,1D = Z

3,1D = X

3,2E = Z

3,2E = 0 (2)

X0

F = X0

G, Y0

F = −Y 0

G, Z0

F = Z0

G (3)

Once the novel kinematic structure has been proposed,

carrying out its performance analysis is required. This

analysis will be based on geometrical models that are

detailed in the next section.

sectionMODELLING & KINEMATIC ANALY-

SIS

In order to carry out the kinematic analysis with

the help of a simulation tool, two models have to be

established. These models concern, first, the Inverse

Geometrical Model IGM used to calculate the linear

actuator lengths (Lj , j = 1, 2) for a given posture

of the arm or the leg whenever the shoulder or the

WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

E-ISSN: 2224-2678 220 Volume 16, 2017

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Table 1: Khalil et al. parameters for the generic hybridmechanism

j i σj γj bj αj dj θj rj

Cv C0 0 0 0 0 0 θv 0

Cf Cv 0 0 0 π2

0 −θf − π2

0

C13 Cf 0 0 0 π

2XfA

θ13 − θ1,03 −Y f

A

C14 C1

3 0 0 0 π2

X3,1D

θ14 + θ1,04 0

C15 C1

4 0 0 0 π2

0 θ15 0

R1,leftC

C15 0 0 0 0 0 0 0

C16 C0 0 0 0 0 X0

F θ16 + π −Y 0F

C17 C1

6 0 0 0 π2

0 θ17 + PI2

0

C18 C1

7 0 0 0 π2

0 θ18 − θ1,08 0

C19 C1

8 1 0 0 α19 0 0 −R1

R1,rightC

C19 0 0 0 0 0 −π

20

C23 Cf 0 −π

20 π

2XfB

θ23 − θ2,03 −Y f

B

C24 C2

3 0 0 0 π2

X3,2E

θ24 + θ2,04 0

C25 C2

4 0 0 0 π2

0 θ25 0

R2,leftC

C25 0 0 0 0 0 0 0

C26 C0 0 0 0 0 X0

G θ26 + π −Y 0G

C27 C2

6 0 0 0 π2

0 θ27 + π2

0

C28 C2

7 0 0 0 π2

0 θ28 + θ2,08 0

C29 C2

8 1 0 0 −α29 0 0 −R2

R2,rightC

C29 0 0 0 0 0 −θ2C 0

hip mechanism is considered. The other model con-cerns the kinematic performance will be presented inthe second part of this work.

3.1 Inverse Geometrical Model - IGM

As mentioned above, there are two kinematic closedloops named Cj , depicted in Fig. 3. Each of them iscomposed of the links jCi as follows: (Cs, Cv, Cf ,Cj1 , Cj

2 , Cj3 , Cj

4 , Cj5 , Cj

6 , Cj7 , Cj

8 , Cj9) with 1 ≤ j ≤ 2.

The spherical joints that link the linear actuator to thebase platform of the fully parallel subpart are split onthree independent orthogonal axes (See Fig. 3). Theconnection of the linear actuator to the moving plat-form of the fully parallel subpart consists of a univer-sal joint and a rotational one; the former allows therotational movement of the linear actuator around itsown axis and is chosen to be the ”broken” joint to es-tablish the IGM of the fully parallel subpart as shownin Figure ??. The technique of breaking the kinematicclosed loops to identify the equivalent kinematic openloop has been used to get the desired IGM. This choicewas justified by the need to split the kinematic closedloops into two equivalent halves whenever the num-ber of joints is considered. The upper script Left andRight are added to each closed Cj to identify the leftand the right parts, respectively.

To generalize our model, we take into consider-ation the fact that the center of the links Ci

j (withi ∈ {1, 2} and j ∈ {3, 4, 6}) is variable.

The inputs parameters of the hybrid mechanismare the linear actuator lengths Lj . The outputs aregrouped in a three-dimension vector named qa =

(qs, qv, qf )t. All other ith passive joints of the two

closed loops are named θji where j is the closed loopindex. Table 1 gives the required parameters for thedescription of the two branches of the two closed loop.

To establish the IGM model of the mechanism,the pitch rotation is straight forward since it belongsto the serial part. However, getting the roll and yawrotations (parallel part) requires eliminating all pas-sive joints angle θji in the geometrical constraints ofclosing the kinematic loops Cj .

Hence, the base of the fully parallel mechanismcan be considered, without any loss of generalization,to be fixed to link C1. The target is to establish the re-lations giving the lengths of actuators function of theelements of vector qa. Since the closed loops Cj werebroken at the joint Zj

5 of each, two sub-branches haveto be considered. The first one, named left branch,connects links Cj

4 to Cv, and the other, named rightbranch, links the limbs going from Cj

v to Cj9 . The

homogenous transformation matrix between the twoframes R0 attached to link Cv and R5 fixed on Cj

5 canbe expressed in the two circuits, using either the rightor the left sub-branch. The closure loop relation yieldsthe obvious equation between both homogenous ma-trices 1TRight,j

5 and 1TLeft,j5 :

1TRight,j5 = 1TLeft,j

5 1 ≤ j ≤ 2 (4)

The expressions of the elements of the above ma-trices are arrived at by multiplying all successive ho-mogenous transformation matrices and using the fol-lowing notations: Sj

k = sin(θjk) and Cjk = cos(θjk).

The same notations are used for the sine and cosinefunctions of α1, α2, γ2 (see table 5 for the defini-tion) and for the vector qa elements. To exemplify,the first loop C1 closing relation (Eq. 4) is detailedbelow. Using the equivalence between the third andfourth columns of each matrix, we obtain the follow-ing relations:

(Ci3)

2ai1,k + Si3C

i3a

i2,k + Ci

3ai3,k + Si

3ai4,k + ai5,k = 0

(5)The way to obtain the above equations (5) and the

expression of aij,k are detailed in the Appendix for i ∈{1, 2}, j ∈ {1, 2, 3, 4, 5} and k ∈ {1, 2, 3}The equation(5)for k=2 gives:

Si3 = −

(Ci3)

2bi1 + Ci3b

i3 + bi5

Ci3b

i2 + bi4

(6)

by replacing equation (6) with equation (5) fork=1 and k=3, we obtain:

(Ci3)

3bi1,n + (Ci3)

2bi2,n + Ci3b

i3,n + bi4,n = 0 (7)

WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

E-ISSN: 2224-2678 221 Volume 16, 2017

Page 5: Kinematic Modelling for Glenohumeral Shoulder of … · Kinematic Modelling for Glenohumeral Shoulder of ... for a hybrid structure proposed for the Glenohumeral shoulder of humanoid

withbi1,n = ai1,ka

i2,2 − ai2,kai1,2 (8)

bi2,n = ai1,kai4,2 − ai2,kai3,2 + ai3,ka

i2,2 − ai4,kai1,2 (9)

bi3,n = −ai2,kai5,2+ai3,kai4,2−ai4,kai3,2+ai5,kai2,2 (10)

bi4,n = −ai4,kai5,2 + ai5,kai4,2 (11)

with n ∈ {1, 2}Combining equation (7) for n = 1 and equation

(7) for n = 2, we obtain a second order polynomialequation in Ci

3

Li1(C

i3)

2 + Li2C

i3 + Li

3 = 0 (12)

withLi1 = bi1,1b

i1,2 − bi1,2bi2,1 (13)

Li2 = bi1,1b

i3,2 − bi1,2bi3,1 (14)

Li3 = bi1,1b

i4,2 − bi1,2bi4,1 (15)

Solving equation (12) when even δ = (Li2)

2 −4Li

1Li3 >= 0, we obtain:

θi3 = ± arccos(−Li

2 ±√δ

2Li1

) (16)

if δ < 0 no solution for θi3 and the chains cannot beclosed. Meanwhile, equation ( 16) shows 4 solutionsθi3,j for θi3 with i ∈ {1, 2} and j ∈ {1, 2, 3, 4}. Tochoose the right solution θi3,sol, we adopted the fol-lowing design criteria. To prevent the overloading onthe link and the interference between the parts, thelink Ci

3’s rotation should be limited. This yields thefollowing rotation:

θi3,min < θi3,sol < θi3,max

On the other hand, as θi3,sol is obtained numerically, itshould satisfy equations (5). Hence, a numerical errorErr(θi3,sol) can be established as the sum of the errors

induced by each equation: Err(θ13,i) =3∑

r=1Err2i,r.

Erri,r = (C13,i)

2ai1,r + S13,iC

13,ia

i2,r + C1

3,iai3,r +

S13,ia

i4,r + ai5,r

The used condition for the choice of the appro-priate θi3,sol solution can be stated as: Err(θi3,sol) <ε, i ∈ {1, 2}. From the forth column of the firstmember of the closure loop relation for chain 1, andusing the value θ13,sol, the following can be estab-lished:

X0D =(−CvSfC

13,sol + SvS

13,sol)X

3,1D − CvCfZ

3,1D

− CvSfXfA + CvCfY

fA + SvZ

fA

(17)

Y 0D =(−SvSfC1

3,sol − CvS13,sol)X

3,1D − SvCfZ

3,1D

− SvSfXfA + SvCfY

fA − CvZ

fA

(18)Z0D = −CfC

13,solX

3,1D + SfZ

3,1D − CfX

fA − SfY

fA

(19)Since the center F is fixed, we have the length of thepiston of Chain 1:

L1 =√(X0

D −X0F )

2 + (Y 0D − Y 0

F )2 + (Z0

D − Z0F )

2

(20)The same calculation for chain 2 leads to the follow-ing conditions of point E coordinates:

X0E =(−CvCfC

23,sol + SvS

13,sol)X

3,2E + CvSfZ

3,2E −

CvSfXfB + CvCfY

fB + SvZ

fB

(21)Y 0E =(−SvCfC

23,sol − CvS

23,sol)X

3,2E + SvSfZ

3,2E −

SvSfXfB + SvCfY

fB − CvZ

fB

(22)Z0E = SfC

23,solX

3,2E +CfZ

3,2E −CfX

fB−SfY

fB (23)

Since the center G is fixed, we have the length of thepiston of Chain 2:

L2 =√

(X0E −X0

G)2 + (Y 0

E − Y 0G)

2 + (Z0E − Z0

G)2

(24)In case of hip mechanism, the center of the links Ci

4 iscoincident with the center of the links Ci

3. Therefore,the following relations can be written:

X3,1D = X3,1

E = Z3,1D = Z3,1

E = 0

Hence, the new expression of centers D and E coor-dinates is given in the following set of equations:

X0D = X0

A = −CvSfXfA + CvCfY

fA + SvZ

fA (25)

Y 0D = Y 0

A = −SvSfXfA + SvCfY

fA − CvZ

fA (26)

Z0D = Z0

A = −CfXfA − SfY

fA (27)

X0E = X0

B = −CvSfXfB + CvCfY

fB + SvZ

fB (28)

Y 0E = Y 0

B = −SvSfXfB + SvCfY

fB − CvZ

fB (29)

Z0E = Z0

B = −CfXfB − SfY

fB (30)

To get the IGM of the hip mechanism, the previousvalues of centersD and F coordinates have to be usedin equations (20) and (24). Once the IGM model isestablished, we present in the next results section howit is used to optimize the proposed solution for the hipand shoulder mechanisms.

WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

E-ISSN: 2224-2678 222 Volume 16, 2017

Page 6: Kinematic Modelling for Glenohumeral Shoulder of … · Kinematic Modelling for Glenohumeral Shoulder of ... for a hybrid structure proposed for the Glenohumeral shoulder of humanoid

4 Optimization

In the early stage of designing a robotic system, itis required to determine the appropriate stress on themechanical part. The figure 5 presents a kinematicschema for the proposed solution for the roll and yawmotion of the shoulder. The Mechanism are projectedon the transverse plan for clarification purposes. Me-chanical part 1 in figure5 is taken as an example forthe following study. Supposed that the linear actuatorare hydraulic cylinder, we can get, for each pressure,the generated force and torque and its influence thanksto the established IGM . For each roll and yaw angleθy and θz , the IGM provides the new coordinates forthe points D and E and then we get the vectors ~FD

and ~GE as the point F and G are always fixes. Basedon these vectors, the direction of the force producedby the linear actuators become known. F0,0, F1,1 andF2,2 are an example for the produced force for differ-ent roll and yaw angle. In addition, The moment vec-tors ~My and ~Mz produced axis will be defined. Eachtorque is called a quasi-static torque since it is basedon the geometrical effects of the lever arm betweeneach linear actuator and the axis of rotation. This isthe first step in pre-dimensioning the proposed mech-anism that has to be extended to kinetostatic and dy-namic analysis in order to manage an external effortapplied on the arm. The figure 4 presents the quasi-static torque generated by the 2 linear actuators foreach roll and yaw angle. Based on the force and mo-ment acting on the mechanical part, we can get an ideaabout the stress on this part function of the angle mo-tion.

σi 7→ f(θyi, θzi) (31)

Figure 4: Quasi-static torque function of the yaw androll angle

The future work will be based on this quasi-static

torque provided by the mathematical model of theIGM in order to begin in the phase of mechanical de-sign optimization. This will help the designer to get atool for obtaining a light weight and optimized struc-ture.

Figure 5: Kinematic schema for the proposed solutionfor the roll and yaw motion of the shoulder

5 ConclusionIn this paper, we present the kinematic model pro-posed for the glenohumeral shoulder for HYDROı̈Drobot. We justify our hybrid solution by presentedthe benefits attained by using both serial and paral-lel mechanisms. Then, a generic Inverse GeometricalModel (IGM) has been detailed for the hybrid struc-ture to be the first step toward the optimization pro-cess. This will be given in the second part of thiswork.

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WSEAS TRANSACTIONS on SYSTEMSAhmad Tayba, Samer Alfayad,

Fethi B. Ouezdou, Faycal Namoun

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Fethi B. Ouezdou, Faycal Namoun

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