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1、Mechanic Design of Anthropomorphic Hand for Shapeless Objects SubjectionDr. Vctor Javier Gonzlez VillelaMember of IEEEvjgvunam.mxIng. Vctor Gustavo Arnez Paniaguaarnezvictorcomunidad.unam.mxIng. Ernesto Hernndez Avilsernie_bar12Departamento de Mecatrnica, Facultad de Ingeniera, Universidad Nacional

2、Autnoma de MxicoAbstractIn this paper it is presented the design of amechanic hand, for a future use in a tele-operatedproject, which counts with movements closed to thosemade by a human hand, due to the number of joints (22DOF) and to its structure built from the wrist; givingrelative movement betw

3、een knuckles, keeping arelationship of three mean flexible arcs that givebigger work space and better behavior to graspvoluminous and shapeless bodies, making difference ofanthropomorphic hands presented in other mechanicsdesigns based on the rigid palm.1. Introduction.In recent years, solutions for

4、 anthropomorphichands have been presented1-3, each one of theseachieving to complete posture and trajectory moreproximate to those found in the human hand,nevertheless, completed results have never beenpresented, being that there is still work spaces that ahuman hand can reach, and these solutions c

5、ant, forexample, the solutions developed use a palm with aplane and rigid shape, use very simplified mechanismsfor the little finger and the ring finger; in other words,they have a kinematic model simplified4.The main topic for this research is the developmentof an anthropomorphic hand, basing his s

6、tructure inthree main arcs of the human hand5, to obtain a palmwith flexible curves.The importance of studying this design, based inflexible arcs, is due to the human hand and its ability tohave a mayor surface contact with big volumes,offering a mayor subjection and manipulation of these.Solutions

7、previously proposed without these arcs, havefailed to truly recreate the grasping of spherical andvoluminous objects4.The principal objective is to create a mechanichand, with the capacity to partially recreate the kineticof the human hand.For this design, the idea of independent structureswas used

8、for each finger. With articulations that gofrom the carpometacarpal articulation (wrist withmetacarpal) up to the last phalange. With an inspirationon the human hand, the structure with tubal sectionslike bones was design, making emphasis in theconservation of the degrees of freedom by articulationa

9、nd that the instant central rotations points, when morethan one movement are present, concur in the samepoint.2. Project description.The future project has the main objective ofdeveloping a work tool, without a specific use,obtaining a general and versatile solution to differentwork fields.There exi

10、sts situations where the human dexterity isrequired to manipulate objects, but the environment inwhich it unrolls might be dangerous for humanpresence, besides, it is possible that somebody not inthe place is required. That is why is necessary to bringthe its abilities to a specific place, and that

11、his abilitiesmight be repeated with human dexterity.The description of the project is presented in thefollowing diagram:Figure 1. Schematic of the full process.In a first step, the positions are acquired through aninstrumented glove, which transmits the data to acomputer, for a next step of telecomm

12、unication. Here,the information collected and filtered is sent to acomputer that will assign the desired positions to themechanic hand. At last, this hand will have sensorsequivalent to those in the glove so it can be controlledby the second computer, and at the same time, afeedback to the operator

13、can be counted; using thesame glove with actuators that give a tactile perceptionand also using a video-graphic interface, for spatiallocation.All this with the end of give the operator a betterperception in a workplace different of the one that heis, without the need of being actually there. And so

14、 likethis, the situations of risks can be avoided.3. Design based in flexible arcs.To solve the lack of natural movement is necessaryto simplify the mechanics of the human hand, toadapted to a design integrated with bolts, bar anduniversal joints. Thats why it all started with theinvestigation of th

15、e human anatomy.Figure 2. Name and location of the joints, such as thenumbers assigned for each finger.The structure and shape of the hand was defined bythe osseous system, from where the dimensions of thefingers, palm and angles can be obtain. The bones arearranged in three arcs, two of them transv

16、ersals andone longitudinal.The proximal transversal arch, with the capitates aspivot, is relatively fixed and concave to the palm; it iscalled carpal arch. The distal transversal arch, with thehead of the third metacarpal is mobile, and alsoconcave to the palm; it is called metacarpal arch. Thesearc

17、s are formed by the normal tension of the ligamentsthat hold them up, and for the action of thecorresponding muscle shorten. Both transversal arcsare connected by a longitudinal one. Any failure in thesystem of arcs in the hand may contribute to aninability of it, that is why the importance.The capa

18、city of the human hand comes from theability of these arcs, to adjust to different postures,accomplishing a better control over the objects that thehand manipulates, besides of being able to graspobjects of irregular shapes and considerable volumes.Figure 3. Human hand arcs.To design the kinematic o

19、f the mechanic hand isnecessary to be aware of the movements andtrajectories that the average human hand is capable todo.The angles by which the articulations from thesecond to fifth finger moves are from 10 to 15 degreesin the carpometacarpal (CMC) for the fourth finger,and from 20 to 30 degrees fo

20、r the fifth. For themetacarpophalangeal (MCP) goes from 0 to 90degrees, for the proximal interphalangeal (PIP) is from0 to 100 degrees, and the distal one (DIP) is to 90degrees5.Figure 4. Movement in degrees that the fingers can have.For the thumb it can be observed that more thandefined angles, it

21、is needed to search for the maintrajectories in our hand, which are abduction, rotationand flexion.Figure 5. Indispensable movements of the thumb.There is a controversy about the use of the littlefinger, nonetheless, the implementation of it wasdecided due to the advantage that it represents at thet

22、ime of manipulate voluminous and heavy objects,offering a wider work space up to 20% bigger.4. Mechanics simplifications.To obtain the longitudinal outlines of the fingers, adesign of variable outlines was required, which isexpensive in its manufacture. A proposal to simplify isthe use of an aluminu

23、m tube and work after it to obtainthe longitudinal outlines of each phalange. As it isshowed is figure 5, the pieces of red tone constitute thestructure and works as the phalanges of the fingers.A mechanic simplification exists when the fingersare flexed, and it can be applied without compromisingth

24、e objective of the project, due to a relation in therelative angle between the distal and medial phalange,with the relative angle between medial and proximalphalange of the index, middle, ring and little fingers6.Improvements are presented over the referenced thesisto achieve more closed trajectorie

25、s in the last phalangeof the fingers from II to V.Figure 6. Longitudinal outlines of a finger with its fourbars mechanism.It is possible to simulate the movements of thethumb using three rotational axles, two of them in thecarpometacarpal joint of the thumb, and the third is thewrist (joint between

26、the trapezium and trapezoid)7 tomove the first two ones, and making possible to closecompletely the hand. This is appreciated in figure 6.Figure 7. Mechanism for the thumb.Another of the main simplifications is the effect ofrotation-translation presented in the joints of the humanhand; nevertheless,

27、 the existing translation can benegligible, compared to the rotation achieved. That iswhy the prototype counts with articulation of rotationalmovements.To obtain the configuration of the two transversalarcs wanted in the mechanic hand, it starts with a fixedbase compound of the metacarpals of the in

28、dex andmiddle fingers, and the wrist with the shape of the firsttransversal arch at the carpal level. From the heads ofthe metacarpals mentioned, it is formed a secondtransversal mobile arch at this level. The mobileproperty of this arch is achieved with a mechanism ofuniversal joint in the union of

29、 the ring and little fingerswith the wrist (CMC). For the third arch, thelongitudinal one, the configuration is proper of thenatural movements of the hand, due that it is formed bythe position of the fingers in a lateral view.5. Functional design.In each phalange was built an outline to carry outwit

30、h characteristics alike in shape with those in thehuman hand, with a final vision of making it capable ofgrasp objects with different shapes, and open to thepossibility of adding a material that works as skin,besides, that can cover the tendons that goes throughthe middle of the phalange.During all

31、the design, a special care was made tolook that every angle; every joint, has the same run tothat found in the human hands, so it was needed togenerate special outlines and pieces.Figure 8. Lateral view of a finger, angle measurementbetween phalanges.The medial phalange has a maximum displacementof

32、143 degrees, when this occurs, the distal phalangereaches to displace 58 degrees. In the other side, if thisangle is compared with the reference when the middlephalange is 100 degrees, a rotation of 63 degrees canbe reached in the distal phalange. The maximum angleof rotation obtained between the me

33、tacarpal andproximal phalange is 93 degrees.Figure 9. Use of main flexible arcs in spherical objects ofdifferent diameter.With figure 9, the two transversal arcs by which themechanic hand was design are pointed out, the redcurve represents the carpal arch, and the blue one is themetacarpal arch. Bot

34、h are responsible to do the neededcurvature for subjection of spheres of differentvolumes.To observe the versatility of the thumb, the nextfigures are presented, in which, based in the review,the main positions that must be obtain with this fingerare showed. Such positions are flexion to the tip of

35、thelittle finger, abduction and rotation.Figure 10. Positions achieved.6. Kinematics of the mechanic hand.Using a simulation in Solid Edge, the angles andtrajectories that the mechanic hand can do areestimated, such as the distances and limits ofmovement.To corroborate these estimations and using th

36、ehomogeneous matrix method for mechanism in space,the next equations are obtained for the little finger:Tz3am1.Tz5m1. Tz4m2. Tz3am2. Tz5m3. Tz4m4.Tz3am3. Tz4m5. Tz3am4. Tz4m6.Tz3am5=Tz1xm.Tz2ym. Tz3zm. Tz4m1. Tz5m2And for the thumb:Tz6p1.Tz1ap1. Tz3ap2. Tz5p2. Tz4p3. Tz3ap3.Tz5p4. Tz3ap4. Tz5p5.r=xp

37、,yp,zp,1TWhere:Tz1= Translation in x axe.Tz2= Translation in y axe.Tz3= Translation in z axe.Tz4= Rotation in x axe.Tz5= Rotation in y axe.Tz6= Rotation in z axe.am1= Constant distances from the base of the structureto the CMC of the little finger.am2= Constant distances of the metacarpal of the lit

38、tlefinger.am3= Constant distances of the proximal phalange ofthe little finger.am4= Constant distances of the middle phalange of thelittle finger.am5= Constant distances of the distal phalange of thelittle finger.ap1= Constant distances of the thumb from the base ofthe structure to the CMC.ap2= Cons

39、tant distances of the metacarpal of the thumb.ap3= Constant distances of the proximal phalange of thethumb.ap4= Constant distances of the distal phalange of thethumb.mi= Degrees of freedom of the Little finger.pi= Degrees of freedom of the thumb.xm, ym, zm= Coordinates from the inertial base to thee

40、xtremity of the distal phalange of the little finger.xp, yp, zp= Coordinates from the inertial base to theextremity of the distal phalange of the thumb.mi= Variable rotations.An image for the inertial base is presented; thefollowing bases are created using the transformationmatrix described above.Fi

41、gure 11. Inertial bases for the thumb and the littlefinger.Afterwards, a trajectory is proposed and the data isintroduced to all degrees of freedom, with the idea tomake the hand to go from a close position in fist-shape,to a completely open position.The evaluated results are presented for the littl

42、efinger; the graph for the finger II, III, and IV have veryalike shapes to those showed for this finger.Figure 12. Simulations of the movements for the fingersII to IV.With the four bars mechanism simplified in thesimulations as just one line, the finger represented hasmovement from the wrist, and i

43、s able to reach positionsthat allow the hand to close and open, not just in a fistshapeposition, but also to open the palm wide.Finally the trajectories and work space for thethumb are presented. The wrist is represented as twolines to continue with the idea of homogeneous matrix.Figure 14. Trajecto

44、ries for the thumb to differentmovements of the joints.As it can be observed in figure 14, two trajectories ofmany are created by changing the values of the degreesof freedom in the thumb, in the first case; the left one,all degrees of freedom goes from their minimum valueto their maximum at the sam

45、e time, and in the rightone, just the degrees of freedom in the base of thethumb (in the wrist) move from their minimum value,to their maximum.And so, changing the degrees of freedom, manytrajectories can be obtained, and the thumb can becharacterized by its movements.7. Conclusions.It can be verifi

46、ed in figure 9 that the use of flexiblearcs in this design, allows a better subjection andbigger work space for different volumes. Likewise, infigure 10, they allow the contact between the thumb andthe tip of the little finger.In the simulations, the positions of the mechanichand come to be close en

47、ough to those made by thehuman hand.By having a previous study6, the behavior of thefour bars mechanism was improved. The angle deficitin the distal phalange is compensated by achieving abigger displacement in the middle phalange, to attainthe position of the tip of the finger in the right place.Due to the base mechanism of the thumb, thefunctionality and operation trajectory can be repeated,giving as a result a wider work space and similar to theaverage found in the bibliography5.It can be observed too, that the use of bolts