Material Selection for the Prosthetic Hand

International Journal of Biomedical Engineering Vol. 3: Issue 1

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Material Selection for the Prosthetic Hand Punit Kumar Rohilla1, Suresh Verma1, Dinesh Bhatia2, Nitin Sahai2, Sudip Paul2*, Angana Saikia2, Sushmi Mazumdar2 1

Department of Mechanical Engineering, Deenbandhu Chhotu Ram University of Science and Technology, Murthal (Sonepat), Haryana, India 2 Department of Biomedical Engineering, North-Eastern Hill University, Shillong, Meghalaya, India

ABSTRACT Science and technology are touching the sky in today’s scenario. As the time passes technology has been used for the betterment of the human life as much as possible. Recent development leads various researchers in the field of biomedical and biotechnology engineering. Considering the current scenario this work is related with the design of a prosthetic hand for the amputee. It requires that a number of parameters should be considered but material selection is one of the key parameter in the design of the artificial hand. As the material selection directly affects the strength, weight and cost of the prosthetic hand. In present work stress analysis using ANSYS is performed for various materials and their comparative study is done. This work helps the design engineers as well as manufacturers to select better material with low cost, low weight and high strength. It is observed from the study that Nylon 6 can be used for prototype manufacturing of the prosthetic hand. The quality of life of the amputee would be improved with the improvement in the prosthetic hand technology. Keywords: amputee, ANSYS, artificial hand, prosthetic, stress *Corresponding Author E-mail: [email protected]

INTRODUCTION With the growing technology, advancement in the fields of robotics, artificial intelligence, and highly sophisticated bio mimetic robotic systems can easily be observed. In recent decade main focus of the research is to provide better possible artificial limb to the amputees, such that they can live their life comfortably. Upper limb amputations can be due to sudden trauma to the body or from congenital deficiencies and vascular diseases.[1] To cure this amputation upper limb prosthesis is used. The prosthetic hands were designed primarily only for the grasping tasks. They can’t be used for performing manipulative tasks. As for manipulation tasks it requires

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high dexterity, advanced sensors, complex control strategies and neural interfaces.[2,3] Although several sophisticated mechanical hands are produced in the field of robotic hands,[4,5] still its requirements are not matched for two main reasons: the lack of a natural interface between the Peripheral Nervous System (PNS) and the artificial device[6] and the lack of light weight, compact actuators with high output torque.[7] Human finger involves both curling action and side by side motion that is flexionextension and adduction-abduction respectively. It helps fingers to make grip on the objects and thumb helps in positioning of the object. Two basic grip forms identified and named on the basis of

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Material Selection for the Prosthetic Hand

their functional aspects by Napier are: Precision and Power. Iberall’s described these two more accurately as, Precision where the tips of the fingers oppose the tip of the thumb and, Power where the thumb opposes the palm area.[8–10]. Since the human hand physiology is very complex as it involves a large number of joints and different possible motions resulting in multiple degrees of freedom for it. Keeping in view the complexity of human hand, one has to develop the artificial hand in such a way that it can be used worldwide by the possible user. A prosthetic hand must have the characteristics such as lightweight, compact, reversible, noiseless, high strength, appearance, and cost. These characteristics briefly described as:[10]  Lightweight: the weight of the prosthetic hand as well as of its fitting arrangement is directly connected to the body of the operator. Blood flow can be obstructed in the skin and resulting symptoms can range from discomfort to skin breakdown.  Compact: length of the residual limb of the users vary, so all its drives and power sources should retain in the device as small an possible, if possible within the hand profile.  Reversible: It must ensure that the device can be used by a large number of people and due to simplicity of manufacturing it can be used for both left and right hands.  Noiseless: The functioning of a prosthetic hand should be such that it must not attract the attention of the user unnecessarily.  Strength: It should be able to withstand the load which the user may carry. It should not get deformed or distorted while carrying the small load within a predefined region. Hence the prosthetic hand should have high strength.  Appearance: The artificial hand must be attractive. Anthropomorphism is a key criterion that often contributes to a


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

user’s acceptance of the prosthetic hand. Cost: Any artificial limb must be useable by all possible users. The prosthetics field is very cost sensitive. This means the artificial limb must be produced at a cost that will allow the prosthetic hand to be priced competitively.

Any aid to rehabilitation should have two important features that are aesthetics and optimal design as the rehabilitation field has a history of crudely fashioned devices. It is noticed that with respect to the above characteristics the material selection for the prosthetic hand plays a very important role. Here the candidate materials for prototype manufacturing can be Plexiglas, Polystyrene, Nylon 6, Nylon 66, Teflon, etc. Out of these materials on the basis of their characteristics (lightweight, strength, and cost) three candidate materials are selected for stress analysis that are Plexiglas, Nylon 6, and Nylon 66. So in this paper stress analysis of index finger developed in computer aided design (CAD) modelling software is carried out by considering selected candidate materials. On the basis of comparative analysis of these materials, the best material is selected for the prototype manufacturing of the artificial hand. This helps in achieving the desired characteristics of a prosthetic hand that is lightweight, high strength, and low cost, etc. MODEL DEVELOPMENT In development of artificial hand, materials selection is utmost importance with respect to bio-mimetic design approach. For that we have to study the behavior of selected candidate materials using computer aided design (CAD) model. The model developed using CAD modelling software. The model dimensions are based on existing literature

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study and the survey of the human normal hand. The CAD model of artificial hand is shown in Figure 1, and dimensions of the various fingers are shown in Figure 2.

solve complex integration problems using finite element method approach. It provides the approximate solution to our complex problems. It works in three steps i.e. pre-processing, solution, and postprocessing. In pre-processing we define the geometry and all the constrained related to it. In solution it solves for the results and all the calculations are made in this step. Finally it provides the result data and graphs for interpretation of results. The index finger to be analyzed is shown in Figure 2, it is 94 mm long. The entire model is assumed to be made of selected candidate material i.e. either Plexiglas or Nylon 6 or Nylon 66. Young’s modulus (E) and Poisson’s ratio (ν) for Plexiglas, Nylon6, and Nylon 66 are E = 3.3GPa, ν = 0.37, E = 1.4GPa, ν = 0.39 and E = 1.4GPa, ν = 0.40 respectively. The load is applied on the distal portion of the index finger. Results obtained for the same dimensions of index finger in all cases with maximum safe load drawn from ANSYS are shown in Table 1.

Fig. 1. CAD model.

Fig. 2. The dimensions of various fingers. STRESS ANALYSIS The developed CAD model is used for the stress analysis of Index finger in ANSYS. This is a numerical analysis tool used to

Table 1. The results obtained for selected candidate materials. Considered material (Load)

Plexiglas (At 2.238 N)

Nylon 6 (At 2.797 N)

Nylon 6,6 (At 1.865 N)

Various Stresses

Equivalent (vonMises) stress (Pa)

Maximum Principal Stress (Pa)

Normal Stress (Pa)

Shear Stress (Pa)

Total deformation (m)

Min.

0

–44.063

–406.23

–430.68

0

Max.

3516.1

2030

522.97

1296.1

3.739×10-3

Min.

0

–19.762

–123.19

–144.23

0

Max.

1139.8

658.05

181.3

425.42

2.9023×10-3

Min.

0

–43.572

–216.76

–272.17

0

Max.

2113.5

1220.2

349.12

794.36

5.424×10-3

Figures 3–5 show various results in index finger for selected candidate materials i.e. Plexiglas, Nylon 6, and Nylon 66, respectively.


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Material Selection for the Prosthetic Hand

(a)

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(b)

(c) Fig. 3. (A) Deformation, (b) equivalent stress, (c) maximum principal stress in index finger for Plexiglas at load 2.238 N.

(a)

(b)

(c)

Fig. 4. (a) Deformation, (b) equivalent stress, (c) maximum principal stress in index finger for Nylon 6 at load 2.797 N.

(a)

(b)

(c)

Fig. 5. (a) Deformation, (b) equivalent stress, (c) maximum principal stress in index finger for Nylon 66 at load 1.865 N. From the results it is observed that all three candidate materials vary in their load carrying capacity. The load shown in Figures 3–5 are the maximum safe load on which the selected candidate materials can work without deformation or failure. Further it shows that load carrying


capacity of Nylon 6 is greater than other two candidate materials. Also it has lowest equivalent stress as compared with other two candidate materials. This results in higher strength of the Nylon 6 material as compared with the other two selected candidate material. These results reveal

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that Nylon 6 has higher capability to withstand the load for longer duration. Hence this candidate material can be the most appropriate material candidate for the prototype manufacturing of the prosthetic hands. CONCLUSION On the basis of result analysis it can be concluded that Nylon 6 matches the required characteristics in much better way than the other two selected candidate materials. The results shows that Plexiglas and Nylon 66 have less capacity to withstand high load for longer duration as they show high equivalent stress values than Nylon 6. Also the deformation is higher in Plexiglas and Nylon 66 as compared to the Nylon 6 for a given load. Hence, with these results it is concluded that Nylon 6 may be used for the prosthetic hand technology. Nylon 6 is light in weight, high in strength, and comparatively low in price, this material is therefore can be selected for prototype manufacturing. ACKNOWLEDGEMENT This study is funded by research grant (Ref.: BT/532/NE/TBP/2013, Dated: 11/8/2014) from the Department of Biotechnology (DBT), Government of India to the University. The authors acknowledge the support they get from the government and others involved in the research. REFERENCES [1] Saikia A., Mazumdar S., Sahai N., et al. Recent advancements in prosthetic hand technology, J Med Eng Technol. 2016; 1–10p.


[2]

Massa B., Roccella S., Carrozza M.C., et al. Design and Development of an Underactuated Prosthetic Hand, Proceedings of the 2002 IEEE International Conference on Robotics & Automation. Washington, DC, May 2002. [3] Lalibertk T., Gosselin C.M. Simulation and design of underactuated mechanical hands, Mechanism Mach Theory. 1998; 33(1) 39–57p. [4] Bicchi A. Hands for dexterous manipulation and robust grasping: a difficult road toward simplicity, IEEE Trans Robot Autom. 2000; 16(6): 652–62p. [5] Salisbury J.K., Craig J.J. Articulated hands: force control and kinematic issue, Int J Robot Res. 1982; 1(1): 4– 17p. [6] Carrozza M.C., Massa B., Micera S., et al. The development of a novel prosthetic hand-ongoing research and preliminary results, Mechatron IEEE/ASME Trans. 2002; 7(2): 108– 14p. [7] Hirose S. Connected differential mechanism, Int Conf Adv Robot. 1985; 319–26p. [8] Kyberd P.J., Light C., Chappell P.H., et al. Nightingale, Dave Whatley and Mervyn Evans, The design of anthropomorphic prosthetic hands: a study of the Southampton Hand, Robotica. 2001; 19: 593–600p. [9] Napier J.R. The prehensile movements of the human hand, J Bone Joint Surg. 1956; 38B(4): 902– 13p. [10] Iberall T. Human prehension and dextrous robot hands, Int J Robot Res. 1997; 16(3): 285–99p.

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