Personalized Fingers Design with Silicone Rubber Texture Fingertip for Increased Grip in Transmetacarpal Powered Hand Prostheses

There is a lack of powered prosthetics for transmetacarpal and congenital amputees with partial hand loss, mostly because there is little space available for actuators and electronics. Thus, body powered prostheses are the common solution for these cases and many open-source designs can be found, such as the Raptor Hand prosthesis, which can be used by both transmetacarpal and congenital amputees, and flexes the fingers with a tendon mechanism powered by the user’s wrist. Its main disadvantage is that grasping requires high forces on the wrist and causes fatigue to the user. This issue could be addressed with myoelectric control of powered fingers. State-of-the-art micromotors allow us to design for the available volume.

Another important limitation of active upper limb prosthetics is the size standardization, which results in a noticeable difference between the user’s prosthesis and the healthy hand. The need of customization of fingers and palm design is achieved with parametric modeling and 3D printing for rapid prototyping. A four-bar linkage mechanism for the fingers allows us to modify the length of the links or phalanges according to the user specific anthropometric data with no significant impact on grip force and speed.

Additionally, to increase the actual force that the prosthesis can exert on grabbed objects, it is essential to take into account its friction coefficient, which depends on the material. Commercial powered prosthesis, such as the i-limb and Bebionic, have powerful micromotors with torques comparable to the exerted in human hand articulations. However, they lack the compliant texture of human skin and fingertips ridges which are significant factors for grasp effectiveness. These ridges coefficient of friction is comparable to that of elastomers, and in this work they are designed for the customizable fingers using a bio-inspired texture based on silicone rubber.

Recommended citation: R. Mio and M. Bustamante. “Personalized fingers design with silicone rubber texture fingertip for increased grip in transmetacarpal powered hand prostheses”, Cybathlon Symposium’16 (Booklet pp42).
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