Human mimetic forearm mechanism towards bionic arm

The paper presents a mechanical forearm mechanism to extend the pronation and supination (P/S) movement of the trans-radial amputee when he/she is able to conduct the P/S motion partially with his/her remaining forearm. The P/S motions of the existing prostheses and robotic arms developed till now are completely different from those of the human. When we are to develop the robotic prostheses for the amputees, two important issues should be considered such as cosmetic issue to look like normal arm and motion harmony issue between robotic prosthesis and the amputated living arm. Most prostheses do not realize the human-like P/S motion, but the simple rotational motion at the wrist by using the electric motor. In this paper, the well-known spatial four-bar mechanism is adopted in order to mimic human P/S motion as if the person does, because it is one of the best candidates to describe actual human forearm movement. To obtain the design parameters of the mechanism, first, 3D data of the amputated arm as well as the opposite side non-amputated arm are captured by using MRI (Magnetic Resonance Imaging) and 3D scanner. The design parameters such as link lengths, joint locations, and volumetric shape are determined from the measured data. Second, mathematical analysis is performed to simulate one degree-of-freedom P/S motion realized from the spatial four-bar mechanism, and the simulation results are suggested to confirm whether or not it acts like the relative movement between human ulnar and radius bones. Finally the effectiveness of the proposed mechanism is verified through two ADL (activities of daily living) tests.