A Monolithic Cable-Driven Compliant Wrist for Prosthetic Arms

This article presents a new design for a two-degrees-of-freedom compliant robotic wrist for upper limb prostheses that matches the maximum range of motion of a human wrist by utilizing cross axis flexural pivot (CAFP) as compliant joints. The wrist design is manufactured using additive manufacturing technology as a single, monolithic component. An optimization routine that utilizes the bi-beam constraint model technique to synthesize compliant joints in the wrist design is presented and verified using finite element analysis (FEA). This optimization routine includes the computation of passive contact profiles through the centroid approach to prevent buckling in the CAFP compliant beams caused by external forces. Furthermore, an accurate analysis of various tendon routing paths for the actuation of the wrist is conducted, providing a flexible and reliable solution to avoid unnecessary power consumption. The proposed wrist is lightweight, cost-effective, easy to maintain, and thanks to the utilization of CAFP joints, it is frictionless and immune to backlash. Experimental tests are conducted to verify the FEA results and confirm the range of motion achieved by the joint (i.e., $\pm 80^{\circ }$ of flexion/extension, $\pm 40^{\circ }$ of ulnar/radial deviation). Overall, this article demonstrates the development of a novel compliant robotic wrist that offers several advantages over traditional prostheses, including a wider range of motion, increased flexibility, and reduced maintenance costs.