Analysis and Synthesis of Underactuated Compliant Mechanisms Based on Transmission Properties of Motion and Force

This article analyzes and designs the transmission structure for underactuated compliant mechanisms (UCMs). The transmission structure of UCMs consists of serial and parallel transmission chains. At first, the UCMs are classified systematically according to the number and distribution of the serial and parallel transmissions. Next, the active and passive transmission properties of motion and force in UCMs are analyzed on the defined four subspaces of tangent and cotangent spaces of joint space. Synthesizing the classification and the transmission properties of UCMs, the congruent relationship between mechanical structure and transmission function is established, and different cases of UCMs are discussed and compared. A novel type of UCMs can achieve the independent regulation of passive stiffness, active force, and active motion that is useful for improving the transmission performance in robotic and prosthetic hands. Finally, a functional oriented design method is proposed and used to design a single-actuator two-fingered gripper for enveloping and precision grasps. The results demonstrate the validity of the proposed method.