Conceptual Design of Compliant Parallel Mechanisms

This chapter presents the conceptual design of compliant mechanisms. The fundamental idea behind it is to establish the relationship between freedom and constraint space of a compliant mechanism according to the reciprocal relationship between twists and wrenches. By using the constraint-based design approach, a flexible element can be represented by the constraint wrench exerted from it. Thus by knowing the preferred mobility of a compliant mechanism, the configuration of constraints can be determined according to the reciprocal relationship, which further leads to the layout design of the compliant mechanism. Without the loss of generality, compliant parallel mechanisms with single degree-of-freedom flexible elements are selected to verify the proposed design approach. Particularly a physical prototype implemented with shape-memory-alloy (SMA) actuators is built and tested. By employing SMA springs, the single DOF flexible element that resists the translation along its axis can be transformed into a linear actuator that generates a stroke along its axis. Both finite-element-simulations and experimental tests were carried out to verify the mobility of the compliant parallel mechanism, thus validating the initial conceptual design approach.