Tailoring unconventional actuators using compliant transmissions: Design methods and applications

Matching a drive system to the force-displacement characteristics of the load is the cardinal principle in electromechanical systems design. Unconventional actuation schemes, such as piezoelectric, electrostatic, and shape-memory alloys (SMA's), seem to exhibit certain limitations in terms of power density, stroke length, bandwidth, etc., when one attempts to employ them directly to an application. Integrating them with mechanical transmission elements so that the integrated actuator-transmission system matches the load characteristics of the application can enhance the utility of such unconventional actuators. Conventional mechanical devices are sometimes difficult to integrate with unconventional actuating schemes. For instance, the two-dimensional nature of microelectromechanical systems (MEMS) and no-assembly constraints arising from their batch fabrication make it difficult to fabricate, assemble, and integrate a conventional micromechanism with an electrostatic actuator. However, a monolithic "solid-state" mechanical transmission device enables easy integration. This paper presents a systematic method of designing such unconventional mechanisms. The paper presents a generalized methodology for designing compliant mechanisms. Our systematic synthesis formulations provide a mathematical basis for designing compliant mechanisms for: 1) topology generation-that is, establishing a feasible configuration to meet given functional requirements and 2) size and shape optimization-to meet the prescribed quantitative performance requirements, such as mechanical advantage, stroke amplification, etc, Design examples illustrate integration with electrostatic, piezoelectric, and SMA actuators for MEMS and smart-structures applications.