Tailoring unconventional actuators using compliant transmissions: Design methods and applications

Matching a drive system to the force-displacement characteristics of the lo ad is the cardinal principle in electromechanical systems design. Unconvent ional actuation schemes, such as piezoelectric, electrostatic, and shape-me mory alloys (SMA's), seem to exhibit certain limitations in terms of power density, stroke length, bandwidth, etc., when one attempts to employ them d irectly to an application. Integrating them with mechanical transmission el ements so that the integrated actuator-transmission system matches the load characteristics of the application can enhance the utility of such unconve ntional actuators. Conventional mechanical devices are sometimes difficult to integrate with unconventional actuating schemes. For instance, the two-d imensional nature of microelectromechanical systems (MEMS) and no-assembly constraints arising from their batch fabrication make it difficult to fabri cate, assemble, and integrate a conventional micromechanism with an electro static actuator. However, a monolithic "solid-state" mechanical transmissio n device enables easy integration. This paper presents a systematic method of designing such unconventional mechanisms. The paper presents a generaliz ed methodology for designing compliant mechanisms. Our systematic synthesis formulations provide a mathematical basis for designing compliant mechanis ms for: 1) topology generation-that is, establishing a feasible configurati on to meet given functional requirements and 2) size and shape optimization -to meet the prescribed quantitative performance requirements, such as mech anical advantage, stroke amplification, etc, Design examples illustrate int egration with electrostatic, piezoelectric, and SMA actuators for MEMS and smart-structures applications.