Strength of Zero-stiffness Microactuators*

Many popular microactuators, including piezoelectric actuators, suffer from incomplete conversion of input energy into mechanical output work. The culprit is their inherent stiffness. Energy used in the elastic deformation limits the output displacement and force and thus the work. At full stroke, all force is used to deform the material itself and all energy is stored as internal elastic energy. Therefore, microactuators with zero internal stiffness (in the direction of actuation) are desired for high energy conversion efficiency. These actuators use either field actuation (electrostatic, magnetic) or zero stiffness statically-balancing structures. Only when the system requires energy storage, e.g. in dynamic systems, should actuators with internal stiffness be considered. These microactuators must be integrated with proper force transfer structures to achieve optimal actuation configurations for different actuation purposes. Distributing these actuators in series and in parallel allows us to achieve the desired large displacement and force outputs resulting in distributed actuator structures with optimal energy performance.