High-precision, multiple degree-of-freedom piezoelectric actuator

This paper describes the construction and control of a two Degree-Of-Freedom (DOF) piezoelectric actuator. This actuator is part of a 6 DOF manipulator(1) capable of linear resolution to 2 nanometer and angular resolution to 1 are-second. Design of this actuator differs from the existing ones in that it has a monolithic structure which enables a high bandwidth, high force realization. The actuator is controlled by the TMS320C31 Digital Signal Processor (DSP) residing on a standard Pentium PC. A number of nonlinearties exist in the actuator, stemming from the geometry and materials properties. For example, coupling of the actuator elements can be modeled as a soft spring which increases scale factor at high actuation levels. In this work, a combination of feedforward (input shaping) and feedback control are applied to reduce the effects of 1) scale factor nonlinearties, 2) hysteresis, and 3) output oscillations. Application of this actuator include: optoelectronics assembly, optical fiber alignment, and semiconductor processing.