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 capable of linear resolution to 2 nanometer and angular resolution to 1 arc- 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 residing on a standard Pentium PC. A number of nonlinearities 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 nonlinearities, (2) hysteresis, and (3) output oscillations. Application of this actuator include: optoelectronics assembly, optical fiber alignment, and semiconductor processing.