Piezo actuator hybrid modeling and nonlinear control for active error compensation in diamond turning.

摘要

A precision machine tools is usually constructed with, for example, high geometric and kinematic accuracy, increased stiffness and damping, and reduced thermal deformation. However, the cost for implementing these measures, in general, increases exponentially with the level of desired accuracy. Therefore, this research focuses on developing and implementing a new add-on method to improve the accuracy of an existing machine tool.; The new method is an active error compensation method which consists of (1) a metrology system with an in-situ error separation method to determine the workpiece error, (2) advanced nonlinear models and controllers to compensate the workpiece error, and (3) a fast piezo tool micro-positioning system to execute the control command.; The foundation of the new error compensation method is new piezo actuator models which are hybrid models integrating Preisach model and a neural network. These models can predict not only the static behavior of the piezo actuator but also its frequency dependent behavior. Based on the models, a feedforward and feedback controller is implemented to achieve high positioning accuracy for the piezo tool micro-positioning system. In addition, a repetitive controller is used to determine the motion that the tool should follow from one pass to the next to improve the workpiece form accuracy.; The method was implemented in a diamond turning lathe and validated with real cutting tests. Significant reduction in flatness error was accomplished by the active error compensation method.