Design, Construction and Validation of a Fast Tool Post Using a PI-C~2-D Controller

摘要

This work deals with the development of a Fast Tool Post (FTP) for the rapid positioning of a tool during ultra-precision machining in the nanometric range. Precision engineering design aspects applied to the development of the FTP are discussed. Based upon the aspects discussed and taking into consideration overriding factors, such as nanometric positioning accuracy and requirement for near zero friction in the bearings, a model for the FTP is proposed including flexural bearings and a piezoelectric actuator. Finite-element analyses (FEA) are conducted both for static and dynamic behaviour of the model. Computer simulations for the verification of the vibrating modes of the FTP, identifying the natural frequencies were carried out. Based upon this model, all components were manufactured and assembled. To confirm the validity of this model, a simple PID controller was used. Experimental step response tests and MATLAB~® simulations were performed for various proportional and derivative gains. Control techniques such as PID, PID + feed forward and PID + phase-lag compensator (C) were discussed. A control strategy based on the processing of signals acquired during the positioning of the tool to identify the positioning condition and to obtain information to be used by a PI-C~2-D controller was proposed. This controller was applied to reduce the influence of model's errors from external sources. Experimental tests were performed to verify the effectiveness of the proposed controller in terms of position settling time, overshoot and steady state error. The results showed that the tracking performance and robustness of the Fast Tool Post were greatly improved when using PI-C~2-D control technique.