Performance optimization of a fast tool servo for single-point diamond turning machines

This paper describes a new, fast tool servo system designed for fabrication of nonrotationally symmetric components using single-point diamond turning machines. A prototype device, designed for flexible interfacing to typical machine tool controllers, is described, along with performance testing data of tilted flat and off-axis conic sections. Techniques for controlling the piezoelectric actuator to less than 1% error are discussed. The performance of a standard integral controller shows a significant error due to hysteresis in the actuator. The effects of the hysteresis were reduced by implementing two control schemes, an optimized PID controller and a technique that utilizes a dynamic compensator module in conjunction with the linear controller. The compensator samples the hysteretic voltage/displacement relationship in real time and modifies the effective gain accordingly. Experimental implementation results in an 80% reduction in the motion error caused by hysteresis, but peak-to-valley errors are limited by side effects from the compensation.