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 proportional, integral, derivative 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. Simulation results indicate that errors in the performance of the system caused by hysteresis in the system can be compensated and reduced by 90%. 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.