Detachment modeling of a novel workpiece micro-positioning table under preloaded hertz contact

A micro-positioning table for precision machining applications is developed utilizing a piezoelectric translator to generate high speed precision motions with accelerations up to 33.51 g. The piezoelectric translator is preloaded by four springs such that the moving part in the table keeps contact with the translator. The contact between the translator and the moving part is of the hertz contact type. It is a typical design for high performance micro-positioning devices. It is found that the hertz contact may not be maintained and detachment occurs when implementing large step motions. The detachment phenomenon is analyzed and the models to determine the separation time and the maximum overshoot are established. It is found that the stiffness of the preloading springs and the distance of compression for preloading are the key parameters of the detachment. A pseudo-step command signal design is proposed to use as a solution in order to conveniently reduce the overshoot without compromising the settling time. Experimental tests have been carried out, verifying the established models for the micro-positioning device.