Tri-axial Fast Tool Servo Using Hybrid Electromagnetic-Piezoelectric Actuation for Diamond Turning

A high-performance tri-axial fast tool servo (FTS) with the hybrid electromagnetic-piezoelectric actuation and the hybrid parallel-serial-kinematic structure is reported. Featuring the balanced and uniform actuation, a novel axis-symmetric linearized reluctance actuator is proposed to generate the planar motion in parallel, and the piezo-actuated vertical motion is then serially carried by the planar motion within a limited space. Verified by the finite element analysis, a two-stage design strategy is developed to optimally determine the multi-physical system parameters for the tri-axial FTS, assisted by an analytical model of the electromagnetic circuit as well as the mechanical mechanism. As for the trajectory tracking, the loop-shaping tuned PID controller with a feedforward compensator is employed for each axis, and a damping controller is additionally designed for the planar motion. Finally, both open-loop and closed-loop performance of the prototype are carefully demonstrated.