Trajectory Tracking Control of a Fast Tool Servo System Driven by Maxwell Electromagnetic Force

Abstract

Maxwell electromagnetic actuator can overcome the inherent small stroke limitation of piezoelectric actuators as well as the insufficient driving force of voice coil actuators, and tends to be very promising for applying in fast tool servo (FTS). To achieve a high-performance trajectory tracking, a damping controller is designed for the FTS to modify its basic dynamics, and a high-gain PID controller is accordingly developed through the loop-shaping method to gain a wide bandwidth. To decrease the model order of the damped control system, a static gain is adopted as the feedforward compensator where the unmodeled part is estimated and compensated by a disturbance observer. By conducting sweep excitation of a designed FTS actuated by the Maxwell electromagnetic force, the nominal transfer function is identified, and the controller parameters are accordingly determined. Experiment result demonstrates that the designed damping controller can effectively suppress the resonance and improve the closed-loop bandwidth of the FTS, and the disturbance observation-based feedforward compensation can significantly reduce the trajectory tracking error. Finally, the obtained motion error is about ±0.16 μm for tracking a harmonic trajectory with 25 μm amplitude and 25 Hz frequency.