On Force-Position Hybrid Control Of Fast Tool Servo Driven By Maxwell Electromagnetic Force

Fast tool servo(Fast tool servo,hereinafter referred to as FTS)processing technology is widely used in the processing of optical free-form surfaces by virtue of its processing efficiency,high precision,and low cost.FTS driven by Maxwell electromagnetic force can overcome the inherent small stroke limitation of piezoelectric actuators as well as the insufficient driving force of voice coil actuators.It has great application prospects in FTS systems.This article introduces the system composition and working principle of the FTS driven by Maxwell electromagnetic force.It analyzes the mechanics model and the circuit model,and carries on the dynamic modeling to it.Based on the model,the robust control is adopted,combined with the feedforward compensator based on disturbance observation as the position control inner loop.The generalized impedance model is used to construct a force control loop to realize FTS force-position hybrid tracking control.The main contributions of this article are:1)From the analysis of the mechanical model and circuit model of FTS driven by Maxwell electromagnetic force,the corresponding dynamic model is established,and the parameters are identified by sweeping frequency excitation,and the mathematical model of the system is obtained,which provides a basis for the design of the control system.At the same time,the system’s uncertainty range is obtained by measuring the system frequency response diagram at different positions.2)In the design of the position control inner loop,in order to solve the problem of system uncertainty,a robust controller with strong fault tolerance is used as the main controller,and a proportional gain approximation is proposed to replace the transfer model of the system,and the unmodeled portion of feed-forward gain is estimated and actively compensated by the disturbance observer.The introduction of the feedforward compensation controller based on the disturbance observer greatly reduces the tracking error of the position trajectory,and the system’s anti-interference ability is also improved.3)In order to effectively track the force trajectory,the cutting force self-sensing method is used to construct a force observer of the cutting process through the FTS model to estimate the interaction force between the tool and the workpiece during cutting.The difference between the displacement when the end effector is not cutting and the actual displacement when cutting is used as the equivalent of the interaction force for force control.The robust generalized impedance control method is adopted to realize the synchronous control of force and displacement.The results of the scratch experiment show that the proposed generalized impedance control method can achieve the force-position hybrid control of the cutting process by adjusting the parameters of the target impedance.