Research On Electromagnetic Stress Fast Tool Servo Trajectory Tracking And Disturbance Compensation Control

Fast tool servo(FTS)processing technology is an effective method for ultraprecision manufacturing of complex optical surfaces.It can ensure the surface quality and surface accuracy of the micro-structured surface during the processing process,as well as high processing efficiency and process flexibility,strong material adaptability and other advantages.Compared with other driving principles,the electromagnetic stress-driven FTS has the characteristics of larger driving stroke and high force density,and has irreplaceable advantages in the application of large-stroke FTS.This article introduces the working system and driving principle of the electromagnetic stressdriven FTS,and analyzes the modeling from the two parts of the mechanical model and the circuit model.The closed-loop position control of the FTS system takes into account the external random disturbances,periodic cutting force disturbances and unmodeled dynamic items in the actual working process of the FTS,and the disturbance compensation control method is used to suppress the adverse effects of disturbances on the FTS system.The main contributions of this article are:(1)Through the small signal sweep frequency excitation test,the FTS model parameters are obtained.Since the system model has the characteristics of a nonminimum phase system,the system inverse dynamics compensation is first used to improve the dynamic characteristics of the controlled object.The improved controlled system uses PID and model-based inverse feedforward compensation as the main controller,so that the control system has a high closed-loop bandwidth(-3d B)of 1k Hz.The parallel resonance controller based on internal model principle is incorporated into the control system to realize ultra-high-precision tracking of the harmonic trajectory at a specific frequency.(2)Due to the various disturbances and uncertainties in the actual work of FTS,these factors will adversely affect the actual cutting of FTS.Disturbance observer(DOB)and iterative learning control(ILC)are used to eliminate disturbances.Through theoretical derivation and simulation tests,it is proved that the combination of the two can converge the FTS tracking error to a smaller range.In complex work It can effectively improve the tracking accuracy of FTS in the environment.(3)The designed control method was applied to FTS,and the milling experiment was initially completed.Take the preset motion trajectory of the workpiece as the system reference input,control the FTS to ensure its motion accuracy,and process the expected lens array surface through actual milling.It shows the practicality and high robustness of the designed control method in the actual machining process.