Research On Control Technology Of Aspheric Surface Compliant Polishing

Magnetorheological fluid is a kind of smart material. In the presence of magneticfield, its properties will change, mainly reflecting in the rank of magnetic particles inthe material and liquid form changes from the Newton fluid to Bingham fluid. Theapplication of the material in the transmission device can realize the torque transfer,and achieve the continuously variable speed through the control of magnetic field.Based on the excellent characteristics，It received more and more attention in modernera. It achieves results in the application, both damper and clutch.The magnetorheological transfer device has the characteristics of excellentcontrollability and overload protection in the rotation. So it was applied to the asphericsurface polishing process, used to transmit torque. Put forward a kind of force positiondecoupling method based on the analysis of coupled problem between force andposition in the aspheric surface polishing process and combined withmagnetorheological torque transfer device. The method combined themagnetorheological torque transfer device and the CNC lathe realized that polishingforce by the position servo control change to torque servo control and polishing path isrealized by CNC lathe. And developed a set of compliant polishing control system. Thecontrol system based on LabVIW platform with the fuzzy PID controller effectivelyimprove the control precision, so that the polishing surface roughness got to a higherlevel.The main research contents and methods are as follows:1. Introduced the application of magnetorheological fluid, aspheric surfacecomponents’ advantages and difficulties of machining, the development status ofaspheric surface precision and ultra precision processing technology at home andabroad, and the gap between our country and western developed countries on theaspheric surface processing equipment.2. Studied on the theory of aspheric surface polishing, found out the influencefactors of material removal rate. Analyzed the coupling principle between force andposition during aspheric surface polishing process, put forward a method of decoupling,and build a material removal model. Analyzed the model by means of Matlab.3. Researched the method of building mathematical model. Systematically studiedthe system identification theory, content, steps and so on. Used the curve fitting by the least square method with the aid of Matlab tools to get the function between theexcitation current and the torque output of magnetorheological torque transfer device.And through the least square method, the program was compiled to calculate theunknown parameters of magnetorheological torque transfer device dynamic model, soas to obtain the dynamic model, laid the foundation of software operating control forthe system.4. Analyzed the torque transmission in the polishing process, and corrected theparameters of polishing force dynamic model. Obtained three time constants of PIDcontroller by the Ziegler-Nichols parameter tuning method. In the Fuzzy module ofMatlab，established the fuzzy PID controller，including the membership function, ruletable and so on. Then made the simulation of dynamic model calibration in Simulinkmodule of Matlab. The system included PID controller and fuzzy PID controller. Theresults showed that the response of fuzzy PID controller was better than PIDcontroller’s. In view of the fuzzy PID controller with good effect, integrated it on theLabVIEW platform, wrote out.VI with the fuzzy PID controller. The results showedgood effection and high reliability in the practical application.5. Through the Mastercam programming software, obtained the required roughturning program, to get the required polishing workpiece. Then wrote finishing turningprogram used for precision polishing process. Results showed that workpiece after thethe CNC polishing platform processing got excellent surface quality. The system wassuitable for polishing many kinds of aspheric surface.Experiments showed that, the magnetorheological torque transfer deviceeffectively solved the force—position coupling problem in polishing process. The fuzzyPID controller made the polishing accuracy improved effectively, the surface roughnessof workpiece could be maintained at about0.02μm.