Research On Ballonet Polishing Of Aspheric Part Based On MRF Torque Servo

Aspheric optical parts are more and more widely applied in the fields of aerospace, military andcivil products due to their unique superiority. In order to get high-precision aspheric optical surface,the research on aspheric surface processing technology and equipments has become the focal pointof modern precision manufacturing. Nowadays, however, the finishing of aspheric surfaces stilldepends on the manual operation of skilled workers, and some problems in aspheric polishingprocessing systems, such as high equipment cost and force-position-posture coupling, are requiredto be solved. Therefore, it is of great importance to extend the research on automatic finishingprocessing technology and method with high precision, high efficiency and low cost.The thesis proposes a polishing method that realizes aspheric numerical control polishing bycombining Magnetorheological Fluid Torque servo (MRT) and ballonet polishing tool system. Inthe theses, a kind of aspheric ballonet polishing tool system was developed based on a MRT andintegrated with a CNC lathe, and by using the integrated polishing system the separate control offorce, position and posture in the process of polishing was realized. Exploiting the advantages offlexible ballonet in polishing process—small processing area, good consistent feature, highmaterial removing rates, stable contact area and exquisite texture, the ultra-precise efficientpolishing of aspheric components is achieved by controlling the motion trail and dwell time ofpolishing ballonet on the surface of the workpiece; the paper proves that this method is a practical,economical and high-precision quantitative polishing technique through the experimental study.Firstly, establish pressure distribution model that polishing ballonet exerts on the asphericworkpiece based on the coordinate transformation and Hertz Contact Theory, guide to pressuredistribution expressions which is between the ballonet andassociating with the workpiece curvaturebased on distribution model of pressure that polishing ballonet exerts on the aspheric workpiecederiving from the coordinate transformation and Hertz Contact Theory.. Analyze the velocitydistribution of polishing contact area according to the polishing motion features of CNC lathe. Setup an aspheric workpiece material uniform removal model by using the famous Preston materialremoval equation and the relation between aspheric parts removal quantity and remove depth. Byanalysis of the dwell time in each polishing point, polishing working hours and arriving time ofevery polishing position, aiming at uniform removal of workpiece surface, figure out the relationship model between the feed velocity of polishing points and the feed velocity of CNCcutter-location point.Next, conduct a study of Magnetorheological fluid Torque servo (MRT) and propose the valueranges and measuring method of elasticity coefficients of ballonet. Build the torque output modelof MRT and numerical simulation. Obtain the transfer function of tool system by its systemidentification, guarantee the constancy of polishing pressure through real-time control of themagnetizing current with PID control strategy. Make use of ADAMS simulation analysis to verifythe stability of polishing force control system.Finally, using four patterns—constant pressure constant speed, constant pressure constant linearvelocity, constant torque constant speed and constant torque constant linear with the correspondingpolishing process parameters, conduct ellipsoid workpiece polishing experiments. Theexperimental results showed that the MRT aspherical ballonet polishing techniques, methods andapparatus can be realized on the aspheric optical parts sophisticated, efficient, low-cost automatedpolishing.