Optimization of removal function parameters in CCOS

Computer controlled optical surfacing (CCOS) technique is widely used in machining process of large and medium aspheric surfaces, because of its high accuracy, simple process conditions, low cost and other merits. The characteristic of the removal function of a polishing tool is a key factor in determining convergence rate in CCOS process. The shape parameters, which influence the characteristic of the removal function of a dual-rotation polishing tool, are the rotational speed ratio and the eccentricity ratio. A method is presented to optimize these two shape parameters, in which the error correcting capability of the removal function is considered. The optimized parameters are compared with those from other references. The results show that a removal function with a certain size has the highest error correcting capability when the eccentricity ratio is 0.8 and the rotational speed ratio -3. With the optimized parameters, the final figuring of a 500 mm f3 paraboloid mirror is accomplished. With 95 hours of polishing time, the mirror is taken from an rms deviation of 0.241 waves to an rms deviation of 0.015 waves, where a wave is 0.6328 μm. The results show that higher precision and efficiency will be achieved with the optimized parameters in CCOS. © 2009 SPIE.