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Edge effect is unavoidable in polishing process when the polishing pad passes by the workpiece edge, which influences the entire form accuracy of free-form surfaces of optical components in computer-controlled polishing, or even reduces their effective aperture. This article focuses on a theoretical and experimental investigation into the material removal influenced by edge effect for polishing along a certain path. The contact pressure distribution models for polishing the workpiece edge are summarized and modified into four representative models: linear model, skin model, linear skin model and divided skin model, which are adopted to calculate the theoretical material removal profiles orthogonal to the straight or curved polishing path, in this article. So, the material removal models are built in the process of polishing along tool path instead of polishing on a single point. And experiments are carried out to choose the most suitable contact pressure distribution model according to the comparison of experimental profiles and the different theoretical profiles. Experimental results reveal the influences of edge effect on material removal and a modified parameter is introduced into the theoretical material removal profile for the curved path to coincide with the experimental profile better. In addition, some qualitative analyses about how to reduce the edge effect are also given in this article.

This article presents a real-time force-controlled pneumatic compliant polishing tool with self-supplied abrasives making the abrasives added to the contact area between the polishing pad and workpiece, which can lead to good polishing performance. And a force–position decoupling pneumatic servo system for polishing force control is presented to solve the problem of force–position coupling in the traditional polishing process. However, it is difficult to realize satisfactory control performance due to the problems of time variance, compliance, hysteresis and nonlinearity in pneumatic servo system. This article proposes an online tuning neural proportional–integral–derivative controller to improve force control performance. The real-time polishing force control results of pneumatic servo control system are investigated by adopting proposed neural proportional–integral–derivative control strategies with data acquisition card and RTW toolbox in MATLAB/Simulink. The real-time experimental results of polishing force control indicate that the excellent control performance can be achieved by the proposed neural proportional–integral–derivative controller no matter the reference force is constant or varied. Compared with those by traditional proportional–integral–derivative controller, the duration for stabilizing the polishing force is shorter and the error between the output force and the reference is smaller by the proposed neural proportional–integral–derivative controller.

The application of freeform surface in the off-axis three-mirror imaging system can greatly improve its optical performance. However, it is difficult for fabrication of freeform optical surface to high precision by traditional machining technology. This paper focuses on the corrective polishing of the primary mirror and tertiary mirror, which are fabricated on one monolithic substrate and described by NURBS-based freeform surfaces, in an off-axis three-mirror imaging system. The integrated polishing process system is proposed for polishing the two mirrors on the 4-axis CNC polishing machine by use of spherical polishing tool. The tool influence function (TIF) module, polishing path generation and dwell time calculation module included in the integrated polishing process system are described respectively. The material removal on the measurement line of part surface is predicted to validate the dwell time calculation algorithm. The polishing experiments of the primary mirror and tertiary mirror are performed to verify the proposed integrated polishing process system.

Polishing process is the final step for the fabrication of optical surfaces. This paper presents a theoretical and experimental investigation on the removal of material from a surface during the polishing process. The model in this paper assumes that the material removal rate follows Preston equation and the pressure distribution at the contact area is Hertzian. Particularly, the effect of the tool posture, which is described by the inclination angle and declination angle, upon the local material removal profile is modeled and analyzed. On the basis of the analysis, a novel method is proposed to optimize the tool angles. A series of polishing experiments were conducted to verify the effectiveness of the proposed model. The theoretical and experimental results indicate that (1) the inclination angle has large effect on the local removal depth, and (2) the location of the maximum removal depth bias away from the center of the profile and the direction of this bias is determined by the declination angle. The model in this paper is potentially useful for the planning of the polishing posture and the tool path during the polishing process.