Papers by Keyword: Aspherical Surface

Abstract: Elastic modulus error is the key factor influencing to the forming precision of grinding tool bended in the aspheric processing. The mathematical model of the grinding tool bended has been established through mechanics and the mathematics method, the error formula has been inferred and the influence of elastic modulus error has been analyzed, the calculating example has been given. The result indicates had to confirm material’s elastic modulus value according to the precision request of workpiece in choosing grinding tool material and control it in the certain scope, thus guaranteed the grinding tool the forming precision, further improve the workpiece the face shape precision.

Abstract: In this paper an efficient grinding mode which is employed by the Cranfield BoX ultra precision grinding machine is discussed. The equations of workpiece surface and grinding wheel surface are proposed and the grinding motion is simulated via Matlab. The trajectory of the changing cutting region is discussed. The simulation results show that this grinding mode is suit to manufacture low slope surfaces. Generally, the workpiece surface is steeper, and the cutting range of the machine is smaller. The angle of the spindle inclination, the grinding wheel width and the cutting depth should be chose properly for different manufacturing capacity.

Abstract: Plane lapping method using the elasticity of materials has many advantages comparing with current machining method for aspherical surface machining. Due to the deformation of the workpiece, the material removal characteristics of this method are different from the traditional lapping process of flat surface. In this paper, based on the Preston equation and plate theory, the theoretical model of the material remove rate is built in the case of proving experiment. Then the proving experiment of elastic deformation method is carried out, the recorded values fit well with theoretical ones, which shows that the theoretical model of material removal property is valid and the variation of MRR is related to the deformed profile of workpiece.

Abstract: As the consumer market in the optics, electronics and aerospace industries grows, the demand of ultra-precision aspheric surface increases. The shape accuracy of the optical lens changes significantly with deformation conditions and optical properties of the lens varies with stress distribution within the lens. Therefore, determining the deflection and stress of glass lens is very important to improve the quality of the lens. In this paper, the deflection and stress theoretical results of BK7 glass plate have been presented in different cases of elastic deformation processing. The results are compared with the finite element analysis (FEA) to demonstrate the robustness and accuracy of algorithm in calculation of stress and deflection. The mentioned finite element models were established using the software Abaqus/CAE. The analytical and FEA results showed that if the edge of plate is simply supported, the maximum deflection is 4 times larger than in the fixed edge case. Otherwise if the edge and centre point of plate is simply supported, the maximum deflection is 2.5 times lower than in the fixed edge case and 11.3 times lower than in the simply supported at edge case.

Abstract: This paper reported an experimental study on ultra-precision grinding for micro aspherical lens mould. One-point grinding mode and inclined axis grinding mode are employed and investigated in grinding process. Grinding test of a micro-lens mould using form error compensation technique is conducted. The experimental results show that ground micro aspheric mould surfaces with form (PV) around 0.122 µm and a roughness (Ra) less than 2 nm is achieved successfully.

Abstract: A wide-range laser auto-collimation method to measure the surface profiles of targets with steep slopes has been proposed. This method employs a deflecting optical system to enlarge the measurement range of the angle sensor. However, this optical system also changes the sensitivity property of the angle sensor. Therefore, we propose a new in-situ self-calibration method that includes the geometrical designed data of the target and can be applied to wide-range laser auto-collimation method. In the proposed method, the calibration sensitivities at each measurement point are obtained with two sets of measured data, which are acquired before and after performing minute rotation or translation with respect to the measured target, and the simulated shift of the normal angle at each point. The present paper describes the calibration procedure and specific calculation method used in the proposed method.

Abstract: A novel quantitative shadow testing equipment is presented based on the digital imageprocessing technique for characterizing local surface deformations on optical surface. Two magnetic stepping motors control the positions of the knife-edge for cutting the wave-front reflected back from the aspheric surface separately. At each position of the knife-edge blocking the image on the focal plane, it is recorded and analyzed by an image-processing set-up behind the knife-edge under computer control. Based on a group of images recorded, the analysis of local slopes is performed by picking up characteristics of illumination levels. Further the relationship between the changes of illumination level and deformations on surface is built on the principle of Fourier Optics. The results of tests approve that the method is effective on determining the characteristics of two parabolic surfaces using magnetorheological finishing.