Papers by Keyword: Removal Function

Abstract: Magnetorheological finishing (MRF) is an advanced polishing technique capable of rapidly converging to the required surface figure. In this article, dual-rotation MRF tool is used to generate centrosymmetric removal function that can be W-shaped or Gaussian-shaped. Using W-shaped removal function and Gaussian-shaped removal function respectively, this article compares the convergence of surface error by simulating the finishing process through iterative calculations. Furthermore, it compares mid-spatial-frequency surface error caused by the two removal functions, through 2D FFT and PSD estimation in the frequency domain. From simulation, this article proves that Gaussian-shaped removal function is more advantageous than W-shaped removal function. To solve the problem that the removal function obtained in dual-rotation MRF is W-shaped, this paper presents the method of adjusting the distance between the axes of self-rotation and co-rotation to secure Gaussian-shaped removal function. Finally, experiments have been conducted to demonstrate validity of the method.

Abstract: A new method of processing optical aspheric parts by of bending and forming is presented, and the processing is line contact. The grinding principle is given of the bending and forming method. Based on the Preston equation, the grinding conditions is put forward to the bending and forming method. The function of the pressure and the relative velocity on the any point of at the processing surface are made. The material removal function is deduced about the bending and forming method. The experiments shows the grinding average error is 0.0272mm using solid abrasive on parabolic parts, and the maximum error is 1.0038μm using abrasive belt on hyperboloid parts.

Abstract: On the basis of the Preston assumption, the removal function of the annular polishing pad with the structure of the dual-rotor movement has been studied. The level of the similarity of the characteristic curve of the annular polishing pad and the Gaussian distribution has been evaluated by the tending factor. The pulse iteration method and the matrix calculation have been used to compute the residual error and the dwell time. The simulation result proved that the residual error (RMS) polished by the annular polishing pad had dropped 8.7% than that polished by the normal polishing pad with the same initial error condition, the surface quality has been improved by the new method.

Abstract: Large aspheric elements in giant laser facility are fabricated using computer controlled rapid polishing technology. The technological parameters are main influencing factors of efficiency. Base on Preston hypothesis, linear relationship of material removal with polishing pressure, polishing velocity and other conditions are established. According to the material removal function model of computer controlled rapid polishing, the removal function is simulated using MATLAB software. The influencing factors of volume removal efficiency are analyzed. In practice, the optimum polishing parameters are eccentricity 0.4, rotational velocity of principal axis 330 rpm, rotational velocity of polishing pad -600 rpm.

Abstract: Based on the mechanism of magnetorheological finishing(MRF), a material removal model was established. The dwell time function was solved by Jansson-Van Cittert algorithm to accomplish the kernel module design. Thus the control software of aspheric optics in MRF was designed. In order to verify accuracy of the processing control software, experiments were carried out on large aperture aspheric optics and the wavefront error of elements was achieved rapidly convergence. It is proved that the software could control the whole polishing process accurately.

Abstract: Numerical controlled local wet etching is a novel non-contact deterministic figuring method in ultra precision optics fabricating and functional material manufacturing fields, and the cross-sectional shape of the traditional removal spot is a simple cylinder, so the removal function has no adjustability. In order to create more practical and regular removal function, an eccentric rotation system is introduced to improve the LWE system. By controlling the eccentricity, it can achieve varied shapes removal function. When the rotary axis is controlled to a proper eccentricity, the removal function can be close to the Gaussian function. Moreover, the theoretical calculation and experimental validation are coincident and can give the research a steady foundation. The improvement not only can increase the adjustability of the removal function in LWE, but also can expand its applied field and provide reference for other ultra precision machining methods whose removal function does not have circular symmetry.

Abstract: Although Single Point Diamond Turning (SPDT) can do pretty well in optical surfacing of large scale KDP crystal, both the surface accuracy and integrity are considerably high; meanwhile as the defects of micro-waveness and stress are inevitable, the laser-induced damage threshold of KDP optical elements after SPDT still cannot be satisfied. Because of the characters of deliquescent and water-soluble, the process of computer controlled Micro-nano deliquescence is attempted to remove the residual micro-waveness on KDP surface after SPDT. Based on the assumption of Preston and the characters of Micro-nano deliquescence, the model of material removal ratio is suggested, the dwell time for ascertained KDP surface is solved, the processing of computer controlled Micro-nano deliquescence is simulated and the processed surface condition on theory is obtained. Besides, the influences of different parameters on the surfacing efficiency and accuracy are analyzed. Finally, three polishing tracks are comparatively analyzed. The simulation results are quite important in guiding the experimental polishing of large scale KDP by computer controlled Micro-nano deliquescence

Abstract: In order to keep the stability of tool’s removal function, it is required that the anastomosis be tight between the tool and workpiece surface in Computer-controlled Optical Surfacing (CCOS). In this paper, the influence of tool’s character on anastomosis status is firstly studied. The relation model on the ratio of radius to thickness, Young's modulus of the tool, normal asphericity and normal arc height of workpiece surface is established, and the macroscopical condition of tight anastomosis is derived in aspheric optics machining. According to the microcosmic distribution of surface error, the mathematical relation between anastomosis error and removal rate is researched. In the end, the influence rule of anastomosis status on the convergence ratio of residual error is analyzed in machining zone. Based on the conclusion of machining instance, it is found that workpiece material would be fast removed in middle contact zone when the peak value of tool’s removal function locates in its center position.

Abstract: This paper describes a two-dimensional tool-path planning model for minimizing the regularly distributed errors or mid-frequency errors during computer controlled optical surfacing (CCOS) by optimally connecting different tool-path segments. The model was established based on a neuro-fuzzy algorithm, a path neighborhood function which is defined as a victorious output element calculated in a self-organization way, then, the optimum material removal function with a modified weight was derived. The material removal function was studied theoretically and the results of simulation present a Gaussian distribution feature. Discrete removal points and optimized tool-path grid were simulated. Finally, an experiment involving a parabolic mirror was performed for residual error removal and the two-dimensional tool-path planning algorithm was found to be valid.