Dongxu Zhang

Movement modeling and control of precession mechanism for bonnet tool polishing large aixsymmetrical aspheric lenses

Movement modeling and control for bonnet tool polishing large axisymmetrical aspheric lenses is present.The intersection point of the spin axis and the bonnet is selected to be object,after analyzing the structure of bonnet tool and process feature of large axisymmetrical aspheric lenses polishing;a base coordinate is set up with the centre of bonnet to be its origin point.As the included angle of the spin axis of bonnet tool and the local normal is fixed in continuous precession polishing,a corresponding coordinate is set up to get the position parameters of the intersection point of the spin axis and the bonnet when polishing a random point,the position parameters of the intersection point of the spin axis and the bonnet in base coordinate are got according to space coordinate conversion;Movement model is obtained by space matrix transformation,based on the surface equation of large axisymmetrix aspheric lenses,processing control model and the position parameters got in last step;Finally,most efficiency algorithm is added to the movement model,and precession motion curve is got by simulation.The correctness of movement model and control algorithm is confirmed through simulating the trend of spin axis of bonnet follows the local normal and comparing the simulated value of precession angle with the actual value of precession angle.

Effects analysis of processing factors on surface quality in optical grinding using ɛ-support vector regression

The aim of this study was to quantitatively analyze the effects of the processing factors on the surface quality in precision optical grinding. A novel identifying model which incorporates an effect factor is proposed based on ɛ-support vector regression (ɛ-SVR). Experiments were designed and performed to investigate the effects of the processing factors comprising the technological parameters and processing condition factors on the surface quality, and the experimental data were used to train the ɛ-SVR. Subsequently, the values of effect factor were solved to quantify the effects of the respective processing factors on the surface quality. Further experiments were performed to verify the effectiveness of effect factor. ɛ-SVRs of which the input vectors were multiplied and not multiplied by effect factor were respectively used to predict the surface quality including the surface roughness and surface shape peak–valley value. The values calculated by ɛ-SVR using effect factor were found to be much more accurate than those calculated without using effect factor. The results confirmed the effectiveness of identifying model for precision optical grinding.

Movement modeling and control of precession mechanism for bonnet polishing based on static highest-stiffness strategy

Movement modeling and control of a ‘bonnet tool’ polishing machine, based on a strategy of static highest-stiffness, are presented. The aim is to achieve polishing controllability as the bonnet tool executes a precessive motion trajectory. Taking an aspheric optical surface, e.g. lens or mirror, as the workpiece, the precessive polishing tool trajectory is designed as if the moving parts were rigid bodies connected by ideal articulations. Then by establishing the Jacobian stiffness matrix of the bonnet tool machine, the static stiffness of the machine is derived taking into account tool loading along its path. To minimize deformation, the control algorithm that achieves a maximum static stiffness strategy is superposed on the rigid body system tool trajectory model. This combined bonnet tool trajectory is produced by numerical simulation. Finally suitability of the rigid body movement model, compensated for desired static, but not inertial, load deflection, is assessed by simulating the trajectory of the tool’s rotational axis to determine how much angular deviation it sustains from the local surface normal. It was found that this bonnet polishing tool compensation method, based on a greatest static stiffness strategy, will produce satisfactory results.

Optimization of Key Technological Parameters in Bonnet Polishing Using FEA

Bonnet polishing tool is widely used in rough polishing and fine polishing because of its own features. Ranges of key technological parameters are different in various polishing stages, which related to how the key technological parameters affect the polishing process. In this paper, series of simulations to illustrate the interaction effect of bonnet into work-piece surface using ANSYS are present, aims to get the optimal key technological parameters in rough polishing and fine polishing. It found that the inner pressure of bonnet, the height of bonnet compression, the slant angle of bonnet and bonnet radius are the main factors that influence the features of contacting area, moreover, the former two parameters directly determine the contribution of stress in contacting area. Finally, based on the simulated results, key technological parameters selected are roughly discussed according to the purpose of different polishing stages.

An adaptive interpolation method for tool path generation based on iso-phote for large scale wedge /aspheric lens element grinding

The tool path generation based on iso-phote is a kind of feature based path generation method. Iso-phote curves represent the characteristic curves on a parametric surface. Accordingly, iso-phote based tool paths has been proposed as an important path pattern for parametric surface machining. An adaptive interpolation method for tool path generation based on iso-phote interpolation for wedge/aspheric lens element grinding was proposed, which takes into account the symmetry problem of wedge/aspheric process behavior. This paper presents an efficient interpolation method for tool path generation approach based on iso-phote curves and bisection method. By the application of parallel grinding, the approach can guarantee the feature of aspheric lens, maximize machining speed and smooth the machine operation for high surface quality. The interpolation method guarantees that step length of the interpolated points always keep the precision. The method can improve and automate large scale wedge/aspheric lens element grinding for 3-axis CAD/CAM systems. As part of the validation process, the tool paths generated and interpolation error are analyzed and compare with the traditional method.

Study on range selection of key parameters in bonnet polishing using FEA

Bonnet polishing system is mostly used in rough polishing and fine polishing because of its own features. Due to different aims of polishing stages, optimal ranges of key parameters are different in various polishing stages. Simulations in ANSYS are present in order to get optimal ranges of key parameters including inner pressure P and compression of bonnet H in different polishing stages, firstly, the reliability of simulation of bonnet polishing using ANSYS is verified through a series of simulation about fine polishing stage, on the condition of using ranges of key parameters got by former researchers from polishing experiment; secondly, simulations about rough polishing were carried out, and optimal ranges of key parameters were found, which have reference value in future work.

Data processing of on-machine measuring in fine grinding for optical lens

According the features of on-machine measuring and compensation machining, a suitable data processing flow is designed using contact or non-contact sensor to collect measuring data, and the no-linear least square method to correct the inclination error of measuring system. The results of verification experiments for data processing presented well reflect error distribution of the actual surface with suitable measuring accuracy. It is also clarified that the on-machine measuring significantly affects the machining accuracy by the compensation machining experiments.