红外线聚光非球面透镜的单点金刚石镜面切削方法

根据硬脆性材料的延性域加工机理和面形误差补偿加工方法,研究了圆弧形和平头形刀具的单点金刚石延性域切削方法,在加工中直接获得了镜面切除面;并利用数控技术进行误差补偿,克服了因加工试验、刀具磨损、机械振动、热变形等造成的加工误差导致的非球面的面形精度降低和表面粗糙度恶化.并将该方法用于采用圆弧形刀具对红外线聚光的φ70mm非球面锗透镜进行单点金刚石切削实验中.试验结果表明面形误差补偿加工方法可以进一步消除加工误差,将非球面的面形精度PV值从微米级(1.23μm)提高到亚微米级(0.36μm)的程度,表面粗糙度R_a从亚微米级(0.27μm)改善到超亚微米级(0.04μm)的范围.     

Correcting and compressing interpolation algorithm for free-form surface machining

The existing interpolation algorithm cannot meet the need of high-speed and high-accuracy machining of a free-form surface. So this paper proposed a correcting and compressing interpolation algorithm. Depending on the distance and angle evaluated from the adjacent command points, the machining path of free form can be divided into two machining types. For those regions where the accurate figure is critical such as corners, the convention linear interpolation is performed exactly between the adjacent command points. For those regions having a large radius of curvature where the smooth figure is critical, firstly, the interior point selection method based on circle transition is derived to reduce the tolerance between the machining path and the original surface; secondly, the interior point correction method based on the least-square method is proposed to reduce the calculation error and round-off error in the interior point and estimate the first- and second-order derivative vectors of the interior point; thirdly, the shape-defining point is selected by the bend direction of the machining path and fitted to a quintic spline curve which has the C2 continuity; fourthly, the fitting accuracy controlling method is proposed to ensure the machining accuracy; lastly, the curve interpolation is performed on the fitted smooth curve. Machining tests carried out on a vertical machining center show that the proposed algorithm can improve the machining efficiency and machining quality of a free-form surface.     

A study on motion of machine tools’ hexapod table on freeform surfaces with circular interpolation

Accuracy is greatly affected by nonlinear motion of hexapods. This need is more obvious when these mechanisms are used in machining environments where precision and surface qualities are of critical importance. In this paper, comprehensive algorithm for hexapod tool path programming is developed. Using C#.Net, this algorithm is developed based on circular motion and rotation of the table which has the capability of checking nonlinear error and keeping it in a controlled limit as well. Improved Tustin algorithm is used for interpolating circular path. To evaluate the accuracy of the developed algorithm on a freeform surface, a turbine blade is scanned, and its CAD model is developed. Taking zigzag strategies, movement on turbine blade surface is approximated with smaller circles using the algorithm presented in this paper. The output accuracy resulted from interpolation algorithm for passing on turbine blade surface is studied in SimMechanics of MATLAB software. Using Total Station camera, motion path of two turbine blades with different radius curves on the hexapod table is experimentally obtained. Finally, it can be stated that the developed algorithm based on circular interpolation has the capabilities of motion on freeform curves.     

An accurate surface error optimization for five-axis machining of freeform surfaces

This paper presents an accurate surface error interpolation algorithm for five-axis machining of freeform surfaces. One of the most important steps in the interpolation process is to calculate the next cutter contact (CC) point according to the present one. In this paper, the next CC point is calculated by an accurate chord evaluation method. This method is developed based on the cutting simulation process, which can be vividly described as firstly planting dense grasses on the tool path curve and then cutting them when the tool moves by. The left lengths of the grasses either positive or negative are considered to be the machining error. The method is accurate also because the tool geometry and the tool orientation changes during five-axis machining are taken into consideration. With this method, the chord errors between CC points are controlled uniform along the tool path. The proposed interpolation algorithm is compared with the commercial CAM systems like PowerMILL and UG. The results show that the proposed algorithm can significantly reduce the number of cutter locations meanwhile confine the chord error. A real cutting experiment is implemented, and the result indicates its promising value in industrial applications.     

Offner补偿器的结构设计与装调分析

90nm节点光刻投影镜头中使用的非球面都存在高次项,而且对理想球面的偏离量较大。本文设计了一种基于三片式结构的Offner补偿器,实现了对高次非球面面形的高精度检测。采用等量轴向球差补偿非球面各阶系数的方法,主动引入一定量的轴向球差,补偿光线在非球面法线方向的偏离量,结果表明：对初级像差和高级像差很好的平衡,使剩余像差很小;MTF 远远超过衍射极限,系统工作波长为632.8nm,F数达到1.64,均方波差RMS<λ/1250。满足了高精度检测补偿器的设计要求。最后根据现有的检测装置的精度对所设计的结构进行了公差分析,给出了较宽松的公差容限。     

Ф420mm高次非球面透镜的加工与检测

介绍了Ф420mm熔石英高次非球面透镜的加工与检测方法。对现有数控加工工艺进行了优化,通过分工序加工方式,依次采用机器人研磨、抛光和离子束修形技术完成了透镜的加工。进行非球面透镜检测时,考虑透镜的凹面为球面,利用球面波干涉仪对其面形进行了直接检测,剔除干涉仪标准镜镜头参考面误差后,透镜凹面的精度达到0.011λ-RMS;针对透镜的凸面为高次非球面,采用基于背后反射自准法的零位补偿技术对其进行面形检测,其精度达到0.013λ-RMS。最后,采用一块高精度标准球面镜对加工后透镜的透射波前进行了自消球差检测,得到其波前误差为0.013λ-RMS。试验结果表明,非球面透镜各项技术指标均满足设计要求。所述工艺方法亦适用于更大口径的非球面透镜及其他类型非球面光学元件的高精度加工.     

Offner补偿器的结构设计与装调

针对90nm节点光刻投影镜头中使用的非球面存在高次项,且与理想球面偏离量较大的特点,基于像差补偿理论,设计了一种三片式结构的Offner补偿器来实现非球面的高精度检测。采用等量轴向球差补偿非球面各阶系数的方法,主动引入一定量的轴向球差,补偿光线在非球面法线方向的偏离量。结果表明,初级像差和高级像差可很好地平衡,使剩余像差很小;MTF远远超过衍射极限;系统工作波长为632.8nm,F数为1.64,均方波差RMSλ/1250;系统轴向像差0.47μm,满足基本干涉成像条件;各方面指标均满足高精度检测补偿器的设计要求。最后,根据现有检测装置的精度对所设计的结果进行了公差分析,给出了较宽松的公差容限。公差分配后,系统综合残余波像差0.00727λ,满足系统装调精度要求。     

Critical success factors for Kaizen implementation in manufacturing industries in Mexico

To machine a noncoaxial nonaxisymmetric aspheric lens, a new parallel grinding method that employs a fixture with an adjustable gradient (AGF) is proposed. The AGF is developed for a three-axis computer numerically controlled grinding machine. The grinding method is presented according to the proposed grinding system. To ensure the machining accuracy, the main machining errors and the compensation algorithm are discussed for the grinding method using the AGF. Simulation results show that the AGF rotation errors are crucial factors affecting the profile error of the machined workpiece. Experimental results show that employing the compensation algorithm increases machining accuracy.     

A local smoothing interpolation method for short line segments to realize continuous motion of tool axis acceleration

In traditional processing, a large number of G01 blocks are adopted to discretize free surface or curve for NC machining. But, the continuity of G01 line segments is only C⁰, which may lead to discontinuity of axis acceleration, resulting in the frequent fluctuation of tool motion at the junctions in high-speed machining, deteriorating the quality of work piece, and reducing processing efficiency. To solve this problem, a local smoothing interpolation method is proposed in this paper. At first, the analytic relationship between the continuity of the trajectory and the continuity of the axes motion is first systematically described by formula. Based on this relationship, a local smoothing algorithm and a feed-rate scheduling method are proposed to generate a C² continuous tool path motion with axis-acceleration continuity. The local smoothing algorithm smoothes the corners of G01 blocks by the cubic B-spline according to the cornering error tolerance specified by the user. After the feed rate at critical points of smoothed tool path was determined by a modified bidirectional scanning algorithm by considering constrains of chord error and kinematic property, an iterative S-shape feed rate scheduling is employed to minimize residual distance caused by round of time while ensuring the continuity of feed rate and acceleration. Then, a look-ahead interpolation strategy combined with smoothing algorithm and feed-rate scheduling as mentioned is proposed for real-time interpolation of short line segments. At last, simulations are conducted to verify the effectiveness of the proposed methods. Compared with the traditional G01 interpolation, it can significantly improve the processing efficiency and shorten the processing time within error tolerance.     

球面上微透镜阵列超精密慢伺服加工精度影响因素的研究

超精密慢伺服车削可加工出高精度的连续和非连续自由曲面,但是在微透镜阵列的加工过程中,不同位置的透镜加工精度也不同,个别子透镜的质量降低可能引起整个功能部件的失效。为了研究曲面上微透镜阵列超精密慢伺服加工精度的影响因素,本文采用实验的方法分析基面几何形状和子透镜位置对球面上微透镜阵列慢伺服车削加工精度的影响,通过在三种不同球径的基面上加工微透镜阵列,并使用Bruker GT-X白光干涉仪测量所加工的基面和微透镜阵列,分析了不同基面上不同位置的子镜表面粗糙度和形状精度的变化趋势。实验结果表明,同一基面上不同位置的子透镜,慢伺服车削加工表面微观形貌不同,表面粗糙度和形状精度也不同;基面的几何形状也会影响子镜的加工精度,当基面球径从50 mm增大至150 mm时,外圈子镜的表面粗糙度从75.78 nm(Ra)变小为69.08 nm(Ra)。在超精密慢伺服加工微透镜阵列过程中,必须考虑基面几何形状和子透镜位置两个因素对加工精度的影响,这将有助于提高微透镜阵列加工精度的一致性并保证微透镜阵列功能的有效性。     

小口径非球面斜轴磨削及磁流变抛光组合加工工艺及装备技术研究

为提高小口径非球面模具加工效率和加工精度,提出一种结合斜轴超精密磨削和斜轴磁流变抛光的组合加工方法,将两种超精密加工方法集成在一台机床上,以缩短装夹时间以及降低装夹误差。研制新型的小口径非球面超精密复合加工机床,对直径Ф6.6 mm的非球面碳化钨模具进行了加工试验。斜轴磨削后加工表面粗糙度达到R_a 6.8 nm,斜轴磁流变抛光后表面粗糙度达到R_a 0.7 nm,面型精度可以达到PV 221 nm。结果表明,所开发的小口径非球面超精密复合加工装备能达到加工要求,可有效提高加工精度和加工效率。     

基于Levenberg-Marquardt算法的超精密非球面镜面误差分析及研究

根据超精密非球面补正加工的要求,应用误差理论及其数据处理方法对其测量数据进行了分析研究,建立了优化数学模型,采用Levenberg-Marquardt(LM)优化迭代方法对数学模型进行参数拟合求解.在VC 环境下实现该算法的程序,得出形状误差PV(Peak-Valley)值.通过分析误差曲线图,来验证优化的光学参数的正确性.实例计算表明该算法能很好的应用于超精密非球面镜面形状误差分析,为评价超精密非球面镜的加工质量和后续的补正加工提供了理论依据.     

新型并联机床数控系统插补算法的研究

提出一种用于新型并联机床的粗、精插补策略和算法 ,粗插补采用直接对加工曲面进行插补的方法。以NURBS曲线为例 ,运用合理计算方法推导出粗插补计算公式 ,并对粗、精插补进行了误差分析。插补实例结果表明 ,该插补算法具有恒速进给、加工表面轮廓误差易于控制等特点     

A real-time surface interpolator methodology for precision CNC machining of swept surfaces

A real-time surface interpolator is developed to machine a family of swept surfaces directly from their high-level procedural definitions. All the computations required for machining are performed in real time based on the exact surface geometry, including tool path planning, tool path interpolation, tool offsetting, and tool path step-over to achieve a prescribed scallop height. A G-code command (G05) is introduced to concisely communicate the precise surface geometry and all necessary process parameters to the controller. The swept surface interpolator offers profound accuracy and efficiency advantages over the traditional approach of generating voluminous piecewise–linear/circular tool path approximations as a preprocessing step. For example, in one instance, a 36,000-line piecewise-linear (G01) approximate part program file is replaced by a 3-line exact swept surface (G05) part program file. The methodology is verified by machining a variety of swept surface forms in aluminum and wax, using a 3-axis milling machine with the surface interpolator incorporated into an open-architecture CNC controller.     

NC machining of free-form Kriging surfaces

An algorithm for three-axis NC tool path generation on sculptured surfaces is introduced when the free-form surface is modeled parametrically by free-form surface Kriging. The flexibility of dual Kriging that easily defines the intersection of the surfaces with a set of parallel planes and Cartesian method are combined to generate the tool-paths automatically. The presented algorithm can simultaneously generate the tool path with a predefined machining accuracy and remove gougings along the tool path. The algorithms are validated by three experiments in rough and finish machining and the results prove its reliability. Since Kriging is based on the interpolation of data points, the proposed algorithm can be used for reverse engineering applications. The system was executed on a standard micro-computer and the software was structured to offer a library of machining functions for endusers.     

Form error compensation in single-point inclined axis nanogrinding for small aspheric insert

Based on an examination of traditional arc-enveloped grinding method, a single-point inclined axis nanogrinding method is presented to grind an aspheric insert by compensating tool setting error, radius error, and residual form error. Profile data from on-machine measurement are used to obtain the tool setting error and radius error of grinding wheel, as well as the normal residual form error. Compensation method of single-point inclined axis nanogrinding is built up for generating new compensation path. Grinding test of aspheric tungsten carbide insert with diameter 9.5 mm is conducted to evaluate performances of the grinding mode and compensation method. A last form error of 200 nm in peak to valley and surface roughness of 2.243 nm in Ra are achieved. These results indicated that the form error compensation method and single-point inclined axis nanogrinding mode can significantly improve form accuracy and surface roughness of ground surface.     

NC Machining of Freeform Pockets with Arbitrary Wall Geometry Using a Grid-Based Navigation Approach

A tool path must be determined in an efficient manner to generate NC (numerical control) code for machining. This is particularly important when machining freeform pockets with arbitrary wall geometry on a three-axis CNC machine. In this paper, a grid-based 3D navigation algorithm for generating NC tool-path data for both linear interpolation and a combination of linear and circular interpolation is presented for three-axis CNC milling of general pockets with sculptured bottom surfaces. The pocket surface is discretised by defining a grid and the navigation algorithm plans the tool motion. The grid size and the cutter diameter are chosen so that a predefined tolerance for surface roughness is satisfied. The grid-based navigation algorithm is simulated graphically and verified experimentally.     

曲线的三参数路径规划车削插补算法研究

为了保证数控加工中复杂曲线零件的车削加工精度,在普通二参数车削加工的基础上,提出了一种三参数路径规划车削插补算法。该算法将复杂曲面数控加工插补过程的路径规划分解为若干插补点之间的最优路径搜索和选取问题,根据不同加工要求设置决策变量,并进行取值判别,通过3个参数联动对曲线进行插补运算,优化加工过程中刀具的路径,并应用于相关的实例分析。研究结果表明,该优化算法能保证加工曲线的光滑性,有利于提高曲线的加工质量,并且该算法还具有计算规模小、求解迅速、数控加工插补误差小等优点。     

Tool path optimization in postprocessor of five-axis machine tools

Generally, tool path is generated in a computer-aided manufacturing software considering only the geometry of machining parts. It is converted into numerical control (NC) codes in the postprocessor based on the particular machine kinematics. For some special types of five-axis machine tools, e.g., non-orthogonal five-axis machine tools, the generated NC codes may produce unqualified parts because of the existence of the non-linear error. Conventional commercialized postprocessors usually do not have the function of non-linear error checking. Observing that the tool path is a non-smooth trajectory full of corners and a series of connected line segments, cubic spline interpolation is applied to smooth the tool path at regular points in this study. The cutter tip center points are computed by the cubic spine interpolation, while the cutter posture vectors are obtained via linear interpolation. At the splines (for regular points) and the line segments (feature points), more points are chosen to be converted into NC codes to reduce the non-linear error, which is called data densification. Using the cubic spline to smooth the tool path and the data densification to reduce the non-linear error, a novel tool path optimization algorithm in postprocessor is proposed. Experiments were carried out on an inclined rotary spindle axis non-orthogonal five-axis machine tool. It shows that the proposed tool path optimization provides improved accuracy and surface quality.     

Profile evaluation of radial Fresnel lens directly machined on roller molds by rotating-tool diamond turning

In Roll-to-Roll manufacturing of high-quality optical Fresnel lens films, a high-precision roller mold with super-fine surface quality is essential to precisely transfer the functional microstructures from the periphery roller surface onto the flexible substrate. Unfortunately, direct diamond turning of deep circular grooves on the periphery surface of a roller mold was considered infeasible. Recently, the team has developed a novel 4-axis interactive tool-workpiece motion, Rotating-tool diamond turning (RDT), as a solution to overcome this challenge. Experiments were conducted to justify the capability of the proposed RDT process by directly machining a radial Fresnel lens on a brass roller mold, but without precise 3D profile evaluation of the lens on the roller surface. On-machine measurement of the machined lens structures using 3D touch probe is not applicable because the diameter of the probe is relatively large to penetrate into steep grooves of the Fresnel lens. On the other hand, off-machine measurement using stylus profilometer will introduce inevitable alignment errors during the measurement and lead to mismatched machining and measurement coordinates, making it difficult to evaluate the 3D lens profile generated by the RDT process eventually. In this study, a compensation and comparison algorithm is presented to precisely evaluate the form error between the machined and designed features in a three dimensional manner. Alignment errors generated when positioning the roller mold on the stylus profilometer are investigated and quantified through analyzing the characteristics of this unique micro structure with Fresnel lens wrapped on the roller periphery. As a conclusion, the machined lens structure is compensated and restored to compare with the designed profile, and the form error is obtained with the sources of errors analyzed. Such profile compensation and comparison method can be applied in other measurement and characterization studies on evaluation of complex optical structures patterned on roller molds for Roll-to-Roll manufacturing of advanced functional films.