大行程快速刀具伺服装置的设计

基于快速刀具伺服(Fast Tool Servo,FTS)的金刚石车削加工技术是一种非常有发展前景的光学自由曲面加工手段。以柔性铰链和音圈电机为主要元素,研制一套大行程快速刀具伺服系统,该系统具有刚度大、工作稳定性好、阻尼可调等优点。详细介绍了柔性铰链的设计与分析、FTS系统性能测试和自由曲面切削试验,新型FTS系统的跟踪误差为0.12%,运动分辨率优于0.04μm,可以获得Ra30nm的光学自由曲面。测试和加工结果表明,新型的FTS系统可以用光学自由曲面高效、高精密金刚石车削加工。     

新型直线/回转式快速刀具伺服装置的设计

基于快速刀具伺服(Fast Tool Servo,简称FTS)的金刚石车削加工技术被认为是一种非常有发展前景的光学自由曲面加工方法,针对目前单自由度FTS加工技术中存在的刀具伺服运动与机床同步问题,以及刀具在x向匀速进给带来的影响,设计了一种新型的直线/回转式FTS装置,采用压电陶瓷驱动柔性铰链实现,能够输出z向的线性位移和绕y轴摆动,用于调节刀具在x向和z向的位置,使刀具的伺服运动与机床运动完全同步,并实现自由曲面的变进给车削加工,可提高加工精度以及改善被加工表面质量。根据应用的实际情况,详细分析了FTS设计要求,并对设计的柔性铰链结构进行了有限元分析,结果表明该结构在内应力和共振频率方面满足应用的要求,可用于光学自由曲面的车削加工。     

复杂曲面慢刀伺服加工刀具半径补偿方法

随着机床技术的进步,一种基于慢刀伺服技术的超精密金刚石车削创成加工方式成为可能,能够一次加工获得精度很高的各种复杂曲面。在复杂曲面慢刀伺服车削加工路径规划中,针对存在的刀具过切现象,传统刀具半径补偿算法为计算曲面刀触点的等距点,通过分析传统等距点刀具半径补偿算法的不足,提出了一种基于等距点的刀具半径补偿算法,弥补了传统等距点刀具半径补偿算法的不足,通过实例证明该算法有效地改进了传统刀具半径补偿算法的不足,提高了曲面加工的精度。     

光学自由曲面超精密加工方法综述

介绍了几种典型的光学自由曲面,如离轴非球面、环曲面、Zernike曲面、微结构光学曲面、样条曲面和双对称曲面。评述了目前光学自由曲面超精密加工的方法,包括复制成型、CNC磨削/抛光、飞切加工、慢速溜板伺服和快速刀具伺服等,同时分析对比了上述方法的优点和不足之处,并展望了光学自由曲面的加工方法的发展方向。     

自由曲面光学零件的慢刀与快刀车削技术分析

分析比较了慢刀伺服和快刀伺服两种先进车削方式在机床结构、进刀方式、伺服特点及适应对象等方面各自的特性,并给出了各自可加工光学零件的实例.     

曲面数控车削加工的预标定补偿试验

现代机械加工对数控机床的加工精度提出了更高的要求 ,若能有效地对机床加工误差进行补偿 ,则可以极大地提高机床的加工精度。为此 ,人为地产生新的误差去抵消加工系统中的已有误差 ,从而实现加工精度的提高 ,这就是误差补偿。误差补偿的方法主要有硬件补偿法和软件补偿法。硬件补偿法又分机械式补偿和电路补偿 2种。但硬件补偿方法中控制装置要与各自数控系统相连 ,一般只适用于具体的机床 ,通用性差 ,而且成本相对较高。软件补偿是通过误差模型 ,计算出误差值 ,进而控制进给系统 ,修改机床加工程序 ,完成误差的补偿。因此 ,与机床硬件无关…     

光学自由曲面研抛机床的综合误差建模与补偿

为提高光学自由曲面的加工精度,本文基于多体系统理论建立了五轴数控研抛机床综合误差模型。采用直接测量方式对各轴的移动误差和转角误差进行重复测量与分析,发现不同进给速度和测量间距对移动误差和转角误差没有显著影响。把误差数据代入综合误差模型中,得出研抛机床综合误差在x轴、y轴和z轴轴向上的移动误差和转角误差分量的变化规律,进而获知线性位移误差是影响综合误差最主要的因素。依据综合误差模型进行补偿实验,补偿后x轴、y轴和z轴的线性位移误差分别下降88%、89%和84%,补偿效果显著。实验结果证明本文所提出的综合误差建模及补偿方法具有较高的精度和较好的鲁棒性。     

光学自由曲面金刚石车削CNC仿真程序编译系统

为了解决光学自由曲面金刚石车削(DTOFS)NC代码的验证问题,保证NC代码的正确性和合理性,将计算机仿真技术应用到DTOFS加工中。利用面向对象的编程语言Visual C++为平台,结合OpenGL库函数,开发了DTOFS CNC仿真程序编译系统。根据所提取的刀具坐标信息,建立了刀具运动轨迹方程,以实现刀具的插补过程。研究结果表明,该系统能够对数控加工程序进行检查,提前发现程序中的错误并及时地进行修改。与传统插补方法相比,本系统极大地提高了仿真精度。     

超精密慢刀伺服车削零件的面型分析与刀具设计方法研究

研究首先分析总结了当前自由曲面复杂零件超精密慢刀伺服车削加工中的具体加工技术挑战,进而系统地研究了自由曲面零件面型特性,零件面型关键参数提取,零件面型参数与刀具参数之间的关联关系。进一步研究了超精密慢刀伺服车削金刚石刀具的几何参数确定方法;并针对自由曲面零件的可加工性,提出了超精密慢刀伺服车削加工中金刚石刀具选用准则。另外,通过超精密慢刀伺服车削加工实际案例和应用加工试验,证明零件面型分析及金刚石刀具几何参数的合理选用,对实现高效稳定的工业化超精密慢刀伺服车削加工至关重要。     

虚拟制造中基于刀具磨损的复杂曲面加工误差补偿

铣削加工过程中刀具的磨损是产生曲面加工误差的重要原始误差,将刀具磨损引起的误差通过建立的误差模型进行定量补偿,是虚拟制造中的一项关键技术。研究了虚拟制造环境下基于球头铣刀磨损的曲面加工误差补偿,建立了与加工参数相关的球头铣刀磨损模型,用以衡量球头铣刀切削刃磨损量,提出球头铣刀铣削加工误差补偿方法,并经实验验证有效。     

Application of a fast tool servo for diamond turning of nonrotationally symmetric surfaces

The fabrication of nonrotationally symmetric surfaces by diamond turning requires tool actuation at a bandwidth significantly higher than the rotational frequency of the surfaces. This requirement cannot be met by standard slide drives due to their large mass and consequent low natural frequency. This articles describes the development of a laboratory-scale diamond-turning machine with piezoelectric-driven fast tool servo. The capability of this apparatus will be demonstrated for high-speed features such as sine wave, square wave, and ramp-shaped surfaces. Also described is the implementation of this fast tool servo on a commercial diamond-turning machine. Several nonrotationally symmetric surfaces have been machined, and their images are included.     

A novel surface analytical model for cutting linearization error in fast tool/slow slide servo diamond turning

Fast tool/slow slide servo (FTS/SSS) technology plays an important role in machining freeform surfaces for the modern optics industry. The surface accuracy is a sticking factor that demands the need for a long-standing solution to fabricate ultraprecise freeform surfaces accurately and efficiently. However, the analysis of cutting linearization errors in the cutting direction of surface generation has received little attention. Hence, a novel surface analytical model is developed to evaluate the cutting linearization error of all cutting strategies for surface generation. It also optimizes the number of cutting points to meet accuracy requirements. To validate the theoretical cutting linearization errors, a series of machining experiments on sinusoidal wave grid and micro-lens array surfaces has been conducted. The experimental results demonstrate that these surfaces have successfully achieved the surface accuracy requirement of 1 μm with the implementation of the proposed model. These further credit the capability of the surface analytical model as an effective and accurate tool in improving profile accuracies and meeting accuracy requirements.     

Fast tool servo diamond turning of optical freeform surfaces for rear-view mirrors

The International Journal of Advanced Manufacturing Technology - Optical freeform surfaces have been applied in optoelectronic systems more and more widely, but it is difficult to fabricate this...     

Forced-based tool deviation induced form error identification in single-point diamond turning of optical spherical surfaces

In the single-point diamond turning (SPDT) of optical spherical/aspheric surface, tool deviating from the spindle rotation center significantly deteriorates the form accuracy of the spherical/aspherical surface and its optical performance. In this study, the influence of tool deviation on the form accuracy of a convex spherical surface and the cutting force forms during the turning process were studied first, following which a force-based tool deviation model was derived to identify the tool deviation using cutting force. Finally, by analyzing the influence of tool deviation on the three-dimensional (3D) form of residual structures at the center of the convex spherical surface, the 3D form of the convex spherical surface was predicted online. Results indicate the existence of a mapping relation between the tool deviation and the cutting force form, which could be further used to online predict the 3D form of the machined convex spherical surface in SPDT through the established geometric model.     

辊筒模具微透镜阵列的慢刀伺服成形加工

目的：为实现辊筒模具表面微透镜阵列高效率、高精度加工,本文对微透镜阵列成形法加工轨迹的拟合方法和机床伺服参数的优化方法进行了理论与实验研究。首先,分析了微透镜阵列的原始轨迹特征,确定了过渡台阶的突变是微透镜表面振纹的主要诱因。其次,为保证加工轨迹二阶导数的连续性,本文提出了三次样条插值与傅里叶级数拟合拼接的方法优化加工轨迹。最后,在优化加工轨迹的基础上,通过调整伺服系统的前馈参数,提高了进给轴响应能力,减小了因驱动质量和阻尼效应而产生的跟踪误差。口径800μm、深度26.7μm的微透镜阵列加工实验表明,采用优化的刀具轨迹和伺服参数,机床加工效率可以达到8Hz,进给轴跟踪误差小于300nm,消除了微透镜阵列的表面振纹。微透镜单元口径的尺寸误差约为设计值的1.075%,随机检测结果表明口径尺寸变化范围为2μm,加工一致性良好。三次样条插值与傅里叶级数拟合优化的加工轨迹可有效抑制进给轴的振动,改善了微透镜阵列表面质量。     

Tool force model development for diamond turning

Accurate determination of forces in the three-dimensional turning process is important for the development of a model to describe diamond turning (DT). This paper describes a dynamometer system which measures force magnitude in steady-state cutting. To build a quantitative model, the forces are experimentally separated into components. The response of these components to a variation of cutting parameters is explained in part by a hardness gradient near the part surface. This gradient is due to work hardening by the tool during previous passes. The extent of plastic work, and thus the hardness gradient, is dependent on the tool edge sharpness (≈ 100 nm). Therefore, the turning forces are strongly influenced by the condition of the tool edge. This paper illustrates the feasibility of finding the connection between edge sharpness and tool forces. It also demonstrates the ability to monitor tool forces over extended periods of time. These relationships are important in predicting the diamond tool edge condition from tool forces during a turning operation.     

Development of a piezoelectrically actuated two-degree-of-freedom fast tool servo with decoupled motions for micro-/nanomachining

The limited degrees of freedom (DOFs) of servo motions is an inherent deficiency in conventional, fast-tool-servo-(FTS)-assisted, diamond-turning, highly blocking applications of the FTS technique. In this paper, the concept of two-DOF FTS (2-DOF FTS)-assisted diamond turning is proposed and demonstrated. A piezoelectrically actuated 2-DOF FTS mechanism is developed to enable the cutting tool to move along two directions with decoupled motions. A novel guidance flexural mechanism constructed using the newly proposed Z-shaped flexure hinges (ZFHs) is introduced to generate motions along the z-axis, which is based on the bending deformation of the beams of the ZFHs. Additionally, using the differential moving principle (DMP), bi-directional motions in the x-axis direction can be achieved. Using the matrix-based compliance modeling method, the kinematics of the mechanism are analytically described, and the dynamics are also modeled using the Lagrangian principle. The theoretical results are then verified using finite element analysis (FEA). Certain increases in performances over conventional two-DOF flexural mechanisms are achieved: (a) a more compact structure with lower moving inertia, (b) theoretically decoupled motions of the output end, and (c) less than one actuator per DOF. To investigate the practical performance of the 2-DOF FTS system, both open-loop and closed-loop tests are conducted. Finally, the developed 2-DOF FTS technique is implemented to realize an innovative Pseudo-Random Diamond Turning (PRDT) method for the fabrication of micro-structured surfaces with scattering homogenization. The cutting results demonstrate not only the superiority of the concept but also the efficiency of the developed 2-DOF FTS system.     

利用电磁场有限元分析进行超快刀具伺服机构设计

快速刀具伺服系统足光学复杂面形加工的重要手段,现有直线伺服机构在原理上存在频响低的问题,严重限制被加工面形的复杂程度.分析电磁正应力驱动伺服机构的基本原理,利用有限元分析原理计算伺服机构的最大驱动力和最高频响,证明该方式驱动的伺服机构可以实现高频响应.根据有限元分析结论改善伺服机构的机械结构及选材,并设计伺服机构驱动器.实验研究优化设计的伺服机构响应频率为10.lkHz,工作行程为13μm.     

快速伺服刀架迟滞特性的Preisach建模

使用压电陶瓷作驱动元部件的快速伺服刀架是一种新的加工手段。本文介绍了基于Preisach模型的快速伺服刀架迟滞特性建模方法。作为快速伺服刀架的驱动元部件,压电陶瓷微位移器自身的迟滞、蠕变等非线性特性严重影响了快速伺服刀架的动态性能。为了精确建立快速伺服刀架的迟滞模型,给出了Preisach模型的数字表达方式,通过一系列实验测得的数据证明快速伺服刀架系统具有一致特性与擦除特性,满足Preisach模型的两个必要条件,最后在实验数据的基础上建立了基于Preisach模型的迟滞特性模型。实验表明,该迟滞模型可以很好地预测快速伺服刀架的迟滞位移曲线,其预测误差不超过0.65 μm。