数控机床定位精度的测量和评定

介绍如何使用激光多普勒位移测量仪测量数控机床的定位误差,并根据ISO 230—2（1997）标准确定数控机床的定位精度和重复定位精度,为进一步进行误差补偿提供基础。     

Self-adjustment computing method for time-partition interpolation in motion trajectory control of CNC machine tools

For time-partition interpolation in computer numerical control of the motion trajectory of a machine tool, the trajectory in a sampling cycle is approximated by a line segment from the current position of the tool to another on the expected trajectory; and locating the terminal of the line is the goal of the interpolation. In this paper, a self-adjustment computing method applicable to any explicit curve type is proposed. With the method, the terminal of the linear moving path in a cycle is first estimated by the motion information in the previous cycle, then adjusted according to the ratio of the desired moving distance to the computed linear path length. The result of the computation is fairly accurate, and it can be further enhanced with more adjustments performed in a sampling cycle, which is demonstrated in the simulation results. Furthermore, an adaptive feedrate adjustment algorithm is also introduced to enable the proposed method to control the trajectory contour errors.     

数控机床位置精度的检测与补偿

主要介绍使用双频激光干涉仪对西门子840D闭环系统的数控机床进行位置精度的检测与补偿,并对该系统的闭环误差进行分析。实践表明,通过使用该方法能有效地提高数控机床的位置精度。     

一种五轴联动机床动态精度检测及优化方法

提出一种用于机床动态精度快速检测与优化的方法。在完成机床静态精度调整基础上,通过S形试件检验机床加工精度是否达标。基于S件测量结果及机床五轴联动(RTCP)精度检测,搜寻并分析存在问题的驱动轴,通过编制特定程序并测量机床运动轨迹,在对轨迹进行频域分析、圆度分析的基础上,完成机床机械结构和动态性能参数的调整,进而提升机床动态精度。通过在20多台五轴联动数控机床上应用,大幅提高了机床的加工精度,验证了上述方法的有效性。     

Bayesian degradation assessment of CNC machine tools considering unit non-homogeneity

Field reliability assessment and prediction is critical for the estimation, operation and health management of CNC machine tools. The classical methods for field reliability of CNC Machine Tools assessment and prediction are challenged with the issues of expensive reliability tests, small sample size and unit non-homogeneity. In order to solve these problems, this paper introduces a degradation analysis based reliability assessment method for CNC machine tools under performance testing. Since the degradation is an independent increment process, the gamma process is employed to characterize the degradation process of CNC machine tools. The random effects are introduced to accommodate performance degradation model with unit non-homogeneity. The parameters of model are updated by Bayesian estimation approach. As a case study, the CNC Machine Tools is studied to illustrate the approach. And the proposed method is demonstrated precise for practical use.     

Geometric accuracy long-term continuous monitoring using strain gauges for CNC machine tools

The accuracy retentivity has become one of the most important performance index of CNC machine tools, which are affected by many complicated factors, such as stress-induced deformations, bolt preload loss, wear, and the manufacturing process itself. The long-term continuous monitoring can bridge the wide gap between the accuracy retentivity and the manufacturing processing of machine tools. In this research, a geometric accuracy monitoring approach using the discrete strain gauges is proposed. The machine basis is firstly simplified based on the structural characteristics and stress condition. And, the straightness is evaluated through the reconstructed strain field of machine tool basis. Finally, to verify the validity of our method, a vertical machining center has been monitored for 7 months using the established wireless monitoring system.     

基于改进型拉开档次法的数控机床综合性能评价

针对现有数控机床性能评价研究存在的问题,提出了一种新的基于改进型拉开档次法的静态递阶综合评价方法。利用拉开档次法原理确定了数控机床综合性能评价指标的权重系数,进一步建立了基于改进型拉开档次法的数控机床综合性能评价模型。应用实例的计算结果表明,所建立的数控机床综合性能评价模型合理有效。     

A new thermal error modeling method for CNC machine tools

Shape memory superelastic alloys as NiTi have mechanical properties and biocompatibility characteristics quite interesting for a set of industries, amongst which is the medical industry. They find applications in tools and devices where frequently joining between them and to other alloys as austenitic stainless steel is required. However, permanent joining of NiTi to stainless steel is problematic due to the formation of Fe–Ti intermetallics. Pulsed laser welding was studied to join thin foils of NiTi in similar and dissimilar joints to stainless steel. Joining NiTi to NiTi was succeeded with no weld defects. When joining NiTi to stainless steel, it was found that the material impinged by the laser determined the weld pool shape and structure, and it was better when the stainless steel foil was placed below the laser, because nickel enrichment of the weld pool was found to minimise cracking. The factors controlling the weld pool composition and, consequently, the quality of the weld were investigated and discussed.     

面向重型数控机床的加工工艺参数优化方法

为提高重型数控机床的加工质量与效率,提出一种基于数值模拟与优化算法相结合的加工工艺参数优化方法。通过为重型数控机床的加工过程所构造的非线性动力学模型,建立加工工艺参数与加工表面粗糙度的映射关系,以加工工艺参数组合为决策变量,以加工表面粗糙度和加工尺寸精度等为目标函数,建立重型数控机床加工工艺参数多目标数学优化模型,并采用网格直接寻优算法对数学优化模型进行寻优求解,最终得到重型数控机床的最优加工工艺参数组合。以某重型数控机床的铣削加工过程为例进行实例验证,并通过对比单目标优化结果验证了该多目标优化方法的优越性。     

Measurement and compensation for volumetric positioning errors of CNC machine tools considering thermal effect

The measurement and compensation of volumetric positioning errors can be used to significantly improve the accuracy of machine tools. In this paper, a sequential step diagonal measurement is introduced to measure nine volumetric positioning errors in a short time. Measurements under various thermal conditions are preformed to understand the relationship between the volumetric positioning errors and the machine temperature field and variations. A radial basis function neural network is used to predict the volumetric positioning errors at all positions based on the temperature distribution of the machine. Compensation experiment is carried out to validate the performance of the measurement and the prediction method. The experimental results show that the volumetric accuracy of the machine tool is significantly improved by the error compensation.     

面向数控机床随机误差的加工优化方法研究

针对随机误差难以进行误差补偿,同时,随机误差在机床加工区域内分布不均的问题。提出一种根据机床随机误差分布规律,结合待加工零件尺寸精度要求,优化零件加工区域的方法,提升零件加工精度。首先采用多体系统运动学原理,建立机床随机误差对加工位置和姿态的关系;而后结合待加工零件精度要求,建立零件加工位姿的优化模型,并通过KS函数,将局部最优化问题,转化成全局可导优化模型;并针对零件位姿与优化目标和约束函数难以获得显式表达关系的问题,通过RBF响应面,建立优化元模型;最后通过优化算法进行寻优,优化零件加工位姿,提高零件加工精度。为验证所提方法的正确性和有效性,进行了仿真实验分析对比。     

应用CNC技术提高精加工机床的加工精度及加工柔性

针对多缸柴油机机体缸套孔及离合器壳定位销孔精加工中存在问题，应用经济型数控系统对专用机床实行机、电、液一体化控制的改造，对应用CNC技术精确设定开环控制系统的机械原点，提高传动精度及专用机床加工柔性化的方法进行研究。     

数控机床维修举例

数控机床采用数字控制系统 ,能够实现多轴联动 ,实现三维形体的加工 ,加工出几何形状复杂的零件 ,从而备受人们的青睐。近年来随着数控机床的广泛应用 ,人们已经对数控技术有了相当的了解 ,对于一些常见的故障也能进行排除 ,从而提高了机床的使用率 ,但是对一些不常见的故障还是感到比较棘手。下面介绍笔者近年来在从事数控机床维修中遇到的几个例子 ,供大家参考。大家知道 ,旋转编码器或光栅尺在数控机床上一般作为位置反馈元件使用 ,机床每次开机后都要寻找参考点 ,以确定机床的坐标点 ,即我们常说的“回零”。旋转编码器出现故障后 ,一般…     

数控机床精度评价和螺距误差补偿技术研究

建立了螺距误差补偿的数学模型，设计了利用光栅尺进行螺距误差补偿的装置。对补偿前后的螺距误差进行了精度评价，结果表明，经过螺距误差的补偿，数控机床位置误差降低，实现了机床精度的软升级。     

Variable speed compensation method of errors of probes for CNC machine tools

Systematic errors of kinematic touch-trigger probes for CNC machine tools may exceed errors of the machine tool itself. As a result, the machining accuracy is strongly dependent on the probe's accuracy. Numerical correction of probes’ systematic errors can be used. However, it requires executing calculations by the CNC machine tool controller. To avoid this troublesome requirement, a new method of errors compensation is proposed. In this approach, a modification of the probe's pre-travel in a given direction is achieved by modification of measurement speed in this direction. Because all measurement speeds can be calculated offline, the controller does not have to do any calculations. The proposed method has been tested for sample kinematic probes and the error reduction was at least 10-fold.     

Efficient computation of smooth minimum time trajectory for CNC machining

Previous computation approaches of smooth trajectory for computer numerical control machining either cannot fully utilize the maximum ability of machines, fail to minimum machine time, or cannot be computed efficiently because of the nonlinearity formulation of problem. In this paper, an efficient computation approach is proposed that has been designed as solving a convex optimization problem to generate smooth minimum time trajectory. Since smoothness of trajectory can be adjusted by confining the value of jerk (rate of acceleration change), the proposed approach uses a pseudo-jerk to approximate the real jerk and to realize smoothing trajectory. The difference between the real jerk and pseudo-jerk is that the proposed pseudo-jerk can be linearity formulation in the problem. By using pseudo-jerk constraints, smooth minimum time trajectory planning problem is formulated as a convex optimization problem. Since of convexity of the optimization problem, the solution process can be efficient by using ordinary gradient-based optimization techniques and the optimal numerical solution is uniqueness. The effectiveness of the approach is demonstrated in machining simulations of two plane patterns.     

A control strategy with motion smoothness and machining precision for multi-axis coordinated motion CNC machine tools

The advanced manufacture technology requires that multi-axis coordinated motion computer numerical control (CNC) machine tools have the capability of high smoothness and high precision. At present, the study of the motion smoothness mainly concentrates on the acceleration and deceleration control method and the look-ahead process of velocity planning in the interpolation stage. The control strategy of the contouring error mainly focuses on tracking error control, cross-coupling control, and optimal control. In order to improve the motion smoothness and contouring precision for multi-axis high-speed CNC machine tools, a multi-axis modified generalized predictive control approach was presented in this paper. In the control strategy, the estimation models of tracking error, contouring error, velocity error, and acceleration error were structured separately. A new improved quadratic performance index was proposed to guarantee the minimum of these errors. Generalize predictive control was also introduced, a multi-axis generalized predictive control model was deduced for motion smoothness and machining precision for multi-axis coordinated motion CNC system, and an approved multi-axis generalized predictive controller based on the model was designed in this paper. The proposed predicted control approach was evaluated by simulation and experiment of circular, noncircular, and space line trajectories, respectively. These simulative and experimental results demonstrated that the proposed control strategy can significantly improve the motion smoothness and contouring precision. Therefore, the new position control method can be used for the servo control system of multi-axis coordinated motion CNC system, which increases motion smoothness and machining precision of CNC machine tools.     

数控机床平动轴几何误差辨识方法改进

为解决测量数控机床平动轴几何误差常用的九线法在实际应用中存在的误差溯源困难、辨识稳定性差的问题,系统分析了九线法的测量过程和辨识原理,提出一种改进的辨识方法.利用几何误差和测量坐标系之间的依附关系,合理布置坐标系的位置,保证了辨识结果的溯源价值,有利于指导机床加工和调试.通过增加测量维度和搜索最优测点布局,对辨识模型的...     

应用光化学方法眼声加工工具

论述光化学加工超声波加工综合在一起的非金属材料加工技术。它扩大了超声波加工技术的应用范围,提高了其精细程度。