基于前馈控制的数控机床进给运动轮廓误差分析

轮廓运动控制是运动控制领域研究的重要课题之一,其广泛应用于数控机床与其它自动化运动控制系统中。由于位置伺服系统跟随误差的存在,导致直线和圆弧运动时产生轮廓运动误差。前馈控制是一种有效减小跟随误差的方法,已广泛应用于数控机床进给运动控制。文章研究了两轴匹配时前馈控制增益和前馈控制滤波器带宽对两轴轮廓运动精度,特别是圆弧运动精度的影响。结论对合理选择前馈控制参数,提高轮廓运动精度具有实际应用价值。     

一种进给伺服系统非线性PID交叉耦合控制

提高多轴伺服系统的轮廓跟随性能是现代计算机数控加工的重要应用之一。针对传统交叉耦合控制方法对自由曲线轨迹的轮廓跟踪精度较差以及传统PID控制系统抗扰性和鲁棒性较差的问题,提出一种基于自抗扰控制的交叉耦合轮廓误差补偿综合控制策略,该策略由用于位置环反馈控制和轮廓误差补偿的新型非线性PID (NLPID )、位置伺服控制器 TNP-ADRC 和基于NLPID的变增益交叉耦合控制器组成。在MATLAB/Simulink环境下对方波信号跟踪和标准圆轮廓加工过程中轮廓误差的变化情况进行仿真,仿真结果表明：与传统PID交叉耦合控制相比,该方法不仅能够有效提高系统的鲁棒性以及抗干扰能力,并且能够显著提高多轴运动控制系统的轮廓加工精度。     

数控机床轮廓误差的插补预测补偿控制研究

伺服系统的基本原则是闭环控制,跟踪误差必然存在.如果多轴联动设备上使用伺服系统驱动进给轴,跟踪误差会引起加工轮廓误差.高精度数控机床要求轮廓误差越小越好.文章在定位过程中的伺服系统位置跟踪误差曲线等效成梯形曲线的基础上,从插补控制器着手研究跟踪误差的预测补偿控制.试验结果证明该控制方法简单有效.     

永磁直线电机驱动XY平台精密轮廓跟踪控制

为了减少高速进给率条件下轮廓跟踪过程中产生的轮廓误差,提出了一种将PDFF位置控制器与模糊交叉耦合控制器相结合的控制策略。首先,通过调节前馈增益,PDFF位置控制器可以综合利用PDF控制和PI控制的优点;其次,基于自由曲线轮廓误差模型来计算轮廓误差,并且提出一种以两轴的位置跟踪误差以及轮廓误差为输入的模糊交叉耦合器来减少轮廓跟踪过程中产生的轮廓误差;最后,空载与负载实验结果表明,与传统的交叉耦合结构相比,该方法在高速进给率条件下可以有效降低XY平台的轮廓误差,并且可以提高轮廓跟踪系统的鲁棒性。     

轮廓误差补偿方法研究

综合运用单轴误差增益补偿和交叉耦合控制技术,以PID交叉耦合控制思想为基础设计一种复合式交叉耦合控制器来直接减小轮廓误差,这种控制器在大误差状态时采用专家控制的基本思想设计5种控制原则迅速减小轮廓误差,以保证快速性;小误差状态时切换到改进型单神经元PID控制器以获得较高的控制精度.仿真结果表明新方法能够有效的提高轮廓加工精度.     

基于数据驱动的凸轮磨削轮廓误差补偿

针对数控凸轮磨削机床在加工过程中存在的周期性、重复性轮廓误差和不易建模等问题,提出一种基于数据驱动的轮廓误差补偿策略。在数控凸轮磨削机床的单轴伺服跟踪系统中加入无模型自适应迭代学习控制,该方法沿迭代轴引入伪偏导数,将复杂的非线性系统动态线性化处理。针对两轴之间由于伺服跟踪误差不同导致的滞后量不同,利用交叉耦合迭代学习控制,将补偿量按照交叉耦合系数反馈到单轴伺服控制系统中,实现对凸轮磨削轮廓误差的补偿。最后通过仿真实验验证了提出的轮廓误差补偿策略可以有效减小凸轮的轮廓误差,提高了数控凸轮磨削机床的加工精度。     

基于ZPETC和CCC的直驱XY平台高精度控制

针对直接驱动XY平台轮廓加工中存在的电气--机械延迟、系统参数不确定性及两轴驱动系统参数不匹配等因素的影响,提出了将零相位误差跟踪控制器(ZPETC)与交叉耦合控制器(CCC)相结合的控制策略对两轴的运动进行协调控制,实现跟踪误差与轮廊误差同时减小.ZPETC作为前馈跟踪控制器,克服了伺服滞后,使系统实现准确跟踪,减小了跟踪误差;CCC作用于两轴之间,用以增加两轴间的匹配程度,以减小轮廓误差.仿真和实验结果表明所提出的控制方案具有较好的跟踪性和鲁棒性,进而大大提高了跟踪精度和轮廓精度.     

基于迭代学习交叉耦合的轮廓误差控制方法研究

针对进给伺服系统传统控制方法产生的各轴特性不匹配、控制精度不佳、抗扰动能力不足等问题,提出一种基于自抗扰控制(ADRC)和迭代学习交叉耦合控制(ILCCC)的轮廓跟踪控制算法。对于空间任意轮廓曲线,所提算法在三轴联动条件下,通过不断的迭代学习过程,优化分配给各轴的轮廓误差补偿量,加快伺服轴动态响应的同时,有效抑制伺服系统的轮廓误差。在仿真平台下建立控制器数学模型,对空间直线和空间螺旋线轨迹进行了三维跟踪验证。研究结果表明：与ADRC控制算法和ADRC+PIDCCC控制算法相比,ADRC+ILCCC控制算法在轮廓误差的最大绝对值、累计值以及平均值等指标上均有很大改善,证明了所提算法的优越性。     

直驱H型平台的Laguerre迭代轮廓控制研究

针对直驱H型平台在跟踪大曲率复杂轮廓时,轮廓精度低的问题,提出一种精密轮廓跟踪迭代控制方法.采用有理多项式求根的方法精确计算在大曲率高速运动过程中的轮廓误差精确模型,应用Laguerre迭代估计方法结合交叉耦合控制器设计了综合考虑多轴协同运动的控制方案,以切实保证此类系统在实际应用中的高性能轮廓跟踪.系统实验结果表明,...     

基于禁忌搜索优化的直线进给系统矢量控制

数控机床的直线进给矢量控制系统中包含多个PID调节器,其控制参数直接影响系统性能。而直线进给系统是一个复杂的非线性时变系统,为了优化PID调节器控制参数,文章提出了改进的禁忌优化算法(Tabu),并将其应用于直线进给系统。在分析现有禁忌算法基础上,对Tabu算法的邻域范围、Tabu表和算法终止条件进行了改进,以直线进给系统的跟踪性能指标为目标函数,应用该算法对直线进给矢量控制系统各调节器的PID参数进行优化,并进行了实验验证。结果表明,应用文中方法优化控制器参数后,与传统PID控制相比,直线进给系统在负载改变时转速波动和位置跟踪误差显著减小,提高了直线进给系统的稳态和动态性能。     

Integral design of contour error model and control for biaxial system

This paper focuses on the contour following accuracy improvement for biaxial systems using cross-coupled control (CCC). It proposes an integral design method including contour error model, contour control effort distribution and the CCC algorithm. First, a contour error model using the contour algebraic equation and its partial derivatives is established without the small tracking error assumption. This model satisfies the condition that it equals to zero if and only if the real contour error value vanishes, which makes perfect contour following become possible in theory. Then, in order to decouple the contour following the feed-direction tracking, contour control effort distribution is decided to be in line with the normal vector at the desired point. Through expanding the proposed contour error model with Taylor series to make it be related to tracking errors of both axes, the stability condition of CCC is analyzed by the contour error transfer function (CETF). Experiments are carried out on an X–Y motion stage to verify the proposed method. The results show that it improves the contour following accuracy greatly in various conditions, even when large tracking errors occur.     

Precise contour following for biaxial systems via an A-type iterative learning cross-coupled control algorithm

This paper proposes an A-type iterative learning cross-coupled control (CCC) algorithm for biaxial systems. An algebraic equation based contour error model is used as the CCC input. This model has the advantage that it is zero if and only if the real value vanishes. The iterative learning CCC is designed to make its input converge to zero. Hence, it is expected to that the contour error will converge to zero as well. After analyzing the control algorithm convergence condition in the frequency domain, the proposed method is implemented on a motion stage. Experimental results show that the algorithm perfectly follows contours as the cycles approach infinity regardless of whether tracking errors are small or large.     

A novel cross-coupling control design for Bi-axis motion

A new structure of cross-coupling controller for precise tracking in motion control is proposed in this paper. When compared with the conventional cross-coupling system, this new structure has the advantage that the compensators in CCC have a simpler design process than conventional ones and so does its stability analysis. The proposed compensator (or controller) is evaluated and compared experimentally with a traditional uncoupled controller on a microcomputer controlled dual-axis positioning system. The experimental results show that the new structure of cross-coupling controller remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine.     

Surface Reconstruction for Interactive Modeling of Freeform Solids by Virtual Sculpting

This paper presents a new method for surface reconstruction from dexel data for virtual sculpting. This is part of our research efforts to develop a dexel model based sculpting system with the capability of interactive solid modeling with haptics interface. Dexel data are converted to a series of planar contours in parallel slices (i.e. cross sections). Then triangular meshes are created by connecting the contour points in adjacent slices. Examples are given to demonstrate the ability of the described method to convert from dexel data to triangular meshes for the viewing of a sculpted model in different directions.     

Analysis of chatter in contour grinding of optical materials

Chatter that limits ground surface finish has been observed in the deterministic microgrinding of brittle optical materials. In this article, the classical single degree of freedom model for chatter, accounting for both work and tool regenerative effects, is adapted for contour grinding optical surfaces. A linearized expression for the cutting stiffness is developed for the contour grinding geometry based on Preston’s law. Techniques developed to measure the machine frequency response function (FRF) and the Preston coefficient, needed as inputs to the simulations, are described. Numerical simulations based on this model are used to predict the grinding system behavior and to investigate process parameters affecting chatter stability. The stability limits observed during grinding experiments on optical glasses are in good agreement with the simulation results.     

参数化转换凸轮轮廓及自动生成NC代码

通过Autolisp语言编程,将凸轮从动件运动规律转变为凸轮轮廓,再通过MasterCAM软件,生成数控加工所需的NC代码。该方法避免手工描点、拟合轮廓曲线等带来的误差和麻烦,为复杂、精密、高速运动的凸轮设计和加工,以及凸轮参数化设计提供了一种行之有效的方法。     

数控伺服系统跟踪及轮廓误差分析

分析了数控加工中伺服系统跟踪误差和轮廓误差的计算方法,详细讨论了双轴数控加工中轴跟踪误差和轮廓误差之间的关系。指出了多轴加工中轮廓误差建模和误差控制方法的理论意义和应用价值。     

Pre-compensation of servo contour errors using a model predictive control framework

Methods for pre-compensating contour errors in servo systems by adding components of the predicted contour error to the reference position command have recently been proposed in the literature. Such methods are very effective when the curvatures of the desired path are small but their performance degrades at locations of sharp curvature because they lack look-ahead capabilities. This paper presents an improved method for pre-compensating contour errors in servo systems by modifying reference position commands using a model predictive control framework. The pre-compensation value at any given location along the desired path is defined as a weighted average of contour errors within a prediction horizon, and the weights are selected to minimize the sum of squares of the estimated contour errors over the chosen prediction horizon. Constraint enforcement functionalities are also built into the proposed method to ensure that the pre-compensated reference commands stay within specified velocity and acceleration limits. Simulations and experiments are used to compare the performance of the proposed method to a recently proposed pre-compensation approach which lacks look-ahead and constraint enforcement capabilities. Significant improvements in contouring accuracy over the existing method are demonstrated.     

面向逆工程的实体再现方法的研究—图象滤波和边界提取

本文探讨和实现了一种灵活的、适应性较强的图象滤波方法,并提出一种新的边界提取算法。与传统的算法相比,在抽取边界的同时,能有效地分离出内轮廓和外轮廓,并使算法效率也大大地提高。     

Tool wear and profile development in contour grinding of optical components

Wear induced changes in grinding tool profile have been studied for a CNC contour grinding process designed for the fabrication of precision optical components. Tool profile was measured experimentally by examining the “footprint” left by the tool when subsequently fed into a prepared surface. A numerical model was developed to predict detailed tool profiles as a function of the process parameters and total removal. Wear caused the development of approximately flat bevels on tools initially trued to a spherical shape, changing both the height and position of the lowest cutting point on the tool, with the potential to produce significant profile errors on the workpiece surface. The observation of approximately flat tool bevels was also used to develop an analytic solution for the tool shape evolution. With this analytic approximation contact height and width can be readily estimated and could be incorporated into an algorithm to adjust the tool path.