Research of contour error compensation control for X-C non-circular grinding in polar coordinates

In the X-C linkage grinding of non-circular parts,the computation and control method of contour error in polar coordinates platform is different with that in the XY coordinates platform.To solve this problem,the analysis of the definition and computation methods for contour error and track error in polar coordinates platform will be made.Through the relative lead-lag relation of the linkage axes in the grinding process,the range of the estimation contour error is narrowed and a contour error calculation model is constructed.Then the contour compensation controllers along contour error direction and trajectory tracking error direction are designed respectively,and the error compensation decoupling matrix of the X-C linkage axes is given as well.In the end of this paper,we take the machining of the cylinder contour in Wankel rotary piston engine as an example.A simulation experiment of contour error compensation control based on relative lead-lag quantity is made.The result shows that the designed contour compensation controller can increase the contour machining accuracy effectively.

Research on Contour Error Based on CNC Multi-axis Motion Control System

The contour error was analyzed based on CNC multi-axis motion control, the contour error model was obtained focused on beeline and different radius of curvature and common contour of curve, for a CNC biaxial motion control system and the mechanism of producing contour error and the relationship between tracking error and contour error were presented. The theoretical and practical significance of modeling error and controlling error in motion control systems was carried out.

Cross-coupled controller design for triaxial motion systems based on second-order contour error estimation

The cross-coupled control(CCC)is widely applied to reduce contour errors in contour-following applications.In such situation,the contour error estimation plays an important role.Traditionally,the linear or second-order estimation approach is adopted for biaxial motion systems,whereas only linear approach is available for triaxial systems.In this paper,the second-order contour error estimation,which was presented in our previous work,is utilized to determine the variable CCC gains for motion control systems with three axes.An integrated stable motion control strategy,which combines the feedforward,feedback and CCC controllers,is developed for multiaxis CNC systems.Experimental results on a triaxial platform indicate that the CCC scheme based on the second-order estimation,compared with that based on the linear one,significantly reduces the contour error even in the conditions of high tracking feedrate and small radius of curvature.

TWO-COORDINATE DUAL-SERVO CONTOURERROR COMPENSATION TECHNOLOGY FOR ULTRA-PRECISION MANUFACTURING

A technology of two-coordinate dual-servo(TCDS) is proposed. Using this technology which is based on error compensation, workpieces of higher contour accuracy could he turned on ultra-precision machine tool with Poor dynamic performances. The principle, constitute and operation of a TCDS system are described. Mathematical proof and experiments are achieved in addition.

Chord error constraint based integrated control strategy for contour error compensation

As the traditional cross-coupling control method cannot meet the requirements for tracking accuracy and contour control accuracy in large curvature positions, an integrated control strategy of cross-coupling contour error compensation based on chord error constraint, which consists of a cross-coupling controller and an improved position error compensator, is proposed. To reduce the contour error, a PI-type cross-coupling controller is designed, with its stability being analyzed by using the contour error transfer function. Moreover, a feed rate regulator based on the chord error constraint is proposed, which performs speed planning with the maximum feed rate allowed by the large curvature position as the constraint condition, so as to meet the requirements of large curvature positions for the chord error. Besides, an improved position error compensation method is further presented by combining the feed rate regulator with the position error compensator, which improves the tracking accuracy via the advance compensation of tracking error. The biaxial experimental results of non-uniform rational B-splines curves indicate that the proposed integrated control strategy can significantly improve the tracking and contour control accuracy in biaxial contour following tasks.

Interpolation-based contour error estimation and componentbased contouring control for five-axis CNC machine tools

High accuracy contour error estimation and direct contour error control are two major approaches to reduce the contour error.However, two key factors make them complex for five-axis machine tools: the nonlinear kinematics and the coupling between the tool position and orientation. In this study, by finding the reference point nearest to the current actual position, and interpolating the point with two neighboring reference points and using the distance ratio, a new contour error estimation method for five-axis machine tools is proposed, which guarantees high accuracy while depending on only the reference points. By adding a weighted contour error on the tracking error in the workpiece coordinate system, and specifying a desired second-order error dynamics based on the error variable, an effective contouring control method is proposed, which can alleviate the problem: when the contour error components are introduced into the controller, the contour errors increase instead in some regions of the tracking trajectory. A series of experiments are performed on a tilting-rotary-table(TRT) type five-axis machine tool. The results reveal that the proposed estimation method has high accuracy, and compared with the case without contour error control, the proposed control approach can reduce the contour error along the whole trajectory.

基于线结构光扫描的工件高精度三维测量方法

为了提高工业中对复杂轮廓工件的测量精度和效率,设计了一套高精度非接触三维测量系统,并提出了一种基于线结构光扫描的工件轮廓三维测量方法。首先,利用高精度相机和三轴移动平台采集线结构光图像。然后,通过基于差分区间的灰度质心算法,精确而高效地提取出线结构光中心线,并生成原始点云模型。接着,对采集到的点云数据进行必要的点云滤波和精简预处理。最后,将预处理后的点云数据与CAD模型精确配准,进行工件表面轮廓的测量与误差评定。实验结果表明:测量工件轮廓高度的绝对误差小于0.07 mm,相对误差小于0.5%。所提出的三维测量系统及方法测量误差较低,能够实现工件的高精度三维测量,具有一定的工业应用价值。

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。

基于神经网络的双轴音圈电机驱动系统智能控制

在双轴或多轴驱动伺服系统中,各轴之间的动态特性互相耦合,严重影响了平台的定位精度和轮廓精度,而传统控制方法运算量大,寻找最优值困难。该文在基于设定值前向补偿的交叉耦合控制方法的基础上,提出了一种基于神经网络的智能控制策略。利用S函数实现了神经网络的在线调整、参数自动调整寻优。改变了系统学习速度,增强了其自适应能力,简化了操作复杂度,实现了系统的智能跟踪控制。用Matlab对文中方法进行仿真,并且与其它方法进行比较,结果表明,改进后的方法在减小轮廓误差和提高定位精度等方面有很好的效果,且在实验平台上进一步验证了该控制策略的可行性和有效性。

直线拟合椭圆轮廓曲线数控加工误差分析

数控编程中,不仅要关注程序语句逻辑正确,还要关注加工精度问题。用直线拟合法编制椭圆轮廓数控加工程序时,首先要计算逼近误差,然后根据逼近误差确定各节点步距。通过数学推导,得到等间距和等角度直线逼近椭圆轮廓曲线时的逼近误差计算公式,可用于编制椭圆轮廓数控加工程序时确定循环语句或条件跳转语句的步距,提高椭圆轮廓加工精度。给出了确定步距的一些技巧。

基于MEMD的双轴直线电机平台迭代学习控制

针对双轴直线电机平台交叉耦合迭代学习控制系统中的轮廓误差积累问题,提出了一种改进经验模态分解算法的控制策略。首先,设计单轴的PDFF位置控制器,以满足PMLSM的高精度定位需求;其次,设计了一种具备自适应调节特性的PD型交叉耦合迭代学习控制器;此外,针对经验模态分解算法的端点效应以及模态混叠问题,提出了一种基于交互直线延拓与互补集合经验模态分解的新型改进算法。该算法可以将各次迭代的轮廓误差进行分解,并剔除影响误差收敛的分量。经过仿真分析,对比传统迭代学习控制,所提方法具有更快的收敛速度,能够以较少的迭代次数实现双轴直线电机平台的高精度轮廓跟踪控制。

鼻咽癌放疗头颈部摆位误差及外轮廓变化对放疗剂量的影响

目的:采用千伏级锥形束CT(CBCT)获取分次间鼻咽癌调强放疗中的外轮廓变化及摆位误差,分析其对靶区及危及器官剂量分布的影响。方法:选取21例鼻咽癌患者,将全部患者的137次CBCT图像与定位CT图像匹配后得到左右、头脚、腹背方向的摆位误差数据。选取颈部3个不同层面,测量其外轮廓横切面宽度,并利用Pearson系数和独立样本t检验分析其对摆位误差的影响。基于CBCT影像制定模拟计划,分析摆位误差和外轮廓变化对放疗剂量的影响,并应用Mann-Whitney秩和检验进行显著性分析。结果:左右、头脚、腹背方向的摆位误差分别为(1.04±0.73)、(1.13±0.87)、(1.38±0.95)mm。A、B、C层面上的头颈部最大外轮廓变化率分别为15.36%、14.94%、14.99%。模拟计划显示GTV D_(98)、CTV1 D_(95)、CTV2 D_(95)靶区的模拟计划的剂量均小于执行的计划剂量,差异有统计学意义(P<0.05);脑干和脊髓的模拟计划D_(max)均大于计划剂量,差异有统计学意义(P<0.05)。结论:通过模拟计划可知,当摆位误差和外轮廓变化等不确定性因素存在时,靶区的剂量变化较大,其中GTV D_(98)最大减小11.49%,CTV1 D_(95)、CTV2 D_(95)最大变化率分别为12.88%、21.64%。除左右晶体和左腮腺之外,其余的危及器官和靶区剂量均有显著性差异,表明实际放疗中摆位误差和外轮廓变化的存在会对剂量分布造成显著影响。

基于数字孪生模型的轮廓误差估计和预补偿方法

针对数控机床进给系统的轮廓误差影响加工精度问题,提出一种基于数字孪生模型和交叉耦合相结合的轮廓误差预测与预补偿方法。该方法针对数控进给系统的多领域交叉耦合的特点,首先构建了机电一体化的联合仿真机理模型,同时基于融合了SE注意力机制(SE)的卷积循环神经网络(CNN-BiLSTM)和交叉耦合补偿构建了数据驱动补偿模型,二者共同构成了进给系统数字孪生模型。其次,通过数据驱动模型预测轮廓误差,同时基于预测结果对数字孪生模型进行预补偿。最后将数字孪生模型预估的轮廓误差与预补偿得到的耦合控制增益更新到实际进给系统的控制部分,提高了轮廓的控制性能。通过实验在进给系统上验证了轮廓误差预测与预补偿的可靠性,同时利用虚实同步实验验证了实际轮廓误差补偿的有效性。与补偿前相比,相对误差均保持在6%以下。结果表明:该方法能够有效的预测并控制轮廓误差,在精密运动控制领域有良好的应用前景。

数控机床多维度多层级数字孪生建模方法及应用

针对数字孪生建模技术在数控机床领域的工程实践中实施难度大、成本高等问题,提出数控机床多维度多层级数字孪生建模方法,并开发数字孪生系统,实现数控机床运行过程的可视化。首先,从物理实体、数字孪生模型、信息物理融合数据和服务4个维度以及几何、物理、行为和数据4个层级构建数控机床数字孪生模型;其次,基于该方法设计并开发数控机床数字孪生系统,实现数字孪生建模技术的软件化;最后,以某型数控机床为应用案例,采用NC代码控制机床实体运动,借助数字孪生模型与机床实体间的连接关系,驱动机床模型进行运动仿真,并将模型运行状态和各项数据进行可视化展示。结果表明系统各项功能均正常运行,所提方法具备可行性,为数字孪生建模技术在数控机床领域的工程应用提供参考。

基于指数增益迭代学习三轴运动平台轮廓控制

为了得到三轴运动平台精确的轮廓误差估计值,提出了一种基于指数增益型迭代学习的轮廓控制方法。以永磁直线同步电机驱动的三轴运动平台为研究对象,建立三轴运动平台的数学模型,采用泰勒扩展轮廓误差估计法对轮廓误差进行估计,并设计了基于指数增益的PD型迭代学习控制器。采用交叉耦合控制策略,选取按比例的分配方式将轮廓误差补偿到原始参考轮廓上。仿真结果表明,针对给定马鞍形和心形曲线采用指数增益迭代学习比传统迭代学习控制的轮廓误差最大值以及均方差值均有所减小,可证明该方法能够有效减小系统轮廓误差,提升轮廓控制精度。

基于轮廓误差灵敏度函数的增益匹配研究

现有数控系统和伺服驱动系统开放性有限,实时轮廓误差控制策略难以实现,为避免加工设备二次开发,研究了精密加工轮廓误差的离线补偿方法,本文提出了一种以减少轮廓误差为目的的跟踪误差匹配方法。首先在构建各进给系统的机电混合控制模型的基础上,推导轮廓误差关于参考轨迹的灵敏度函数;然后以轮廓误差灵敏度函数为理论依据,针对数控加工过程中常用的G01直线和G02/G03圆弧指令,分析伺服参数在不同运动学参数下对加工轨迹的影响;最后通过调整各伺服轴的控制参数,匹配动态误差系数,提高轮廓精度。此方法可在不增加控制系统复杂性的同时减小各轴动态特性导致的误差,对提高多轴联动加工轮廓精度具有参考价值。

基于GA-BP网络的数控机床动态误差预测研究

动态误差是高速高精度数控机床的重要误差源,针对实际加工过程中动态误差对工件精度影响较大的问题,提出了一种基于遗传算法优化的反向传播(GA-BP)神经网络以预测动态误差。首先,为了提高神经网络对动态误差的预测精度,从线性特征与非线性特征两方面对动态误差影响因素进行了深入分析,确定了神经网络输入输出参数;然后,采用了遗传算法对BP神经网络进行了优化,建立了动态误差模型,获得了最优网络学习参数,从而实现了对动态跟随误差的精准预测;之后,采用三次样条插值的方法对理想轨迹与实际轨迹之间的轮廓误差进行了计算,有效提高了轮廓误差估算精度;最后,采用了五轴数控机床进行了实验,对模型的有效性进行了验证。研究结果表明:所建神经网络模型可以精准预测机床反向越冲特性对轮廓误差的影响,各轴的动态误差预测精度为±3μm,复杂轨迹轮廓误差预测精度为±1.5μm。实验结果验证了所建模型的可靠性,为后续机床动态误差建模与控制研究提供了一定的参考价值。

基于插补算法的多轴数控机床刀具加工轮廓误差控制方法

多轴数控机床刀具在高速加工时容易出现振动和弯曲等现象,导致加工轮廓误差增大。为此提出一种基于插补算法的多轴数控机床刀具加工轮廓误差控制方法。首先构建刀具加工轮廓误差计算模型,运用实时采样周期中刀具实际位置与上一周期刀具位置的差值,计算刀具在坐标轴上的轮廓误差分量,获取轮廓误差。然后采用插补算法,建立刀具加工轮廓插补控制器,根据设定的缩放因子对比修正轮廓误差,实现误差控制。实验结果表明:该方法控制精准度高,对刀具加工轮廓误差改善效果好,且轮廓误差控制在0.025 mm以内,刀具加工轮廓运行同步性强。

层次多叉树映射布尔体廓后验误差的自适应层切

在给定构建方向下,层切厚度影响熔融沉积成型零件表面的阶梯效应,层切轮廓及其层次关系是路径规划的研究基础.为此,提出基于布尔体廓运算的自适应层切方法,在零件模型不同高度层切面上构建局部轮廓拓扑并计算内核域,根据内核点连线与轮廓环的交点,将轮廓环数据映射到一维坐标轴,基于拓扑映射判定轮廓环层次关系.建立层次关系多叉树,以树高映射体廓特征变化的布尔运算,根据层变阈值设计自适应层厚,通过体廓后验误差估计任意层厚的体积误差,验证自适应层切的有效性.实例打印及不同自适应层切方法对比结果表明,采用体廓后验误差计算的层切体积误差精度比牙尖高度法的更高;通过控制体廓特征部位的层厚来减小体积误差,有助于提高模型特征部位的表面成型精度.

五轴机床运动学建模与几何误差补偿

相对三轴机床,五轴机床包含三个线性轴和两个旋转轴,轴数和轴类型的增加使得五轴机床的几何误差建模更加复杂。本文基于齐次坐标变换理论,构建各线性轴和旋转轴的DH矩阵和误差矩阵,通过运动链配置关系获得考虑几何误差的五轴机床的运动学模型;基于梯度方法,构建轴空间和笛卡尔空间的微分运动映射雅克比矩阵;结合考虑误差的正运动学和误差映射模型,获得末端位姿偏差与轴端位置偏差的补偿量映射关系;实现考虑误差的通用五轴机床逆运动学迭代求解。仿真和分析证明所提方法可以有效改善机床各运动轴装配偏差引起的加工轮廓误差。