基于稳定裕度的机床轮廓控制器增益设计方法

机床轮廓控制器通常被设计为P控制器,其控制增益是决定控制效果的关键参数。为定量设计轮廓控制器增益值,提出了基于稳定裕度的控制器增益设计方法。首先基于最小二乘法辨识机床各轴的离散传递函数模型,然后根据传递函数模型及Jury准则确定增益的稳定域,最后根据稳定裕度构造目标函数,并在稳定域内求解满足稳定裕度要求的轮廓控制器增益值。在三轴机床上设计轮廓控制器,实施轨迹联动实验,以验证方法的有效性。实验结果表明,基于稳定裕度设计的轮廓控制器可在保证机床运动平稳性的条件下使螺旋形轨迹的轨迹误差最大值减小39.06%,扇形轨迹的轨迹误差最大值减小少34.33%。     

基于误差模型的三轴联动加工轨迹预补偿方法

为了减小由于进给系统动态特性造成的多轴联动加工轮廓误差,提出了一种基于轮廓误差模型的三轴联动加工轨迹预补偿方法。首先建立了关于轨迹曲率、加工速率及进给系统动态特性参数的轮廓误差模型;然后根据读取的插补数据,利用轮廓误差模型实时预测三轴联动加工过程中的轮廓误差补偿向量并对加工轨迹指令进行补偿;最后通过对圆、变曲率和螺旋线轨迹的MATLAB仿真和机床加工实验,证明该补偿方法将轮廓误差减小了85%以上,可显著提高数控机床加工精度。     

基于交叉耦合与迭代学习的伺服系统运动控制研究

针对数控机床进给伺服系统各轴动态响应不一致,导致零件加工精度降低的问题,对数控机床进给伺服系统运动控制进行了研究。采用了迭代学习控制与交叉耦合结构相结合的控制方法,设计了进给伺服系统单轴位置环的迭代学习控制器,抑制了单轴跟随误差,设计了多轴的变增益交叉耦合迭代学习控制器,来抑制多轴轮廓误差;利用在MATLAB/SIMULINK环境中搭建的仿真模型,对三叶玫瑰曲线轨迹进行了跟踪验证;将所设计的控制器与其他控制方法进行了对比分析。研究结果表明:与其他控制方法相比,所设计的控制器跟踪曲线的最大轮廓误差和平均轮廓误差都得到了降低,证明所设计的单轴和多轴运动控制器能够实现降低轮廓误差,提高零件加工精度的目的。     

面向伺服动态特性匹配的轮廓误差补偿控制研究

在多轴数控加工中,轮廓误差直接决定零件最终加工精度。交差耦合控制和任务坐标系法通过估计轮廓误差,并设计轮廓跟踪控制器来提高轮廓精度。这两种方法存在大曲率位置轮廓误差估计精度差,轮廓控制增益整定依赖于工程经验等问题。为此,从伺服轴动态特性匹配出发,提出了一种基于轮廓误差精确计算的轮廓误差补偿控制方法。根据足点定义,采用解析方法快速准确计算轮廓误差。将轮廓误差分量分别补偿到各伺服轴的速度环和转矩环,提高各伺服轴动态特性的匹配程度。采用两维和三维NURBS曲线开展轮廓跟踪试验。试验结果表明:所提出的轮廓误差计算方法可以精确求解轮廓误差;所提出的轮廓误差补偿控制方法不需要建立轮廓误差与伺服跟踪误差间的映射关系,且可通过调整控制器增益定量显著减小轮廓误差。     

半闭环三轴机床静态解耦轮廓控制及螺距误差补偿

为提高半闭环三轴机床加工精度,首先提出单伺服轴的螺距误差补偿方法;在建立半闭环三轴机床解耦轮廓系统模型基础上,研究了静态解耦轮廓控制器的设计,并在所提出的静态解耦轮廓控制系统上实现了螺距误差补偿.实验结果表明,算法有效地实现了轮廓的切线、法线和副法线方向的解耦跟踪控制.加入螺距补偿后,机床加工半球的最大圆度误差由55μm缩小到12μm.     

一种新型五轴联动机床的运动控制研究

以一种基于三坐标并联动力头的五轴联动机床为研究对象,通过矢量链方法建立机构从工作空间到关节空间的运动学模型,基于Turbo PMAC控制器设计运动控制需要的的硬件平台,在LabVIEW开发环境下基于Active X技术开发软件平台,采用驱动器增益自整定结合控制器的PID及运动学前馈方法进行伺服驱动控制,针对并联机构运动学特点,在控制器内嵌入运动学算法,经过工作空间和关节空间二次插补的方式进行轨迹控制,最后通过五轴加工实验检测伺服驱动控制和轨迹控制的有效性。     

多功能体能运动训练器PMAC多轴控制方法

针对当前PMAC多轴控制方法未考虑预补偿多轴轮廓误差,导致多轴控制延误以及控制误差较大,容错率下降的问题。提出多功能体能运动训练器PMAC多轴控制方法。通过多轴轮廓误差模型,采用辨识传递函数对实际位置进行预测,完成轮廓误差的预补偿。利用浮动坐标系描述方法,构建多功能体能运动训练器的拉格朗日动力学模型,通过模糊推理中的模糊规则自适应,调整PMAC多轴控制器控制参数。采用自适应学习算法,计算隶属度函数参数,确定输入数据和输出数据,实现多功能体能运动训练器PMAC多轴控制。实验结果表明,所提方法的控制误差较小,能够有效降低控制延误,提升容错率。     

基于双深度神经网络的轮廓误差补偿策略研究

五轴数控机床的加工精度通常由轮廓误差指标来衡量。传统的轮廓误差降低策略主要包括精确的轮廓误差估计和有效的轮廓控制器设计。然而,传统策略存在刀具路径轮廓误差在线估计或控制器设计复杂等问题。为此,从机床输入驱动指令和输出末端位姿的映射出发,针对五轴数控机床加工大批量工件提出基于数据驱动的轮廓误差补偿策略。调整PID控制器参数保证系统单轴伺服的稳定跟踪,同时采集各伺服轴的输入指令和机床的实际输出位姿。针对五轴数控机床的刀具位姿和刀轴方向分别搭建位姿和方向两个深度神经网络,并基于数据训练所得的神经网络模型预测系统新的输入参考指令。采用五轴刀具路径开展轮廓跟踪试验。试验结果表明:所提出的基于深度神经网络的轮廓误差补偿策略不需要刀具路径轮廓误差的在线估计和控制器的有效设计,即可有效降低刀具路径的位置和方向轮廓误差。     

基于内置传感器的数控机床多轴联动精度检测方法

多轴联动精度是评价机床性能的核心指标,针对传统数控机床多轴联动精度检测存在的占机时间长、频次低、离线检测等问题,提出了一种基于内置传感器的数控机床精度快速检测方法。首先建立了机床的误差模型,然后基于数控机床伺服控制原理采集了机床运行S试件轨迹时各轴的插补器、编码器、光栅尺等位置数据,并将位置数据输入机床误差模型得到刀尖点轨迹误差,实现了机床多轴联动精度的检测,最后通过检测机床切削S试件的轮廓精度,验证了方法的有效性,为机床多轴联动精度快速检测提供了重要途经。     

光纤透镜研磨抛光的轮廓成形控制系统的研究

为了有效地减小光纤透镜的研磨抛光轮廓误差,设计一种两轴联动的交叉耦合轮廓控制器,并且针对光纤透镜研磨抛光机床的运动特点,给出了交叉耦合轮廓误差模型.然后利用Matlab软件对该交叉耦合轮廓控制的效果进行了仿真研究与分析.仿真结果表明,利用该控制器能使系统轮廓误差从0.075 μm减小到0.03 μm,但由于加入了交叉耦合器的补偿量,Z轴的跟随误差也从0.05 μm增大到0.07 μm.同时也表明两轴联动的交叉耦合控制系统远远优于单轴PID控制系统.     

Robust iterative learning contouring controller with disturbance observer for machine tool feed drives

In feed drive systems, particularly machine tools, a contour error is more significant than the individual axial tracking errors from the view point of enhancing precision in manufacturing and production systems. The contour error must be within the permissible tolerance of given products. In machining complex or sharp-corner products, large contour errors occur mainly owing to discontinuous trajectories and the existence of nonlinear uncertainties. Therefore, it is indispensable to design robust controllers that can enhance the tracking ability of feed drive systems. In this study, an iterative learning contouring controller consisting of a classical Proportional-Derivative (PD) controller and disturbance observer is proposed. The proposed controller was evaluated experimentally by using a typical sharp-corner trajectory, and its performance was compared with that of conventional controllers. The results revealed that the maximum contour error can be reduced by about 37% on average.     

Centralized PI controllers for interacting multivariable processes by synthesis method

In this article, two methods of designing a centralized control system for multi-input, multi-output (MIMO) processes are presented. Centralized proportional-integral (PI) controllers are designed based on a direct synthesis method. The inverse of the process transfer function matrix in the direct synthesis method is approximated based on the relative gain array concept. The method is further improved by using a relative normalized gain array, and an equivalent transfer function for each element in the process transfer function matrix is derived for the closed-loop control system. The transpose of the effective transfer function is used to approximate the inverse of the process transfer function matrix. The simulation studies demonstrate the effectiveness of this method. The proposed centralized controllers reduce the interactions better than recently reported decentralized controllers do. A centralized controller designed based on a relative normalized gain array (RNGA) gives a better performance than a centralized controller designed based on a relative gain array (RGA).     

Controller Parameter Tuning of Delta Robot Based on Servo Identification

High-speed pick-and-place parallel robot is a system where the inertia imposed on the motor shafts is real-time changing with the system configurations.High quality of computer control with proper controller parameters is conducive to overcoming this problem and has a significant effect on reducing the robot’s tracking error.By taking Delta robot as an example,a method for parameter tuning of the fixed gain motion controller is presented.Having identifying the parameters of the servo system in the frequency domain by the sinusoidal excitation,the PD+feedforward control strategy is proposed to adapt to the varying inertia loads,allowing the controller parameters to be tuned by minimizing the mean square tracking error along a typical trajectory.A set of optimum parameters is obtained through computer simulations and the effectiveness of the proposed approach is validated by experiments on a real prototype machine.Let the traveling plate undergoes a specific trajectory and the results show that the tracking error can be reduced by at least 50%in comparison with the conventional auto-tuning and Z-N methods.The proposed approach is a whole workspace optimization and can be applied to the parameter tuning of fixed gain motion controllers.     

A Linear Cross-Coupled Control System for High-Speed Machining

We present a linear cross-coupled controller to improve highspeed contouring accuracy independently of tracking accuracy in a biaxial machine tool feed drive servomechanism. Unlike conventional cross-coupled controllers, the cross-coupled controller presented here is a linear system, so it is very easy to perform the stability and steady-state error analysis, and to optimise the controller parameters. The proposed controller is evaluated experimentally on a CNC LOM machine and compared to an uncoupled controller and a conventional cross-coupled controller. Controller performance is evaluated for a circular contour at a feedrate of 30 m min _1 . The experimental results show that the proposed controller can greatly reduce the contour error at large feedrates. The linear cross-coupled controller is simple to implement and is practical.     

Fuzzy logic cross-coupling controller for precision contour machining

This paper introduces a new cross-coupling controller with a rule-based fuzzy logic control. It is asserted that (i) fuzzy logic controllers provide a better transient response (which is essential for better contour accuracy during transient motions) than the conventional controllers, such as PID controllers, and (ii) cross-coupling controllers perform better than axial controllers in trajectory tracking by machine tools. In this paper, a fuzzy logic controller and a cross-coupling controller are combined to reduce contour errors. A simulation of the FLCCC was performed and the FLCCC was implemented on a CNC milling machine. The simulation and the experimental results show improved contour accuracy over the conventional cross-coupling controller.     

Multi-loop PI controller design based on the direct synthesis for interacting multi-time delay processes

In this article, a new analytical method based on the direct synthesis approach is proposed for the design of a multi-loop proportional-integral (PI) controller. The proposed design method is aimed at achieving the desired closed-loop response for multiple-input, multiple-output (MIMO) processes with multiple time delays. The ideal multi-loop controller is firstly designed in terms of the relative gain and desired closed-loop transfer function. Then, the standard multi-loop PI controller is obtained by approximating the ideal multi-loop controller using the Maclaurin series expansion. The simulation study demonstrates the effectiveness of the proposed method for the design of multi-loop PI controllers. The multi-loop PI controller designed by the proposed method shows a fast, well-balanced, and robust response with the minimum integral absolute error (IAE).     

Determination of all feasible robust PID controllers for open-loop unstable plus time delay processes with gain margin and phase margin specifications

This paper proposes a novel alternative method to graphically compute all feasible gain and phase margin specifications-oriented robust PID controllers for open-loop unstable plus time delay (OLUPTD) processes. This method is applicable to general OLUPTD processes without constraint on system order. To retain robustness for OLUPTD processes subject to positive or negative gain variations, the downward gain margin (GM_down), upward gain margin (GM_up), and phase margin (PM) are considered. A virtual gain-phase margin tester compensator is incorporated to guarantee the concerned system satisfies certain robust safety margins. In addition, the stability equation method and the parameter plane method are exploited to portray the stability boundary and the constant gain margin (GM) boundary as well as the constant PM boundary. The overlapping region of these boundaries is graphically determined and denotes the GM and PM specifications-oriented region (GPMSOR). Alternatively, the GPMSOR characterizes all feasible robust PID controllers which achieve the pre-specified safety margins. In particular, to achieve optimal gain tuning, the controller gains are searched within the GPMSOR to minimize the integral of the absolute error (IAE) or the integral of the squared error (ISE) performance criterion. Thus, an optimal PID controller gain set is successfully found within the GPMSOR and guarantees the OLUPTD processes with a pre-specified GM and PM as well as a minimum IAE or ISE. Consequently, both robustness and performance can be simultaneously assured. Further, the design procedures are summarized as an algorithm to help rapidly locate the GPMSOR and search an optimal PID gain set. Finally, three highly cited examples are provided to illustrate the design process and to demonstrate the effectiveness of the proposed method.     

Cross-coupling control method of the two-axis linear motor based on second-order terminal sliding mode

When the dual-axis linear motor is processing components, its accuracy will be affected by the uncertainty and nonlinearity of the system, and the complexity of the processing curve trajectory. The goal is to improve the machining accuracy and response speed of the XY dual-axis permanent magnet synchronous linear motor two-dimensional platform, improve the anti-interference ability, and reduce the contour error. This paper proposes a coupled control method based on dual closed-loop single-axis high-order terminal sliding mode position control (TSMC). First, an improved mathematical model of equivalent contour error is established. Combine the coordinated controller to get the coupling link. Then, to accelerate error convergence and suppress chattering, a high-order terminal sliding mode controller is designed. The single-axis current controller is designed using high-order sliding mode algorithms. Simulations and experiments show the effectiveness and feasibility of the proposed method.

     

平面冗余驱动并联机构自适应滑模同步控制

基于Kane方程,建立了平面二自由度冗余驱动并联机构的动力学模型。基于轨迹轮廓误差,定义了机构的同步误差及滑模面,将动力学方程线性化,设计了自适应滑模同步控制器并对机构进行了稳定性分析。通过MATLAB仿真计算,并与计算力矩法进行比较发现,自适应滑模同步控制法优于计算力矩法,能够很好地实现轨迹跟踪。     

Sliding mode control with third-order contour error estimation for free-form contour following

To reduce the contour error in contour-following tasks, the most common method is to design a contour controller based on the contour error model. Therefore, how to estimate the contour error in real-time and with high accuracy plays an important role in contour-following control. It is difficult to guarantee real-time performance, high estimation accuracy and strong robustness against arbitrary trajectories at the same time. In this paper, a contour error estimation method based on the third-order osculating helix is proposed. The osculating helix can fully consider the geometric characteristics of the interpolation trajectory and is closer to the desired interpolation trajectory. On this basis, PD-type tracking error sliding mode surface and PD-type contour error sliding mode surface are redesigned to fully take into account the regulating effect of the velocity tracking error and velocity contour error. Experimental results demonstrate the effectiveness of the proposed contour control approach.