Discrete-time robust adaptive multi-axis control for feed drive systems

This paper presents a robust adaptive controller design for multi-axis feed drives systems. The proposed method is designed to compensate for the coupling effects among multiple axes that are neglected in most feed drive controllers. Because inertial force from one axial motion affects the contact force between mechanical parts in other axes, the magnitude of friction at the contact surface varies. Considering this coupling effect in controller designs can improve control performance. Because the coupling effect cannot be known in advance, and it varies with respect to environmental conditions such as temperature, this paper first presents an adaptive controller design. Next, the design is extended to have robust stability for unanticipated plant modelling errors disturbances, because the robustness of adaptive controllers is known to be low due to the complex mechanism of controllers and estimators of plant model parameters. The design problem of the robust controller is formulated as a minimization problem under the linear matrix inequality constraints. The effectiveness of the adaptive multi-axis controller is demonstrated by comparative experiments with an adaptive controller that neglects the coupling effect. In addition, the robust adaptive controller is confirmed to be effective by comparison with a non-robust adaptive controller.     

Robust contouring control for biaxial feed drive systems

Contouring control is an effective method of providing precision machine tool control, and various such methods have been proposed to date. However, most existing methods require prior exact knowledge of feed drive dynamics. This paper presents a robust contouring control system design that takes into account dynamics modelling errors and disturbances such as friction. We first present a controller design for biaxial feed drive systems that enables assignment of controller gains, for reducing the error component orthogonal to the desired contour curve, independent of the tangential error component. Although this design provides better control performance with small control input variance, an inherent contour error exists because of the difficulty in calculating the exact contour error for any contour curve in real time. To address this problem, a reference adjustment method is used to estimate the actual contour error. A robust contouring controller is proposed based on the variable structure control. The effectiveness of the robust controller is demonstrated by experimental results using circular and non-circular contour curves.     

带有摩擦前馈补偿的伺服控制器设计的研究

为了克服系统摩擦给系统带来的稳态误差和低速爬行问题，利用控制策略来补偿摩擦非线性对系统运动的负面影响是降低摩擦非线性负面影响的有效且节俭的途径。首先对交流伺服驱动的工作台进给系统进行了摩擦力测量实验，根据实验数据，建立了用于摩擦补偿控制的简化Stribeek摩擦力模型：由于XY工作台进给传动机构中存在的伺服滞后和摩擦是降低工作台位置跟踪精度两个主要因素，所以一个完整的前馈补偿方案应该包括两个部分：摩擦前馈补偿器和命令前馈补偿器。分别对命令前馈控制器和摩擦前馈补偿控制器进行了理论设计，借助于现有的GT-400运动控制器的功能，添加摩擦力补偿模块提升了工作台的跟踪精度，并和没有前馈补偿的传统控制器进行了对比研究，实验结果表明带有命令前馈和摩擦前馈的控制方案能取得更好的控制性能。     

自适应控制在水压伺服缸系统中的应用分析与研究

与电驱动、液压油驱动、气体驱动相比,水压伺服缸系统具有高功率、高安全性和环保性,且其具有较大的摩擦转矩和泄漏量,其稳态误差和超调量成为精准控制的主要问题。目前,传统模型参考自适应控制系统(MRAC)被广泛应用于水压伺服缸控制系统,且其具有较好的跟踪性,但其控制器结构复杂,阶次较高,且对外界干扰的鲁棒性不足。为此,应用简单自适应控制系统(SAC)对水压伺服缸进行控制,并对其跟踪性和鲁棒性进行研究分析。研究结果表明,SAC具有较好的跟踪性,且比MRAC具有更好的控制精度、更高的鲁棒性。     

时变周期性参考输入的自适应重复控制系统设计

在凸轮研磨加工应用中,为符合特定加工条件,凸轮需要操作在变转速条件,这将使得输入信号变成所谓的时变周期信号,即是位置或角度的周期信号.因此,为降低时变周期信号的跟踪误差,提出了一种基于重复控制理论设计的具有线性时变特性的自适应重复控制器,使得角位移域内的时变周期信号得到衰减.采用自适应重复控制理论将定义在时域内的所有的控制信号转换成定义在角位移域内的信号,以使输入信号变成周期函数.针对直线伺服电机驱动的凸轮加工中心进行了仿真研究,结果表明所提出的控制方案是有效的,提高了系统跟踪精度,大大减小了跟踪误差.     

Tracking control and active disturbance rejection with application to noncircular machining

Control systems are usually required to track reference signals while operating under the influence of disturbances. A fast tool servo system for noncircular machining application works under such conditions, resulting in large control efforts. This paper presents a linear active disturbance rejection controller design for a voice coil motor-driven fast tool servo system for noncircular machining application. The controller is designed through an extended state observer to estimate and compensate the variant dynamics of the system, nonlinearly variable cutting load, and other uncertainties. Then, a simple proportional derivative controller produces the control law. To improve the tracking performance of the fast tool servo, the tracking error from the trial-cutting workpiece is added to the reference input and used as feed-forward error compensation. In such a combined control arrangement, the active disturbance rejection controller provides active disturbance rejection ability for the controller, and the feed-forward error compensation controller improves the tracking precision. Both the tracking control and disturbance rejection performances are thus enhanced. In real-time control and implementation, the effects of finite word length, position feedback resolution, and short sampling period are analyzed and addressed. Machining experiments are conducted, and the results illustrate the control system synthesis procedures and a substantial improvement over the tracking error generated by the linear active disturbance rejection controller alone.     

机器人柔性关节前馈力/位混合控制策略研究

针对机器人关节柔性引起的轨迹跟踪误差问题和末端执行器残余振动现象,在PD反馈控制律基础上,提出一种基于柔体动力学模型的前馈力矩补偿控制算法和后置多模态自适应输入整形算法前馈力/位混合控制策略。建立六轴工业机器人柔体动力学简化模型,在不附加关节编码器和外设的情况下进行柔体动力学参数辨识,再将动力学模型改写为力矩计算方程,经计算得到前馈力矩并加入控制律中进行补偿;计算前馈力矩所用的期望轨迹需经过输入整形器处理,考虑机器人系统的时变性问题,采用后置多模态自适应输入整形算法对期望输入位移信号进行命令整形,从而抑制末端的残余振动现象。结果表明：所提出的前馈力/位混合控制策略能有效减少轨迹跟踪误差,抑制机器人末端的残余振动现象。     

直线电机进给系统摩擦自适应补偿控制

为消除非线性摩擦干扰对直线电机进给系统定位精度的不利影响,提出一种基于LuGre摩擦模型的自适应补偿控制方法。建立直线电机进给系统的动力学方程,并在系统建模中引入基于自适应因子的改进LuGre模型;采用反步设计法的思想,利用李雅普诺夫第二法推导了自适应控制律;最后进行了半物理仿真实验。仿真结果表明:该自适应控制器应用于直线电机进给系统的摩擦补偿是可行的,有效提高了系统的位移定位精度和速度跟踪精度。     

XY平台直线伺服系统的IP变增益交叉耦合控制

XY平台直线伺服系统中,负载扰动、机械时间延迟及各轴响应速度不同会影响轮廓加工精度,为此提出了一种将积分-比例(I-P)控制、速度前馈控制及变增益交叉耦合控制相结合的控制策略。单轴采用由IP控制和前馈控制构成的复合速度控制器,IP控制具有快速响应和抑制扰动的能力,速度前馈控制可增加系统跟踪能力,降低机械时间延迟效应。间接减小轮廓误差。并且,在X、Y轴间加入变增益交叉耦合控制器,直接减小轮廓误差。仿真结果表明该控制方案可增强系统的鲁棒性,提高系统的快速性和轮廓加工精度。     

双缸液压系统活塞运动轨迹同步模糊控制研究

针对负载不平衡的双液压缸同步运动控制问题,提出一种活塞运动轨迹同步模糊控制方法。该方法首先采用基于轨迹约束的控制器将两液压缸的同步误差限制在一定范围内,并使活塞杆运动平滑。在模糊控制的基础上,引入两个模糊控制器,分别用于消除液压缸的轨迹跟踪误差和液压缸之间的同步误差。实验结果表明:即使两液压缸存在较大的负载不平衡,该复合控制方法仍能将系统的同步运动误差控制在±10 mm以内,且系统运动具有很好的平滑性。     

交流伺服驱动系统模糊自适应控制研究

为提高交流伺服驱动系统控制性能,结合模糊逻辑和神经网络各自的优点,设计了一种在线自适应模糊神经网络控制的交流伺服系统.文章将系统受控对象输入和跟踪误差作为模糊神经网络控制器的输入.设计的控制器不需要跟踪误差的变化率,可以避免以数值方式计算微分值时受采样周期大小的影响.通过仿真和具体实验分别验证了设计的合理性.结果表明:该控制方法不论对于调节还是设定值跟踪,均具有很好的控制效果,而且对感应电机伺服驱动系统有很好的抗干扰性能和较强的的鲁棒性.     

Application of active disturbance rejection control to variable spindle speed noncircular turning process

In application of variable spindle speed machining to noncircular turning process, the tracking control of the fast tool servo yields a periodic sampling rate in the real-time domain. However, in the view of the angle domain, the sampling rate is constant. Moreover, the reference acceleration signal is easily available. This implies that it is advantageous to design the control system from the angle domain perspective, but the plant for a linear time-invariant system will become a periodically time-varying system. In this paper, the active disturbance rejection control strategy is applied to actively estimate the time-varying dynamics and other disturbances and compensate for them in the control law. The acceleration feed-forward strategy is employed to achieve better tracking performance. The stability analysis based on the lifting technique is proposed. Experimental machining results demonstrate the tracking performance of the proposed design, as well as the ability to increase machining stability using variable spindle speed machining.     

Application of MRAC theory for adaptive control of a constrained robot manipulator

This study presents the compliance control of a robot manipulator under a constrained environment. Considering the impact of frictional force allows us to more accurately simulate the relationship between the manipulator and environmental contact forces. The controller design proposed herein is based on the adaptive control scheme. In this design, the feed forward and feedback controllers control the position and the contact force of end-effector. Applying these controllers allows us to adapt the manipulator to the unknown surface of the surrounding environment and to have close contact with the curved surface. A Lyapunov function ensures the stability of the system. For an unknown contour, most controllers fail since the desired trajectory can not be obtained, and the parameters of the manipulator are unknown and may varied with the contact force and position. However, in this study, when performing compliant motion, the desired trajectory is generated from the controller based on the tangential direction of the measured contact force. This tangential direction changes according to the operating point. We approach the original nonlinear system with a second order linear system at each instantaneous operating point. Correspondingly, the contour of workpieces can be measured. Experimental results conform the feasibility of the proposed adaptive control scheme. Without knowledge of the contour of workpiece and gains of the controller in advance, the adaptive controller performs well for various unknown contours.     

A decoupled path-following control algorithm based upon the decomposed trajectory error

This paper proposes a new path-following control algorithm for the machine tool servo systems. The control system first decomposes the contouring error into the normal tracking error and the advancing tangential error. A dynamic decoupling procedure is then applied to the system dynamics. Finally, a dynamic decoupled controller is proposed to compensate the decomposed tangential and the normal tracking errors. The normal control minimizes the perpendicular tracking error while the tangential control maintains a desired feed rate. The proposed method is applied to the control of an experimental x–y table. Experimental results show that the proposed control can achieve good tracking and trajectory following characteristics. The new algorithm also enables the design of a non-overshooting controller along the path. This will result in a no-overcutting process for the machine tool operation.     

基于H∞反馈的直接驱动XY平台切向轮廓控制设计

为了提高XY平台的轮廓加工精度,在分析系统轮廓误差的基础上,提出将H∞速度反馈控制器和切向-轮廓控制器(TCC)相结合的控制策略.在速度环内采用H∞鲁棒控制理论设计反馈控制器,在具有模型摄动及外部干扰的情况下,保证了闭环系统的鲁棒稳定性和鲁棒性能,TCC使得XY平台之间的耦合作用消除,且轮廓控制器设计变得更加直接和简单.单轴系统采用IP(积分-比例)控制与速度前馈控制相结合的复合控制器.仿真结果表明所设计控制系统在保证具有较好的跟踪性能、鲁棒性能的同时轮廓精度大大提高.     

串联型机械臂的自适应鲁棒容错控制研究

针对串联型机械臂关节空间内的轨迹跟踪控制,提出了一种自适应鲁棒容错控制方法。在机械臂动力学模型中加入了外界干扰、关节摩擦与故障模型,并将其等价成二阶被控系统。在此基础上,结合非奇异快速终端滑模面和反步法控制策略,设计一种新型的反步非奇异快速终端滑模控制器。通过李亚普诺夫准则验证了控制策略的全局渐近稳定性;引入自适应技术估计系统不确定性的上界,提高控制器的鲁棒性。以二自由度机械臂为被控对象,对所设计控制器的有效性进行了验证,结果表明:与传统的非奇异快速终端滑模控制器及反步非奇异快速终端滑模控制器相比,该控制器具有响应速度快、鲁棒性强、抖振小的优点,能有效应对系统故障和实现机械臂的高精度轨迹跟踪控制。     

电液比例系统的广义预测控制研究

针对具有非线性和时变特性的电液比例系统,研究了自适应预测控制器的设计问题.采用隐式广义预测控制算法,无需辨识对象模型参数,而是利用输入/输出数据直接辩识控制器参数,以求解最优控制增量,具有计算量小、实时性高的特点.仿真结果表明,在不需要关于被控对象先验知识的情况下,隐式广义预测控制器可以很好地跟踪设定值的变化,同时对于系统外部干扰和模型参数的变化具有很好的适应能力,在电液比例系统控制器的设计中具有良好的应用前景.     

电液位置伺服系统的自适应抗饱和控制

针对电液位置伺服系统的不确定性与输入饱和问题,提出自适应抗饱和控制策略。建立阀控缸系统的数学模型;在基于反步法的设计框架下,将输入饱和导致的跟踪误差加入到李亚普诺夫函数当中,并根据该李亚普诺夫函数设计控制器。通过使李亚普诺夫函数渐近稳定,使得系统跟踪误差收敛于零。针对系统模型中的不确定参数,通过自适应算法对其进行迭代更新,以保证控制器的有效性。以跟踪误差最小为目标函数,采用粒子群搜索算法优化控制器的4个参数。结果表明：加入抗饱和时的控制信号比未考虑输入饱和时的控制信号的幅值明显减小,消除了输入饱和现象;在参数不确定和输入饱和情况下液压缸活塞的最大跟踪误差仅为5.8×10-6mm,相对无抗饱和算法时的跟踪误差有了大幅减小。     

超精密数控机床的规则可调自适应模糊控制系统的研究

介绍了一种能够根据位置误差和误差变化率自动调整模糊规则和比例因子的规则可调自适应模糊控制器。仿真实验表明了该模糊控制系统不但能很好地适应伺服系统的非线性特点，而且具有很高的动态跟踪精度、静态定化精度和鲁棒性．其性能优于PID控制器和常规的模糊控制器，能更好地满足超精密机床数控系统极高的轮廓跟踪精度、定化精度和抗干扰性能的要求。     

基于自适应滑模控制的进给系统运动精度和节能的研究

为了提高进给系统的运动精度和降低其能耗,设计一种自适应滑模控制方法。对进给系统的机械结构进行剖析,分析其组成。通过丝杠导程和效率计算丝杆的负载扭矩,并在丝杆负载扭矩的基础上得出丝杆的动力学方程。在电机转矩的作用下,建立电机轴的运动方程。进而在电机的作用下,得到进给系统的状态方程。以系统的跟踪误差为依据,构建非线性滑动面,在进给系统状态方程的基础上,以驱动系统状态趋于期望滑动面为目的,设计滑模控制律,并控制误差的薄边界层为约束,构造自适应增益模型,完成自适应滑模控制方法的设计。采用所提方法和神经网络方法对直线变化和圆周期望运动轨迹进行跟踪实验。结果表明：在跟踪直线变化和圆周期望运动轨迹时,所提方法的跟踪精度比神经网络方法分别提高了37.52%和32.72%,所提方法的能耗也比神经网络方法降低了10.37%。