A novel disturbance-observer based friction compensation scheme for ball and plate system

Friction is often ignored when designing a controller for the ball and plate system, which can lead to steady-error and stick-slip phenomena, especially for the small amplitude command. It is difficult to achieve high-precision control performance for the ball and plate system because of its friction. A novel reference compensation strategy is presented to attenuate the aftereffects caused by the friction. To realize this strategy, a linear control law is proposed based on a reduced-order observer. Neither the accurate friction model nor the estimation of specific characteristic parameters is needed in this design. Moreover, the describing function method illustrates that the limit cycle can be avoided. Finally, the comparative mathematical simulations and the practical experiments are used to validate the effectiveness of the proposed method.     

Modeling and high-precision control of a ball-screw-driven stage

The demand for high-precision stages has received great attention due to the progress of nano-technology in recent years. Systems to provide long-range and high-precision performance for positioning, tracking and contouring actions have become stringent issues. Among these systems, the ball-screw-driven systems have been widely used in industrial applications and academic researches. In such systems, the friction behavior dominates the resulting performance and is usually known as the stick-slip phenomenon. The friction dynamics can be divided into the static and the dynamic regimes according to the conventional usage. In this paper, friction models are introduced to describe the dynamic behavior of a conventional ball-screw-driven x–y stage. The coherence between the theoretical and experimental data supports the validity of these models. Two sets of controllers corresponding to the static and the dynamic friction models are proposed based on the integral type sliding mode control (SMC) law. Experimental results demonstrate that the system achieves high-precision (10 nm) and long-range (10 cm) positioning performance with repeatability and robustness by the proposed control approaches.     

Precision positioning of a DC-motor-driven aerostatic slide system

This paper deals with precision positioning in the presence of friction. The object studied is an aerostatic slide system driven by a DC motor with brushes that introduce friction to the system. For such systems, models that do not account for friction can only be used to describe the macrodynamic behavior. The microdynamic behavior is significantly different. Instead of designing two controllers for the different dynamics, a single-step precision positioning using a high-gain controller designed according to the macrodynamics alone is proposed. A proportional-integral-derivative (PID) controller with finite-gain derivative and a modified anti-windup integral reset is designed. Controller parameters are obtained by pole placement rather than manual tuning or other rules of thumb. Identification of the microdynamics is avoided. Single-step precision positioning and uniform response to different sizes of step input are achieved. This method is particularly effective when the friction has uncertainty. Experimental and simulated results indicate that the PID controller can provide a sufficiently high loop gain. In point-to-point positioning for step inputs from millimeter size down to submicrometer size, the positioning error is within ±2 nm and the response dynamics is satisfactory.     

数控伺服进给系统中摩擦补偿控制研究进展

首先分析在高精度数控机床工作台伺服进给系统中进行摩擦补偿控制的必要性,其次介绍摩擦力模型研究方面的现状,然后着重总结数控机床工作台进给伺服系统领域采用的各种摩擦补偿技术研究成果。最后,指出了该领域研究存在的问题,展望了该领域的发展方向。     

Positioning and tracking of a linear motion stage with friction compensation by fuzzy logic approach

In this paper, the development of a fuzzy controller that compensates for nonlinear friction in a linear motion stage is presented. The experimental work and instrumentation set up is presented for this research. Based upon a nonlinear friction model, friction parameters were estimated from experimental results. Simulation and experimental validation on a ball-screw mechanism is presented, showing the effectiveness of the proposed controller. Furthermore, it is shown that the proposed fuzzy control scheme offers several implementation advantages such as smaller control effort, and reduced effect of measurement noise. Moreover, the fuzzy logic methodology displays superior performance when compared to a conventional PID controller. It also shows good and robust tracking with respect to system parameters variation.     

Development of a digital control system for high-performance pneumatic servo valve

Pneumatic servo systems are used in many fields, such as pneumatic robot systems or vibration isolation systems. To improve the controllability of the pneumatic servo system, a higher performance servo valve is needed.In the present paper, a pneumatic spool type servo valve having an air bearing and a high-resolution position sensor was developed. We attempted to achieve high-frequency, high-accuracy flow rate control by digitization of the controller. We present herein a control algorithm for digital control of this valve.The characteristics of this valve were measured and the natural frequency of the valve was clarified to be up to 300 Hz. The spool position accuracy and the dynamic characteristics of the developed servo valve are greatly improved compared to existing valves.     

二维精密定位系统的误差分析与补偿

针对所设计的基于运动控制卡的精密定位平台,提出了一种测量系统总体误差状况的方法,通过对精密定位系统中宏动平台进行定位误差的测量和分析,根据测量的误差情况提出了误差补偿的方法,采用闭环控制对系统的误差进行补偿,使其定位精度得到了大幅的提高.     

Double-integrator control for precision positioning in the presence of friction

In order to achieve good performance in precision positioning systems where friction is present, a straightforward approach is using single-integrator controllers to suppress the effect of friction. In this paper, double-integrator (DI) control, in which two integrators are involved, is proposed to enhance controller gain at lower frequencies. A new integral anti-windup scheme is developed for the DI control and is shown to be effective. Performance of a DI controller is compared with that of a proportional-integral-derivative controller (I-PD) and a pole-placement-with-integration controller (PPI) by experiment on a slide system driven by a dc motor. In the system, the dc motor has brushes that give rise to friction, and all other frictional contacts are removed by frictionless aerostatic support. Because of the unmodeled high frequency dynamics caused by aerostatic dynamics, closed-loop bandwidth with the I-PD controller is limited at a lower value than in the cases with the DI and PPI controllers. With the three controllers having parameters for similar closed-loop bandwidths, the DI controller gives uniform closed-loop responses to step inputs of different heights, while for the other two controllers the responses are obviously dependent on the height of the step inputs.     

提高精密工作台定位精度的温度补偿研究

精密定位工作台温度的变化直接影响工作台的定位精度。通过建立精密定位工作台热膨胀模型,分析工作台在不同固定方式下的温度变化对定位精度的影响,给出了基于温度精密测量的工作台定位精度实时补偿方法,并通过实验对补偿方法的效果进行了验证,证明方法有十分明显的补偿效果。     

高加速度运动系统的非线性摩擦前馈补偿控制

高加速度运动系统中非线性摩擦的建模补偿对提高轨迹跟踪性能至关重要。本文针对传统参数化模型难以准确预估高加速度运动启停阶段摩擦过冲等非线性摩擦的问题,在传统模型结构的基础上,结合扩展Stribeck模型,提出一种扩展参数化模型,模型参数的训练和学习样本源于高精度迭代学习控制获取的有限轨迹下非线性摩擦前馈补偿数据,并采用Levenberg-Marquardt算法拟合模型参数。最后,在音圈电机驱动的高加速定位平台上针对不同运动轨迹进行了实验验证。结果表明,该方法能够克服传统参数化模型难以消除高加速度启停阶段摩擦过冲等非线性摩擦对轨迹跟踪精度的影响;且与迭代学习控制的轨迹跟踪精度接近,有效避免了迭代学习泛化性差等问题,可实现工作空间下任意轨迹的摩擦补偿。     

自动跟踪补偿消弧系统综述

针对电网发生单相接地故障时,系统无法快速、准确地对单相接地电容电流进行有效补偿的问题,对中性点电压和补偿原理进行了研究,通过采用中性点经消弧线圈的接地方式,建立了自动跟踪补偿消弧系统,同时提出了自动调谐原理.该系统主要由消弧线圈和控制系统组成,在发生单相接地故障时,自动进入补偿状态,接地故障消除后,自动退出补偿状态.调谐原理是系统进行自动跟踪补偿的关键技术,在很大程度上影响系统的跟踪补偿速度与精度.通过对国内外几种常用的调谐原理进行总结和对比,指出了各自存在的优缺点及适用范围.研究结果表明,不同结构特点的消弧线圈所适用的调谐原理也不同,选择合适的调谐原理才能快速、有效地补偿接地电容、电流.     

光雷一体化测量系统的谐振特性及组合补偿

针对光雷一体化测量系统中复杂谐振对伺服单元的不利影响,提出了采用自适应陷波器及观测器滤波反馈组合实现谐振补偿的方法。首先,结合机械结构及频响测试结果分析了系统的谐振特性,指出系统存在雷达天线谐振、雷达机体谐振和天线高阶及轴系耦合谐振等3类主要谐振模式,并求得谐振特性随俯仰角变化的规律。讨论了对这种复杂谐振的补偿方法,提出采用自适应陷波器补偿雷达天线和雷达机体谐振,并利用Kalman观测器滤波反馈抑制天线高阶及轴系耦合谐振的方法。结果表明：经过谐振组合补偿后,各类谐振均得到有效抑制,速度环闭环带宽期望值达到了115 rad/s,阶跃过程过渡时间为0.35 s,在保证闭环控制稳定性的同时满足了系统带宽要求。     

A stable friction compensation scheme for motion control systems

In mechanical positioning control systems, friction phenomenon makes undersirable responses. Friction compensation scheme is frequently implemented to the control system together with the friction estimator in order to cancel the effect of the friction. However, the error in the estimation of the friction results in undercompensation or overcompensation, which also makes undesirable responses. In this paper, a new friction compensation scheme is proposed. The stability analysis is performed based on the circle criterion, which provides a sufficient condition for asymptotic stability of a system. For an application example, the scheme is implemented to a mechanical positioning system of a second-order plant with nonlinear friction. The effectiveness of this scheme is illustrated with the time responses obtained by computer simulation.     

Disturbance observer and adaptive controller design for a linear-motor-driven table system

This paper presents a disturbance observer and adaptive controller design for a direct drive motion control system. An indirect adaptive controller is implemented to achieve desired tracking performance as well as deal with system parameters variation. To reduce tracking errors, a newly designed adaptive feed-forward controller is proposed based on an on-line estimated inverse model of the linear motor drive system. A digital disturbance observer is implemented to be included in the proposed feedback-feed-forward control structure to compensate for the undesired nonlinearity and external load disturbance of the direct drive system. Experimental results show that this control scheme can achieve superior contouring accuracy, disturbance rejection and robustness under the influence of friction and cogging force.     

Robust control of nonlinear MAGLEV suspension system with mismatched uncertainties via DOBC approach

Robust control of a class of uncertain systems that have disturbances and uncertainties not satisfying “matching” condition is investigated in this paper via a disturbance observer based control (DOBC) approach. In the context of this paper, “matched” disturbances/uncertainties stand for the disturbances/uncertainties entering the system through the same channels as control inputs. By properly designing a disturbance compensation gain, a novel composite controller is proposed to counteract the “mismatched” lumped disturbances from the output channels. The proposed method significantly extends the applicability of the DOBC methods. Rigorous stability analysis of the closed-loop system with the proposed method is established under mild assumptions. The proposed method is applied to a nonlinear MAGnetic LEViation (MAGLEV) suspension system. Simulation shows that compared to the widely used integral control method, the proposed method provides significantly improved disturbance rejection and robustness against load variation.     

GA-optimized feedforward-PID tracking control for a rugged electrohydraulic system design

Rugged electrohydraulic systems are preferred for remote and harsh applications. Despite the low bandwidth, large deadband and flow nonlinearities in proportional valves valve and highly nonlinear friction in industry-grade cylinders that comprise rugged systems, their maintenance are much easier than very sophisticated and delicate servocontrol and servocylinder systems. With the target of making the easily maintainable system to perform comparably to a servosystem, a feedforward control has been designed here for compensating the nonlinearities. A PID feedback of the piston displacement has been employed in tandem for absorbing the unmodeled effects. All the controller parameters have been optimized by a real-coded genetic algorithm. The agreement between the achieved real-time responses for step and sinusoidal demands with those achieved by modern servosystems clearly establishes the acceptability of the controller design.     

Reliability-based robust dynamic positioning for a turret-moored floating production storage and offloading vessel with unknown time-varying disturbances and input saturation

In this paper, we derived a mathematical model for a floating production storage and offloading (FPSO) vessel and its buoy mooring system and developed a new robust positioning controller to keep vessels in a desired region in the presence of unknown time-varying disturbances with uncertainties and input saturation. Different materials (chain and polyester) and buoys are considered in the model of mooring system to make the developed model more realistic. We employed a disturbance observer to estimate the disturbances and designed an auxiliary dynamic system integrated with the structural reliability's derivative to quantify the input saturation's influence, and its states are used to the control design. Our proposed controller can keep the structural reliability and heading at desired values with arbitrarily small errors while guaranteeing the uniform ultimate boundedness of all signals in the closed-loop control system. It is easier for the control design because disturbances and input saturation are handled simultaneously and so is the stability analysis because only one Lyapunov function is needed. Simulations are conducted to demonstrate our proposed controller's effectiveness and a comparison with a robust controller based on hyperbolic tangent functions shows our proposed controller can avoid steady errors with desired control goals.     

光电跟踪器传递函数参数的测试及其相位补偿

由于电视跟踪器图像信号建立、图像处理等原因造成的延时和采样频率直接影响了电视跟踪伺服系统的性能.针对电视跟踪器对跟踪伺服系统影响进行探讨,给出测试电视跟踪器滞后时间常数的方法;针对电视延迟和零节保持环节造成的相位损失提出了补偿方法.经过插值外推补偿和零阶保持器补偿以后,系统的阶跃响应超调量减小约6%～9%,而稳定时间基本不变,改善了电视跟踪系统的动态性能.在实际工程应用中所述方法对于指导电视跟踪系统的伺服设计和拓展频带取得显著效果.     

前馈式多轴CNC系统跟随误差补偿控制模块的设计

采用不变性原理构建前馈补偿控制系统的理论结构模型,并进行系统幅值误差的分析。建立零件空间线性轮廓误差的数学模型,并由此确定前馈补偿量的算法。设计了以单片机为核心的前馈补偿控制模块的硬件原理电路和补偿数据处理程序的软件结构。通过仿真实验,验证了控制模块的补偿功能。结果表明,该设计能够有效地消除计算机数控(CNC)系统的相位滞后和幅值误差,提高普通数控系统对零件轮廓的加工精度。     

Control system design of a linear motor feed drive system using virtual friction

This paper proposes a friction compensator and a design method for control systems to improve the response characteristics of linear motor feed drive systems. The proposed friction compensator cancels the real nonlinear friction of feed drive systems by using the nonlinear friction model proposed in this study and introduces virtual linear friction to facilitate the control system design. The proposed design method enables the determination of servo gains and friction compensator parameters that lead to desirable tracking performance and disturbance rejection without many trial-and-error tuning processes. In addition, the proposed method facilitates the design of the velocity feedforward compensator by using the inverse transfer function of the velocity control loop to correct the position tracking errors for various position commands. The effectiveness of the proposed method with the friction compensator and the velocity feedforward compensator was verified in simulations and experiments using a one-axis feed drive system consisting of a rod-type linear motor and linear roller guides. The results confirmed that the proposed method enables desirable overshoot-free responses and corrects motion trajectory errors due to nonlinear friction characteristics, and the proposed velocity feedforward compensator can correct tracking errors in both constant velocity motion and circular motion.