Precision tracking control of a piezoelectric-actuated system

In this paper, precision tracking control of piezoelectric-actuated systems is discussed. In order to obtain precision tracking control, a modified Prandtl–Ishlinskii (MPI) model is used to model the hysteresis nonlinearity. Then, the inverse MPI model is used to reduce the hysteresis nonlinearity, and a sliding-mode controller is used to compensate for the remaining nonlinear uncertainty and disturbances. In general, the piezoelectric-actuated system can be modeled as a linear model coupled with a hysteresis. When the linear model is identified, it is used to design the sliding-mode controller. Finally, this design method is applied to the motion control of a nano-stage, and experimental results are presented to verify the usefulness of this method.     

Precision coordinated control of multi-axis gantry stages

High precision motion control of gantry stages has found numerous applications in the manufacturing industries where precise positioning is crucial. This paper presents a survey of existing control schemes as well as the development of enhanced schemes for the coordinated motion control of moving gantry stages. In particular, a robust control scheme is proposed which uses a feedback controller with a sliding mode to correct for the tracking error and to coordinate multiple axis to move in tandem. Simulation and experimental results will illustrate and compare the performance of the control schemes presented in the paper.     

Controller design for high-frequency cutting using a piezo-driven microstage

Controller design consists of a feedforward and a feedback controller to support a microstage with flexure hinge structure driven by piezoelectric ceramic actuator for high-frequency nanoscale cutting is developed in this article. The feedforward controller is designed based on a hysteresis dynamic model in order to reduce the nonlinear hysteresis effect of piezoelectric actuator. The position feedback controller is designed based upon an exponentially weighted moving average (EWMA) method embedded in an internal model control (IMC) structure constructing a run-to-run IMC (RtR-IMC) control scheme in order to deal with system bias or modeling inaccuracy. Also, disturbance due to temperature rise will influence actuator's performance, hence an additional compensator is included in the IMC structure. Surfaces dimple micro-machining utilizes piezoelectric-driven microstage for high-speed cutting is selected as an example to investigate system performance. The developed control algorithm is implemented on a DSP-based system to provide 1 kHz operating speed. In experiment, the proposed feedforward and feedback controller is verified to be able to overcome those negative factors efficiently and preserve good positioning accuracy.     

Model reference adaptive control for a piezo-positioning system

Piezoelectric (PZT) actuators having the characteristic of infinitely small displacement resolution are popularly applied as actuators in precision positioning systems. Due to its nonlinear hysteresis effect, the tracking control accuracy of the precision positioning system is difficultly achieved. Hence, it is desirable to take hysteresis effect into consideration for improving the trajectory tracking performance. In this paper, a model reference adaptive control scheme based on hyperstability theory is developed for a moving stage system driven by a PZT actuator. It is worth emphasizing that the controller can be constructed without a nonlinear hysteresis dynamic equation to compensate the hysteresis effect. According to simulation results, the tracking error was only nanometer order. Through experimental examinations, the tracking performance was obtained as precision as ten nanometers order which is the resolution limitation of the measurement system. The effectiveness of the proposed adaptive control scheme was validated.     

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.     

Dynamic characteristics and dual control of a ball screw drive with integrated piezoelectric actuator

This paper describes the precision continuous path tracking control by using a dual-actuated single stage. First, fine-drive mechanism and the dynamic model of the entire drive system are described. In the simulation model, the dynamic characteristic of the dual-actuated stage is investigated to see whether it can provide precise motion by using dual control. Second, the fine motion controller is designed. Adjusting the control parameters, a positioning resolution of 20 nm and a bandwidth of 260 Hz were obtained. Third, the frequency responses of coarse and fine drives are experimentally investigated. After that, the dual controller is designed based on the investigated dynamics. Finally, whether coarse motion and fine motion could work complimentarily by the dual servo is examined in the experiments. By using the simultaneous dual controller, tracking errors were reduced sufficiently compared to the single coarse control.     

Robust fault-tolerant tracking control design for spacecraft under control input saturation

In this paper, a continuous globally stable tracking control algorithm is proposed for a spacecraft in the presence of unknown actuator failure, control input saturation, uncertainty in inertial matrix and external disturbances. The design method is based on variable structure control and has the following properties: (1) fast and accurate response in the presence of bounded disturbances; (2) robust to the partial loss of actuator effectiveness; (3) explicit consideration of control input saturation; and (4) robust to uncertainty in inertial matrix. In contrast to traditional fault-tolerant control methods, the proposed controller does not require knowledge of the actuator faults and is implemented without explicit fault detection and isolation processes. In the proposed controller a single parameter is adjusted dynamically in such a way that it is possible to prove that both attitude and angular velocity errors will tend to zero asymptotically. The stability proof is based on a Lyapunov analysis and the properties of the singularity free quaternion representation of spacecraft dynamics. Results of numerical simulations state that the proposed controller is successful in achieving high attitude performance in the presence of external disturbances, actuator failures, and control input saturation.     

Practical and intuitive controller design method for precision positioning of a pneumatic cylinder actuator stage

The present paper describes a practical and intuitive controller design method for precision positioning of pneumatic cylinder actuator stages. Pneumatic actuators are easy to use and have numerous advantages, which has led to these actuators having a wide variety of applications. However, pneumatic actuators have notable nonlinear characteristics, which make precision positioning difficult to achieve. The purpose of the present study is to clarify a practical and intuitive controller design procedure for precision positioning of a pneumatic cylinder actuator. In addition to positioning performance, the present study focuses on the realization of easy controller design without the need for the exact model parameters or knowledge in control theory for general-industrial-use pneumatic cylinder actuators with friction characteristics. These considerations are important in order to fully exploit the advantages of pneumatic cylinder actuators in a wide variety of applications. As such, three elements are added to the conventional continuous-motion nominal characteristic trajectory following (CM NCTF) controller. A new design procedure of the improved CM NCTF controller for pneumatic cylinder actuator stages is introduced, and the positioning performance of the designed control system is examined experimentally under several conditions. The positioning results generally indicate a positioning error of 50 nm, which is equal to the sensor resolution.     

应用控制理论实现反馈控制

明确阐述了控制理论和控制工程的关系,指出应用控制理论设计控制系统是整个控制工程的锦上添花部分.文章分析了控制理论应用方面的现况和问题,并且谈了笔者的看法和建议.希望工程人员在控制工程中应用控制理论,实现真正意义上的自动控制.     

Precision control system of two-DOF stage with linear ultrasonic motor

Using an appropriate control method, linear ultrasonic motors can be used in applications requiring high position accuracy. In this paper, a closed loop PI control system is designed to achieve high position accuracy during the control of a two-DOF stage driven by linear ultrasonic motors. Two ultrasonic motors are mounted on the stage to generate motion in two orthogonal directions. The PI control algorithm is used to increase the stability and accuracy of position control. The x-axis mover covers 30 mm forward and backward in less than 0.3 s settling time and the y-axis mover in less than 0.4 s. Experimental results denote that the control strategy proposed in this paper appears to have high efficiency, quick response, and high accuracy.     

Real-time tracking control of electro-hydraulic force servo systems using offline feedback control and adaptive control

This paper focuses on an application of an electro-hydraulic force tracking controller combined with an offline designed feedback controller (ODFC) and an online adaptive compensator in order to improve force tracking performance of an electro-hydraulic force servo system (EHFS). A proportional-integral controller has been employed and a parameter-based force closed-loop transfer function of the EHFS is identified by a continuous system identification algorithm. By taking the identified system model as a nominal plant model, an H_∞ offline design method is employed to establish an optimized feedback controller with consideration of the performance, control efforts, and robustness of the EHFS. In order to overcome the disadvantage of the offline designed controller and cope with the varying dynamics of the EHFS, an online adaptive compensator with a normalized least-mean-square algorithm is cascaded to the force closed-loop system of the EHFS compensated by the ODFC. Some comparative experiments are carried out on a real-time EHFS using an xPC rapid prototype technology, and the proposed controller yields a better force tracking performance improvement.     

Differential resistance feedback control of a self-sensing shape memory alloy actuated system

There is a growing trend towards miniaturization, and with it comes an increasing need for miniature sensors and actuators for control. Moreover situations occur wherein implementation of external physical sensor is impossible, here self-sensing lends its hand appropriately. Though self-sensing actuation (SSA) is extensively studied in piezoelectric, exploring this property in shape memory alloy is still under study. A simple scheme is developed which allows differential resistance measurement of antagonistic shape memory alloy actuated wires to concurrently sense and actuate in a closed loop system. The usefulness of the proposed scheme is experimentally verified by designing a one link manipulator arm and is performed in a real time tracking control. In a practical implementation of the self-sensing actuator a newly proposed signal processing electronic circuit is used for direct differential resistance feedback control upto a bandwidth of 1.8 Hz. The control design uses fuzzy PID which requires no detailed information about the constitutive model of SMA. At an operating frequency of 1 Hz, the result of the self-sensing feedback control with an angular tracking accuracy of ±0.06° over a movement range of ±15° is demonstrated.     

Precision thread grinding using a laser feedback system

Thread grinding to obtain a leadscrew with high lead accuracy is studied. A closed-loop compensation system using a laser to measure the table feed error of the thread grinder is applied to an existing grinding system, resulting in a simplified techinique for obtaining leadscrews with high lead accuracy.     

数控车削多头螺纹（或蜗杆）的精度控制方法

应用数控车床加工多头螺纹（或蜗杆）是目前生产中常用的方法,对于精度要求较高的多头螺纹（或蜗杆）加工,要经过粗车和精车两个工艺过程,并且要在粗车和精车两个工艺过程之间加上测量环节,根据测量值进行数控车床的磨耗调整后再进行精加工,就能达到很高的加工精度。     

Accuracy enhancement of a small overhung boring bar servo system by real-time error compensation

This paper is concerned with the work involved in reducing the machining errors of a small overhung boring bar by real-time error compensation. A boring bar developed is made with a pair of concentric bars with an outer diameter of 14 mm and length of 140 mm, representing an overhang ratio of 10:1. A piezoelectric (PZT) actuator was incorporated in the boring bar servo to achieve on-line compensation. Results of cutting tests show that improvement of 40% in the roundness errors can be achieved through on-line compensation of machining errors in precision boring of holes with high aspect ratios.     

精密隔振平台振动的LQG控制

建立了以空气弹簧作为被动隔振元件、超磁致伸缩致动器作为主动隔振元件的精密隔振平台隔振系统，应用LOG控制算法设计其主动控制器。采用MATLAB软件进行了仿真分析以验证系统的振动控制效果。仿真结果表明所设计的振动主动控制系统可在非常宽的频率范围对基础干扰和由仪器设备产生的直接干扰所引起的精密隔振平台振动进行有效的控制。     

Modal space vibration control of a beam by using the feedforward and feedback control loops

This paper introduces a vibration control method for a flexible beam subjected to arbitrary, unmeasurable disturbance forces. The concept of independent modal space control is adopted. Here, we choose the modal filters as the state estimator to obtain the modal coordinates and modal velocities for the modal space control. Because of the existence of the disturbance forces, applying only the state feedback to suppress the vibration usually cannot achieve the desired control performance. The modal space feedforward control is then introduced to cancel out the disturbance forces. In this paper, the feedforward and feedback control method is implemented to reduce the beam vibration. The disturbance force observer is established to observe the disturbance modal forces for the feedforward control. The control gains are derived from the extended optimal control algorithm, where the disturbance modal forces are treated as exogenous state variables. By combining the feedback, feedforward control laws and the disturbance force observer together, the vibration control performances are discussed.     

步进扫描光刻机扫描运动轨迹规划及误差控制

研究一种步进扫描投影光刻机工作台扫描运动超精密轨迹规划算法及误差控制策略。在分析三阶扫描运动与步进运动轨迹规划异同点的基础上,提出三阶扫描运动轨迹规划算法。针对扫描运动精确性与严格同步性要求,分析扫描运动轨迹规划误差补偿的几个关键问题。根据扫描运动轨迹算法离散实现存在的误差,结合内部整数积分策略,提出扫描运动轨迹规划加减速段与扫描速度稳定段运动距离的离散积分策略误差控制方法。此外,为克服切换时间圆整引起的扫描曝光匀速段位置误差,提出一种基于常速扫描运动段位置修正因子的误差补偿方法。以上方法共同实现光刻机工作台扫描运动轨迹规划精度控制。实例证明提出算法是有效和精确的。该算法成功应用于100nm步进扫描投影光刻机工作台的超精密运动控制系统中。     

The long-range scanning stage: a novel platform for scanned-probe microscopy

This paper describes a magnetically suspended six degree-of-freedom precision motion control stage with a horizontal positioning noise of less than 0.6 nm three sigma. The vertical positioning noise is less than 2.2 nm three sigma. The stage utilizes four levitation linear motors to suspend and servo the moving element (platen) throughout its 25 mm × 25 mm × 0.1 mm range of travel. Position feedback is provided by three plane mirror interferometers and three capacitance probes. The suspended platen (12 kg mass) is floated in oil to enhance the stage’s disturbance rejection and to reduce power dissipation in the actuators. The stage has been designed to achieve a positioning accuracy of 10 nm and is used to position samples beneath a scanned probe microscope. The ultimate purpose of this measuring machine is to provide a means of measuring submicron-scale features with nanometer-scale accuracy. The technology can easily be scaled to larger travels, with accuracy limited primarily by the wavelength instability of the HeNe light source. This article gives an overview of the LORS project, emphasizing the system error terms, tolerancing, and experimental results.     

利用测星实现经纬仪外场静态精度检测

介绍在电影经纬仪上实现的通过解算星体理论值，实时引导经纬仪测星捕星解算经纬仪系统误差、随机误差、总误差的方法