基于滑模控制的航空气动伺服控制系统

本文提出了一种滑模控制方法并应用在无杆汽缸气动执行机构的位置控制中。由于受空气可压缩性、摩擦力以及随时间变化的系统参数的非线性影响,气动系统的精确数学模型很难获取。本文选用了一个三阶气动系统的动态模型,并且不考虑比例控制阀的动态特性。同时为了避免控制信号引发高频振荡,在建模过程中用平稳光滑的饱和度函数代替sgn(.)函数。仿真和实验结果表明,本文提出的滑模控制策略能够保证位置控制在合理的精度范围内并取得了良好的控制效果,尤其适用于比例伺服阀控制的无杆汽缸电气控制系统。     

Tracking control of a piezo‐actuated stage based on a frictional model

The tracking control accuracy of a piezoelectric actuator (PEA) is limited due to the actuator's inherent hysteretic nonlinearity. Direct drive of PEA on a positioning stage with friction force will cause control problems. An approximated dynamic model of PEA with consideration of friction force is novel synthesized for control. This model is based on a second‐order transfer function with two parameterization terms. The first time delay term consists of the hysteresis of piezo effect combined with frictional force lag with varying velocity. The second term is comprised of both presliding and sliding regimes. The H‐infinite tracking controller is designed to compensate for the structural uncertainty associated with time delay and the unstructured frictional force in the PEA stage. Iterative Learning Control is implemented to reduce the unmodeled repetitive error by a factor of 20. Numerical simulations and experimental tests consolidate the root mean square (RMS), positioning error close to the hardware reproducibility and accuracy level. Experimental results show the controlled stage can be potentially used for precise positioning. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Precision Synchronization Motion Trajectory Tracking Control of Multiple Pneumatic Cylinders

This paper deals with the synchronized motion trajectory tracking control problem of multiple pneumatic cylinders. An adaptive robust synchronization controller is developed by incorporating the cross‐coupling technology into the integrated direct/indirect adaptive robust control (DIARC) architecture. The position synchronization error and the trajectory tracking error of each cylinder are combined to construct the so‐called coupled position error. The proposed adaptive robust synchronization controller is designed with the feedback of this coupled position error and is composed of two parts: an on‐line parameter estimation algorithm and a robust control law. The former is employed to obtain accurate estimates of model parameters for reducing the extent of parametric uncertainties, while the latter is utilized to attenuate the effects of parameter estimation errors, unmodelled dynamics, and external disturbances. Theoretically, both the position synchronization and trajectory tracking errors will achieve asymptotic convergence simultaneously. Moreover, the effectiveness of the proposed controller is verified by the extensive experimental results performed on a two‐cylinder pneumatic system.     

A dual step precision multi-DOF stage for maskless digital lithography

A design and implementation of a dual step position align stage for digital exposure process and analytical analysis of the presented hardware architecture are introduced in this paper. A mobile plate of the proposed dual step position align stage is connected to its base with four independent dual degree of freedom (DOF) decoupled actuator assembly. The dual DOF decoupled actuator assembly is driven with a brushless DC motor, two pneumatic locking devices, and four kinematic mechanisms. Thanks to the dual degree of freedom independent actuation unit combined with pneumatic locking device, the proposed mechanism provides fully decoupled vertical and horizontal motions. The design specification for the operational accuracy and the repeatability are determined by the primitive digital pattern generation scheme based upon a point array method. A kinematic formulation using a geometric approach is provided for the proposed dual step position align mechanism. In addition a numerical simulation for the mechanism is also carried out and a series of system testing is followed.     

Design and experimental study of a dynamical adaptive backstepping–sliding mode control scheme for position tracking and regulating of a low‐cost pneumatic cylinder

A dynamical adaptive backstepping–sliding mode control scheme is designed and implemented for the first time, to track and regulate the position of a low‐cost pneumatically driven single‐rod, double‐acting cylinder. The mass flow rate of compressed air into and out of the cylinder is regulated by a 5/3‐way proportional directional control valve. The derivation of the controller, utilizing a design procedure that guarantees stability of the control system, is presented first. Next, experimental evaluation of the controller is conducted with respect to performance and robustness to parametric uncertainties. Experiments employ a sinusoidal reference trajectory with tracking frequencies of 0.05, 0.1, and 0.2 Hz; a multiple‐step polynomial reference trajectory having step sizes of 0.0125, 0.025, 0.05, and 0.1 m; and three external loads of 4.4, 9, and 16 kg operating in two modes (motion assisting and resisting). From over 70 experiments involving various operating conditions, average root mean square of tracking error of 1.73 mm and steady‐state error of 0.71 mm are achieved for the position tracking and regulating, respectively. As compared with the classical sliding mode control scheme alone, the new controller outperforms by more than twofold. The adaptive LuGre‐based friction observer applied in this control scheme significantly assists in compensating the adverse effect of friction with the average of 55% less tracking error. Copyright © 2015 John Wiley & Sons, Ltd.     

基于单UWB融合里程计的多机器人相对定位方法

针对卫星信号受阻,无预设基础设施(定位基站、地标等)环境下多机器人间的相对定位问题,提出了一种基于单个超宽带(ultra-wideband, UWB)融合里程计的多机器人相对定位方法。该方法利用滑动窗口截取历史时刻的多组机器人间测距信息与里程计预测的机器人位姿,构建非线性最小二乘问题,实现机器人间的相对位姿估计;利用扩展卡尔曼滤波算法估计里程计协方差,并将其以加权的方式运用于非线性优化,抑制滑动窗口内里程计累积误差对定位结果的影响;最后,利用图优化算法融合里程计与非线性优化获得的相对位姿作进一步优化,抑制UWB测量误差影响,以获得稳定的相对定位结果。实验结果表明,在6 m×12 m的真实测试环境中,所提方法能够获得0.32 m的相对位置精度和4.16°的相对角度精度,相比于现有多机器人相对定位方案,该方法具有高精度、低成本、部署简单以及定位稳定的优点。     

Design,kinematic modeling and sliding mode control with sliding mode observer of a novel 3-PRR compliant mechanism

Compliant mechanisms have great advantages to be used as micropositioning stages for high-precision applications but they are very sensitive to manufacturing tolerances and assembling errors. In this work, a novel compliant stage having 3-PRR kinematic structure and actuated by piezoelectric actuators is introduced. A kinematic modeling based on compliance of the flexible elements and finite element analysis based model have been extracted. It is found out that the experimental results are not compatible with the theoretical results due to the manufacturing, actuator assembly errors. The position control of the mechanism has been achieved using sliding mode control which is a great method for unpredictable varying parameters in the system. Sliding mode observer has also been used for the hysteresis and nonlinearities of the piezoelectric actuators. Experimental models for each actuation axis have been used as the nominal models for the sliding mode observer. In order to see the advantage of the control method simple PID control has also been implemented. It is seen that sliding mode control with sliding mode observer using experimental models reduces the position tracking errors to the range of the accuracy of our available measurement.     

基于PLC的落锤标定装置自动控制系统

针对传统手动的落锤标定装置操作复杂、精度低和安全性不高的问题,设计了自动控制系统.采用PLC-步进电机-光栅尺闭环控制的方法,实现落高精确定位.设计了以无杆汽缸为执行机构的气动系统,控制重锤提升、下降和反弹重锤的防二次撞击.系统以西门子PLC和触摸屏作为控制核心与人机交互工具,编制了专用的控制和组态软件,实现了实时显示重锤落高、下落速度与落高精确定位及自动试验等功能,满足操作简便、精度高、安全的试验要求.     

基于路径表的室内地图匹配方法

地图匹配算法能有效地提升定位精度,是定位技术不可或缺的一部分。为提高路径匹配正确率,并适应室内定位环境,提出一种基于路径表的室内地图匹配方法,在传统地图匹配方法的基础上建立一个路径表存放候选路径的信息,每次路径匹配时,都从表中选取具有最优权重值的路径进行匹配。在匹配过程中多处设置查错和纠错机制,即使在出现匹配错误的情况下,也能及时从路径表中重新选取正确路径。较强的查错和纠错功能使其特别适合用于室内复杂环境下的地图匹配。实验结果表明,与传统的地图匹配方法比较,能有效地提升匹配精确度。     

Accurate position control of servo pneumatic actuator systems: an application to food packaging

An accurate position control strategy for servo pneumatic actuator systems is proposed in the paper. There are two key algorithms in the control strategy: time-delay minimisation and target position compensation. This control strategy has been applied in combination with a modified PID controller to a pusher mechanism in the packaging of confectionery products. Both the positioning and the time accuracy required by the production task are achieved using such a control strategy.     

ULTRA‐FINE TRACKING CONTROL ON PIEZOELECTRIC ACTUATED MOTION STAGE USING PIEZOELECTRIC HYSTERETIC MODEL

The tracking control accuracy of the piezoelectric actuator (PEA) is limited due to its inherent hysteresis nonlinearity. A new piezoelectric‐actuator model is synthesized based on two first‐order transfer systems in parallel with two tuned parameters determined from one experiment. Two open‐loop tracking controllers are implemented with the proposed model to compensate the hysteresis of linear positioning. Numerical simulations and experimental tests on the tracking of sinusoidal and triangular waveforms with signal frequencies ranging from 1Hz to 30 Hz are revisited and compared with the conventional Bouc‐Wen and Duhem models. Experimental results reveal that the RMS tracking error can be reduced to less than 2% of the maximum traveling distance without any feedback sensor. When a piezoelectric actuated on a two Degree‐Of‐Freedom (DOF) monolithic motion stage was employed, the RMS tracking error was 50 nm within the measured sensor accuracy.     

Distributed structural dynamics control of flexible manipulators—II. Distributed sensor and active electromechanical actuator

Structural oscillation of lightweight robot arms can degrade the accuracy and precision of a robot's high-demanding performance. This paper is the second of two on vibration control of elastic or flexible robot structure. The proposed electromechanical device has both sensing and control capabilities. Effects of active damping treatment on elastic robot arms are discussed. The proposed active distributed sensor and controller is a layer, or multi-layer, of piezoelectric polymer directly attached to the flexible component which is required to be monitored and controlled. By utilizing direct and converse piezoelectric characteristics, respectively, the integrated piezeoelectric sensor/controller can monitor the vibration due to induced mechanical stress/strain in the polymer; and it can also actively and directly constrain the undesirable vibration of flexible component by injecting high voltages. Experimental results and finite element simulations of the electromechanical sensor/actuator are presented and discussed.     

Sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner

This paper presents the sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner (Z, θ_x, θ_y). This nanopositioner is actuated by piezoelectric actuators. Capacitive gap sensors are used for position feedback. In order to design the feedback controller, the open‐loop characteristics of this nanopositioner are investigated. Based on the results of the investigation, each pair of piezoelectric actuators and corresponding gap sensors is treated as an independent system and modeled as a first‐order linear model coupled with hysteresis. When the model is identified and the hysteresis nonlinearity is linearized, a linear system model with uncertainty is used to design the controller. When designing the controller, the sliding‐mode disturbance (uncertainty) estimation and compensation scheme is used. The structure of the proposed controller is similar to that of a proportional integral derivative controller. Thus, it can be easily implemented. Experimental results show that 3‐nm tracking resolution can be obtained. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

MODELING OF A PIEZO‐ACTUATED POSITIONING STAGE BASED ON A HYSTERESIS OBSERVER

Piezo‐actuated positioning stages contain two parts: a Piezo Electric Actuator (PEA) and a positioning mechanism. The tracking control accuracy of the piezo‐actuated positioning stage is limited due to the hysteretic nonlinearity of the PEA and the friction behavior of the positioning mechanism. This loss in precision restricts the use of the piezo‐actuated stage in an ultra‐high‐precision optical system. This paper presents an inversion‐based approach to reduce the nonlinearity of the PEA by using a proposed hysteresis observer. To reduce the degredation in precision due to the friction behavior of the positioning mechanism, a PI feedback controller with a feed‐forward controller based on a hysteresis observer is proposed to solve tracking problems with modelling uncertainties and external disturbances.     

Image‐guided robotic navigation system for neurosurgery

This paper presents an image‐guided robotic navigation system for neurosurgery, which can be applied to the electro‐stimulation treatment of Parkinson's leisure, the biopsy of deep tumors, and haematoma evacuation. The system integrates a computer containing CT images for surgical planning, a magnetic tracking device for measuring the coordinates of the markers and surgical instruments, and a robot manipulator for guiding surgical instruments to the preplanned position and orientation. The computer display of brain anatomy offers a convenient tool for surgeons to diagnose brain diseases and to plan safe surgical paths, while the tracking device guides the robot manipulator to automatically move surgical instruments to the preplanned position and orientation. An experiment of using a skull model for simulating a robotic biopsy of brain tumor has been done to verify the performance of the robotic navigation system. The results show that the positioning accuracy of the robot relative to the tracker frame is only related to the positioning resolution of the robot manipulator and the positioning accuracy of the tracking device. In other words, the positioning accuracy of the robot manipulator does not affect the final positioning accuracy of the surgical instruments. Therefore, using a robot manipulator for precise surgical navigation is feasible and reliable. © 2000 John Wiley & Sons, Inc.     

High-fidelity sliding mode control of a pneumatic haptic teleoperation system

For a pneumatic teleoperation system with on/off solenoid valves, sliding mode control laws for position and force ensuring low switching (open/close) activity of the valves are developed. Since each pneumatic actuator has two pneumatic chambers with a total of four on/off valves, 16 possible combinations (‘operating modes’) for the valves’ on/off positions exist, but only seven of which are both functional and unique. While previous work has focused on three-mode sliding-based position control of one pneumatic actuator, this paper develops the seven-mode sliding-based bilateral control of a teleoperation system comprising a pair of pneumatic actuators. The proposed bilateral sliding control schemes are experimentally validated on a pair of actuators utilizing position-position and force-position teleoperation architectures. The results demonstrate that leveraging the additional modes of operation leads to more efficient and smoother control of the pneumatic teleoperation system. It was found that viscous friction forces were crippling haptic feedback in the position-position architecture. Through the use of force sensors, the force-position architecture was able to compensate for the heavy viscous friction forces.     

By-pass valve control to improve energy efficiency of pneumatic drive system

In order to improve the performance and energy efficiency of the pneumatic drive, the by-pass valve control scheme is designed and studied. For pneumatic positioning application, in the constant speed phase, the inlet and outlet chambers will be connected via by-pass valve to reduce the overshoot and allow some exhaust compressed air to be reused. Therefore, compared with the traditional control of the motion of the asymmetric cylinder, a 12–28% saving in energy use can be acquired and meanwhile the position accuracy is maintained. Preliminary results from the simulation and experiment studies will be reported.     

无杆气缸驱动的柔性机械臂振动控制

提出了一种无杆气缸驱动的柔性机械臂定位和振动抑制系统,采用脉冲码调制(pulse code modulation,PCM)方法实现.首先,推导了气动驱动柔性臂的系统模型,对采用的复合定位和振动抑制控制算法进行理论分析.其次,气缸行程长、气体具有压缩性以及气动驱动存在非线性和阀门开关有时延等因素会引起控制作用的滞后问题,容易激发高阶模态的极限环振荡,导致观测和控制溢出,这将影响控制系统的稳定性.为了克服上述问题,在控制算法中引入时延补偿、低通滤波法.最后,进行气动驱动柔性臂同时定位和振动抑制的试验研究.试验结果表明,采用的气动驱动控制方法可以有效地抑制柔性臂的低频模态振动,并同时实现定位.     

An intelligent fuzzy sliding mode control system with application on precision table positioning

In this paper, an intelligent fuzzy sliding mode control system, which cooperates with a new learning approach called modulus genetic algorithm, is proposed. Furthermore, it is applied to a high precision table positioning system for verifying its practicability. Fuzzy sliding mode controller (FSMC) is a special type of fuzzy controller with certain attractive advantages than the conventional fuzzy controller. The learning and stability issues of FSMC are discussed in the paper. Furthermore, to overcome the encoding/decoding procedure that leads to considerable numeric errors in conventional genetic algorithm, this paper proposes a new algorithm called modulus genetic algorithm (MGA). The MGA uses the modulus operation such that the encoding/decoding procedure is not necessary. It has the following advantages: (1) the evolution can be speeded up; (2) the numeric truncation error can be avoided; (3) the precision of solution can be increased. For verifying the practicability of the proposed approach, the MGA‐based FSMC is applied to design a position controller for a high precision table. The experimental results show the proposed approach can achieve submicro positioning precision. © 2001 John Wiley & Sons, Inc.