Precision stage using a non-contact planar actuator based on magnetic suspension technology

The precision stage using a novel contact-free planar actuator based on magnetic forces, magnetized force and Lorentz force, is suggested. In the promising magnetic structure, a mover is levitated by magnetized force between iron-core electromagnets attached under the upper-side of a stator and ferromagnetic plates belonging to the mover. And the mover is driven by Lorentz force that acts on permanent magnets with an identical polarity put under magnetic field by air-core coils. Namely, the mover is driven directly without any transmission mechanism, and does not need any auxiliary driver for its posture calibration. Then it is estimated that the proposed operating principle is very suitable for work requiring high accuracy and cleanness, or general-purpose nano-stage. In this paper, we discuss a driving principle of the planar system including the magnetic force generation mechanism, a framework for the force model, governing characteristics of the levitated plate, and a planar motion control of the constructed prototype. And experimental results are given to verify the derived theoretical model and the feasibility of the system.     

Tracking control of a piezoceramic actuator with hysteresis compensation using inverse Preisach model

This paper presents the classical Preisach hysteresis modeling and tracking control of a curved pre-stressed piezoceramic patch actuator system with severe hysteresis. The actuator is also flexible with very small inherent damping. It has potential applications in active antennas. A series of tests are conducted to study the hysteresis properties of the piezoceramic actuator system. The numerical expressions of the classical Preisach model for different input variations are presented. The classical Preisach model is applied to simulate the static hysteresis behavior of the system. Higher order hysteresis reversal curves predicted by the classical Preisach model are verified experimentally. The good agreement found between the measured and predicted curves showed that the classical Preisach model is an effective mean for modeling the hysteresis of the piezoceramic actuator system. Subsequently, the inverse classical Preisach model is established and applied to cancel the hysteresis the piezoceramic actuator system for the real-time microposition tracking control. In order to improve the control accuracy and to increase damping of the actuator system, a cascaded PD/lead-lag feedback controller is designed with consideration of the dynamics of the actuator. In the experiments, two cases are considered, control with major loop hysteresis compensation, and control with minor loop hysteresis compensation. Experimental results show that RMS tracking errors are reduced by 50% to 70% if the hysteresis compensation is added in the feedforward path in both cases. Therefore, hysteresis compensation with the feedback controller greatly improves the tracking control accuracy of the piezoceramic actuator.     

Precision tracking control of a biaxial piezo stage using repetitive control and double-feedforward compensation

This article presents precision tracking control of an XY piezo stage using repetitive control and double-feedforward compensation. The XY piezo stage is composed of two piezoelectric actuators within a leaf spring mechanism. The study applies two feedback controllers, a Proportional-Integral-Derivative controller and a repetitive controller, to achieve precision trajectory tracking and evaluate performance against benchmarks. Moreover, the investigation applies a double-feedforward compensation approach that integrates a Zero-Phase-Error-Tracking-Controller and an adaptive plant inversion compensator adapted by a Least-Mean-Square algorithm, based on an inverse Prandtl-Ishlinskii model, to improve tracking control performance further. Performance analysis and comparison of the experimental results demonstrate that the proposed control structure improves dynamic tracking accuracy of the XY piezo stage.     

A high-efficiency magnetic suspension actuator with reluctance-balanced permanent magnet biasing and flux-based control

To reduce power consumption of active magnetic bearings (AMBs), permanent magnets (PMs) may be employed to generate a bias flux through the magnetic circuits connecting the actuators with the rotor. In this way, control algorithms based on zero-current operating points and linearized models may be used. This paper describes a new modular design of PM-biased AMB actuator involving a balanced-reluctance topology where the bias flux is set by an auxiliary air gap within the magnetic circuit. A theoretical model and design methodology for achieving a specified range of actuation forces are also defined. Each actuator unit within an AMB suspension system may by positioned freely and operated independently because, unlike many previous PM-biased designs, there is no flux linkage between actuators. To improve the robustness of the actuator control to uncertainty in material properties and air gap sizes, a feedback control scheme is proposed based on inductive sensing of the mean flux density at the actuator pole faces. Testing of the actuator with a current-cancelling flux-based control scheme shows that stable suspension with very low power consumption can be achieved over a range of operating conditions involving both static loading and unbalance excitation.     

Trajectory control of an electro hydraulic actuator using an iterative backstepping control scheme

This paper introduces a new control algorithm for the trajectory control of an electrohydraulic actuator (EHA). The key feature of this paper is the combination of a modified backstepping control with an iterative learning mechanism to perform adaptive tracking control tasks for a symmetrical pump-controlled EHA. Firstly, a mathematical model of the EHA is developed and a strictly feedback form state space is obtained. Next, the control signal is formed based on an iterative learning scheme with a backstepping modifier. Then, stability analyses are also carried out to ensure the convergence of the closed loop system. Finally, four experimental cases of studies are done to evaluate the proposed control method.     

采用压电陶瓷驱动器的高频像移补偿系统

针对成像光谱仪提出了基于压电陶瓷(PZT)驱动器的高频像移补偿技术以提高其成像质量.结合成像系统,分析了像移补偿系统需求,给出了该系统的控制策略和设计方案.针对PZT驱动器大容性负载给出了驱动器的设计方法,能够实现系统所需的高频大信号电压驱动;采用基于AD698集成芯片的信号调理电路和线性差分变压式传感器(LVDT)获...     

Affine motion compensation using a content-based mesh

A content-based approach to the design of a triangular mesh is presented, and its application to affine motion compensation is investigated. An image is first segmented into moving objects, which are then approximated with polygons. Then, a triangular mesh is generated within each polygon, thus ensuring that no triangle straddles multiple regions. Translation and affine motion parameters are determined for each triangle, using bidirectional motion estimation. Results for three test sequences demonstrate the advantages offered by the proposed mesh design method, and by the use of affine motion compensation.     

Multiconstraint Wiener-based motion compensation using waveletpyramids

We have investigated an original motion estimation method that exploits several frequency subbands of wavelet pyramids using a multigrid-multiconstraint strategy. A recursive and iterative solution based on the Wiener approach allows to take into account the reconstruction quality criterion that is crucial to image coding. Experiments show its performances in terms of compression ratio, reconstruction quality, and reduction of implementation complexity compared to a monoresolution case.     

Fuzzy control of nonlinear electromagnetic suspension systems

This paper presents a T–S model-based fuzzy controller design approach for electromagnetic suspension systems. The T–S fuzzy model is firstly applied to represent the nonlinear electromagnetic suspension systems. Then, based on the obtained T–S fuzzy model, a fuzzy state feedback controller is used to ensure the required mixed ℓ₂–ℓ_∞ performance of original electromagnetic suspension system to be achieved. This controller is designed in a nonparallel-distributed compensation scheme. And sufficient conditions for the existence of such a controller are derived in terms of linear matrix inequalities. Finally, numerical simulation on an electromagnetic suspension system is performed to validate the effectiveness of the proposed approach.     

Vibration control of linear robots using a piezoelectric actuator

This paper presents the results of vibration control strategy for high-speed linear robots using an auxiliary piezoelectric actuator. With acceleration reaching 3 g, rapid horizontal slewing motion inevitably excites the structural resonances of the robot and generates vertical vibration forces exceeding the tolerance of the end-effector. Instead of controlling the robot vibration from the main actuators (ac servomotors with limited bandwidth), a piezoelectric actuator is deployed to provide vibration suppression at the load in the z direction. This way the robot is treated as a disturbance generator while the piezoactuator is considered as the plant. A digital servocompensator is then designed and implemented to suppress these vibration modes. Typically, attenuation is achieved for the dominant mode with 30 dB and other modes with 15 dB. Suppression of vibration up to seven modes has been implemented satisfactorily.     

Closed-loop magnetic bearing and angular velocity control of a reaction sphere actuator

This article presents the first closed-loop magnetic bearing and angular velocity experimental results of a reaction sphere actuator for satellite attitude control. The proposed reaction sphere is a permanent magnet spherical actuator whose rotor is supported by magnetic bearing and can be torqued electronically about any desired axis. The spherical actuator is composed of an 8-pole permanent magnet spherical rotor and of a 20-pole stator with electromagnets. The electromechanical model of the reaction sphere is summarized together with procedures to estimate the rotor magnetic state, the back-EMF voltage, and the rotor angular velocity, which are all fundamental ingredients for controller design. Dynamic controllers are developed to levitate the rotor inside the stator (magnetic bearing) and to control the rotor angular velocity. The magnetic bearing is based on a state-space controller with reduced-order displacement velocity estimator whereas the angular velocity controller is a simple proportional controller with a dedicated angular velocity estimator. The developed control algorithms are experimentally validated using the developed laboratory prototype showing the ability of simultaneously levitating the rotor while rotating it about a given arbitrary axis.     

Motion-vector optimization of control grid interpolation andoverlapped block motion compensation using iterated dynamic programming

The application of advanced motion compensation techniques-control grid interpolation (CGI) and overlapped block motion compensation (OBMC)-to video coding systems provides significant performance advantages, terms of compression ratio and visual quality, over traditional block-matching motion compensation. However, the two-dimensional (2-D) interdependence among motion vectors introduced by these compensation frameworks makes the problem of finding rate-distortion optimal motion vectors, computationally prohibitive. Thus, iterative optimization techniques are often used to achieve good compensation performance. While most reported optimization algorithms adopt an approach that uses a block-matching algorithm to obtain an initial estimate and then successively optimize each motion vector, the over-relaxed motion-vector dependency relations often result in considerable performance degradation. In view of this problem, we present a new optimization scheme for dependent motion-vector optimization problems, one based on dynamic programming. Our approach efficiently decomposes 2-D dependency problems into a series of one-dimensional (1-D) dependency problems. We show that a reliable initial estimate of motion vectors can be obtained efficiently by only considering the dependency in the rate term. We also show that at the iterative optimization stage an effective logarithmic search strategy can be used with dynamic programming to reduce the necessary complexity involved in distortion computation. Compared to conventional iterative approaches, our experimental results demonstrate that our algorithm provides superior rate and distortion performance while maintaining reasonable complexity.     

Ultra precision motion control of a multiple degrees of freedommagnetic suspension stage

A general framework for ultra precision motion control of magnetic suspension actuation systems with large travel ranges in multiple degrees of freedom (DOF) is presented. It encompasses the development of nonlinear electromagnetic force model for 6-DOF actuation, and the design of the necessary control architecture for ultra precision motion control of magnetic suspension actuation systems. A 6-DOF magnetic suspension stage (MSS) was designed and fabricated to illustrate the developed framework. The MSS consists of multiple electromagnets that are located around the flotor and are utilized to suspend and modulate its position and orientation. The control architecture takes the six control parameters provided by a laser measuring system and intends to control the 6-DOF motion by regulating the current in the electromagnets. The developed robust nonlinear control architecture consists of three components: 1) feedback linearization; 2) force distribution; and 3) H_∞ robust controllers for each DOF of motion. Several experiments are designed to illustrate the desired characteristics of the developed system     

Improving time-domain measurements with a network analyzer using arobust rational interpolation technique

A method to efficiently and accurately compute a time-domain waveform from a network-analyzer frequency-domain measurement is presented in this paper. The method is based on a robust interpolation technique to construct a pole-residue representation of the response of the device-under-test. First, the rational function is expressed in terms of Chebyshev polynomials, instead of the usual power series, to accurately determine the poles of the network over a wide frequency range. The properties of a passive system are then utilized to efficiently calculate the residues. The resulting pole-residue model is analytically transformed to obtain the time-domain response in any time window, beyond the limitations of the discrete Fourier transform (DFT) technique. Unlike the DFT technique, the method does not require a large number of equally spaced harmonically related frequency points. The parametric model can also be used to economically store large measurement data. The proposed procedure is computationally inexpensive and less sensitive to numerical instability. To illustrate the validity of the method, examples of frequency- and time-domain measurements of a Beatty structure and simulation data of a low-pass Butterworth filter are given     

Multi-objective control for uncertain nonlinear active suspension systems

Performance requirements for vehicle active suspensions include: (a) ride comfort, which means to isolate the body as far as possible from road-induced shocks and vibrations to provide comfort for passengers; (b) road holding, which requires to suppress the hop of the wheels for the uninterrupted contact between wheels and road; and (c) suspension movement limitation, which is restricted by the mechanical structure. In view of such situations, plus the parametric uncertainties, this paper suggests a constrained adaptive backstepping control scheme for active suspensions to achieve the multi-objective control, such that the resulting closed-loop systems can improve ride comfort and at the same time satisfy the performance constraints in the presence of parametric uncertainties. Compared with the classic Quadratic Lyapunov Function (QLF), the barrier Lyapunov function employed in this paper can achieve a less conservatism in controller design. Finally, a design example is shown to illustrate the effectiveness of the proposed control law, where different initial state values are considered in order to verify the proposed approach in detail.     

Linearization of a current-driven reluctance actuator with hysteresis compensation

This paper investigates the influence of hysteresis present in the ferromagnetic core of a variable reluctance actuators on the force reproducibility. To reduce this influence and to boost reproducibility, a hysteretic inverse actuator model is derived and used to linearize a current-driven reluctance actuator. Furthermore, an identification procedure for identifying the parameters of the hysteresis model and the remaining actuator non-linearities is presented. Two actuators are experimentally tested with the proposed compensator and a linearization error smaller than 0.05% of the maximum force is achieved, which is an order of magnitude improvement over single-valued inverse compensators. A comparably small error is obtained for non-trivial, non-periodic inputs when higher order reversal curves of the actuator hysteresis have to be reproduced as well. The simple structure of the compensator allows a fast implementation in digital controllers.     

HOSIDF-based feedforward friction compensation in low-velocity motion control systems

The paper describes an application of a recently introduced methodology for modeling of a class of nonlinear systems — Higher-Order Sinusoidal Input Describing Function technique (HOSIDF) — to a motion control platform for which a precisely controlled motion at low velocity is required. One of the key challenges for these systems is to compensate for the friction, which is particularly difficult to model at low velocities. The frequency-domain HOSIDF modeling framework is used to assist in designing a feedforward compensator. Experiments with a laboratory benchmark system (gimballed camera platform) prove the technique useful.     

基于惯导系统的机载SAR运动补偿精度分析

该文分析了典型飞机惯性导航系统(INS)的误差特性及其对机载合成孔径雷达(SAR)运动补偿精度和高分辨率成像的影响。分析结果表明INS定位漂移误差是低频误差,并随时间呈级数增加。初始阶段INS漂移误差较小,与杂波锁定和自聚焦方法相结合,可以实现机载SAR高分辨率成像。     

Accurate position control of a pneumatic actuator using on/offsolenoid valves

The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications is described. A novel pulse width modulation (PWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. The open-loop characteristic is shown both theoretically and experimentally to be near symmetrical. A comparison of the open- and closed-loop responses of standard PWM techniques and that of the novel PWM technique shows that there has been a significant improvement in the control. A linear process model is obtained from experimental data using system identification. A proportional integral derivative controller with added friction compensation and position feedforward has been successfully implemented. A worst case steady-state accuracy of 0.21 mm was achieved with a rise time of 180 ms for step inputs from 0.11 to 64 mm. Following errors to 64-mm S-curve profiles were less than 2.0 mm. The controller is robust to a sixfold increase in the system mass. The actuator's overall performance is comparable to that achieved by other researchers using servo valves