Robust nonlinear nominal-model following control to overcomedeadzone nonlinearities

A robust nonlinear nominal-model following control is proposed to overcome deadzone nonlinearities which are unavoidable in many physical systems due to the imperfections of system components. First, an ideal linear nominal model of the plant and a model controller are employed to generate an ideal reference output. Then, a nonlinear robust loop controller is added to force the actual output to follow the ideal reference output. The robust loop controller contains an ordinary proportional-integral-derivative controller combined with a deadband relay. The added deadband relay has the capability of reducing nonlinear effects of the plant. A systematic design methodology is established and it is linked to the conventional control system design. The proposed scheme is practically applied to the control of a DC motor position servo system containing a severe deadzone nonlinearity. Both simulation and experimental results have illustrated the effectiveness and robustness of the proposed technique     

Time optimal control for induction motor servo system

A time-optimal position control scheme based on Pontryagin's minimum principle is proposed for a current-source-inverter (CSI) fed induction motor system. The induction motor with field-oriented control is modeled with a fast time-optimal position control system of second order which has two modes of operation: the first bang-bang mode operates until the position is close to target, followed by second DC braking mode which gives asymptotic stability. In order to realize this aim, the time-optimal controller is added instead of the speed controller to the conventional field oriented control loop of the CSI-fed induction motor. The validity of the time-optimal control solution has been verified by an experimental test. Experimental results are in close agreement with a digital simulation     

A sliding mode torque and position controller for an antagonistic SMA actuator

This paper presents position and torque control of an antagonistic setup for a shape memory alloy (SMA) rotary actuator using a sliding mode controller that takes into account the nonlinear behavior of SMA. The control scheme and model are based on the complete physics model of the system. An accurate model of the actuator is presented and validated by means of an experimental prototype. A nonlinear state observer is also developed in order to estimate temperature and phase state variables that are difficult to measure online due to the small dimensions of the actuator. Experimental results are then presented for different set-point functions. Tracking performance, frequency response and disturbance rejection are evaluated and the advantages of the proposed controller are then discussed.     

Positive acceleration,velocity and position feedback based damping control approach for piezo-actuated nanopositioning stages

This paper proposes a new damping control approach with positive acceleration, velocity and position feedback (PAVPF) scheme for piezo-actuated nanopositioning stages to implement high-bandwidth operation. To achieve this objective, the intrinsic hysteresis nonlinearity of the piezoelectric actuator is firstly handled by a feedforward compensator with a modified Prandtl–Ishlinskii model. Afterwards, the PAVPF controller with the pole-placement method is implemented to suppress the lightly damped resonant mode of the hysteresis compensated system. With the PAVPF controller, the poles of the damped system in a third-model can be placed to arbitrary positions with an analytical method. Finally, for accurately tracking a predefined trajectory, a high-gain proportional-integral (PI) controller is designed, which could deal with the disturbance and the unmodeled dynamics. For verifying the proposed PAVPF-based control approach, comparative experiments with positive velocity and position feedback controller and with PI controller are conducted on a piezo-actuated nanopositioning stage. Experimental results demonstrate that the developed control approach with PAVPF controller is effective on damping control and improves the control bandwidth of the conventional PI controller from 111 Hz to 766 Hz, which leads to the significant increase of the tracking speed.     

Position control of ultrasonic motors using MRAC and dead-zonecompensation with fuzzy inference

The ultrasonic motor has a heavy nonlinearity, which varies with driving conditions and possesses variable dead-zone in the control input associated with applied load torque. The dead-zone is a problem as an accurate positioning actuator for industrial applications and it is important to eliminate the dead-zone in order to improve the control performance. This paper proposes a new position control scheme of ultrasonic motors to overcome dead-zone employing model reference adaptive control with fuzzy inference. The dead-zone is compensated by fuzzy inference, whereas model reference adaptive control performs accurate position control. Mathematical models are formulated and experimental results are given to validate the proposed position control scheme     

Nonlinear PID control to improve the control performance of 2 axes pneumatic artificial muscle manipulator using neural network

The application of a robot to rehabilitation has become a matter of great concern because of the requirement of functional recovery therapy of arm or limb. A novel pneumatic artificial muscle (PAM) actuator which has achieved increased popularity to provide the inherent safety and mobility assistance to humans performing tasks and another advantages such as high strength and power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source and so on. However, the complex nonlinear dynamics of the PAM manipulator makes it a challenging and appealing system for modeling and control design. The problems with the time variance, compliance, high hysteresis and nonlinearity of pneumatic systems have made it difficult to realize precise position control. In order to realize satisfactory control performance, the effect of nonlinear factors contained in the PAM manipulator must be considered.The purpose of this study is to improve the control performance of 2 axes PAM manipulator using a nonlinear PID controller. Superb mixture of conventional PID controller and the neural network, which has powerful capability of learning, adaptation and tackling nonlinearity, brings us a novel nonlinear PID controller using neural network. This proposed controller is appropriate for a kind of plants with nonlinearity uncertainties and disturbances. The experiments were carried out in practical 2 axes PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through the experiments, which suggests its superior performance and disturbance rejection.     

Nonlinear brake control for vehicle CW/CA systems

A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper. The control law has been designed for optimized safety and comfort. A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated. A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed. Both models were found to represent the actual system with good accuracy. Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller. The effects of brake control on CW/CA vehicle response has been investigated via simulations. The simulations were performed using a complete nonlinear vehicle model. The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort     

Throttle actuator control system for vehicle traction control

Accurate and quick positioning of the throttle valve in a gasoline engine is required to implement various systems such as traction control systems (TCS), cruise control systems and drive-by-wire systems. In this research, the throttle actuator system for TCS application was developed. Unlike other systems, this system consists of only one throttle body to obtain small volume and low manufacturing cost, and uses a DC servo motor for quick and accurate responses. In order to drive the DC motor, a PWM signal generator and PWM amplifier were built and interfaced to the motor and controller. This paper also presents the position control logic of the throttle actuator with the TDC (time delay control) scheme with a variable reference model. By varying the reference model based on the size of the step changes in the target throttle angle, the TDC scheme yields good transient response characteristics in that both overshoot prevention and a quick response time are achieved. Actual vehicle tests with this developed system incorporated with the TCS system show that it satisfies all the conditions required for the TCS operation.     

Design and implementation of a fault tolerant controller for EMS systems

Conventional EMS (electromagnetic suspension) systems are susceptible to instability problems, and could even break down upon failures of the air-gap sensor or the accelerometer. Therefore, in order to improve EMS performance, a fault tolerant controller and a fault detection and isolation (FDI) algorithm are presented in this work. The fault tolerant controller is an extended version of the linear fault tolerant controller designed for known actuator or sensor failures, and it adopts the LMI-based H_∞ control for a class of nonlinear systems. The fault detection algorithm employs fuzzy inference. The merits of the proposed control scheme have been verified by the experiments with a single-axis two-magnet suspension system subjected to failures of the actuator or the sensors.     

Inverse model-based real-time control for temperature uniformity ofRTCVD

A reduced-order model describing a rapid thermal chemical vapor deposition (RTCVD) process is utilized for real-time model based control for temperature uniformity across the wafer. Feedback is based on temperature measurements at selected points on the wafer surface. The feedback controller is designed using the internal model control (IMC) structure, especially modified to handle systems described by ordinary differential and algebraic equations. The IMC controller is obtained using optimal control theory on singular arcs extended for multi-input systems. Its performance is also compared with one based on the Hirschorn inverse of the model. The proposed scheme is tested with extensive simulations where the full-order model is used to emulate the process. Several cases of significant uncertainty, including model parameter errors, process disturbances, actuator errors, and measurement noise are used to test the robustness of the controller to real life situations. Both controllers succeed in achieving temperature uniformity well within the desirable bounds, even in cases where several sources of uncertainty are simultaneously present with measurement noise     

Interaction control of an industrial manipulator using LPV techniques

This paper presents the design and implementation of a hybrid force/motion control scheme on a six-degrees-of-freedom robotic manipulator employing a gain-scheduled linear parameter-varying (LPV) controller. A nonlinear dynamic model of the manipulator is obtained and the unknown parameters are estimated. The manipulator is decomposed into an inner and a wrist submodel, and a practical way is proposed to investigate the coupling between them. The motion control part of the hybrid controller which is the main focus of this paper is formed by a combination of an LPV controller and a model-based inverse dynamics controller for the inner submodel and the wrist joints, respectively. A quasi-LPV model with a reduced number of scheduling parameters is derived for the inner submodel, and a polytopic LPV gain-scheduled controller is synthesized in a two-degrees-of-freedom structure including feedback and feedforward parts, which is augmented by a friction compensation term. A PD controller with a feedforward path is designed to control the interaction force. The proposed hybrid force/motion scheme is implemented on the 6-DOF CRS A465 robotic manipulator to perform a writing task. Comparison of the results with those of a hybrid force/motion controller with a plain model-based inverse dynamics motion control and the same force control shows that the proposed controller improves the position tracking performance significantly.     

Modeling and control of a curved pneumatic muscle actuator for wearable elbow exoskeleton

A novel curved pneumatic muscle based rotary actuator for the wearable elbow exoskeleton with joint torque control is proposed. Compared to the general utilization of the pneumatic muscle actuator (PMA) in a rotary joint, this novel structure weakens coupling relationship between the output torque/force and contacting displacement of the PMA so that it can be easily utilized in the tele-robotics with torque/force-feedback or the exciting application in rehabilitation for a wide range. By referred to two physical models, namely beam model and membrane model, the mechanics properties of this mechanical structure is analyzed. In addition a hybrid fuzzy controller composed of bang–bang controller and fuzzy controller is employed for output torque control with high accuracy as well as fast response. In a series of experiments, the actuator exhibits both good static and dynamic performances that well validated the models and control strategy.     

Computed force and velocity control for spatial multi-DOF electro-hydraulic parallel manipulator

A novel dynamic trajectory tracking controller for spatial 6-DOF electro-hydraulic parallel manipulator considering system nonlinearity-computed force and velocity controller is proposed, with a view of improving the control performance with high computational efficiency of control algorithm. The dynamic model of electro-hydraulic parallel manipulator, both mechanical and hydraulic system, is described by using Kane and hydromechanics method. The requisite system states are estimated via forward kinematics based upon global Newton–Raphson with monotonic descent algorithms under the measured actuator position. The desired leg position and velocity required for the proposed controller are calculated by an analytical method corresponding to the desired generalized pose, and the desired driven force is computed with an effectively simplified inverse dynamics. Under feed-forward of the desired driven force and velocity, the computed force and velocity controller is developed with actual leg position as its feedback only, and the desired leg position, velocity and driven force as its input. The control performance of the proposed controller for multi-DOF parallel manipulator is evaluated in theory and experiment, especially for dynamic tracking performance. Experimental results show that the presented controller can greatly improve the dynamic trajectory tracking performance for high real time electro-hydraulic parallel manipulator.     

圆柱-球体三自由度超声电机模糊自适应控制

针对圆柱-球体三自由度超声电机难以建立精确数学模型的特点,设计了模糊自适应定位控制系统。该控制系统由模糊控制器和在线参数自调整环节构成,在线参数自调整环节使该系统的动态特性、稳态性能更好地兼顾,克服了固定量化因子控制性能不理想的缺点。应用该控制器,实现了电机精确定位控制。结果表明,参数自调整模糊自适应控制器的性能优于传统PID控制器及固定量化因子的模糊控制器,得到了满意的控制效果。     

Adaptive Dynamic Sliding Mode Control for Near Space Vehicles Under Actuator Faults

A novel adaptive dynamic sliding mode (ADSM) fault-tolerant control (FTC) methodology is developed for near space vehicle attitude control systems with actuator faults in this paper. The proposed ADSM approach combines dynamic sliding mode with adaptive control strategies that can make the systems stable and accurately track the desired signals in the presence of external disturbances, model parameter uncertainties, and even actuator faults. Firstly, the attitude dynamic model of X-33 and its faulty model are introduced, then the ADSM control and fault-tolerant control laws are designed for outer-loop and inner-loop, respectively. Finally, in comparison with one existing approach, the simulation results are provided to show the effectiveness of the proposed FTC scheme.     

拼接镜面望远镜位移促动器系统的自抗扰控制

针对拼接镜面望远镜主动光学控制技术的要求,设计了一种改进型自抗扰控制器以改善位移促动器系统的位置跟踪性能和提高抗扰动能力。首先,建立了拼接镜面位移促动器系统及扰动风载的数学模型;设计了改进型自抗扰控制器,并给出了控制器参数选择的方法。其次,对位移促动器控制系统进行了仿真分析,验证了控制器的可行性。最后,利用风载扰动模拟装置,在位移促动器系统中引入扰动,并对比改进型自抗扰控制器与线性自抗扰控制器以及PID控制器控制性能。实验结果表明,改进型自抗扰控制器系统阶跃跟踪的稳定时间为201 ms,稳态均方差为7.1 nm,无超调;风载干扰实验中,改进型ADRC的最大偏差值为38.8 nm,稳态均方差为7.6 nm,改进型ADRC的性能明显优于线性自抗扰控制器和PID控制器,对提高位移促动器系统的性能有较高的实用性。     

Modeling, control and experimental validation of a novel actuator based on shape memory alloys

The paper presents the development of a mechanical actuator using a shape memory alloy with a cooling system based on the thermoelectric effect (Seebeck–Peltier effect). Such a method has the advantage of reduced weight and requires a simpler control strategy as compared to other forced cooling systems. A complete mathematical model of the actuator was derived, and an experimental prototype was implemented. Several experiments are used to validate the model and to identify all parameters. A robust and nonlinear controller, based on sliding-mode theory, was derived and implemented. Experiments were used to evaluate the actuator closed-loop performance, stability, and robustness properties. The results showed that the proposed cooling system and controller are able to improve the dynamic response of the actuator.     

Control of ionic polymer metal composites

Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined through the unblocked maximum displacement and blocked force output. An open-loop position control and closed-loop position proportional-integral-derivative (PID) control are then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).     

A new set-point controller with bounded torques for robotmanipulators

In this paper, we propose a simple controller for set-point control of robot manipulators. The structure of this controller is composed by a saturated proportional-saturated derivative feedback plus gravity compensation. Such a control scheme has two practical features. First, for all desired joint positions, this controller delivers torques inside prescribed limits according to the actuator capability and second, the steady-state position errors owing to static friction can be arbitrarily reduced. In the case of absence of friction, we show global asymptotic stability of the closed-loop system. The performance of the proposed controller is illustrated via experiments on a two-degrees-of-freedom (2-DOF) direct-drive robot system     

Study and implementation of a simplified and robust positiondigital controller for a PM synchronous actuator

This paper presents a fully digital position control system for small power surface mounted PM synchronous actuators. The control algorithm relies on a simplified decoupling state feedback in order to obtain field orientation. There is no current measurement, and the current values needed to compute the control algorithm are predicted from a model. This makes it possible to use a fully digital position controller by using low cost 8 bit microprocessors with only a position sensor. Moreover, it is shown in this paper that it is preferable to use, in the decoupling state feedback, an estimated, instead of a measured, value of the current to ensure stability and to improve the robustness of the system regarding parameter uncertainties. Furthermore, as the actuator model is linearized by a decoupling state feedback, the robustness of the system has been further improved by using appropriate techniques evolved for linear systems to synthesize the position controller. The performance of the proposed control system is analyzed by a theoretical study and digital simulations. It has been implemented around two 8 bit MCS 8051 microcontrollers and tested on a 2 kW machine