Variable Structure Model-following Control Research Articles

Variable Structure Control on Active Suspension of 4 DOF Vehicle Model

in this paper, the theory of a variable structure model following control (VSMFC) is employed to the design of the controller for an active suspensions of 4-degree-of- freedom (4-DOF) automobile model. The sliding mode equation is derived by applying VSMFC theory and the parameters of the switching function are obtained by using the method of pole assignment; a hierarchical algorithm with control variables started in sequence is applied to solve the active force; a method of exponential approach law is used to improve the dynamic performance of the controller. The efficacy of the controller is verified by simulation carried out with the help of Matlab/ Simulink. The results show that the active suspension controller based on VSMFC theory is superior in both robustness and performance.

Fault detection and accommodation via neural network and variable structure control

This paper proposes a novel idea that classifies faults into two different kinds: serious faults and small faults, and treats them with different strategies respectively. A kind of artificial neural network (ANN) is proposed for detecting serious faults, and variable structure (VS) model-following control is constructed for accommodating small faults. The proposed framework takes both advantages of qualitative way and quantitative way of fault detection and accommodation. Moreover, the uncertainty case is investigated and the VS controller is modified. Simulation results of a remotely piloted aircraft with control actuator failures illustrate the performance of the developed algorithm.

Globoidal cam indexing servo drive control by IVSMFC with load torque estimator

This paper introduces an integral variable-structure model-following control (IVSMFC) incorporated with a load torque estimator based on variable-structure technique for a globoidal cam indexing system. IVSMFC features excellent robustness and performance properties under certain disturbances and parameter variations. However, heavy time-varying load may influence expected performance. In a cam system, when it is in motion, the load produced by inertia forces deflects the driving motor speed and, as a result, degrades the indexing precision. To fulfill the constant driving speed assumption, a load torque estimator is employed and fed forward to compensate the load torque variations. A digital-signal-processor-based globoidal cam indexing servo drive is presented and the experimental results show the effectiveness of the proposed scheme.

A toggle mechanism servo system with variable-structure model-following control

A toggle mechanism, which is driven by a permanent-magnet synchronous servo motor, with variable-structure model-following control (VSMFC) is proposed in this study. The rod and crank of the toggle mechanism are assumed to be rigid. The Hamilton principle and L agrange multiplier methods are applied to formulate the equation of motion. Based on the principles of the adaptive model-following control and the variable-structure control, a VSMFC system is developed to control the position of a slider of the toggle mechanism servo system. Numerical and experimental results show that the dynamic behaviour of the proposed controller-motor-mechanism system is robust to parametric variations and external disturbances.

Variable structure model following control for industrial robots

A variable structure model following control (VSMFC) strategy for the control of most types of industrial robots (according to a classification ofCoiffet 1983) has been presented. For 99% of the robots given in the classification of Coiffet (1983), the dynamics of each link can be represented by a simple model with the nonlinearities and coupling dynamics decoupled from the linear part (Stoten 1985). This facilitates the designer to have a modified VSMFC law, which will maintain sliding mode motion of the error and its derivative, referred to as the representative point (RP), on a user chosen switching line and to drive the RP to the origin of the error plane (error is defined as the difference between the states of the reference model and those of the plant). When in sliding mode the system remains insensitive to parameter variations and disturbances

A recurrent neural network-based adaptive variable structure model-following control of robotic manipulators

A novel scheme for integrating a neural network approach with an adaptive implementation of variable structure control for multijointed robotic manipulators in complex task executions is presented. The control strategy is developed within the general framework of nonlinear model-following control and attempts to minimize the total regulation time while ensuring a specified percentage of time on the sliding manifolds in order to exploit the disturbance attenuation features present during the sliding motions. These objectives are realized by tailoring an adaptation process that appropriately adjusts the controller gains to keep the motion on the sliding manifolds and also progressively updates the sliding manifold parameters. Rapid execution of the adaptation process is facilitated by a multilayer recurrent neural network. The resulting control scheme is decentralized, and permits design of independent joint controls. A quantitative performance evaluation of the neural network-based adaptive variable structure controller is given in several task scenarios, namely regulation, trajectory tracking and model-following.

Theoretical and experimental study of PI control, adaptive control and variable structure control for converted traditional milling machines

In this paper, the control plant is a traditional lead screw with a hand wheel-actuated milling machine that has been converted to a d.c. servo-motor control type. This old-fashioned machininingi table is a non-linear, time-varying system due to the effects of obvious backlash and irregular Coulomb friction between sliding surfaces. Three different control methods are employed for this plant to investigate the operating performance. The theoretical derivations of these control methods are described briefly. Since the control parameters have significant change, the traditional PI with relay control has to adjust the suitable gain values for each case. It is not a convenient application. The variable structure model-following control methods needs to select appropriate logical gain values and a suitable relay offset. Additionally, these two approaches cannot guarantee a stable closed-loop system. The third method for this non-linear system is a stable convergent one-step-ahead adaptive control algorithm. The experimental results show that these control methods give reasonable performance of transient response, tracking and robustness under the influence of the delay of the motor driver and 1 mm backlash of each axis. For a low speed trajectory tracking control ( V s < 3 mm/s), the traditional PI with relay control and the variable structure model-following control give better performance.

An adaptive variable structure model following control design for robot manipulators

An adaptive variable structure model-following control (AVSMFC) design is proposed for trajectory tracking in a nonlinear robot system which ensures the stability of the intersection of the surfaces without necessarily stabilizing each individual one. The approach avoids the difficulties linked to the strict positive realness requirement in traditional AMFC by taking advantage of the inherent positive definiteness of the manipulator's inertia matrix, and is easily extendible to a higher number of links. The controller does not require any knowledge of a nonlinear robotic system and does not necessarily need the occurrence of a sliding mode at each individually stable discontinuity surface. It thus greatly reduces the complexity of design. In the closed loop, the joint angles asymptotically converge to the reference trajectory with a prescribed transient response. Chattering is eliminated by restricting the state of the system to slide within a boundary layer rather than along the intersection of the surfaces.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A variable structure model following control design for robotics applications

A variable structure model following control (VSMFC) design method is proposed for robotics applications. The method allows the designer to model the nonlinear dynamic interactions among the different mechanical components of the robot system even when an adaptive control solution is called for to satisfy stringent performance requirements. A VSMFC design for a planar two-link robot arm is considered as an example.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of variable structure model-following control systems

A new design concept for adaptive model-following control systems capable of shaping the error transient responses is developed using the theory of variable structure systems and sliding mode. It is shown that the resulting model-following control system exhibits adaptive properties inherent in adaptive model-following systems designed by existing methods. An aircraft control problem which has been approached using various model-following techniques is considered and a performance comparison with the present design is made.