Showing papers on "Variable structure control published in 1992"
TL;DR: In this article, the authors discuss the use of nonlinear dynamic inversion in the design of a flight control system for a Superman aircraft and compare it with a more conventional, gain-scheduled system and yield better performance in terms of lateral acceleration, sideslip, and control deflections.
Abstract: Nonlinear dynamic inversion affords the control system designer a straightforward means of deriving control laws for nonlinear systems. The control inputs are used to cancel unwanted terms in the equations of motion using negative feedback of these terms. In this paper, we discuss the use of nonlinear dynamic inversion in the design of a flight control system for a Supermaneuvera ble aircraft. First, the dynamics to be controlled are separated into fast and slow variables. The fast variables are the three angular rates and the slow variables are the angle of attack, sideslip angle, and bank angle. A dynamic inversion control law is designed for the fast variables using the aerodynamic control surfaces and thrust vectoring control as inputs. Next, dynamic inversion is applied to the control of the slow states using commands for the fast states as inputs. The dynamic inversion system was compared with a more conventional, gain-scheduled system and was shown to yield better performance in terms of lateral acceleration, sideslip, and control deflections.
579 citations
TL;DR: In this article, the concept of sliding modes in abstract dynamic systems described by a semigroup of state space transformations is introduced, and the sliding mode design procedure is used for designing finite observers, sliding mode control for systems with delays and differential-difference systems, which is illustrated by sliding mode controller of longitudinal oscillations.
Abstract: The concept of sliding modes in abstract dynamic systems described by a semigroup of state space transformations is introduced. The sliding mode design procedure is used for designing finite observers, sliding mode control for systems with delays and differential-difference systems, which is illustrated by sliding mode control of longitudinal oscillations
376 citations
08 Mar 1992
TL;DR: In this article, the structure of a fuzzy controller is derived from a nonlinear state equation representing a large class of physical systems, and stability conditions, scaling of the state vector, choice of the switching line, and determination of the break frequencies of the controller are discussed.
Abstract: Fuzzy controllers work like modified sliding mode controllers (SMCs). Compared to ordinary SMCs, fuzzy controllers (FCs) have the advantage of higher robustness. The structure of a FC is derived from a nonlinear state equation representing a large class of physical systems. The following aspects are discussed: stability conditions, scaling of the state vector, choice of the switching line, and determination of the break frequencies of the controller. By the choice of an additional boundary layer in the phase plane the FC is modified so that drastic changes of the manipulated variable can be avoided, especially at the boundary of the normalized phase plane. In this context, the higher robustness of the modified FC over the modified SMC is discussed. An FC for a higher-order system is proposed. >
374 citations
16 Dec 1992
TL;DR: In this paper, a sliding-mode observer for a nonlinear system is proposed, which is based on the equivalent control method and does not require nonlinear state transformation, unlike the output global linearization approach.
Abstract: The sliding-mode observer for a nonlinear system is proposed. The observer is based on the equivalent control method. Compared with the known output global linearization approach it is given in terms of the system variables and does not require nonlinear state transformation. Several examples are presented which illustrate the proposed method. >
236 citations
TL;DR: In this article, the design of variable structure control schemes for uncertain discrete-time systems is considered and theoretical results indicate that such a parallel approach is not necessarily desirable, and a novel design methodology for discrete time variable-time structure control systems is then formulated.
Abstract: The design of variable structure control schemes for uncertain discrete-time systems is considered. Previous work in this area which parallels the discrete-time sliding mode philosophy with that for the continuous-time case is reviewed. Theoretical results are presented which indicate that such a parallel approach is not necessarily desirable. A novel design methodology for discrete-time variable structure control systems is then formulated. A numerical example is given to illustrate the results described.
174 citations
TL;DR: It is demonstrated that as a result of using sliding control, better use of the network's approximation ability can be achieved, and the asymptotic tracking error can be made dependent only on inherent network approximation errors and the frequency range of unmodelled dynamical modes.
Abstract: A neural-network-based direct control architecture is presented that achieves output tracking for a class of continuous-time nonlinear plants, for which the nonlinearities are unknown. The controller employs neural networks to perform approximate input/output plant linearization. The network parameters are adapted according to a stability principle. The architecture is based on a modification of a method previously proposed by the authors, where the modification comprises adding a sliding control term to the controller. This modification serves two purposes: first, as suggested by Sanner and Slotine,1 sliding control compensates for plant uncertainties outside the state region where the networks are used, thus providing global stability; second, the sliding control compensates for inherent network approximation errors, hence improving tracking performance.
A complete stability and tracking error convergence proof is given and the setting of the controller parameters is discussed. It is demonstrated that as a result of using sliding control, better use of the network's approximation ability can be achieved, and the asymptotic tracking error can be made dependent only on inherent network approximation errors and the frequency range of unmodelled dynamical modes. Two simulations are provided to demonstrate the features of the control method.
158 citations
29 Jun 1992
TL;DR: In this paper, a small-signal analysis is performed for the control scheme of peak current-mode control and the relationship between subharmonic oscillation and the line/load condition of charge control is defined.
Abstract: There are many ways to use the inductor current of a PWM converter as part of its feedback control mechanism. A simple and widely used method is peak current-mode control which uses the instantaneous inductor current as part of the control signals. Charge control is a special type of current-mode control. It uses the integration of the on-time inductor current as the feedback control signal. The characteristics of charge control are studied. A complete small-signal analysis is performed for the control scheme. Subharmonic oscillation similar to that of peak current-mode control is found, and the relationship between subharmonic oscillation and the line/load condition of charge control is defined. Based on the analysis, design guidelines which guarantee the stability of the control system under given line and load ranges are proposed. The small-signal model was confirmed experimentally. >
158 citations
TL;DR: In this article, the continuous sliding mode control (CSMC) approach is proposed to satisfy the sliding condition using a continuous control law. But the control chattering due to the discontinuity in the control law is undesirable in most processes applications.
Abstract: Classical sliding mode control (SMC) uses a discontinuous control action to drive the state from an arbitrary initial state to the origin along a user-specified path and exhibits excellent robustness to disturbances and parameter uncertainty. However, the control chattering due to the discontinuity in the control law is undesirable in most processes applications. The continuous sliding mode control (CSMC) approach developed in this paper satisfies the sliding condition using a continuous control law. It therefore retains the positive properties of SMC but without the disadvantage of control chattering. The concept of boundary layer equivalence is used to show that in the presence of unknown disturbances and/or parameter uncertainty, CSMC keeps the state trajectories within a boundary layer of user-specified width. It is also shown that CSMC is equivalent to a cubic feedback control law and can be reduced to a linear form (LSMC) which provides a useful link between sliding mode control and traditional line...
114 citations
TL;DR: In this paper, a sliding mode control algorithm is presented for trajectory tracking of an end-effector on a constrained surface with specified constraint forces by using the theory of variable structure systems.
Abstract: A sliding mode control algorithm is presented for trajectory tracking of an end-effector on a constrained surface with specified constraint forces by using the theory of variable structure systems. The development of the algorithm is based on a new formulation of the dynamic model and the expansion of sliding surfaces to include the constraint force error. The proposed sliding controller is explicit, which ensures the occurrence of the sliding mode on the intersection of the surfaces. A detailed numerical example is presented to illustrate the method. >
97 citations
TL;DR: An approach using variable-structure control with integral compensation is presented for an electrohydraulic position servo control system to achieve accurate servo tracking in the presence of load disturbance and plant parameter variation.
Abstract: An approach using variable-structure control with integral compensation is presented for an electrohydraulic position servo control system to achieve accurate servo tracking in the presence of load disturbance and plant parameter variation. Simulations show that the proposed approach may give a rather accurate servo-tracking result and is fairly robust to plant parameter variation and load disturbance. >
97 citations
TL;DR: In this article, a nonlinear process model for feedback control of pH is proposed to essentially eliminate the bias of the oscillations and to result in an average pH close to the setpoint, whereas standard linear feedback control does not.
Abstract: Methods for continuous control of pH in process streams are treated. Nonlinear models for pH, valid for acid-base reactions in water solutions, are derived from first principles, and a nonparametrized model is introduced for processes with unknown composition. The two basic choices for continuous in-line feedback control of pH are between linear and nonlinear control and between fixed-parameter and adaptive control. A detailed simulation example illustrates properties of pH-control systems in oscillating mode, a common phenomenon in, e.g., wastewater pH-control systems. Use of a proper nonlinear process model for feedback control is shown to essentially eliminate the bias of the oscillations and to result in an average pH close to the setpoint, whereas standard linear feedback control does not. The main reason for the need of adaptation is changing buffering (titration curve). Advantages of adaptive control over nonadaptive control are illustrated with respect to robustness and performance, and convergence properties of nonlinear adaptive control compared to linear-model adaptive control are experimentally illustrated. Practical issues in the implementation of linear and nonlinear self-tuning control of pH are discussed
TL;DR: Simplex type dynamic output feedback variable structure control for stabilizing multivariable linear time-invariant plants is analyzed in this article, where two types of controllers are considered; a compensator type and an observer type.
Abstract: Simplex type dynamic output feedback variable structure control for stabilizing multivariable linear time-invariant plants is analysed. Two types of controllers are considered; a compensator type and an observer type. It is shown that while the compensator-type controller stabilizes the plant only if the plant is minimum-phase, the observer-type controller does not face the same restriction. The design of low-order (less than the order of the plant) observer-type controllers is also considered.
TL;DR: In this article, the problem of output stabilization for uncertain S1SO systems is considered using structural transformations, which can change to the form convenient for output feedback design, and the synthesis of observer-based variable structure control for asymptotical stabilization or uniform ultimate boundedness of the closed-loop system is provided.
Abstract: The problem of output stabilization for uncertain S1SO systems is considered. Using structural transformations uncertain systems can change to the form convenient for output feedback design. Synthesis of observer-based variable structure control for asymptotical stabilization or uniform ultimate boundedness of the closed-loop system is provided. Examples are considered and simulation results are given.
TL;DR: In this article, a variable structure sliding mode control for noncollocated flexible one-link manipulator arm tip position control based on variable structure system theory is presented, where position state variables are obtained directly from the inversion of the output submatrix multiplied by the sensor measurements.
Abstract: A novel controller design for noncollocated flexible one-link manipulator arm tip position control based on variable structure sliding mode control is presented. Using the assumed-mode method, the plant model is derived. The discontinuous control law based on the variable structure system theory for the noncollocated manipulator tip position control is then designed. The position state variables are obtained directly from the inversion of the output submatrix multiplied by the sensor measurements. The velocity state variables are estimated through decoupled estimators-a separate first-order observer for each of the system's modes under consideration. Different sampling periods are used for the estimator and the controller. The performance of the controller is evaluated through a series of simulations, followed by an analysis of the designed control system. >
TL;DR: In this paper, a variable structure control (VSC) method was developed for motion, internal force, and constrained force control of two manipulators grasping a common constrained object, based on a transformed dynamic equation of the entire system in the joint space.
Abstract: A variable structure control (VSC) method is developed for motion, internal force, and constrained force control of two manipulators grasping a common constrained object. Based on a transformed dynamic equation of the entire system in the joint space, a motion and force control are designed together via a VSC method with robustness to parametric uncertainties and external disturbances. The proposed controller guarantees the system with prescribed qualities in the sliding mode and during the reaching transient. Simulation results illustrate the method. >
01 Mar 1992
TL;DR: In this paper, an integral variable structure control (IVSC) approach for robot manipulators is presented to achieve accurate servo-tracking in the presence of load variations, parameter variations and nonlinear dynamic interactions.
Abstract: An integral variable structure control (IVSC) approach for robot manipulators is presented to achieve accurate servo-tracking in the presence of load variations, parameter variations and nonlinear dynamic interactions. A procedure is proposed for choosing the control function so that it guarantees the existence of the sliding mode and for determining the coefficients of the switching plane and the integral control gain such that the IVSC approach has the desired properties. Furthermore, a modified proper continuous function is introduced to overcome the chattering problem. The proposed IVSC approach has been simulated for the first three links of a PUMA 560 robot arm as an illustration. The simulation results demonstrate the potential of the proposed scheme.
TL;DR: A robust state-feedback nonlinear control law is synthesized and this control strategy practically stabilizes the closed-loop system and a state estimator for the nonlinear/uncertain plant is designed and its performance analyzed.
TL;DR: In this paper, the attitude and angular momentum control laws for the Space Station were obtained based on Lyapunov's second method for stability analysis. But the control laws were obtained under the zero disturbance assumption and were tested in the presence of constant disturbance torques.
Abstract: Nonlinear design procedures are presented for obtaining attitude and angular momentum control laws for the Space Station. These are based on Lyapunov's second method for stability analysis. In the absence of disturbances, there exist four stable equilibrium points. Only one of these is desired and its stability boundary is estimated from the gravitational dynamic potential. Simulation results are presented for the current Space Station configuration for large initial deviations from the local-vertical-local-horizontal frame. The control laws obtained under the zero disturbance assumption are tested in the presence of constant disturbance torques. It is shown that the Space Station can be stabilized about a torque-equilibrium attitude and the momentum of the control moment gyroscopes is bounded, provided the disturbance is smaller than the maximum gravity gradient torque that can be produced by the Space Station.
TL;DR: In this article, the use of variable structure feedback control strategies is proposed for the asymptotic stabilization of nonlinear dynamic systems describing chemical processes, which effectively eliminates the traditional bang-bang nature of the control input signals and the associated chattering responses.
Abstract: In this article, the use of variable structure feedback control strategies is proposed for the asymptotic stabilization of nonlinear dynamic systems describing chemical processes. The proposed discontinuous controller is dynamic in nature and it effectively eliminates the traditional bang-bang nature of the control input signals and the associated chattering responses. The controller is based on recent results of the differential algebraic approach to system dynamics; in particular Fliess's generalized observability canonical form is used in the derivation of the dynamical discontinuous controller. Some illustrative examples, including simulations, are provided.
01 Aug 1992
TL;DR: The theorem underlying the present work gives sufficient conditions to ensure the stability of a closed-loop system composed of a robot, an observer, and a controller shows that the joint velocity estimation errors are bounded and the joint position tracking errors are also bounded when time tends to infinity.
Abstract: An algorithm is proposed that combines variable structure control and observation for robot control using only joint position measurements. This algorithm is used to investigate the interactions between the observer and the controller caused by system parameter uncertainties. The theorem underlying the present work gives sufficient conditions to ensure the stability of a closed-loop system composed of a robot, an observer, and a controller. This theorem shows that the joint velocity estimation errors are bounded and the joint position tracking errors are also bounded when time tends to infinity. The experimental results achieved with the direct-drive robot DDR-1 verify the validity of the theoretical results. The experiments also demonstrate that when the end-effector of the robot tracks a 0.5-m-diameter circle at a speed of 0.5 m/s or tracks a 1-m straight line at a speed of 1 m/s, the maximum joint tracking errors are less than 0.05 degrees and the maximum trajectory tracking error is less than 0.5 mm. >
TL;DR: In this paper, the problem of output stabilization for uncertain MIMO systems is considered using structural transformations, and an uncertain system is changed to a "form convenient for output feedback design".
Abstract: The problem of output stabilization for uncertain MIMO systems is considered. Using structural transformations, an uncertain system is changed to a "form convenient for output feedback design. Synthesis of observer-based variable structure control for asymptotical stabilization and uniform ultimate boundedness of the closed-loop system is provided. Examples are considered and simulation results are given.
24 Jun 1992
TL;DR: In this paper, two approaches have been proposed to reduce chattering in variable structure control algorithms: boundary layer approximation in the boundary layer and a localization of high frequency phenomenon in the high frequency loop.
Abstract: In variable structure control algorithms, sliding mode plays a key role in desensitizing the closed loop system with respect to parameter variations, in rejecting unknown disturbances, and in reducing the systems dynamics to a prescribed lower dimension manifold on which desirable dynamic behavior of the plant is attained. In its original theoretical developement, sliding mode corresponds to a special class of system trajectories which is produced by a certain control action that is discontinuous on a switching manifold [1]. However, in the presence of switching nonidealities, such as delays and time lags, the discontinuity in the control variables may excite umodeled fast dynamics in the plant, thus producing unacceptable system dynamic behavior which is commonly referred to as chattering phenomenon. Presently, two approaches have been proposed to reduce chattering. The first one is the use of continuous approximation in the boundary layer [2, 3, 4]. This approach replaces the switching function in the discontinuous control by a continuous approximation in the vicinity of the switching manifold. However, although chattering can be removed, the robustness of sliding mode is comprimised. The second approach utilizes a localization of high frequency phenomenon [5]- it introduces a discontinous control loop which is closed through an asymptotic observer of the plant. Since the model imperfections of the observer are supposedly smaller than that in the plant, and the control is discontinuous only with respect to the observer, chattering is localized to a high frequency loop which bypasses the plant.
01 Mar 1992
TL;DR: In this article, the authors considered the multivariable control of anthropomorphic robot manipulators, and their objective is to develop a control technique which exploits the full potential of the performance of robot arms.
Abstract: The paper considers the multivariable control of anthropomorphic robot manipulators, and its objective is to develop a control technique which exploits the full potential of the performance of robot arms. In its ideal form, the computed torque technique achieves the desired performance in nonlinear time-varying systems. However, its stability cannot be guaranteed, and its performance deteriorates rapidly with the pres ence of disturbances and parametric uncertainties. The variable structure control strategy which can guarantee stability, given bounded parametric uncertainty, is used as an additional input to rectify the uncertainties in the estimated control model of the computed torque technique. The benefits of the combined computed torque/variable structure controller are demonstrated practically on an electrically powered industrial robot, and the performance of the proposed controller is compared to that of the computed torque technique.
16 Dec 1992
TL;DR: In this paper, an adaptive control approach to a class of nonlinear systems with a triangular structure is developed and the constructive procedure used for generating the adaptive controller is shown to result in the closed-loop system being asymptotically stable at the origin.
Abstract: An adaptive control approach to a class of nonlinear systems with a triangular structure is developed. The systems considered here are described by a set of second-order differential equations, and thus there are many applications to the control of mechanical systems. The design procedure of the control law is based on the idea of properly using the structure of the system, and sequentially developing an adaptive controller that is globally stable. A class of single-input single-output nonlinear systems with a triangular structure is defined and the stabilizability conditions are derived. A control strategy to stabilize the same class of systems with unknown parameters is developed and an adaptive controller for realizing the strategy is systematically designed. The constructive procedure used for generating the adaptive controller is shown to result in the closed-loop system being asymptotically stable at the origin. The approach is illustrated using an example of a coupled mechanical system. >
TL;DR: In this article, the sliding mode control (SMC) is applied to a magnetic bearing system and compared with the PID control method for the flexible rotor supported by magnetic bearings by simulation and experiments on both the lift off and rotation.
Abstract: In this paper, the sliding mode control, a typical method of nonlinear adaptive control and robust control, is applied to a magnetic bearing system. It has its roots in the relay and bang-bang control theory. Sliding mode control is a high-speed switching feedback control; for example, the gains in each feedback path switch between two values according td certain rules. This control law drive system's state trajectory to a user-chosen surface in the state space is called the sliding surface for all subsequent time. The sliding surface is called the switching surface by another name because if the state trajectory is above the surface, a control path has one gain and a different gain if the trajectory drops below the surface. From this control, the system is restricted to this surface and is stabilized. This method is very robust for parameter change, modelling error, disturbance, and so on. The sliding mode control method is compared with the PID control method for the flexible rotor supported by magnetic bearings by simulation and experiments on both the lift off and the rotation.
16 Dec 1992
TL;DR: In this article, the nonlinear adaptive digital control of a synchronous motor using a nonlinear modelization in the (d, q) frame is discussed, and it is shown that a multirate control strategy provides an appropriate framework for achieving speed regulation.
Abstract: The nonlinear adaptive digital control of a synchronous motor using a nonlinear modelization in the (d, q) frame is discussed. It is shown that a multirate control strategy provides an appropriate framework for achieving speed regulation, thereby ensuring the stability of the whole control system. When parametric uncertainties on the resistance of the stator windings and the load torque occur, this scheme is completed with an adaptation law deduced from hyperstability concepts. This results in the asymptotic satisfaction of the control objectives at the sample instants. Simulation results are presented. >
TL;DR: In this paper, a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances.
Abstract: A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense.
TL;DR: In this paper, an approach to the design of large variable structure systems subject to control bounds is introduced, which includes a switching hyperplane design based on generalized inverses and system decomposition.
Abstract: An approach to the design of large variable structure systems subject to control bounds is introduced. The method includes a switching hyperplane design based on generalized inverses and system decomposition. To ensure reaching the hyperplane and achieving a sliding condition, the control is switched between local equivalent control and bounded corrective control. The design of the corrective control component is completed using system decomposition into smaller subsystems. An estimate of the domain of attraction corresponding to the bounded control is obtained and used to select the appropriate controller bounds. The method is illustrated using a fifth-order numerical example. >
13 Sep 1992
TL;DR: It is shown for the first time that, even if there exist nonlinear unknown dynamics, aPD feedback control without higher-order nonlinear compensation can guarantee global stability for the trajectory following problem of a robot manipulator.
Abstract: It is shown that, even if there exist nonlinear unknown dynamics, a PD (proportional derivative) feedback control without higher-order nonlinear compensation can guarantee global stability for the trajectory following problem of a robot manipulator. The PD control under investigation is a position and velocity feedback control with a time-varying gain and does not contain any higher-order nonlinearity. Another novel and interesting result is that a measure of protection against saturation of actuators may be incorporated into the control design and robustness analysis. >