Showing papers on "Observer (quantum physics) published in 1990"

Robot control by using only joint position measurements

Abstract: An observer for reconstructing the joint velocities of rigid-joint robots is proposed. The approach consists of exploiting the structural properties of the robot dynamics. The associated error dynamics are shown to be asymptotically stable. The observer furnishes the state estimate directly in the physical coordinates, so that no transformation is needed. The stability of some state feedback controllers having the proposed observer inserted in the feedback loop is proved. The structure of the observer and its convergence are shown. The stability of the whole system is analyzed when the observer is used in connection with a point-to-point controller and a trajectory controller. >

Observability of discrete event dynamic systems

Abstract: A finite state automaton is adopted as a model for discrete event dynamic systems (DEDS). Observations are assumed to be a subset of the event alphabet. Observability is defined as having perfect knowledge of the current state at points in time separated by bounded numbers of transitions. A polynomial test for observability is given. It is shown that an observer may be constructed and implemented in polynomial time and space. A bound on the cardinality of the observer state space is also presented. A notion of resiliency is defined for observers, and a test for resilient observability and a procedure for the construction of a resilient observer are presented. >

Observer synthesis for state-affine systems

Abstract: The problem of synthesis of observers for nonlinear systems is considered. An observer for state-affine systems is constructed and it is shown that it depends on the inputs of the system. The inputs for which the observer converges are classified, and some topological properties are given. >

Inherent Observer Property in a Class of Anti-Windup Compensators

Abstract: Owing to the types of non-linearities involved, the analysis and the comparison of different anti-windup compensators that are available in the literature become difficult. Towards achieving a better understanding of the mechanisms of these anti-windup compensators, we here expose the observer property inherent in a class of anti-windup compensators. This observer property allows us to unify these anti-windup compensators as special cases of the generalized anti-windup compensator due to Astrom and Wittenmark (1984), and provides a general framework to investigate their performance.

VSS observer for linear time varying system

Abstract: The problem of designing an observer for state estimation using variable structure system (VSS) theory is discussed. The theory and design principles for linear time-varying systems are presented. The observer is constructed by introducing a block-observable from which is similar to a lower triangular matrix. The convergence of the observer is guaranteed by a sliding mode with first-order filter. Simulation results show that the proposed observer is able to provide correct estimated values of the states. >

A Comparative Study of a Luenberger Observer and Adaptive Observer-Based Variable Structure Speed Control System Using a Self-Controlled

Abstract: Abstmct-This paper presents an analysis of the state observer-based robust speed control of a self-controlled synchronous motor (SCSM) . A variable structure control (VSC) technique is utilized to achieve robust ( parameter-insensitive) characteristics. The speed and acceleration signals required for the implementation of the variable structure speed control (VSSC) are dynamically estimated with state observers. Two kinds of observers-the Luenberger full-order observer and an adaptive observer- are explored in this paper. The results obtained illustrate that Luenberger observers do not estimate the system states accurately when the system parameters vary. This inaccuracy in the state estimation results in a deteriorated performance of the VSSC. Therefore, the possibility of using an adaptive state observer (ASO) is investigated. As expected, the AS0 estimates the system parameters and the system states simultaneously, thus making VSSC possible. The design methods and the simulation results presented demonstrate the potential of the proposed scheme.

A comparative study of a Luenberger observer and adaptive observer-based variable structure speed control system using a self-controlled synchronous motor

Abstract: An analysis of the state-observer-based robust speed control of a self-controlled synchronous motor (SCSM) is presented. A variable-structure control technique is utilized to achieve robust (parameter-insensitive) characteristics. The speed and acceleration signals required for the implementation of the variable-structure speed control (VSSC) are dynamically estimated with state observers. Two kinds of observers-the Luenberger full-order observer and an adaptive observer-are explored. The results obtained illustrate that Luenberger observers do not estimate the system states accurately when the system parameters vary. This inaccuracy in the state estimation results in a deterioration of the VSSC performance. Therefore, the possibility of using an adaptive state observer (ASO) is investigated. It is shown that the ASO estimates the system parameters and the system states simultaneously, thus making VSSC possible. The design methods and simulation results are presented to demonstrate the potential of the scheme. >

Discrete computer control of a triple-inverted pendulum

Abstract: Stabilization of a triple-inverted pendulum is studied in this paper. The overall control structure is based on a state space approach and employs the computer-aided design package ‘KEDDC’. The complete set of state variables needed for state feedback are provided by a reduced-order observer. Theoretical analysis, supported by successful experimental results, shows that our stabilization objective can be achieved by measuring the angles of the three arms of the pendulum as well as the position and velocity of the supporting cart.

Experimental results in state estimation of industrial robots

Abstract: A simple asymptotic observer, with linear and decoupled structure, is proposed for the estimation of the generalized velocities of a robotic manipulator. High-gains are used in the attenuation of the nonlinearities characterizing the dynamic behavior of the robot. Lyapunov stability theory is used to prove the convergence of the proposed observer and of the control laws based on such a high-gain observer. The accuracy of the proposed algorithm is verified through some experimental tests. >

Newton, observers and nonlinear discrete-time control

Abstract: Development of exact asymptotic observers for nonlinear discrete-time systems is addressed. It is argued that instead of trying to imitate the linear observer theory, the problem of constructing a nonlinear observer can be more fruitfully studied in the context of solving simultaneous nonlinear equations. In particular, it is shown that Newton's algorithm, properly interpreted, yields an asymptotic observer for a large class of discrete-time systems. The utility of the observer for closed-loop, observer-based, feedback control is also established. Some non-local aspects of the results are also discussed. >

Computed Torque Control via a Nonlinear Observer

Abstract: High-precision measurements of joint displacements are available on robot manipulators. In contrast, the velocity measurements obtained through tachometers are in many cases contaminated by noise. It is therefore economically and technically interesting to investigate the possibility of accurately estimating the speed from direct available measurements such as the angular positions. This paper proposes a ‘smooth non-linear observer’ (i.e. an observer with ‘smooth’ or ‘differentiable’ gains) and a modified computed torque law which is a function of estimated velocities and measurement positions for rigid industrial robot manipulators. We derive local conditions for asymptotic stability of the closed-loop system.

A pole-placement design approach for systems with multiple operating conditions

Abstract: The author proposes design procedures based on state-space pole-placement techniques for systems with multiple operating conditions. This is the so-called simultaneous pole-placement problem. First, the full state feedback problem is studied, in which a nonlinear local pole-placement solution is proposed. The design condition is formulated in terms of the rank condition of a multimode controllability matrix. Then, the output feedback problem is approached using a multimodel controller design, which is an extension of the observer design to multimode systems. The design is decomposed into separated global pole-placement subproblems and a local pole-placement subproblem. For a system with some operating conditions having modes on the j omega -axis, but no modes at the origin in the open right-half of the complex plane, stabilizability and detectability conditions for the design of an asymptotically stabilizing control are established, without any restriction on the number of inputs or outputs. Relations of this approach to other simultaneous control design approaches are pointed out. >

Application of nonlinear observers for rotor position detection on an induction motor using machine voltages and currents

Abstract: The principles and operation of a unique, terminal properties-based speed and position sensing approach for induction machines are demonstrated. A closed-loop nonlinear observer is proposed which uses an analytical model to calculate, in real time, the mechanical states of rotor speed and position given the torque command to the system and the induction motor terminal voltages and line currents. The uniqueness of this observer is that it uses inherent machine magnetic saliency and winding asymmetry to develop a magnetic encoder model of the machine itself. The error between the measured and calculated spatial harmonic EMFs is then used to drive the observer to accurate position and speed estimates in the presence of model parameter errors. Experimental data are included which show harmonic flux terms identified, measured and compared with an analytical model using a slip-ring induction motor with the rotor windings open and short circuited. >

Adaptive robust observers for non-linear uncertain systems

Abstract: A new class of observers for non-linear uncertain dynamical systems is proposed. The non-linearity and uncertainty in the systems are assumed to be bounded. The bound is however unknown. Adaptive schemes are designed for the estimation of the bound. The observer, based on this estimation, is then able to estimate the system's state regardless of the realization of the uncertainty.

Performance improvement using time delays in multivariable controller design

Abstract: A new controller for linear multivariable ordinary systems is suggested in which distributed delays are included in the feedback loop. A general design approach to obtain this type of controller is suggested. It is shown that the resulting closed-loop system is asymptotically stable under some sufficient conditions. Sufficient conditions are derived under which the disturbance attenuation, the robustness against parameter variations, and the time-delay stability margins are improved by the proposed controller. The state feedback tracking controller and the dual-state observer are obtained by modification of the proposed controller.

Approximate loop transfer recovery method for designing fixed-order compensators

Abstract: An approach is outlined for designing fixed-order dynamic compensators for multivariable time-invariant linear systems, based on minimizing a linear quadratic performance index. The formulation is done in an output feedback setting that exploits an observer canonical form to represent the compensator dynamics. The formulation also precludes the use of direct feedback of the plant output. The main contribution lies in defining a method for penalizing the states of the plant and of the compensator, and for choosing the distribution on initial conditions so that the loop transfer matrix approximates that of a full-state feedback design. When linear quadratic regulator theory is used to do the full-state feedback design, the approach can result in good gain and phase margin characteristics. Two examples are given to illustrate the effectiveness of the approach. The first treats the problem of pointing a flexible structure, and the second is a helicopter flight control problem using a tenth-order model for the fuselage and rotor dynamics. Both of the examples considered in this paper are for nonsquare plants.

On fault-tolerant observers

Abstract: The problem of designing asymptotic observers for multioutput systems with one unreliable output measurement is addressed. It is shown that observers designed on the basis of observability indexes are not fault tolerant, and an observer for linear systems which tolerates failures in one a priori known output is given. The results are extended to nonlinear systems with no inputs: it is pointed out that the proposed design procedure may enlarge the class of nonlinear systems for which a nonlinear observer can be obtained. >

Optimal reduced-order observer-estimators

Abstract: A unified approach to designing reduced-order observer-estimators is presented. Specifically, an attempt is made to design a reduced-order estimator satisfying an observation constraint which involves a prespecified, possibly unstable subspace of the system dynamics and which also yields reduced-order estimates of the remaining subspace. The results are obtained by merging the optimal projection approach to reduced-order estimation of D.S. Bernstein and D.C. Hyland (IEEE Trans. Autom. Control, vol.AC-30, p.583-5, 1985) with the subspace-observer results of the authors (Proc. IEEE Conf. on Decision and Control, p.2364-6, Dec. 1988). A salient feature of this theory is the treatment of unstable dynamics within reduced-order stable-estimation theory. In contrast to the standard full-order estimation problem involving a single algebraic Riccati equation, the solution to the reduced-order observer-estimator problem involves an algebraic system of four equations consisting of one modified Riccati equation and three modified Lyapunov equations coupled by two distinct oblique projections. >

Integrated direct optimization of structure/regulator/observer for large flexible spacecraft

Abstract: Since the approach takes into account the uncontrolled residual modes, it will not only optimize them, based on an actual performance index affected by the residual modes, but will also suppress the spillover instability. The approach is applied to the design of a controller for a simple supported beam. The example demonstrates that the resulting controller is stable even when the linear quadratic Gaussian (LQG) controller is unstable. Insensitivity of the resulting system to parameter variations is also demonstrated in comparison with the LQG controller

Modeling and adaptive control of a flexible one-link manipulator

Abstract: The dynamics modeling and payload adaptability of a light-weight flexible one-link manipulator are studied. Using the FEM (Finite-Element Method) model of a flexible manipulator, a lower order Linear Quadratic Gaussian compensator can provide satisfactory performance without controller/observer spillover. Moreover, the payload can be separated from the beam model, therefore, it is expected that the identification algorithm should have better robustness than the other schemes. The simulation results have shown that the proposed payload-adaptation synthesizer, which synthesizes a payload identifier and a nominal regulator/estimator interpolator to obtain a near-optimal compensator, has good adaptability with varying payload. And the resulting synthesizer also provides a near-optimal damping for this sensor-actuator noncolocated system.

Theory of LTR for nonminimum phase systems, recoverable target loops, recovery in a subspace. I. Analysis

Abstract: A complete analysis of the loop transfer recovery (LTR) problem using full order observer-based controllers for general systems that are not necessarily left invertible and minimum phase is considered. The analysis focuses on three fundamental issues. The first is concerned with what can and cannot be achieved for a given system and for an arbitrarily specified target loop transfer function. The second is concerned with the development of necessary and/or sufficient conditions for a target loop to be either exactly or asymptotically recovered for a given system. The third issue deals with the development of method(s) to test whether recovery is possible in a given subspace of the control space. Such an analysis pinpoints the limitations of the given system for the recovery of arbitrarily specified target loops by observer-based controllers. Furthermore, the analysis discovers a multitude of ways to shape the loops as closely as possible to the target shapes. Also, possible pole-zero cancellations between the eigenvalues of the controller and the input and/or output decoupling zeros of the plant are characterized. >

Vibration suppression of induction-motor-driven hybrid vehicle using wheel torque observer

Abstract: The vibration phenomenon occurring under indirect field oriented control or vector control when induction motors drive an inertia load through a spring under overload conditions at high speed is described. The vibration mechanism is clarified, and a suppression method is proposed. The subject of this study is a hybrid vehicle consisting of a front engine-driven system and two rear motor-driven systems, which are designed to improve the driving stability. A stability analysis of the total system, including a vector control system and a mechanical system, reveals that the vector control system is essentially unstable under extreme overload and demagnetization conditions, even if the motor is perfectly controlled. Therefore, suppression of vibrations was attempted using an observer for estimating wheel torque and a regulator for state feedback from the outside of the vector control system. These methods perfectly suppressed the vibration, realizing a compact, light motor-driven system with rapid, stable performance. >