Showing papers on "Control theory published in 1983"

A New Class of Stabilizing Controllers for Uncertain Dynamical Systems

Abstract: This paper is concerned with the problem of designing a stabilizing controller for a class of uncertain dynamical systems. The vector of uncertain parameters $q( \cdot )$ is time-varying, and its values $q(t)$ lie within a prespecified bounding set Q in $R^p $. Furthermore, no statistical description of $q( \cdot )$ is assumed, and the controller is shown to render the closed loop system “practically stable” in a so-called guaranteed sense; that is, the desired stability properties are assured no matter what admissible uncertainty $q( \cdot )$ is realized. Within the perspective of previous research in this area, this paper contains one salient feature: the class of stabilizing controllers which we characterize is shown to include linear controllers when the nominal system happens to be linear and time-invariant. In contrast, in much of the previous literature (see, for example, [1], [2], [7], and [9]), a linear system is stabilized via nonlinear control. Another feature of this paper is the fact that the...

Adaptive linear controller for robotic manipulators

Abstract: This paper presents a new approach to the position and velocity control of a manipulator by using an adaptive controller of the self-tuning type for each joint. The complicated manipulator system is modeled by a set of time series difference equations. The parameters of the models are determined by on-line recursive algorithms, which result from minimizing the sum of the squared equation errors. The adaptive controller of each joint is designed on the basis of the difference equation model and a chosen performance criterion. The controller gains are calculated on-line using the model with the estimated values of system parameters. Simulation results are presented to demonstrate the applicability of the approach. Some aspects of the implementation are also discussed.

A self-tuning controller with a pid structure

Abstract: Some self-tuning controllers are proposed which have the same structure as conventional PID controllers. The new self-tuning PID controllers are based on a modified version of the design method of Clarke and Gawthrop (1975, 1979). Experimental and simulation studies for a stirred-tank heating system indicate that the new self-tuners perform well and can be easily adjusted on-line.

Predictive control for systems with time delay

Abstract: A Smith predictor has been known as an effective controller to overcome a dead time. If the plant, however, is unstable, the closed-loop system cannot be stabilized with a Smith predictor. In order to stabilize an unstable plant with time delay, we propose a predictive control which is composed of an observer, a predictor and a controller. We refer to the realization of the predictor, and indicate an available type of model for it. In addition, we suggest the possibility that predictive control with a stable approximate model may be applied to an astatic plant.

Self-Tuning Controller for Generator Excitation Control

Abstract: It has long been recognized that the generator excitation control is an effective and low cost means for improving the power system stability. Recent developments in control theory and digital technology suggest an extension of the results obtainable through analog control to derive potential improvements through the use of digital control. There has been reluctance to apply real time digital control in electric power engineering, perhaps this is due to lack of experience and confidence in this technology. In addition to advances in technology, motivation for investigating the control of a generator at the end of a long transmission line comes from the common occurrence of generation being remotely located. Such is the case, for example, at Liu Jia Xia in the People's Republic of China where a 330 KV, 332 mile single circuit line connects a 400 MW station with the main grid. It is reasonable to attempt to use excitation control to permit line loading to the transmission limit. Much work has been done with many interesting results by applying linear optimal feedback control theory to the excitation control. Most of the results are based on the assumption that an explicit deterministic mathematical model of the system to be controlled is available. The system model is then linearized around some fixed operating point with the system parameters assumed constant. By numerous off-line simulation studies, suitable weighting factors involved in an index of quality can thus be found by trial and error.

Fuel control system for a gas turbine engine

Abstract: A fuel control system for a gas turbine engine comprises a main fuel controller and an overspeed limiter arranged to prevent overspeed of the engine in the case of a fault in the main controller To ensure that the limiter is tested regularly, the logic capacity of the main controller (which is preferably a digital electronic unit) is used to vary the parameters of the limiter each time the engine is started up This variation is such as to cause the limiter to operate and produce an observable reduction in the engine speed which is detected by the main controller and uses as an indication of correct limiter operation

Feedback Stabilization of Linear Diffusion Systems

Abstract: This paper treats the feedback stabilization of linear diffusion systems by using a finite dimensional feedback dynamic controller. We construct a finite dimensional observer using the output functions from sensors, and the control inputs to the system are given by the feedback of the observer output. Assuming, for some fixed finite number L, that the first L modes are controllable and observable, we prove that it is possible to construct a finite dimensional feedback dynamic controller such that the diffusion system has an arbitrarily large damping constant.

Remote control system for a video computer game

Abstract: A remote control system for a video computer game having a portable controller unit with transmitter circuits responsive to manipulation of a joy stick for generating RF signals indicative of such manipulations. A reset switch and a game select switch is also provided for generating signals which are also sent as RF signals. A central receiver receives the RF signals from the portable controller unit and converts the manipulation signals into signals applicable to control the video game. The reset signal and the game select signal are sent to an actuator unit which is physically mounted onto the master control center and includes mechanical actuator mechanisms to mechanically engage the reset and game selector buttons on the master control center. The central receiver also includes detection elements to prevent random signals from disturbing the game during such time periods when it is not receiving signals from the transmitter controllers.

A direct approach to compensator design for distributed parameter systems

Abstract: We present a direct approach to finite-order compensator design for distributed parameter systems, i.e., one that is not based on reduced order modelling. Instead, we use a parametrization around an initial compensator which displays both controller order and closed-loop stability in a convenient way. The main result is an existence theorem which holds for a wide class of linear time-invariant systems (parabolic, delay, damped hyperbolic). The most important assumptions are: bounded inputs and outputs, finitely many unstable modes, completeness of eigenvectors. An example is included to illustrate the feasibility of our method for purposes of design.

Controller for a brushless DC motor

Abstract: A controller for regulating the current applied to the windings of a brushless DC motor by pulse width modulating transistors arranged in a six-switch bridge. Current feedback signals are obtained from sense resistors provided in the lower legs of the bridge circuit and are employed to generate a loop error signal. A bilateral arrangement of hysteresis comparator circuits monitors the current feedback signals and provides signals that disable the transistor switches when the current is sensed to be in excess of a safe level of operation for the transistors. The shutdown circuit continues its disablement of the transistors until the current is sensed to fall back within the designed range of control. To ensure smooth transition between regenerating and motoring modes, a circuit monitors both positive and negative excursions of the integrated error signal. When the error signal is sensed to exceed the operating range of the pulse width modulation circuitry, the sense of the motor excitation is reversed in order to produce the desired motor torque. An absolute value circuit enables the use of both positive and negative values of the error signal to control the production of pulses by the pulse width modulation circuit.

A direct approach to compensator design for distributed parameter systems

Abstract: We present a direct approach to finite-order compensator design for distributed parameter systems, i.e., one that is not based on reduced order modelling. Instead, we use a parametrization around an initial compensator which displays both controller order and closed-loop stability in a convenient way. The main result is an existence theorem which holds for a wide class of linear time-invariant systems (parabolic, delay, damped hyperbolic). The most important assumptions are: bounded inputs and outputs, finitely many unstable modes, completeness of eigenvectors. An example is included to illustrate the feasibility of our method for purposes of design.

A Quantitative Analysis of Induction Motor Performance Improvement by SCR Voltage Control

Abstract: Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. These two criteria are shown to yield perceptibly different results when the motor is driven from a silicon-controlled rectifier (SCR) voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criteria yield results which are closer to the ideal than the constant power factor controller.

Pattern-recognizing self-tuning controller

Abstract: A pattern-recognizing, self-tuning controller is provided for controlling a process wherein measured characteristics including at least one peak of an error signal, derived from the differences occurring over time between the values of a process controlled variable and a desired set-point level for that variable, are used for identifying the behavior pattern of the error signal so that an operating parameter of the controller can be changed as required to minimize process recovery time whenever the process is subsequently disturbed or an abrupt change is made to the set-point level at some later time. The preferred embodiment of the device is in the form of a proportional-integral-derivative (PID) controller in which the PID coefficients are calculated in accordance with prescribed relationships that are based on damping, overshoot and time period characteristics of the error signal. Provisions are also made for including a user-specified noise threshold in order to reduce substantially the possibility of detecting a noise peak as a true peak of the error signal. A pre-adapt mode is also included, in which the controller automatically determines the initial values of the PID coefficients, the noise threshold, and the approximate time scale of the process, before on-line adaptive control of the process is given to the controller.

Method of inputting machining information to a machine tool numerical controller and apparatus therefor

Abstract: A numerical controller for a machining center comprising a microprocessor, which selectively executes an automatic programming function and a numerical control function. The microprocessor selectively displays on a CRT display unit various information which instructs an operator to input machining information regarding the blank and finished shapes of a workpiece and the mounting position of the workpiece on a work table. The operator inputs the machining information with a key board-type data input device in response to the information displayed on the CRT screen, and the machining information is stored in a data storage device. Based upon the stored machining information, the microprocessor then displays on the CRT screen the blank shape and the finished shape of the workpiece so that the operator can observe if the machining information has been correctly input. Unless modification of the stored machining information is required, the microprocessor prepares the numerical control (NC) program based upon the stored machining information. The microprocessor, in response to a machining start command, executes the numerical control function and controls the operation of the machining center in accordance with the NC program.

A simple adaptive Smith-predictor for controlling time-delay systems: A tutorial

Abstract: This heuristic paper presents several simple techniques for analyzing the stability of time-delay systems. It explains the Smith predictor control scheme for time-delay systems and shows how errors in modeling the plant parameters can cause instability. Then an adaptive controller is added to the Smith predictor system; this pedagogical example offers a complete derivation of a simple adaptive control system. Finally, a new control scheme is discussed that allows zero-latency tracking of predictable targets by a time-delay system.

Optimal Adaptive Control of Linear-Quadratic-Gaussian Systems

Abstract: We consider the problem of adaptively controlling an unknown linear-Gaussian system with a standard quadratic cost criterion, including a control cost. By means of a counterexample, it is shown that a commonly mentioned adapative control scheme can lead to severe problems. To overcome this, a new adaptive control law, based on biasing the usual least-squares parameter estimation criterion with a term favoring parameters associated with lower optimal costs, is introduced. A salient feature of this adaptive control scheme is its imperviousness to the closed-loop identification problem. Properties such as closed-loop system identification, convergence of the adaptive control law to an optimal control law, overall stability of the controlled system and optimality with respect to the long-term average cost of the adaptive controller are proved.

High speed bulk compounder.

Abstract: A fast, efficient, precise method and apparatus for compounding solutions for use in hyperalimentation therapy. The apparatus (10) includes a controller (26) for entering the volume and specific gravity of the solution to be compounded. A load cell (28) monitors the weight of the solutions that have been transferred to a collection vessel (18) and in connection with the controller (26) thereby maintains the precise amount of each therein. The controller (26) also surveys various process conditions and warns of any failure of those conditions. Peristaltic pumps (20), (22) and (24) are used for the delivery of the compounding solution to maintain the solutions in a sterile condition.

Partial and robust linearization by feedback

Abstract: It is argued that if the nonlinearities in a system are mild, and the controller is sufficiently stabilizing, the inaccuracies of a linear model, which is often taken to be sufficient for a controller design, can be safely neglected. For systems with severe nonlinearity a linearizing technique is described, based on the change of state coordinates and nonlinear feedback; in the total context of a stable feedback design the linearization technique is considered robust. Furthermore, attention is paid to partial linearization using the same transformations. It is found that there always exist maximally linearizing transformations which are not necessarily unique.

A Newton Method for Solving Non-Linear Optimal Control Problems with General Constraints

Abstract: Optimal control of general dynamic systems under realistic constraints on input signals and state variables is an important problem area in control theory. Many practical control problems can be fo ...

Automatic ground speed controller

Abstract: An automatic control varies the ground speed of a combine due to changing field conditions, based on engine speed and combine feeder conveyor load variables.

A New Approach to Design of Fuzzy Controller

Abstract: We have heuristically designed fuzzy controllers so far since we have lacked a fuzzy model of a system. The authors have recently developed a method of multi-dimensional fuzzy reasoning that enables one to build a dynamic model of a system just as we do in terms of differential equations. This paper presents a new idea of designing a fuzzy controller based on a fuzzy model of a system.

Reliable stabilization using a multi-controller configuration

Abstract: Given a plant P, we consider the problem of designing a pair of controllers C1 and C2 such that their sum stabilizes P, and in addition, each of them also stabilizes P should the other one fail. This is referred to as the reliable stabilization problem. It is shown that every strongly stabilizable plant can be reliably stabilized; moreover, one of the two controllers can be specified arbitrarily, subject only to the constraint that it should be stable. The stabilization technique is extended to reliable regulation.

Adjustable gain controller for valve position control loop and method for reducing jitter

Abstract: An adjustable gain controller for a steam turbine valve position control loop includes an electronic operator, a proportional controller, a derivative controller and an integral controller A steam flow condition error signal is amplified by the reciprocal of the valve's regulation value The amplified error signal is supplied to the electronic operator and to the integral controller The electronic operator includes means for initially selecting a value of A and n and generating a gain factor from a nonlinear gain characteristic function utilizing those values in combination with the valve's regulation value and the normalized error signal The electronic operator multiplies the amplified error signal by the gain factor and applies the resultant signal to the proportional controller and the derivative controller The output signals from the proportional, derivative and integral controllers are summed together and that sum is input into an electrohydraulic valve actuator system The electrohydraulic valve actuator directly positions the steam valve Hydraulic and mechanical jitter is reduced by adjusting the values of A and n to reduce the jitter in the electrohydraulic valve actuator system

Multiple chiller control method

Abstract: A multiple chiller control system includes a temperature controller TC, a data base and optimizer DBO, and a plurality of driven-servo loops DSL1, DSL2, . . . DSLn. The temperature controller and the data base and optimizer monitor various parameters of the chilled water system. At periodic intervals, the system determines and stores the current values of these parameters. From this data, and from data determined from operator-selected signals supplied to the temperature controller, the temperature controller determines if a change in total operating capacity is required. If this determination is affirmative, the temperature contoller supplies a request for a system capacity adjustment to the data base and optimizer, which then proceeds to select the chillers to be operated and to adjust the capacity of the chillers so selected. In doing so, the data base and optimizer refers to a data base consisting of a matrix for each chiller that has stored therein chiller coefficient of performance values that are periodically updated to reflect actual chiller operation. The data base and optimizer uses an investigation of its data base to determine that combination of chillers and the operating capacity of each that will provide an optimum system coefficient of performance in meeting the requirement for a system capacity adjustment and correspondingly provides start/stop signals and desired operating capacity signals to the driver-servo loops which responsively provide capacity adjustment signals to the chillers.

Programmable load controller

Abstract: A control method and system for minimizing the on-peak power demand of a residential electric utility user having a plurality of loads is implemented by determining the average energy demand over predetermined sliding time windows and comparing them with a control point. Non-priority loads are shed in an attempt to decrease the demand below the control point. If the energy demand is still above the control point after all non-priority loads are shed, the control point is dynamically adjusted upward and no priority loads are shed. Loads are shed by transmitting bits of information to the loads when the average energy demand over the predetermined time windows increases beyond the control point. Upon receiving bits of information indicating a load should be shed, the receiver deenergizes its load. The bits of information are synchronized to the zero crossing of the AC line. The bits are transmitted simultaneously and periodically. Central load control may decrease the power demand of the user in one or more predetermined steps. A method is provided for controlling multi-phase demand where the angles between phases are not necessarily equal.

Video game hand controller

Abstract: A hand controller for use with a home electronic video game produces electrical control signals in response to manipulation of a control stick extending through an aperture in the controller housing. The control stick is attached to an actuator stem which forms part of a multi-position switch assembly within the housing. The switch assembly includes a helical coil spring which is attached at one end to an interior surface of the housing and is arranged to concentrically receive the actuator stem so as to support the actuator stem and control stick in an upright non-actuated position. Displacement of the control stick and actuator stem causes the helical spring to contact one or more of a plurality of electrical contact pads disposed generally concentrically around the spring. This causes appropriate control signal to be produced for application to the video game. The contact pads are shaped and positioned to create favored positions for the control stick which enhance the sense of control provided by the controller.

Inherent Overload Protection for the Series Resonant Converter

Abstract: The overload characteristics of the full bridge series resonant power converter are considered. This includes analyses of the two most common control methods presently in use. The first of these uses a current zero crossing detector to synchronize the control signals and is referred to as the ? controller. The second is driven by a voltage controlled oscillator and is referred to as the ? controller. It is shown that the ? controller has certain reliability advantages in that it can be designed with inherent short circuit protection. Experimental results are included for an 86 kHz converter using power metal-oxide-semiconductor field-effect transistors (MOSFETs).