Showing papers on "Control theory published in 1989"

Bilateral control of teleoperators with time delay

Abstract: A control law for teleoperators is presented which overcomes the instability caused by time delay. By using passivity and scattering theory, a criterion is developed which shows why existing bilateral control systems are unstable for certain environments, and why the proposed bilateral control law is stable for any environment and any time delay. The control law has been implemented on a single-axis force-reflecting hand controller, and preliminary results are shown. To keep the presentation clear, a single-degree-of-freedom (DOF) linear time-invariant (LTI) teleoperator system is discussed. Nevertheless, results can be extended, without loss of generality, to an n-DOF nonlinear teleoperation system. >

Flight Stability and Automatic Control

Abstract: 1Introduction 2 Static Stability and Control 3 Aircraft Equations of Motion 4 Longitudinal Motion (Stick Fixed) 5 Lateral Motion (Stick Fixed) 6 Aircraft Response to Control on Atmospheric Inputs 7 Automatic Control Theory-The Classical Approach 8 Application of Classic Control Theory to Aircraft Autopilot Design 9 Modern Control Theory 10 Applications of Modern Control Theory to Aircraft Autopilot Design Appendixes A Atmospheric Tables B Geometric, Mass, and Aerodynamic Characteristics of Selected Airplanes C Mathematical Review of Laplace Transforms and Matrix Algebra D Review of Control System Analysis Techniques

Learning to control an inverted pendulum using neural networks

Abstract: An inverted pendulum is simulated as a control task with the goal of learning to balance the pendulum with no a priori knowledge of the dynamics. In contrast to other applications of neural networks to the inverted pendulum task, performance feedback is assumed to be unavailable on each step, appearing only as a failure signal when the pendulum falls or reaches the bounds of a horizontal track. To solve this task, the controller must deal with issues of delayed performance evaluation, learning under uncertainty, and the learning of nonlinear functions. Reinforcement and temporal-difference learning methods are presented that deal with these issues to avoid unstable conditions and balance the pendulum. >

Controller reduction: concepts and approaches

Abstract: The problem of passing from a linear time-invariant high-order controller designed for a linear time-invariant plant (of presumably high order) to a low-order approximation of the controller is discussed. The approximation problem is often best posed as a frequency-weighted L/sub infinity / approximation problem. Many different controller representations are possible, giving different performances of the various reduction algorithms. >

Development of fuzzy algorithms for servo systems

Abstract: Consideration is given to the possibility of applying fuzzy algorithms in a microprocessor-based servomotor controller, which requires faster and more accurate response compared with other industrial processes. The performance of proportional-integral-derivative control, model reference adaptive control, and fuzzy controllers is compared in terms of steady-state error, settling time, and response time. Limitations of fuzzy control algorithms are described. >

Microprocessor controlled arthroscopic surgical system

Abstract: An apparatus for controlling the speed of a plurality of DC motors, comprises a device for supplying voltage to one of the plurality of DC motors, first selector for selecting one of the DC motors to be connected to the device for supplying voltage, second selector for selecting a desired speed for the selected DC motor, a device for producing a feedback signal representative of an electrical current drawn by the selected DC motor and a controller for: (i) producing a reference voltage in response to the first and second selectors (ii) producing a load voltage in response to the feedback signal and (iii) outputting a control signal which is the sum of the reference voltage and the load voltage to the device for supplying voltage so that the selected DC motor is operated at the desired speed.

Force and position control of manipulators during constrained motion tasks

Abstract: Trajectory control of a manipulator constrained by the contact of the end-effector with the environment represents an important class of control problems. A method is proposed whereby both contact force exerted by the manipulator, and the position of the end-effector while in contact with the surface are controlled. The controller parameters are derived based on a linearized dynamic model of the manipulator during constrained motion. Hence the method is valid only in a neighborhood about the point of linearization. Additionally, a perfect kinematic model of the contact surface is assumed. The proposed method utilizes the fundamental structure of the dynamic formulation of the manipulator's constrained motion. With this formulation, the trajectory control problem is naturally expressed in terms of the state vector variables of the model of the constrained dynamic system. A detailed numerical example illustrates the proposed method. >

An adaptive controller for power system load-frequency control

Abstract: An adaptive controller is presented for load-frequency control of power systems. It uses a PI (proportional-integral) adaptation to satisfy the hyperstability condition for taking care of the parameter changes of the system. Only the available information on the states and output are required for the control. No explicit parameter identification is needed. The controller can be designed by using a reduced plant model to simplify the design without degrading the performance much, so it is very easy to implement practically. The simulation results indicate that good control performance can be obtained and that the performance is sensitive to the plant parameter changes. The control remains effective in the presence of generation rate constraints. >

Object impedance control for cooperative manipulation: theory and experimental results

Abstract: The dynamic control module of the Dynamic and Strategic Control of Cooperating Manipulators (DASCCOM) project for aerospace robotics is presented. The cooperative manipulation problem is analyzed from a systems perspective, and the desirable features of a control system for cooperative manipulation are discussed. A control policy is developed that enforces a controlled impedance not of the individual arm endpoints, but of the manipulated object itself. A parallel implementation for a multiprocessor system is presented. The controller fully compensates for the system dynamics and directly controls the object internal forces. Most importantly, it presents a simple, powerful, intuitive interface to higher level strategic control modules. Experimental results from a dual two-link-arm robotic system show the effectiveness of the object impedance controller compared to other strategies, both for free-motion slews and environmental contact. >

Analysis and Synthesis of Time Delay Systems

Abstract: Intended as a comprehensive review of the modern theory of control systems described by functional-differential equations, this book gives emphasis to methods and results which are applicable to analysis and synthesis of industrial control systems with time delays. It is designed for those with knowledge of mathematical methods of control theory, although not all chapters require this. The introductory chapters have examples of systems with delays and typical control problems. Also included are basic results of the mathematical theory of functional-differential and discrete equations.

An analysis of contact instability in terms of passive physical equivalents

Abstract: The authors explore the sources of and solutions to robot contact instability associated with force feedback. The behavior of several linear robot models is analyzed in terms of the properties of their admittances. Using the novel technique of passive physical equivalents, an explanation for the often-observed instability of a force-controlled robot contacting a stiff surface is offered, and it is shown that a fundamental limit exists to the efficacy of any force feedback controller implemented on a robot with noncolocated actuators and sensors. Suggestions for improved force control involving both mechanical design and compensator design are also presented. >

Real-time application of neural networks for sensor-based control of robots with vision

Abstract: A practical neural network-based learning control system is described that is applicable to complex robotic systems involving multiple feedback sensors and multiple command variables. In the controller, one network is used to learn to reproduce the nonlinear relationship between the sensor outputs and the system command variables over particular regions of the system state space. The learned information is used to predict the command signals required to produce desired changes in the sensor outputs. A second network is used to learn to reproduce the nonlinear relationship between the system command variables and the changes in the video sensor outputs. The learned information from this network is then used to predict the next set of video parameters, effectively compensating for the image processing delays. The results of learning experiments using a General Electric P-5 manipulator are presented. These experiments involved control of the position and orientation of an object in the field of view of a video camera mounted on the end of the robot arm, using moving objects with arbitrary orientation relative to the robot. No a priori knowledge of the robot kinematics or of the object speed of orientation relative to the robot was assumed. Image parameter uncertainty and control system tracking error in the video image were found to converge to low values within a few trials. >

A novel position sensor elimination technique for the interior permanent-magnet synchronous motor drive

Abstract: An approach to the position sensor elimination of an interior permanent magnet (IPM) synchronous motor drive is proposed. The phase inductance of an IPM synchronous motor varies appreciably as a function of the rotor position. This feature is utilized to get an estimate of the rotor position. Analytical equations are developed for the calculation of the phase inductance of an IPM motor driven by a current-controlled PWM power converter with a hysteresis controller. The calculated phase inductance is used to estimate the position of the rotor. To obtain an unambiguous relation between the phase inductance and the rotor position, the phase inductance of phases a, b, and c is calculated during different segments of each electrical cycle. A direct approach to inductance calculation is proposed. Simulation results show the effectiveness of the controller. The position error is very small for speed control applications. A current regulator using constant-frequency switching is analyzed in order to avoid the random switching of the hysteresis current controller. >

Novel space vector based current controllers for PWM-inverters

Abstract: Two novel, simple control strategies for current-controlled pulse-width modulated (PWM) transistor inverters are presented. Both methods are based on the three-level hysteresis comparators which select appropriate inverter output voltage vectors via a switching electrically programmable read-only memory (EPROM) table. The first controller works with current components represented in a stationary coordinate system (AC components) and the second with components represented in a rotated (field-oriented) coordinate system (DC components). The theoretical principles of these methods are discussed. The results of a comparative study, which illustrates the performance of the proposed controller in comparison to the most popular scheme (based on three independent two-level hysteresis comparators), are presented. >

Nonlinear stabilizing control of multimachine systems

Abstract: It is of great importance to improve stability as well as dynamic performances of power systems for both small and large disturbance. Such issues have received a great deal of attention and many contributions have been made to this objective. However, some of the design methods developed previously are based on second-order synchronous generator model, so excitation systems or/and governor systems could hardly be considered by them, the others based on linear models, which are set up by approximate linearizing at an equilibrium point of the system. Since, in fact, a power system is a nonlinear dynamic one, the controller designed by using the approximate linearized model may cause untolerable errors, while the state point of the system is changed away from the equilibrium point at which the linearization is realized. A new approach to nonlinear decoupled optimal control based on the differential geometric control theory for interconnected power systems is proposed. And it is successfully applied to nonlinear steam valving control of multimachine systems. For an m-machine system the optimal steam valving control law of the ith-machine can be expressed as ui= TS; ii(K1-M& 1+ K2 cw-+ K3; | wdt + TsiPei+ (Pmj-Pmjo) (18) where Mi inertia coefficient (in sec.) Tsi, time constant of servomotor and steam (in sec.) wi, speed (in per unit) Di damping coefficient Pei electrical power (in per unit) Pmi mechanical power (in per unit) and K1j, K2j, and K3j are optimal feedback gain coefficients.

Decentralized adaptive control of manipulators: theory, simulation, and experimentation

Abstract: The author presents a simple decentralized adaptive control scheme for multijoint robot manipulators based on the independent joint control concept. The control objective is to achieve accurate tracking of desired joint trajectories. The proposed control scheme does not use the complex manipulator dynamic model, and each joint is controlled simply by a PID (proportional-integral-derivative) feedback controller and a position-velocity-acceleration feedforward controller, both with adjustable gains. Simulation results are given for a two-link direct-drive manipulator under adaptive independent joint control. The results illustrate trajectory tracking under coupled dynamics and varying payload. The proposed scheme is implemented on a MicroVAX II computer for motion control of the three major joints of a PUMA 560 arm. Experimental results are presented to demonstrate that trajectory tracking is achieved despite coupled nonlinear joint dynamics. >

Instability analysis and robust adaptive control of robotic manipulators

Abstract: The robustness of adaptive controllers with respect to uncertainty is examined. The uncertainties include bounded input disturbances, unknown and time-varying plant parameters, and unmodeled dynamics. A simple example shows instability of a recent manipulator control scheme in the presence of bounded disturbances. The adaptive laws for updating the controller parameters are modified so that instabilities are counteracted and robustness is guaranteed. >

Digital Control Of Repetitive Errors In Disk Drive Systems

Abstract: Tracking errors in disk drive systems have a significant repetitive component that is not explicitly taken into account in conventional servo controllers. Three specialized digital controllers applied as plug-in modules to a winchester disk drive with a pre-existing analog feedback controller to demonstrate their efficacy in the reduction of this periodic component. These controllers include the discrete time repetitive controller which is based on the internal model principle and feedforward cancellation controllers based on an adaptive prediction algorithm and on input and output measurements of the system.

Torque limited path following by on-line trajectory time scaling

Abstract: A feedback scheme for path following by trajectory time scaling is presented. The scheme is used in execution of fast trajectories along a geometric path, where the motion is limited by torque constraints. The time scaling is done by using a secondary controller that modifies a nominal trajectory during motion. The nominal, high-performance trajectory typically leads to torques that are at the limits, hence leaving no control authority to compensate for modeling errors and disturbances. By modifying the time scaling of the nominal trajectory when the torques saturate, closed-loop action is possible. A key idea is that a scalar quantity, the path acceleration, is modified, resulting in coordinated adjustment of the individual joint motions. Two algorithms for online trajectory scaling are presented. One is based on online bounds on path acceleration, and one is designed to handle nominal minimum-time trajectories. The functionality of the secondary controller is verified by simulations and experiments. >

Control strategies for direct torque control using discrete pulse modulation

Abstract: A scheme for direct torque control of AC machines using discrete pulse modulated inverters, such as the resonant DC link inverter, is presented. A unique feature of the control method presented is that only one current sensor in the DC link is required. Excellent control of torque, stator flux and motor current waveshapes is obtained without affecting the high dynamic performance associated with the direct self-control of machines. A control that does not use the zero voltage vector is defined, and an observer is proposed for estimation of the motor current using only one current sensor in the DC link. A direct bang-bang (sliding mode) torque controller is then derived on the basis of this current observer. Experimental verification of simulation results on a resonant DC link inverter drive with a switching frequency of 27 kHz is included. The inverter switching scheme is implemented using a real-time Motorola DSP56000 digital signal processor-based controller. >

Adaptive design of Petri net controllers for error recovery in automated manufacturing systems

Abstract: The concept of Petri net controllers is extended to include automatic error recovery and adaptive design. In the Petri net controller considered, a place that represents an operation or a state of a machine is attached to two functions and a constant so that it can represent a system working with both normal states and abnormal states. In addition, it is possible to detect an error with the controller using watchdog timers. Four basic Petri net augmentation methods for error recovery are investigated: input conditioning, alternate path, feedback error recovery, and forward error recovery. The authors demonstrate that when these methods are used to augment the Petri net controller, some important properties of the controller are guaranteed to be preserved. These properties include boundedness or safety, liveness, reversibility and the essentially decision-free property. An example of augmentations for error recovery for a piston insertion cell with two robots is given. >

Adaptive control of flexible joint manipulators

Abstract: The authors present an adaptive control result for flexible-joint robot manipulators. Under the assumption of weak joint elasticity, a singular perturbation argument is used to show that recent adaptive control results for rigid robots can be used to control flexible-joint robots, provided a simple correction term is added to the control law to damp out the elastic oscillations at the joints. In this way, fundamental properties of rigid robot dynamics can be used to design robust adaptive control laws for flexible-joint robots. The implementation of the full controller requires only joint position and velocity information. Thus, robustness to parametric uncertainty is achieved without the need for acceleration and jerk measurements. >

Some tractable supervisory control problems for discrete-event systems modeled by Buchi automata

Abstract: Discrete-event systems (DES) are modeled by Buchi automata together with a means of online control. In this setting the concept of a controllable language is extended to infinite strings, and conditions for the existence of a supervisor (controller) to implement a prescribed closed-loop behavior are derived. The focus is on a class of DES called product systems. These are DES composed of a finite set of asynchronous components. A control problem for such a system typically requires the synthesis of an online controller so as to achieve some prescribed coordinated behavior of the component subsystems. One of the principal difficulties in this task is that the size of the state space increases exponentially with the number of components. It is shown that despite this fact several interesting control synthesis problems for such systems are computationally feasible, and algorithms are developed for solution. >

Variable speed DC motor controller apparatus particularly adapted for control of portable-power tools

Abstract: A portable electric power tool having a DC motor for driving tool bit is controlled according to speed and torque by employing a zero displacement switch means which is coupled to the tool and operative to provide an output voltage porportional to the pressure applied to the switch means via the hand of the user. The zero displacement switch interfaces with a piezoresistive array which produces a voltage output proportional to the pressure applied to the zero displacement switch. The voltage output of the array is applied to control circuit means which are coupled to the motor and which controls the speed of the motor according to the pressure applied to the switch. There is further included motor control circuitry which operates to monitor the current through the DC motor to control the speed of the motor according to the torque imparted upon the tool bit being accommodated by the portable electric tool.

Deadtime compensation for nonlinear processes

Abstract: Many industrially important processes feature both nonlinear system dynamics and a process deadtime. Powerful deadtime compensation methods, such as the Smith predictor, are available for linear systems represented by transfer functions. A Smith predictor structure in state space for linear systems is presented first and then directly extended to nonlinear systems. When combined with input /output linearizing state feedback, this Smith-like predictor makes a nonlinear system with deadtime behave like a linear system with deadtime. The control structure is completed by adding an external linear controller, which provides integral action and compensates for the deadtime in the input/output linear system, and an open-loop state observer. Conditions for robust stability with respect to errors in the deadtime and more general linear unstructured multiplicative uncertainties are given. Computer simulations for an example system demonstrate the high controller performance that can be obtained using the proposed method.

Neural Network Control of Unknown Nonlinear Systems

Abstract: A method for using neural networks to control unknown dynamic systems is presented. The method can be regarded as an adaptive controller for time-invariant nonlinear systems with completely unknown dynamics, except for the system order. A backpropagation neural network is used to model the unknown nonlinear system on-line, based on a functional representation relating plant inputs to plant outputs. The same neural network is used to generate the control signals given the measurements of the current states and the desired values of future states. Although a backpropagation network with supervised learning is used, the training is based on measurement data obatined during the system operation, so that there is no need for an outside "teacher" telling the neural controller about the correct control signals.

Fluid delivery control and monitoring apparatus for a medication infusion system

Abstract: A fluid delivery monitoring and control apparatus for use in a medication infusion system is designed for use with a disposable fluid pathway that incorporates a sterile cassette containing pumping elements and sensor interfaces. The apparatus comprises a multi-segment drive mechanism, controller, and monitoring system. Fluid pumping is accomplished by controlling DC motors in the drive mechanism, each of which is coupled to two valves and a reciprocating piston for an individual pumping channel in the cassette. The motor is geared down to provide an appropriate maximum speed and torque. A cam sequentially actuates an inlet valve, piston, and an outlet valve in the cassette. A range of fluid delivery rates is achieved by periodically sending pulses to the motor. The output flow rate of the pump is maintained by a digital feedback controller which uses closed-loop feedback control to provide accurate regulation. At regular time intervals, the controller computes the motor voltage pulse width based upon feedback information from an encoder.

Application of precomputed control laws in a reconfigurable aircraftflight control system

Abstract: A self-repairing flight control system concept in which the control law is reconfigured after actuator and/or control surface damage to preserve stability and pilot command tracking is described. A key feature of the controller is reconfigurable multivariable feedback. The feedback gains are designed off-line and scheduled as a function of the aircraft control impairment status so that reconfiguration is performed simply by updating the gain schedule after detection of an impairment. A novel aspect of the gain schedule design procedure is that the schedule is calculated using a linear quadratic optimization-based simultaneous stabilization algorithm in which the scheduled gain is constrained to stabilize a collection of plant models representing the aircraft in various control failure modes. A description and numerical evaluation of a controller design for a model of a statically unstable high-performance aircraft are given.