Showing papers on "Control theory published in 1992"

Gaussian networks for direct adaptive control

Abstract: A direct adaptive tracking control architecture is proposed and evaluated for a class of continuous-time nonlinear dynamic systems for which an explicit linear parameterization of the uncertainty in the dynamics is either unknown or impossible. The architecture uses a network of Gaussian radial basis functions to adaptively compensate for the plant nonlinearities. Under mild assumptions about the degree of smoothness exhibit by the nonlinear functions, the algorithm is proven to be globally stable, with tracking errors converging to a neighborhood of zero. A constructive procedure is detailed, which directly translates the assumed smoothness properties of the nonlinearities involved into a specification of the network required to represent the plant to a chosen degree of accuracy. A stable weight adjustment mechanism is determined using Lyapunov theory. The network construction and performance of the resulting controller are illustrated through simulations with example systems. >

Trust, control strategies and allocation of function in human-machine systems.

Abstract: As automated controllers supplant human intervention in controlling complex systems, the operators' role often changes from that of an active controller to that of a supervisory controller. Acting as supervisors, operators can choose between automatic and manual control. Improperly allocating function between automatic and manual control can have negative consequences for the performance of a system. Previous research suggests that the decision to perform the job manually or automatically depends, in part, upon the trust the operators invest in the automatic controllers. This paper reports an experiment to characterize the changes in operators' trust during an interaction with a semi-automatic pasteurization plant, and investigates the relationship between changes in operators' control strategies and trust. A regression model identifies the causes of changes in trust, and a ‘trust transfer function’ is developed using lime series analysis to describe the dynamics of trust. Based on a detailed analysis of ...

Learning and tuning fuzzy logic controllers through reinforcements

Abstract: A method for learning and tuning a fuzzy logic controller based on reinforcements from a dynamic system is presented. It is shown that: the generalized approximate-reasoning-based intelligent control (GARIC) architecture learns and tunes a fuzzy logic controller even when only weak reinforcement, such as a binary failure signal, is available; introduces a new conjunction operator in computing the rule strengths of fuzzy control rules; introduces a new localized mean of maximum (LMOM) method in combining the conclusions of several firing control rules; and learns to produce real-valued control actions. Learning is achieved by integrating fuzzy inference into a feedforward network, which can then adaptively improve performance by using gradient descent methods. The GARIC architecture is applied to a cart-pole balancing system and demonstrates significant improvements in terms of the speed of learning and robustness to changes in the dynamic system's parameters over previous schemes for cart-pole balancing. >

Output feedback stabilization of fully linearizable systems

Abstract: An observer-based controller is designed to stabilize a fully linearizable nonlinear system. The system is assumed to be left-invertible and minimum-phase. The controller is robust to uncertainties in modelling the nonlinearities of the system. The design of the controller and the stability analysis employs the techniques of singular perturbations. A new ‘Tikhonov-like’ theorem is presented and used to analyse the system when the control is globally bounded.

Active Structural Control: Theory and Practice

Abstract: Actively controlled structures control algorithms - practical considerations control mechanisms optimization of actively controlled structures. Appendices.

Exponential stabilization of mobile robots with nonholonomic constraints

Abstract: An exponentially stable controller for a two-degree-of-freedom robot with nonholonomic constraints is presented. Although this type of system is open-loop controllable, this system has been shown to be nonstabilizable via pure smooth feedback. A particular class of piecewise continuous controllers is shown to exponentially stabilize the mobile robot about the origin. This controller has the characteristic of not requiring infinite switching like other approaches, such as the sliding controller. Simulation results are presented. >

Evolving dynamical neural networks for adaptive behavior

Abstract: We would like the behavior of the artificial agents that we construct to be as well-adapted to their environments as natural animals are to theirs. Unfortunately, designing controllers with these properties is a very difficult task. In this article, we demonstrate that continuous-time recurrent neural networks are a viable mechanism for adaptive agent control and that the genetic algorithm can be used to evolve effective neural controllers. A significant advantage of this approach is that one need specify only a measure of an agent's overall performance rather than the precise motor output trajectories by which it is achieved. By manipulating the performance evaluation, one can place selective pressure on the development of controllers with desired properties. Several novel controllers have been evolved, including a chemotaxis controller that switches between different strategies depending on environmental conditions, and a locomotion controller that takes advantage of sensory feedback if available but th...

System identification and control using genetic algorithms

Abstract: It is shown how genetic algorithms can be applied for system identification of both continuous and discrete time systems. It is shown that they are effective in both domains and are able to directly identify physical parameters or poles and zeros. This can be useful because changing one physical parameter might affect every parameter of a system transfer function. The estimates of poles and zeros are then used to design a discrete time pole placement adaptive controller. Simulations for minimum and nonminimum phase systems and a system with unmodeled dynamics are presented. >

Multiple control-point control system and method of use

Abstract: A control system for rapid fault tolerant control of a multiple control-point apparatus is disclosed The system comprises: a host subsystem acting as a user interface; a plurality of control-point actuators; a master controller subsystem which receives initialization data from the host terminal and which generates behavior commands; and a control-point controller subsystem which receives behavior commands from the master controller subsystem and generates control-point actuator commands The control-point controller subsystem is made fault tolerant by using a plurality of control-point processors connected to control-point interfaces through a programmable crossbar switch such that if any of the control-point processors develops a fault, the crossbar switch will connect one of the other control-point processors to the control-point interface previously serviced by the faulty control-point processors The master controller subsystem can be made fault tolerant by including an odd number of at least three master processors in the master controller subsystem such that each master processor runs a common control program in parallel with every other master processor and the master control output for each master processor is compared with the other master control outputs to generate the output common to the majority of master processors as the majority control output

A passivity approach to controller-observer design for robots

Abstract: Passivity-based control methods for robots, which achieve the control objective by reshaping the robot system's natural energy via state feedback, have, from a practical point of view, some very attractive properties. However, the poor quality of velocity measurements may significantly deteriorate the control performance of these methods. In this paper the authors propose a design strategy that utilizes the passivity concept in order to develop combined controller-observer systems for robot motion control using position measurements only. To this end, first a desired energy function for the closed-loop system is introduced, and next the controller-observer combination is constructed such that the closed-loop system matches this energy function, whereas damping is included in the controller- observer system to assure asymptotic stability of the closed-loop system. A key point in this design strategy is a fine tuning of the controller and observer structure to each other, which provides solutions to the output-feedback robot control problem that are conceptually simple and easily implementable in industrial robot applications. Experimental tests on a two-DOF manipulator system illustrate that the proposed controller-observer systems enable the achievement of higher performance levels compared to the frequently used practice of numerical position differentiation for obtaining a velocity estimate. >

Applications of hysteresis switching in parameter adaptive control

Abstract: The hysteresis switching algorithm of R.H. Middleton et al. (ibid., vol.33, no.1, p.50-8, Jan. 1988) is reexamined in a broader context. To demonstrate its utility, the algorithm is applied to various families of identifier-based parameterized controllers of both the direct and indirect control types. Application to the direct control type results in a model reference adaptive controller capable of stabilizing, without excitation, any SISO process which can be modeled by a minimum phase linear system whose transfer function has relative and McMillan degrees not exceeding prescribing integers m and n, respectively. It is shown that such processes can also be adaptively stabilized with indirect adaptive controllers and hysteresis switching. A simple numerical example involving a non-minimum-phase process model is used to illustrate how hysteresis switching might be applied to implicitly tuned parameterized controllers to realize an adaptive controller with capabilities which might prove very difficult, if not impossible, to achieve without hysteresis switching or some other form of discontinuous control. >

Predictive Control: A Unified Approach

Abstract: Unified predictive controller design analysis of design parameters predictive control with controller output constraints applications conclusions and suggestions.

An extended Kalman filter approach to rotor time constant measurement in PWM induction motor drives

Abstract: A rotor time constant estimation technique for the purpose of updating the control gains of an induction motor field-oriented controller is described. An extended Kalman filter is employed to estimate the inverse rotor time constant online only using measurements of the stator voltages and currents and rotor speed of an induction motor. The motor is driven by a pulsewidth modulated (PWM) inverter with or without current feedback loops. By utilizing the wideband harmonic contents inherent in conventional PWM voltage waveforms, no external random test signal is required for parameter estimation. Both computer simulation and experimental results show that the filter is capable of estimating the rotor time constant while the rotor speed is either constant or time varying. >

Adaptive Control of Plants with Unknown Dead-zones

Abstract: Model reference adaptive controllers are designed for plants with unknown dead-zones. Several control strategies are investigated in which two sets of adjustable parameters, one belonging to a dead-zone inverse and the other to a linear controller, are either kept fixed or adaptively updated. The developed adaptive control schemes ensure boundedness of all closed-loop signals and reduce the tracking error.

6 Degrees of freedom controller with capability of tactile feedback

Abstract: Described and shown is a six degree of freedom physical to electrical converter with capability of tactile feedback, specifically, a human hand operated input controller with the capability of vibration feedback in the handle. Two embodiments, each capable of translating complex three dimensional linear and rotational forces into their constituent orthogonal vectors are described and shown. Also described and shown are various different sensor types which can be implemented in the embodiments. The embodiments have physical space between sensors and actuators maintained by resilient means, enabling tactile feedback (vibration) to be induced directly in the handle without erroneously activating sensors.

A new approach to the discretization of continuous-time controllers

Abstract: A new method for discretizing continuous-time controllers is derived, using principles of controller approximation. It focuses on the closed-loop use of the discrete-time controller. The resulting approximation criterion is a measure for stability of the control system, provides an upper bound on the sampling time for which stability can be guaranteed, and because it is based on continuous-time controller approximation it indicates the cost of discretization in terms of performance degradation. The discrete-time controller is obtained through minimization of this criterion, which can be performed with standard software used in H/sub infinity / controller design. >

DMD display system controller

Abstract: A method and structure for providing system control to a spatial light modulator display are disclosed. The control functions are divided into smaller, easier to implement control blocks and coordination between them is provided. The smaller blocks are a memory controller, a modulator controller and a formatter controller.

Power window or panel controller

Abstract: A controller for energizing a power-operable element, such as a sunroof, window, door, vehicle seat, a component of a major appliance or of a machine or of a conveyor system. The disclosed controller senses both hard and soft obstructions and de-activates or otherwise alters operation of a motor that drives the element when an obstruction is detected. The controller can also be used to actuate a brake. The controller senses obstructions during start-up of the motor and regulates the speed of the power-operable element by pulse width modulating motor energization signals.

Multiple-model adaptive predictive control of mean arterial pressure and cardiac output

Abstract: A multiple-model adaptive predictive controller has been designed to simultaneously regulate mean arterial pressure and cardiac output in congestive heart failure subjects by adjusting the infusion rates of nitroprusside and dopamine. The algorithm is based on the multiple-model adaptive controller and utilizes model predictive controllers to provide reliable control in each model subspace. A total of 36 linear small-signal models were needed to span the entire space of anticipated responses. To reduce computation time, only the six models with the highest probabilities were used in the control calculations. The controller was evaluated on laboratory animals that were either surgically or pharmacologically altered to exhibit symptoms of congestive heart failure. During trials, the controller performance was robust with respect to excessive switching between models and nonconvergence to a single dominant model. A comparison with a previous multiple-drug controller design is made. >

Practical Distillation Control

Abstract: Techniques and methods Methods: Rigorous modelling and conventional simulation Approximate and simplified models Plant-wide process control simulation Selection of controller structure Control structures, consistency and transformations Diagonal controller tuning Dynamic matrix control multivariable controllers Distillation expert systems Robust control case studies Experimental comparison of control structures Industrial experience with double quality control Control of distillation columns via distributed control systems Process design and control of extractive distillation Control by tray temperature of extractive distillation Distillation control in plant-wide control environment Model-based control Superfractionator control Control of vapor recompression distillation columns Heat-integrated columns Batch distillation.

Synchronization of Two Motion Control Axes Under Adaptive Feedforward Control

Abstract: In this paper, motion synchronization of two d-c motors, or motion control axes, under adaptive feedforward control is considered. The adaptive feedforward control system for each axis consists of a proportional feedback controller, an adaptive disturbance compensator and an adaptive feedforward controller. If the two adaptive systems are left uncoupled, a disturbance input applied to one of the two axes will cause a motion error in the disturbed axis only, and the error becomes the synchronization error. To achieve a better synchronization, a coupling controller, which responds to the synchronization error, i.e., the difference between the two motion errors, is introduced. In this case, when a disturbance input is applied to one axis, the motion errors appear in the undisturbed axis as well as in the disturbed axis. The motion error in the undisturbed axis is introduced by the coupling controller and the adaptive feedforward controller. The adaptive synchronization problem is formulated and analyzed in the continuous time domain first, and then in the discrete time domain. Stability conditions are obtained. Effectiveness of the adaptive synchronization controller is demonstrated by simulation.

Extended quadratic controller normal form and dynamic state feedback linearization of nonlinear systems

Abstract: In this paper, a set of extended quadratic controller normal forms of linearly controllable nonlinear systems is given, which is the generalization of the Brunovsky form of linear systems. A set of invariants under the quadratic changes of coordinates and feedbacks is found. It is then proved that any linearly controllable nonlinear system is linearizable to second degree by a dynamic state feedback.

A practical guide to tune of proportional and integral (PI) like fuzzy controllers

Abstract: A method for tuning a PI-like fuzzy controller is proposed. The relationship between parameters and performance of the fuzzy controller is discussed. This includes defining the relationships between parameters and control performance, which parameters are more important and which are less important, which parameters should be tuned first and which later, and in which direction parameters should be adjusted. The result is a guide for tuning fuzzy control systems. >

Methods and apparatus for controlling operating subsystems of a motor vehicle

Abstract: Parameters for operation of a number of vehicle operating subsystems are stored in a vehicle controller and selected to control and configure the operating subsystems. Control and configuration can be based on individual recognized operators of the vehicle or an operating mode can be selected for the vehicle. For example, sport, cruise, luxury, off-road or other performance modes can be set up and selected. If a vehicle is to be operated by an authorized person who is not a recognized operator or is not authorized to select a mode of operation, default operating characteristic parameters are stored and selected. If the authorized person is to be restricted in the possible operation of the vehicle, a further set of limited operating characteristic parameters are stored and selected, preferably by entry of control signals corresponding to a security code. For example, if a valet is parking the vehicle, the limited operating parameters are selected. For security purposes, the limited operating parameters can be invoked after a defined period of time. Diagnostic and maintenance of the vehicle is provided by monitoring at least the operating subsystems connected to the vehicle controller and recording diagnostic data. The controller communicates accumulated data to a service center on a periodic or as needed basis for analysis by the service center. The service center in turn communicates with the controller regarding service needed by the vehicle. The controller then advises operators of the vehicle of the information received from the service center.