Showing papers on "Open-loop controller published in 1997"

The unfalsified control concept and learning

Abstract: Without a plant model or other prejudicial assumptions, a theory is developed for identifying control laws which are consistent with performance objectives and past experimental data-possibly before the control laws are ever inserted in the feedback loop. The theory complements model-based methods such as H/sup /spl infin//-robust control theory by providing a precise characterization of how the set of suitable controllers shrinks when new experimental data is found to be inconsistent with prior assumptions or earlier data. When implemented in real time, the result is an adaptive switching controller. An example is included.

Generalized preisach model for hysteresis nonlinearity of piezoceramic actuators

Abstract: This paper presents a new approach for modeling the hysteresis nonlinearity of a piezoceramic actuator using a modified generalized Preisach model, and the use of this model in a linearizing control scheme. The developed generalized Preisach model relaxes the congruency requirement on the hysteresis loops of a piezoceramic actuator, which must be satisfied when using the classical Preisach model. The congruency property is experimentally proved to not hold when running the actuator on a minor hysteresis loop. A numerical expression of the model is derived in terms of first- and second-order reversal curve experimental datasets. Output prediction using this model is performed on both an exponentially decayed sinusoidal input signal and an arbitrary input signal, and the results show that the model can accurately reproduce the hysteresis response with an error of less than 2.7%. A tracking control system for a piezoceramic actuator is also developed by combining a PID feedback controller with a hysteresis linearizing scheme in a feed-forward loop. The results show that this new control system can achieve 0.25 μm tracking control accuracy, which is 80 and 50% less than that obtained when using an open-loop controller and a regular feedback control system, respectively.

Accurate position control of a pneumatic actuator using on/off solenoid valves

Abstract: The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications is described. A novel pulse width modulation (PWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. The open-loop characteristic is shown both theoretically and experimentally to be near symmetrical. A comparison of the open- and closed-loop responses of standard PWM techniques and that of the novel PWM technique shows that there has been a significant improvement in the control. A linear process model is obtained from experimental data using system identification. A proportional integral derivative controller with added friction compensation and position feedforward has been successfully implemented. A worst case steady-state accuracy of 0.21 mm was achieved with a rise time of 180 ms for step inputs from 0.11 to 64 mm. Following errors to 64-mm S-curve profiles were less than 2.0 mm. The controller is robust to a sixfold increase in the system mass. The actuator's overall performance is comparable to that achieved by other researchers using servo valves.

Linear motor motion control using a learning feedforward controller

Abstract: The design and realization of an online learning motion controller for a linear motor is presented, and its usefulness is evaluated. The controller consists of two components: (1) a model-based feedback component, and (2) a learning feedforward component. The feedback component is designed on the basis of a simple second-order linear model, which is known to have structural errors. In the design, an emphasis is placed on robustness. The learning feedforward component is a neural-network-based controller, comprised of a one-hidden-layer structure with second-order B-spline basis functions. Simulations and experimental evaluations show that, with little effort, a high-performance motion system can be obtained with this approach.

Method and apparatus for synchronization of code in redundant controllers in a swappable environment

Abstract: Methods and associated apparatus for automatically synchronizing the operating code between a plurality of controllers. In a first embodiment after the spare controller is swapped into the storage subsystem, if the native controller determines that the spare controller's operating code is incompatible with the native controller's operating code, then the native controller notifies the spare controller that synchronization is required between both controllers. The native controller creates an image of its operating code including configuration parameters, and copies this "synch info" into a reserved area of cache memory. The spare controller's main CPU utilizes mirroring routines to copy the operating code and configuration parameters into a reserved area of its cache memory. After the transfer is complete, the spare controller's main CPU loads the operating code and configuration parameters into its program memory and resets itself to operate with the modified program memory. In a second embodiment, a co-processor within the spare controller updates the spare controller's operating code by executing a script. The native controller builds the script that includes the operating code, configuration parameters, and instructions to retrieve the operating code and configuration parameters from the native controller's cache memory. The spare controller's co-processor transfers the script to a reserved area in the spare controller's cache memory. The native controller requests the spare controller's co-processor to execute the script which causes the co-processor to retrieve the operating code using mirroring techniques and load the spare controller's program memory with the operating code. The co-processor sends an interrupt to the spare controller's main processor to reset the spare controller.

Controller and expansion unit for controller

Abstract: An extension unit (50, 60 or 70) is connected to the main body (10) of a controller provided with an analogue direction key (12), a digital direction key (14), indicating buttons (20a-20z), indicating levers (22l and 22r), etc. When the unit (50) having a light emitting section (52) is connected to the controller, a cordless controller becomes available. When the unit (60) having a photodetecting section is connected, a gunshot game for shooting enemies on the monitor screen can be played. When the unit (70) having a vibrating section (75) is connected, a realistic gunshot game can be played by vibrating the main body (10). Therefore, a new function can be added to the conventional controller freely without changing the main body (10).

Variable structure control of shape memory alloy actuators

Abstract: A shape memory alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that being limited strain. Time domain open loop experiments were then conducted to determine the intrinsic properties of the actuator. From these experiments and from the knowledge of the underlying physics of SMAs, a multiterm model, including linear and nonlinear elements, was proposed. After further investigation and simulation, it was found that most of these complexities did not need to be considered in order to explain the reported results, and that the model could be reduced to that of a single integrator. A variable structure controller was then applied to a pair of antagonist actuators. The feedback switches between the two actuators according to the sign of the displacement error. A further improvement was added to compensate for known gross nonlinearities by modulating the current magnitude in a discrete manner as a function of the state space position. It was therefore possible to realize smooth and robust control with very little cost in complexity.

Design and analysis of gain-scheduled control using local controller networks

Abstract: This paper describes a nonlinear control structure known as a local controller network. The structure consists of a weighted combination of a number of individual controllers, each of which is valid locally in the state space of the plant. Local controller designs are based upon local models valid in operating regimes which do not necessarily contain any physical equilibria. Consequently, the transient performance can be improved. Some 'scheduling' variables determine the current operating regime, and a validity function is assigned to each local controller. A 'feedforward' component may be used in each local controller in order to compensate directly for the operating-point-dependent model offsets. The application of the local controller network approach to a nonlinear control problem, that of longitudinal vehicle dynamics control, is described. A stability analysis for the discrete-time local controller network is given in this paper and the results are compared with known theoretical guidelines for rel...

Design and experience with a fuzzy logic controller for automatic generation control (AGC)

Abstract: This paper describes the design, implementation and operational performance of a fuzzy controller as part of the automatic generation control (AGC) system in Eskom's National Control Centre. The fuzzy controller was implemented in the control ACE (area control error) calculation, which determines the shortfall or surplus generation that has to be corrected. This paper sets out the problems associated with secondary frequency control and AGC. The difficulties associated with optimising the original standard AGC controller, the design, implementation and optimisation of the fuzzy controller and the operational performance of the new controller over two years, are discussed. The fuzzy controller was integrated into the existing off-the-shelf-AGC system with only a few modifications. The operational performance over two years showed an overall improvement of over 50% in the reduction of control compared to the original AGC controller, and an initial improvement of 20% in the quality of control of the optimised original controller.

Novel motors and controllers for high-performance electric vehicle with four in-wheel motors

Abstract: We have, in accordance with new concepts, undertaken the development of a high-performance electric motor vehicle, designated as the IZA. The main performance features of the IZA are a maximum speed of 176 km/h, a range of 548 km per charge at a constant speed of 30 km/h, and acceleration from 0 to 400 m in 18 s. We have developed a direct driving in-wheel motor and controller in order to achieve high performance characteristics. The in-wheel motor is composed of an outer rotor with a rare earth permanent magnet (Sm-Co) and an inner stator. The motor drive controller consists of a three-phase inverter and a microprocessor-based controller. The maximum output and maximum torque of each total drive system, including motor and inverter, are 25 kW and 42.5 kg/spl middot/m, respectively, and the total efficiency of the drive system is over 90% at the rated speed. The performance of the motor, controller, and drive system have been confirmed by numerous simplex and vehicle transit tests. This paper describes the design concepts, configuration, and performance of the motor, controller, and drive system developed for this high-performance electric vehicle.

Methods and systems for booting a computer in a distributed computing system

Abstract: A field mountable controller boots by transmitting a seed letterbug to a server. The server responds with an initial operating system and program. The program reads configuration information about the controller and transmits it back to the server which responds with a particular letterbug for the controller. The controller then transmits the letterbug to a boot image server which returns a corresponding operating system image to the controller. The controller then boots using the operating system.

Passivity-based control of a class of Blondel-Park transformable electric machines

Abstract: Concerns the extension to the general rotating electric machine model of the passivity-based controller method for induction motors. The motor's passivity properties are used at 2 levels. First, we prove that the motor model can be decomposed as the feedback interconnection of two passive subsystems (essentially, the electrical and mechanical dynamics). Then, we design a torque-tracking controller that preserves passivity for the electrical subsystem and leaves the mechanical part as a passive disturbance. This leads to the cascaded controller structure which is typically analyzed involving time-scale separation. Our aim is to characterize a class of machines for which such a passivity-based controller solves the output feedback torque-tracking problem. The class consists of machines whose nonactuated dynamics are damped and whose dynamics can be decoupled. This requires that the air-gap magnetomotive force must be suitably approximated by the first harmonic in its Fourier expansion. These conditions have a clear physical interpretation in terms of the couplings between its dynamics and are satisfied by many machines. The passivity-based controller presented reduces to the well-known indirect vector controller for current-fed induction machines. Our developments constitute an extension to voltage-fed machines of this de facto standard in industrial applications.

Distributed control system in which individual controllers executed by sharing loads

Abstract: A distributed control system includes a plurality of controllers each composed of a plurality of processors and being coupled through a network. Each controller includes a scheduler for measuring a load; internal backup means for controlling which controller bears the load; backup request means for requesting another controller to bear the load; and backup accept means for answering to a request for bearing the load from another controller in accordance with the load of the requesting controller. Thus, the load which cannot be executed by one controller can be distributed and executed by other controllers in accordance with their loads.

Motor control circuit

Abstract: A motor controller for regulating the application of current to the windings of a motor in order to both control the actuation of the motor rotor and the braking of the rotor. The motor controller includes a speed control circuit regenerating a signal representative of the user-selected speed, a direction controller to signal if the motor is to be driven in the forward, reverse or oscillatory motion and a speed override circuit. There is also a current sensor for monitoring the current drawn by the motor, a brake controller and an energization circuit. The energization circuit regulates the application of a current to the motor to cause the rotation or braking of the rotor. When the motor is to be oscillated, each time the direction controller circuit transitions a FORWARD/REVERSE signal, the speed override circuit causes the energization circuit to momentarily apply energization signals to the motor based on the application of a zero-speed, user-speed signal. During such transitions, the current sensor sends a signal to the energization controller to make it appear that the motor is drawing in a large amount of current. Whenever the motor is operating at a speed higher than the user-speed, the brake controller causes the energization controller to apply braking current to the motor. However, if the rotor is not turning, the brake controller inhibits the assertion of the braking current.

Programmable digital controller for switch mode power conversion and power supply employing the same

Abstract: A programmable controller for switch-mode power converters that operates in a digital domain without reliance on operation software and the ability to vastly reduce or eliminate analog circuitry The digital controller is re-programmable In one embodiment, the substantially digital portion of the controller is a Field Programmable Gate Array that controls operation of the converter by generally converting an analog reference signal(s) (eg the voltage output) into the digital domain The controller then can perform distributed arithmetic to generate a square wave signal capable of controlling at least a main switch of the converter The present invention can, if desired, essentially eliminate analog controllers in power conversion systems such as switch-mode converters

Torque ripple minimization in switched reluctance machines over a wide speed range

Abstract: A torque-ripple minimization technique for switched reluctance motors (SRMs) is presented. The technique is particularly suitable for applications requiring wide speed range of operation. A new, simple, yet efficient commutation strategy is proposed. The commutation algorithm is speed dependent and uses a real-time approach instead of precalculated stored data. The model used for the SRM in the controller can also be updated in real time. Simulation and experimental results verify the feasibility of implementing the proposed control algorithm in real time.

Control-system synthesis for open-loop unstable process with time delay

Abstract: To avoid performance limitations caused by an open-loop unstable pole, a three-element structure, which is equivalent to a two-degrees-of-freedom control design, is proposed to synthesise a control system for an open-loop unstable process with time delay. Through this proposed approach, control problems such as stabilising an unstable pole, servo-tracking and disturbance rejection can be treated independently. The resulting three-element structure can then be used to derive conventional two-degrees-of-freedom elements or conventional PID systems. Tuning rules for a PID controller are also provided. Examples are presented to illustrate the proposed method.

An eigenvalue sensitivity approach to location and controller design of controllable series capacitors for damping power system oscillations

Abstract: This paper presents tools and methods to study the application of controllable series capacitors for damping power system electromechanical oscillations. Two problems are discussed-location and controller design. The location of a controllable series capacitor consists of determining the series capacitor of the power system where the modulation of its series reactance will be more effective to damp out the modes of interest. It also involves the selection of the input variable to the controller. The basic design of the controller requires the design of the phase compensation network and the calculation of the controller gain. Small signal models of the power system and the corresponding eigenvalue sensitivities are used to address both problems.

Remotely controllable programmable controller for irrigation

Abstract: The activation and deactivation of a plurality of irrigation valves in accordance with instructions programmed into a programmable irrigation valve controller can be overridden by signals received by the controller from a remote control unit or a rain delay input. This allows remote control of sprinklers from the area being watered rather than at the location of the controller. This allows sprinkler repairs, modifications to watering patterns, and turning off and back on of sprinklers such as to access a portion of the irrigated area to be done without running back and forth to the controller. It also allows easy delay of watering after a rain. A construction of a programmable controller apparatus allows covering of wires extending from the apparatus and funneling of such wires into a conduit.

Intelligent position/force controller for industrial robot manipulators-application of fuzzy neural networks

Abstract: An intelligent controller, which consists of an intelligent planner and an adaptive fuzzy neural position/force controller, is proposed for a robot manipulator. The proposed controller deals with the human expert knowledge and skills for planning and control. In this paper, it is applied to the task of deburring with an unknown object. The effectiveness of the proposed controller is evaluated by computer simulations.

Synchronous current sharing pulse width modulator

Abstract: Multiple controllers connected in parallel to control external circuits such as dc-dc converters so that the external circuits supply power equally to a load such as a microprocessor. All of the controllers are connected and each controller includes an oscillator and a pulse width modulation circuit to synchronize the frequency of all of the oscillators such that the duty cycle of all the oscillators are equal. Each controller includes an over-current protection circuit and an over-voltage protection circuit which will cause the controller with a fault to discontinue supplying power to the load. Each controller further includes a circuit to adjust the duty cycle of the non-faulty controllers when a controller with a fault is caused to discontinue supplying power to the load.

Iterative controller optimization for nonlinear systems

Abstract: A data-driven model-free control design method has been proposed in Hjalmarsson et al (1994) It is based on the minimization of a control criterion with respect to the controller parameters using an iterative gradient technique In this paper, we extend this method to the case where both the plant and the controller can be nonlinear It is shown that an estimate of the gradient can be constructed using only signal based information It is also shown that by using open loop identification techniques, one can obtain a good approximation of the gradient of the control criterion while performing fewer experiments on the actual system

A study on position control of piezoelectric actuators

Abstract: The hysteresis characteristic of piezoelectric actuators makes precise position control very difficult. In this study a tracking control method for a piezoelectric actuator based on PID controller augmented with a feedback linearization loop based on the Maxwell slip model is presented. Further, the controller design is extended to include a repetitive controller. Experiments were performed on a piezoelectric 2-axis linear positioner for tracking sinusoidal waveforms and circles. The experimental results show that the tracking control performance is noticeably improved by augmenting the PID controller with a feedback linearization loop and repetitive controller.

A self-tuning EWMA controller utilizing artificial neural network function approximation techniques

Abstract: Recent works have shown that an exponentially weighted moving average (EWMA) controller can be used on semiconductor processes to maintain process targets over extended periods for improved product quality and decreased machine downtime. Proper choice of controller parameters (EWMA weights) is critical to the performance of this system. This work examines how different process factors affect the optimal controller parameters. We show that a function mapping from the disturbance state (magnitude of linear drift and random noise) of a given process to the corresponding optimal EWMA weights can be generated, and an artificial neural network (ANN) trained to learn the mapping. A self-tuning EWMA controller is proposed which dynamically updates its controller parameters by estimating the disturbance state and using the ANN function mapping to provide updates to the controller parameters. The result is an adaptive controller which eliminates the need for an experienced engineer to tune the controller, thereby allowing it to be more easily applied to semiconductor processes.

A Digital Robust Controller for Cutting Force Control in the End Milling Process

Abstract: In this work, a digital robust controller is designed via Quantitative Feedback Theory (QFT) to maintain a constant cutting force in the presence of parametric uncertainty for a time varying end milling process. The QFT controller is designed using the delta transform method for discrete systems. The controller is designed to limit the overshoot and settling time of the cutting force levels over a range of cutting parameters. Models are presented for the cutting process and machine dynamics including parametric uncertainty, and these models are used to develop a controller which meets given tracking and regulation specifications for all plant values. Experimental results are obtained by implementing the controller on a milling machine.