Showing papers on "Open-loop controller published in 1989"

Stabilization of uncertain dynamic systems including state delay

Abstract: The authors consider a class of time-varying systems with time-varying state delay and uncertain input and parameters. They present sufficient conditions on the open loop to obtain an arbitrary-degree closed-loop stability. They construct a min-max controller from knowledge of the upper bound of the delay. >

A new technique for robust control of servo systems

Abstract: The robust controller has very simple structures and can be divided into two separate parts: a servo controller and an auxiliary controller. The two controllers are designed independently. The function of the auxiliary controller is to cancel out the plant uncertainties directly without the use of the high loop gain principle. Interpretation of robot controller as a signal-synthesis adaptive controller is given. Practical implementation issues of the auxiliary controller are discussed. Simulations of a design example with large parameter uncertainty, nonlinearity, and external disturbance are presented to demonstrate the effectiveness of the design technique. This technique is further tested with success in an experimental study of joint position control of a PUMA 560 robot arm. >

Distributed multiple irrigation controller management system

Abstract: Separate, but related, firmware programs for multiple microprocessor-controlled irrigation controllers (1) that are interrelated in their control of irrigation within an irrigation system are generated off-line at a personal computer (32). The programs are downloaded into a transportable memory device (30) that holds sixty-four separate programs. The memory device (30) is transported to each irrigation controller (1) and plugged to a digital communication channel (15). The device automatically identifies itself to the controller (1), and vice versa. The appropriate program is automatically uploaded from the device (30) to the controller (1). The controller's (1) old program and its historical irrigation record data is loaded into the device (30) and delivered to the personal computer (30) for validation and analysis. A wireless remote test command assembly (61), an extension maintenance panel (42), or a radio-link central module (50) may be alternatively connected to the controller's digital communication channel (15).

A state space formulation for model predictive control

Abstract: Model predictive control (MPC) schemes such as MOCCA, DMC, MAC, MPHC, and IMC use discrete step (or impulse) response data rather than a parametric model. They predict the future output trajectory of the process {ŷ(k + i), i = 1, …, P}, then the controller calculates the required control action {Δu(k + i), i = 0, 1, …, M − 1} so that the difference between the predicted trajectory and user-specified (setpoint) trajectory is minimized. This paper shows how the step (impulse) response model can be put into state space form thus reducing computation time and permitting the use of state space theorems and techniques with any of the above-mentioned MPC schemes. A series of experimental runs on a simple pilot plant shows that a Kalman filter based on the proposed state space model gives better performance that direct use of the step response data for prediction.

Stabilization of uncertain systems with norm bounded uncertainty-a control

Abstract: A robust stabilization problem in a state-space setting is treated. It is assumed that the states are available for feedback. Using a fixed Lyapunov function approach (quadratic stability) it is shown that an open loop stabilizability condition is equivalent to the existence of a stabilizing memoryless linear state-feedback controller. As a consequence, it is shown that the existence of a quadratically stabilizing nonlinear time-varying dynamic state-feedback controller implies the existence of a quadratically stabilizing memoryless linear time-invariant state-feedback compensator.

Apparatus and method for guaranteed data store in redundant controllers of a process control system

Abstract: In a process control system, having at least one process control unit which includes redundant equivalent controllers to reduce the impact of failure of the controllers in the process control unit, a technique is provided to guarantee that interruption of either the active (primary) controller or the backup (secondary) controller will not adversely effect the storage of data signals or the execution of commands by the process control unit. In the present invention, an information message or packet sent to the process control unit and, hence, to the active controller is forwarded to the backup controller before a response in the form of acknowledgement message is returned to the device issuing the information message or packet. The information message or packet is therefore stored in the same order in both the active controller and the backup controller and is executed in the same order by either controller. This technique is particularly important in a process control network of a process control system to insure successful monitoring and control functions for the process.

An indirect adaptive controller with a self-excitation capability

Abstract: An indirect adaptive pole placement controller is presented which stabilizes and asymptotically regulates any discrete-time single-input, single-output linear time-invariant plant which is of known order n, is controllable, and observable, and has unknown parameters. To avoid singular points in the algorithm, the adaptive controller solves the pole-placement design equation asymptotically with time rather than trying to solve it exactly at each time instant. The stability of the adaptive control system and the asymptotic regulation of the plant output to zero are ensured by an additional self-excitation generated by the adaptive controller. A novel kind of an error signal to control the magnitude of the self-excitation is obtained by suitably filtering the self-exciting signal and monitoring changes of the controller parameters as they are generated by the adaptive algorithm. >

Model reference adaptive control of a direct-drive DC motor

Abstract: An adaptive time-optimal position controller for a direct-drive DC motor with a design based on the model reference adaptive approach is presented. The high-acceleration torque of DC motors with permanent magnets permits direct coupling of the load to the motor axis, avoiding the use of a transmission with its inherent disadvantages (such as backlash and friction). However, direct coupling induces a large sensitivity to load variations, so the desired response and the reference model in the adaptive controller are adjusted to the motor capabilities. This is achieved by estimating the load inertia by means of a least-squares method and adjusting the reference model accordingly. The controller is tested on a direct-drive motor, and the results are compared with those obtained with a fixed proportional-integral-derivative controller. >

Adaptive Tracking Control for High Performance DC Drives

Abstract: This paper presents a novel application of a modified adaptive controller to a dc motor for high performance tracking applications, such as robotics, actuation and manipulation. By the proposed technique, the rotor position and/or the speed of the dc motor is forced to follow preselected tracks, even when the load condition varies. An algorithm based on Minimum Variance Self Tuning control is developed for this purpose. The adaptive controller is effective even in the presence of external disturbances, provided that the system exhibits minimum phase characteristics. The effectiveness of the controller is demonstrated by using a general purpose nonlinear simulation software. The simplicity of the algorithm and the promising test results prove that this proposed controller is very effective in high performance tracking applications.

Robust high-performance control for robotic manipulators

Abstract: A robust control scheme to accomplish accurate trajectory tracking for an integrated system of manipulator-plus-actuators is proposed. The control scheme comprises a feedforward and a feedback controller. The feedforward controller contains any known part of the manipulator dynamics that can be used for online control. The feedback controller consists of adaptive position and velocity feedback gains and an auxiliary signal which is simply generated by a fixed-gain proportional/integral/derivative controller. The feedback controller is updated by very simple adaptation laws which contain both proportional and integral adaptation terms. By introduction of a simple sigma modification to the adaptation laws, robustness is guaranteed in the presence of unmodeled dynamics and disturbances. >

Task-based methods for evaluating electrically stimulated antagonist muscle controllers

Abstract: Single-joint motor neural prosthesis control algorithms were tested in a novel animal model. The model consisted of a human subject who provided joystick inputs to a controller. The controller output determined the stimulus activation levels of two antagonist muscles which manipulated the ankle joint of an intact, anesthetized cat. Using visual feedback, the subject manipulated the system to perform positioning tasks which stimulated normal activity of an intact limb. Three controllers were evaluated: open-loop reciprocal control, proportional-differential (PD) closed-loop reciprocal control, and open-loop cocontraction control. The results demonstrated that, in the presence of visual feedback, open-loop cocontraction control compared favorably in performance to that of a PD closed-loop controller. This has a practical value for the implementation of clinical neural prostheses since it suggests that, in some cases feedback transducers may not be required for fine control. >

A robust self-tuning predictive controller for HVAC applications

Abstract: A robust form of self-tuning controller than has been designed to replace conventional PID controllers in a number of HVAC applications is described. The controller is based on a version of the generalized predictive control algorithm that uses default values for most of its parameters and requires selection of only one commissioning parameter: the control sampling interval. Special jacketing software has been developed to implement a set of expert rules, which are not application dependent, but which supervise the operation of the on-line parameter estimator and the calculation of control action. This ensures satisfactory operation of the controller in most situations. The performance of the controller is evaluated under demanding conditions using a detailed computer simulation of the central air handler in a building.

Nonlinear heat exchanger control through the use of partially linearized control variables

Abstract: The use of partial linearization by nonlinear state variable feedback has been proposed as a means of reducing the detrimental effects of system nonlinearities upon the performance of linear control schemes used with nonlinear systems. In this paper a set of generalized transformed variables are derived for a single pass shell and tube heat exchanger using this technique. The implementation of these generalized transformed variables, which reduce the apparent nonlinear behavior of single pass heat exchangers, eliminates the need to rederive a nonlinear transformation for each heat exchanger controller design. As shown by open loop transient behavior of the system, the transformed variables reduce the nonlinear characteristics of the system response. The closed loop performance of the heat exchanger system has been evaluated for both servo and regulator control, and the effect of model error upon the robustness of the closed loop controller performance has been investigated.

Design, implementation, and testing of an adaptable optimal controller for an electric wheelchair

Abstract: The design, implementation, and testing of an adaptable optimal controller for an electric wheelchair are presented. Optimal control theory and pattern recognition techniques are combined to produce the design of a controller using a modified proportional, integral, and derivative (PID) control method. The controller is adaptable in the sense that multiple sets of control coefficients are used with each set being optimized for a specific range of wheelchair load parameters. The appropriate set of control coefficients may be automatically selected based on load parameter estimates to provide a self-adaptive controller, or manually selected prior to installation to tailor the chair to a particular user. The manually adaptable controller is implemented in a microprocessor-based system. The experimental results obtained from installing and testing the system on an electric wheelchair are presented and discussed. >

Non-linear sliding-mode controller and objective function for surge tanks

Abstract: A non-linear feedback controller is proposed for the ‘averaging’ control of surge tanks subject to step flowrate disturbances. The controller operates by discont-inuously switching between two non-linear feedback rules. A switching function is constructed that results in a sliding-mode that brings the system to a steady state with a finite, bounded, and ultimately monotonic response. The properties of the controller are thoroughly described using a phase plane analysis. The effects of transducer errors are analysed and a controller tuning procedure is described. It is shown that a liquid volume setpoint can be introduced if the relative volume measurement error is less than 26.42 %. A simplified implementation using a piece-wise linear switching function is also proposed for which simulations and phase plane analysis show little performance degradation. Finally, it is shown that (he idealized ‘Ramp Controller’ proposed by McDonald el al. (1986) can be derived from a continuous and differentiable ...

Variable Structure and Time-Varying Parameter Control for Hydroelectric Generating Unit

Abstract: Conventional governor control for hydro-turbines is linear PI or PID with constant parameters. Thus, one set of constant PID parameters is used for different cases. In fact, the hydro-turbine governing system has variable structure and parameters. Therefore, fixed control structure and parameters are not the most suitable for various plant structures and a control with variable structure and parameters is more appropriate. An intelligent self-improving control strategy with both variable structure and parameters is developed. The controller is multistructural and parameter variable. The selection of control structure and the optimization and adjustment of control parameters are directed by a processing unit. This unit bases its action on the information received from another block that tracks the system operating conditions in real-time, and detects and identifies the plant structure and parameters.

An adaptive controller for a one-legged mobile robot

Abstract: An adaptive controller based upon the online minimization of a performance criterion is described. The adaptive controller is used to improve the performance of a one-legged mobile robot, removing problems experienced with previous controllers. Specifically, this controller eliminates the problem of a bias in the forward velocity experienced with the nonadaptive controller and, at the same time, provides the flexibility required to allow a dynamically stabilized legged machine to perform satisfactorily under the widely varying conditions that exist in the real world. The performance of several minimization algorithms is analyzed, and the adaptive step size random search algorithm is selected. Finally, a series of experiments illustrating the ability of the adaptive controller to handle a changing environment is presented. >

Programmable stepper motor controller

Abstract: A motor controller provides a digital monostable circuit which generates a control signal indicating whether a field coil within a motor should be turned on or off. Two registers are provided within the digital monostable to store values indicating a fixed off time and a minimum on time. These registers can be loaded with selected values by a microprocessor or other controller. The stored values are selectively loaded into a counter which, when the field coil current reaches a preselected level, turns the supply to the field coil off for a time corresponding to the off time value, then on again for a period at least as long as the minimum on time value. The values in the off time and minimum on time registers can be changed to suit operating conditions of the system, and the controller can be operated in either PWM or open loop mode.

A novel approach to the explicit pole assignment self-tuning controller design

Abstract: A recursive algorithm for the controller design phase of the adaptive pole assignment controller is presented. Compared to other pole-assignment adaptive controllers, the computation time to get the controller parameters is drastically reduced and the numerical stability of the controller parameters is increased. If persistent excitation is imposed, the system poles will be located at the desired position in the steady state and the global stability of the system can be easily obtained. >

Programmable weld and machine controller

Abstract: A programmable weld and machine controller for use in controlling a welding machine. The controller includes a central processing unit containing a stored control program connected to a memory which operates both the welding operation of the machine as well as the operation of the machine itself. The controller receives inputs from the machine in its various operational states as well as a data entry and display unit and a current monitor of the welding operation which generates outputs through a heat controlled output to activate a firing circuit to control the welding operation. Back-up of the memory program may be attained through an accessory port to a memory back-up storage unit.

Aeroassisted orbital maneuvering using Lyapunov optimal feedback control

Abstract: A Liapunov optimal feedback controller incorporating a preferred direction of motion at each state of the system which is opposite to the gradient of a specified descent function is developed for aeroassisted orbital transfer from high-earth orbit to LEO. The performances of the Liapunov controller and a calculus-of-variations open-loop minimum-fuel controller, both of which are based on the 1962 U.S. Standard Atmosphere, are simulated using both the 1962 U.S. Standard Atmosphere and an atmosphere corresponding to the STS-6 Space Shuttle flight. In the STS-6 atmosphere, the calculus-of-variations open-loop controller fails to exit the atmosphere, while the Liapunov controller achieves the optimal minimum-fuel conditions, despite the + or - 40 percent fluctuations in the STS-6 atmosphere.

Microprocessor implementation of a state feedback control strategy for a current source inverter-fed induction motor drive

Abstract: The realization of a microprocessor-based controller which implements a complete state-feedback control strategy for a current source inverter-fed induction motor drive is reported. The controller design is based on the application of the pole assignment technique of multivariable system regulation theory to a d,q-axis state-space linearized model of the drive and includes a reduced-order observer to achieve fast regulation and stability. The observer is designed to reconstruct the inaccessible states such as d,q-axis rotor current from a knowledge of the system inputs and outputs. The hardware and software implementation of the controller around an 8085-based microprocessor kit is discussed, and typical test results are presented, along with digital simulation results, to show its performance. >

On the characteristics of the robot manipulator controller using neural networks

Abstract: Several robot controller schemes using neural networks are proposed. To extract advantages from the neural network controller, it is necessary to clarify the capabilities of the neural networks to express a nonlinear function as well as the robustness of the controller. For this purpose, an inverse kinematics problem and a force control problem are presented. The characteristics of the neural network are compared to adaptive control for the robot controller using the force control problem as an example. >

Controller and a network controller system

Abstract: A controller for protection and monitoring of devices networked in a distribution system. The controller includes an input or pilot bus (d) enabling communication from and to the controller, a plurality of analog signal inputs (5-18) for receiving signals representative of conditions of the device being monitored and diagnostic circuitry (63) for periodically simulating desired conditions of the device, a plurality of programmable outputs (26-36) for providing control signals for controlling the device output diagnostic circuitry (67) for enabling one programmable output to control the device, a plurality of monitoring inputs (37-41) for receiving signals indicative of the state of the device, a plurality of alarm inputs (42-50), alarm diagnostic circuitry (65), a modulator/demodulator (64) and a computer (50) for controlling the controller.

Electronic control device for a drive system

Abstract: An engine (4) of a drive system (2) is adjusted and controlled by a main controller (24). When the main controller (24) breaks down, the operation of the engine can still be continued as emergency operation with an emergency controller (26). However, the controlling functions of the latter are not as optimum as those of the main controller (24). This functional deficiency of the emergency controller (26) is compensated for at least partly by an emergency program of an electronic transmission control device (28). To compensate for the functional deficiency of the emergency controller (26), the transmission control device (28) appropriately controls or regulates a transmission unit (6, 8, 10) of the drive system (2), which comprises a hydrodynamic torque converter (8) with a bridging clutch (10) that can bridge the latter, and a gear-shift mechanism (6).

High current multiterminal bushing controller

Abstract: An improved bushing controller is shown which utilizes an auxiliary transformer in each of the variable impedance circuits in the controller and the bushing tha the controller is connected to increase the current capability of the controller by a significant percentage. Improved performance of fiber glass bushings producing multiple forming packages is realized.