Showing papers on "Proportional control published in 2001"

Control of mobile platforms using a virtual vehicle approach

Abstract: Two model independent solutions to the problem of controlling wheel-based mobile platforms are proposed. These two algorithms are based on a so called virtual vehicle approach, where the motion of the reference point on the desired trajectory is governed by a differential equation containing error feedback. This, combined with the fact that the proven stable control algorithms are basically proportional regulators with arbitrary positive gains, make the solutions robust with respect to errors and disturbances, as demonstrated by the experimental results.

Contouring control of machine tool feed drive systems: a task coordinate frame approach

Abstract: We show that contouring performance can be viewed as a regulation problem in a moving task coordinate frame that is attached to the desired contour. By transforming the machine tool feed drive dynamics to this task coordinate frame, a control law is designed to assign different dynamics to the tangential and normal directions. The transformation also illustrated the effect of contour curvature and feed rate in the control action as well as the system dynamics in the task coordinate frame. The resulting control law consists of a linear time-varying proportional-plus-derivative (PD) position error feedback control law and a linear time invariant trajectory feedforward control law. Experimental results of the proposed control law on the motion axes of a machining center, Matsuura MC510V, showed significant improvement of the contouring accuracy compared to the existing servo controller as well as the successful decoupling between the tangential dynamics and the normal (contouring) dynamics for feedrate up to 6 m/min (4 in/s).

Two Reconfigurable Flight-Control Design Methods: Robust Servomechanism and Control Allocation

Abstract: Two methods for control system reconfiguration have been investigated. The first method is a robust servomechanism control approach (optimal tracking problem) that is a generalization of the classical proportional-plus-integral control to multiple input-multiple output systems. The second method is a control-allocation approach based on a quadratic programming formulation. A globally convergent fixed-point iteration algorithm has been developed to make onboard implementation of this method feasible. These methods have been applied to reconfigurable entry flight control design for the X-33 vehicle. Examples presented demonstrate simultaneous tracking of angle-of-attack and roll angle commands during failures of the fight body flap actuator. Although simulations demonstrate success of the first method in most cases, the control-allocation method appears to provide uniformly better performance in all cases.

Neural-network-based self-tuning PI controller for precise motion control of PMAC motors

Abstract: In general, proportional plus integral (PI) controllers used in computer numerically controlled machines possess fixed gain. They may perform well under some operating conditions, but not all. To increase the robustness of fixed-gain PI controllers, we propose a new neural-network-based self-tuning PI control system. In this new approach, a well-trained neural network supplies the PI controller with suitable gain according to each operating condition pair (torque, angular velocity, and position error) detected. To demonstrate the advantages of our proposed neural-network-based self-tuning PI control technique, both computer simulations and experiments were executed in this research. During the computer simulation, the direct experiment method was adopted to better model the problem of hysteresis in the AC servo motor. In real experiments, a PC-based controller was used to carry out the control tasks. Results of both computer simulations and experiments show that the newly developed dynamic PI approach outperforms the fixed PI scheme in rise time, precise positioning, and robustness.

Piezomechanics using intelligent variable-structure control

Abstract: The so-called piezomechanics contain three parts: piezoelectric translator, carriage mechanism, and control system. It is well known that piezomechanics have three drawbacks: (1) it should only be loaded axially; (2) it contains a hysteresis feature; and (3) its expansion is dependent on temperature. The first drawback is tackled by the design of the carriage mechanism. This paper focuses on dealing with the second and third drawbacks by using an intelligent variable-structure control. First, a neural network is employed to learn the dynamics of the piezomechanism. Second, a novel forward control based on the learned model is employed to achieve an acceptable tracking result. Because the tracking performance by a forward control cannot be guaranteed as the system is subject to uncertainties, a discrete-time variable-structure control is synthesized to improve the performance. No state estimator is required for the proposed control. The stability of the overall system is verified via the Lyapunov analysis. Experiments are also presented to confirm the effectiveness of the proposed control.

Interconnection and damping assignment approach to control of PM synchronous motors

Abstract: We apply the energy-shaping controller design technique to the speed regulation of permanent magnet synchronous motors. To illustrate different design choices, two controllers are presented along with their stability analysis. The resulting schemes consist of a static state feedback to which a simple nonlinear observer is added to estimate the unknown load torque. It is shown that, for isotropic rotor machines, we can set the tuning gains to recover a controller often used in industrial applications, where a nonlinear observer is used instead of a simple proportional integral (PI) speed loop. Thus, the proposed scheme constitutes a possible upgrade to current practice which, in view of the availability of a complete stability analysis, should be easier to tune and yield an improved performance. Simulations and experimental results are presented to illustrate the performance of the proposed scheme.

Design and implementation of a hard disk drive servo system using robust and perfect tracking approach

Abstract: This paper deals with the problem of a servo system design for a conventional hard disk drive with a single voice-coil-motor actuator using a so-called robust and perfect tracking (RPT) approach. We first model the physical system and then formulate it into a robust and perfect tracking problem, in which a measurement feedback controller can be obtained to achieve a robust and perfect tracking for any step reference, i.e., the L/sub p/-norm of the resulting tracking error with 1/spl les/p

Friction modeling and adaptive compensation using a relay feedback approach

Abstract: In this paper, the application of a dual-relay feedback approach toward modeling of frictional effects in servomechanisms is addressed. The friction model consists of Coulomb and viscous friction components, both of which can be automatically extracted from suitably designed relay experiments. At the same time, the dynamical model of the servomechanical system can be obtained from the experiments. Thus, a proportional-integral-derivative feedback motion controller and a feedforward friction compensator can be automatically tuned in this manner. The friction model obtained is also directly applicable to initialization of an adaptive control scheme proposed. Results from simulation and experiments are presented to illustrate the practical appeal of the proposed method.

Robust PI controller design for nonlinear systems via fuzzy modelling approach

Abstract: The design problem of proportional and proportional-plus-integral (PI) controllers for nonlinear systems is studied. First, a Takagi-Sugeno fuzzy model with parameter uncertainties is used to approximate the nonlinear systems. Then a numerically tractable algorithm based on the technique of iterative linear matrix inequalities is developed to design a proportional (static output feedback) controller for the robust stabilization of the system in Takagi-Sugeno fuzzy model. Thirdly, we transform the problem of PI controller design to that of proportional controller design for an augmented system and thus bring the solution of the former problem into the configuration of the developed algorithm. Finally, the proposed method is applied to the design of robust stabilizing controllers for the excitation control of power systems. Simulation results show that the transient stability can be improved by using a fuzzy PI controller when large faults appear in the system, compared to the conventional PI controller designed by using a linearization method around the steady state.

Sliding integral proportional (SIP) controller for aircraft skid control

Abstract: The sliding, integral, and proportional controller for providing aircraft antiskid braking control includes a reference velocity subsystem, a velocity error ratio subsystem, and a main controller subsystem generating a control command output signal indicative of a command braking pressure. The main controller subsystem includes a one dimensional sliding mode controller subsystem to determine an estimated net wheel torque signal, an adaptive threshold subsystem for generating an adaptive threshold based upon the modified slip ratio signal and a clock signal, integral gain subsystems, a proportional controller subsystem, and a pressure limiter. A method for determining braking efficiency of an aircraft braking system independent of the specific conditions is also provided.

Measurement and control of business processes

Abstract: It is widely accepted that any well-designed organizational process includes a control mechanism through which management decides which aspects of the performance of the process are to be measured and how these measurements are to be used to change the level of resources utilized in the process. Little is known, however, about the best ways to design such a control mechanism for typical business processes. Our goal in this research is to identify control mechanisms for business processes that are effective in different types of environments. In this article we present a system dynamics model of a typical service-sector business process, such as is used in processing administrative paperwork in insurance, banking, and so on. These processes are subject to random, time-varying, and non-postponable demands for service. They are also subject to randomness in processing times, as well as delays in the observation of system performance and in the execution of control actions. We assume management has the dual objectives of maximizing profits (revenues on completed work less the costs of labor employed) and keeping cycle times below a predetermined ceiling. In order to achieve these objectives it observes the state of the process and adjusts its labor force accordingly. Management must chose which of several aspects of process performance to measure (cycle time, backlog, or demand) and the parameters governing the control process. Our analysis highlights the interactions among the demand environment faced by the process (e.g., random or seasonal), the control signal chosen (e.g., cycle time or backlog), and the type of control used (e.g., proportional or differential). Our results suggest that, regardless of the demand environment, a control process based on system backlog is generally more robust than the alternatives in the sense that adequate performance is achieved over a broader range of control parameters. We also find that, in most cases, proportional control by itself is inadequate to provide effective performance and that differential control is a necessary adjunct. We conclude the article with a discussion of the managerial implications of this research.

Neuro-predictive process control using online controller adaptation

Abstract: A novel architecture for integrating neural networks with industrial controllers is proposed, for use in predictive control of complex process systems. In the proposed method, a conventional PI controller is used to control the process. In addition, a recurrent neural network is used in the form of a multistep-ahead predictor to model the process dynamics. The parameters of the PI controller are tuned by a backpropagation-through-time like approach using "parallel learning" to achieve acceptable regulation and stabilization of the controlled process. The advantage of such a formulation is the effective online adaptation of the controller parameters while the process is in operation, and the tracking of the different process operating regimes and variations. The proposed method is used in the stabilization and transient control of U-tube steam generator water level. The proposed predictive controller stabilizes the process and improves its transient performance over the entire operating range.

Model reference robust speed control for induction-motor drive with time delay based on neural network

Abstract: Proposes a novel model-reference robust speed control with a load torque estimator and feedforward compensation based on a neural network (NN) for induction motor drives with time delay. First, a two-layer neural network torque estimator (NNTE) is used to provide real-time identification for an unknown load torque disturbance. The backpropagation algorithm was used as the learning algorithm. In order to guarantee the system's convergence and to obtain faster NN learning ability, a Lyapunov function is also employed to find the bounds of the learning rate. Since the performance of the closed-loop controlled induction motor drive is influenced greatly by the presence of the inherent system dead-time during a wide range of operations, a dead-time compensator (DTC) and a model-reference-following controller (MRFC) using a NN proportional controller (NNPC) are proposed to enhance the robustness of the PI controller. A theoretical analysis, simulation and experimental results all demonstrate that the proposed model-reference robust control scheme can improve the performance of an induction motor drive with time delay, and can reduce its sensitivity to system parameter variations and load torque disturbances.

Improved transient and steady state voltage regulation for single and three phase uninterruptible power supplies

Abstract: Most of the many reported control algorithms for uninterruptible power supplies use either filter inductor or filter capacitor currents as feedback variables to regulate the output voltage. This paper explores the fundamental performance issues associated with the use of these quantities as feedback variables, with a view to determining their contribution to the transient system response in any particular situation. Then a proportional plus resonant (P+resonant) compensator is added into the outer voltage regulation loop to achieve zero steady error, to develop a high performance UPS control algorithm which is applicable to both single and three phase systems. Theory, simulation and experimental results are presented in the paper.

Closed-loop actuator control system having bumpless gain and anti-windup logic

Abstract: A closed-loop actuator control system includes a single PI controller for controlling one or more actuators to minimize an error between an engine operating parameter value and a reference parameter value. In multiple actuator systems, the control system of the present invention is operable to drive one actuator to its upper limit before transferring control to the next actuator. The proportional gain block of the PI controller preferably includes a bumpless gain feature operable to limit the rate of change of the proportional gain to thereby provide smooth gain scheduling. A feedforward block may optionally be included that preferably includes the bumpless gain feature. The actuator control system further includes anti-windup logic operable to disable the PI integrator if the actuator drive signal is upper or lower limit bounded and the error signal is greater or less than zero respectively, thereby creating dynamic saturation of the PI integrator.

Control system design for a rapid thermal processing system

Abstract: Proposes a control system design for a rapid thermal processing (RTP) system, which has four circular concentric lamp zones and four temperature sensors. The control system consists of a least square feedforward controller and an output feedback proportional plus integral (PI) controller. The goal is to maintain uniform temperature tracking for typical ramp-up and hold-steady profiles. A high-order nonlinear model describing the temperature dynamics of the rapid thermal processing (RTP) system is used for the feedforward controller design. A balanced reduced model, obtained from a linear model around a desired uniform steady-state temperature, is used for the design of the multiinput-multioutput PI controller. The PI controller gain matrices are designed using an LQR-based procedure. Tradeoff between robustness and performance of the system is discussed. Simulation results show the control system designed yields robust temperature tracking with good uniformity for a wide temperature range.

Proportional controls used with displayed imagery

Abstract: Proportional (or analog) controls for controlling imagery shown by a display, and more particularly electronic game imagery shown on a television. Proportional controls creating signals according to varying depression applied by a finger or thumb finger of a human user to the proportional control. In one preferred embodiment the proportional controls include resilient dome caps for providing tactile feedback to the user. In another preferred embodiment the proportional controls are included in a controller with active tactile feedback. In another preferred embodiment multiple axes of input are taught and the structures of the various preferred embodiments are taught in combination for controlling three-dimensional electronic game imagery and communicating tactile feedback to the user.

Experimental Evaluation of a High-Gain Control for Compressor Surge Suppression

Abstract: The present paper considers the suppression of surge instability in compression systems by means of active control strategies based on a high-gain approach. A proper sensor-actuator pair and a proportional controller are selected which, in theory, guarantee system stabilization in any operating condition for a sufficiently high value of the gain. Furthermore, an adaptive control strategy is introduced which allows the system to automatically detect a suitable value of the gain needed for stabilization, without requiring any knowledge of the compressor and plant characteristics. The control device is employed to suppress surge in an industrial compression system based on a four-stage centrifugal blower. An extensive experimental investigation has been performed in order to test the control effectiveness in various operating points on the stalled branch of the compressor characteristic and at different compressor speeds. On one hand the experimental results confirm the good performance of the proposed control strategy, on the other they show some inherent difficulties in stabilizing the system at high compressor speeds due to the measurement disturbances and to the limited operation speed of the actuator.Copyright © 2001 by ASME

A parsimonious model for the proportional control valve

Abstract: A generic non-linear dynamic model of a direct-acting electrohydraulic proportional solenoid valve is presented. The valve consists of two subsystems—a spool assembly and one or two unidirectional proportional solenoids. These two subsystems are modelled separately. The solenoid is modelled as a non-linear resistor-inductor combination, with inductance parameters that change with current. An innovative modelling method has been used to represent these components. The spool assembly is modelled as a mass-spring-damper system. The inertia and the damping effects of the solenoid armature are incorporated in the spool model. The model accurately and reliably predicts both the dynamic and steady state responses of the valve to voltage inputs. Simulated results are presented, which agree well with experimental results.

A single-actuator control design for hydraulic variable displacement pumps

Abstract: It has been shown that the conventional two-actuator configuration for the discharge pressure control of variable displacement axial piston pumps essentially is an open loop unstable system, which imposes inherent constraints on the stability and performance of the closed loop control design. In addition, a large force is required to balance the load generated by the two parallel actuators, which in turn requires large size bearings to hold the swash plate in place. To overcome these two drawbacks in the conventional pump configuration, a novel control configuration is proposed in this paper. By balancing the torque induced from the pressure carry-over angle, the presented control design uses only one actuator that is arranged in a manner such that the open loop dynamics are strictly stable. Efficient control algorithms are developed for the proposed new scheme. Experimental tests show some significant advantages of the proposed design over the conventional counterpart.

System and method for closed loop speed control for stop and go applications

Abstract: A system and method for closed loop speed control for stop and go applications allowing adaptive cruise control operation at low speeds below vehicle idle speed by use of traction control system braking. The system comprises: proportional controller to hold the vehicle speed at the desired vehicle speed; integral controller to reduce vehicle speed when the adaptive cruise control cuts off speed control; stopped controller to overcome static friction after a vehicle stop; open loop controller to hold the vehicle speed a set speed below the vehicle idle speed. The system also provides a switch to set the torque command to zero for large positive speed control errors, such as when the desired speed is above the vehicle idle speed, and a transition logic to provide a smooth transition between alternate control mode operation and speed control mode operation.

Temperature control strategies for radiant floor heating systems

Abstract: A dynamic model of a radiant floor heating (RFH) system useful for control analysis is developed. The overall model consists of a boiler, an embedded tube floor slab and building enclosure. The overall model was described by nonlinear differential equations, which were solved using finite numerical methods. The predicted responses from the model were compared with published experimental data. The comparisons were made covering a wide range of weather and operating conditions under several different control strategies. The model predictions compare well with the experimental data. The effective thermal capacity of the floor slab was found being an important parameter in calibrating the model results with the experimental data. Three different control strategies for improving the temperature regulation in RFH systems are proposed. These are: a multistage on-off control, an augmented constant gain control (ACGC) and a variable gain control (VGC). Simulation results show that the multistage control maintains zone air temperature close to the setpoint better than the existing on-off control scheme does. Likewise, ACGC gives good zone temperature control compared to the classical proportional control. A model based approach for updating the controller gains of the VGC is proposed. Both ACGC and VGC are shown to be robust to changes in weather conditions and internal heat gains. The advantage of the control strategies proposed in this thesis is that they eliminate the use of outdoor temperature sensor required in some existing control schemes. Being simple and robust, the multistage control scheme with two stages and the ACGC are good candidate controls for RFH systems.

An adaptive static VAr compensator using genetic algorithm and radial basis function network for enhancing power system stability

Abstract: This paper presents an approach to enhance power system damping with long distant bulk power transmission by a static VAr compensator (SVC) using a radial basis function (RBF) network. A genetic algorithm (GA) employing the concept of hierarchical genetic algorithm (HGA) has been applied for designing an optimal proportional-integral-derivative (PID) controller for a SVC by selecting a necessary control type and optimizing those of control parameters under various operating conditions. An RBF network is then trained by using these data. The effectiveness of this control method is verified by simulation results compared with those from an optimal fixed gain PID controller using a GA without an RBF network.

Adaptive PID controller for stable/unstable linear and non-linear systems

Abstract: Proposes and analyzes a direct adaptive proportional-integral-derivative (APID) control scheme for off-line and online tuning of PID parameters. The tuning algorithm determines a set of PID parameters by minimizing an error function. The theory of adaptive interaction is used to design the APID control law. Two versions of the tuning algorithm are presented: the Frechet and approximation methods. These algorithms are applied to linear and nonlinear plants. Lyapunov stability theory is used to proof the stability of the approximation method. The analysis of the convergence properties and system performance are conducted by using computer simulations and several known adaptation concepts. The approximation method does not require the knowledge of the plant to be controlled; therefore, the control scheme becomes robust to plant changes.

Dynamic model of a pneumatic proportional pressure valve

Abstract: A dynamic nonlinear model of a commercial proportional pressure valve, type Lucifer Honeywell EPP3 J-21-U-100-10, is formulated in order to simulate its behavior in time-domain under several operating conditions. The mechatronic design of the valve and its static and dynamic characteristics are analyzed carefully. Then, the modeling of the valve is carried out by taking into account its main internal devices, which are integrated all together inside the valve in order to allow the pressure control through an input electric signal. Finally, some diagrams given by a computer simulation confirm the validity of the proposed dynamic nonlinear model for this type of proportional valve.

Enhanced control system for a static synchronous series compensator with energy storage

Abstract: A strategy is presented for the decoupled control of real and reactive power flows in an energy storage based static series synchronous compensator (SSSC). State-variable based design methods are employed in the basic design, which uses only proportional control. Increased robustness to ac parameter changes is implemented by enhancing this basic design with a control structure that internally uses a state-variable model of the plant. The design is corroborated via electromagnetic transient simulation.