Conventional Linear Control Research Articles

Intelligent supervision of servo control

In this paper two types of intelligence supervised controllers are proposed with the aim to achieve an overall performance beyond the limit of linear controllers. In each case, the overall controller has a hierarchical structure with two conventional linear controllers in the bottom layer to perform accurate control action under the supervision of a reasoning process in the top layer. The reasoning process consists of heuristic rules drawn from our physical insight, and can easily be implemented either by fuzzy logics or by IF … THEN statements. Both intelligence supervised controllers achieve a performance beyond the limit of linear control laws, and are superior to both a fuzzy controller and a neural controller at least in the sense that their performances are independent of the type of command.

Fuzzy logic control of chip form during turning

Chips produced during lathe turning should be broken so as to prevent snarling and to enhance heat removal from the tool. At present, conservatively written part programs for computer numerically controlled lathes are fine tuned by a human machine operator to produce desirable chip length. K. W. Yee and coworkers have produced an acoustic emission chip form monitor. The use of such an acoustic emission sensor in a simulated chip length control system is described. In this paper a fuzzy logic controller is then substituted for the conventional linear controller.

A new state feedback control of resonant converters

A state feedback control that can be easily implemented is proposed to improve the stability and dynamic characteristics of resonant power converters. An important characteristic of the system with the proposed control is the reduction of order in the discrete time domain. The design parameters of the control are reduced by one, compared with those of the conventional linear state feedback control, and the design procedure is similar to that of a variable structure system (VSS) control. The proposed control is illustrated by its application to a series resonant power converter. The experimental results confirm the validity of the proposed control.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparative Implementation Studies of the Minimal Control Synthesis Algorithm on a Class 1 Manipulator

The minimal controller synthesis (MCS) algorithm (1) is a novel form of adaptive control, which has been shown to be particularly effective in a number of diverse areas (2). In particular, the problem of general manipulator control, using MCS, has been successfully analysed and simulated in previous works (3, 4). The intention of this paper is to provide the first implementation results of MCS upon a manipulator. It is shown that MCS produces results that are far superior to those produced by an equivalent conventional (linear) control algorithm.

Fuzzy hybrid control for DC servomotor.

In recent years, fuzzy control has found significant applications in many engineering fields. However, the design method of fuzzy control systems has not been established yet, and it is difficult to realize a precise control because control signals are derived from fuzzy scheme of inferences. On the other hand, it is well known that a conventional PD linear control can offer a precise control.In this paper, a new hybrid control scheme is proposed, which is attempt to combine the advantages of PD control and a fuzzy control. In the points which are close to the reference point, a PD control is mainly used to obtain the precision, and in other points a fuzzy contol is mainly used to improve the transient response and to cope with the nonlinearity of systems. From the experimental results on position control of DC servomotor, it is confirmed that the proposed hybrid controller performes better than either PD or fuzzy control.

Fuzzy control theory: A nonlinear case

Sources of nonlinearity in a fuzzy controller include the fuzzification algorithm used for the controller inputs; fuzzy control rules; type of fuzzy logic used for evaluating the fuzzy control rules; and the defuzzification algorithm used for the controller output. We analyze the performance of a simple fuzzy controller with linear and nonlinear defuzzification algorithms. We prove theoretically that such a fuzzy controller, the smallest possible, with two inputs (error and rate change of error) and a nonlinear defuzzification algorithm is equivalent to a nonfuzzy nonlinear proportional-integral (PI) controller with proportional-gain and integral-gain changing with error and rate change of error about a setpoint. Furthermore, this fuzzy controller is precisely equivalent to a conventional linear PI controller if a linear defuzzification algorithm is employed. Computer simulation showed that the performance of the fuzzy controller was almost the same as that of the PI controller when first-order and second-order linear processes were used. Furthermore, the fuzzy controller was significantly better when a first-order with a time delay model was used. More importantly, the simulated result illustrated that the fuzzy controller was stable when a nonlinear process model was controlled, but the PI controller was unstable.

Compensation of solid friction in a servo system by an extended Kalman filter.

Solid friction in mechanical control systems causes undesirable effects such as a jerking motion. Taking account of negative gradient characteristics from a static friction to a kinetic one, we propose an extended Kalman filter algorithm for solid friction estimation. An application of this estimation technique to a servo system is proposed in this paper. The proposed controller consists of a conventional linear controller and the extended Kalman filter. The real-time estimate given by the extended Kalman filter is fed back so as to cancel the solid friction. Using hybrid simulation where a plant with a solid friction is simulated by an analogue computer and the controller is simulated by a digital computer, we compare the performance of the proposed controller with that of a controller which neglects the negative gradient characteristics of the friction. The result shows that the proposed controller provides better performance.

State Estimation and Control for Semi-Batch Polymerization Reactors

A strategy is proposed for estimating and controlling properties of a styrene/butadiene rubber (SBR) latex produced in a semi-batch reactor operation. The suboptimal nonlinear strategy features a nonlinear state estimator, a nonlinear open-loop feedforward compensator, and a linear feedback controller to correct for errors in the feedforward control actions. In arriving at a nonlinear state estimator, three approaches, extended Kaiman filtering, extended Kaiman filtering with global reiteration, and a nonlinear optimization approach were considered. The second approach was found to be the most effective and was therefore adopted. The importance of introducing sufficient meaningful nonstationary states is discussed in order to have consistent state estimates when nonideal conditions exist. Using the knowledge of the modelled chemical reaction mechanisms, open-loop feedforward actions are proposed based on establishing conditions for maintaining fixed instantaneous copolymer properties. These open-loop/feedforward policies establish quasi-steady state conditions on the instantaneous copolymer properties to be controlled. This allows the application of conventional linear feedback control to correct for errors remaining after the open-loop/feedforward actions. Simulation results are presented to demonstrate the effectiveness of the proposed scheme.

Stabilizing controls for a doubly fed synchronous-induction machine

The stability of a doubly-fed synchronous-induction machine is investigated through small as well as large perturbation models. Two stabilizing control strategies have been proposed for the small perturbation bilinear model. The first is based on quadratic bilinear regulator theory, and the second provides a suboptimal control based on minimization of time. The responses are compared with the uncontrolled ones as well as those with conventional linear regulator control. While both the proposed strategies stabilize the system, the minimum-time suboptimal control is found to be superior. >

Adaptive Pulse Width Control for Precise Positioning Under the Influence of Stiction and Coulomb Friction

Conventional linear digital control fails to provide precise positioning of a control object under the influence of static friction, Coulomb friction, and backlash. This paper presents an adaptive pulse width control (PWC) scheme for a precise point-to-point positioning system. This scheme is developed based on the relationship between the displacement of a control object due to a single pulse input and the pulse width. The coefficient appearing in this relationship is estimated by a parameter adaptation algorithm. Sufficient conditions for asymptotic stability of this adaptive scheme are developed using Popov hyperstability theorem. This adaptive PWC is tested on a laboratory positioning table and is shown to be effective.

Time-Optimal Control of Robotic Manipulators Along Specified Paths

The minimum-time manipulator control problem is solved for the case when the path is specified and the actuator torque limitations are known. The optimal open-loop torques are found, and a method is given for implementing these torques with a conventional linear feedback control system. The algorithm allows bounds on the torques that may be arbitrary functions of the joint angles and angular velocities. This method is valid for any path and orientation of the end- effector that is specified. The algorithm can be used for any manipulator that has rigid links, known dynamic equations of motion, and joint angles that can be determined at a given position on the path.

Integral load frequency controller with time-varying weighting coefficients

Area control error (ACE) is used as the input variable in conventional load-frequency controllers. ACE is a sum of total tie-line powder deviation and area frequency error with constant weights on each variable. Because the systems are nonlinear, the relative strength of these two variables should be adjusted to match the system operating conditions. A modified algorithm to form ACE with time-varying weights on the two variable is proposed. Results for a two-area system show improved system performance over conventional linear control with constant weights.

Ward-Leonard characteristics from nonlinearly-controlled series-motor drives

Two methods are explored for improving the manoeuvrability of fork-lift trucks driven by chopper-controlled series motors. The first method attempts nonlinear feedforward cancellation of one system state (speed) but is shown to be unstable by simulation and analytical solution of the system equations. The instability results from neglect of field inductive effects in the feedforward model. A second method employs synthesised torque and transient-velocity estimates derived purely from armature current feedback. The method is shown by simulation to be highly tolerant of uncertainty in the vehicle and drive parameter estimates and to produce overall control characteristics resembling those of Ward-Leonard drives. The manual handling of the truck on a variable-gradient test track shows a considerable improvement on conventional linear current control systems.

Online optimal control of arc impedance for an electric-arc-furnace model

The dynamic behaviour of an electrode-position control system for an industrial direct electric-arc furnace is investigated. The electrode-positioning servomechanism is modelled as an electromechanical system with transfer-function relationships and nonlinear valve characteristics defining the hydromechanical system. The electrical-power-transmission-system model is based on single-phase circuit equations and incorporates an empirical arc-discharge characteristic. A dynamic representation of the supply system is also used which incorporates a linear model of an equivalent synchronous machine including both transient and subtransient effects. Dynamic performance of the conventionally controlled system is investigated by analogue/hybrid simulation of the nonlinear-system model. Optimal and suboptimal control of a linearised model is also studied, and methods of solution based on dynamic programming and the algebraic matrix Riccati equation are compared. To investigate online calculations of optimal control, various forms of performance functional are considered. Conventional 4-mode control and linear optimal control of arc impedance are applied in real time by process computer to the analogue-simulated nonlinear-system model. The study demonstrates a relative improvement in the dynamic performance of arc current, and hence power, with changing bath conditions and varying arc-discharge characteristics.

Non-Linear Control of a Neutralisation Process

The paper describes a digital simulation study of the application of a non-linear controller to the regulation of a single stage neutralisation process. In the controller, the proportional gain increases with amplitude of controller error signal. The performance of the non-linear controller is compared with that of a conventional linear controller and with the performance obtained by employing a linear controller with a linearisation network designed to compensate for the non-linear characteristic of the neutralisation curve. Although the performance of the non-linear controller is inferior to that obtained by employing a perfect linearisation network, its performance is still considerably superior to that obtained by using a conventional linear controller when operating at a symmetrical point on the neutralisation curve. In contrast to the linearisation network technique, the non-linear controller contains only one extra parameter and can be readily tuned on-line without prior knowledge of the neutralisation curve. Hence, it can be considered as an attractive alternative for the control of neutralisation processes.

Nonlinear Analog Computing Elements for Process Control

To supplement the conventional linear three-mode controls, a group of nonlinear, analog industrial electronic devices has been developed. Descriptions are given of the circuits and the performance of five of these:

Optimal Control of a Piecewise Linear System†

ABSTRACT A method of determining the control action of a piecewise linear system to minimise a quadratic cost function is presented. The piecewise linear system considered is described by a different set of linear differential equations for each of two regions of the state space ; the two regions are separated by a hyperplane. It is shown that, with certain restrictions, conventional linear control theory can be used, provided the time taken by an optimal trajectory to reach the separating hyperplane can be determined. A mothod for determining this time is given, thus completing the solution.

Optimal control with quadratic performance index and fixed terminal time

The conventional solution for the optimal control of a linear-stationary regulator with quadratic performance index and fixed terminal time leads to a linear control law with time-varying gain coefficients [1]. In addition to the usual disadvantages of time-variable controllers, some of the time-varying gain coefficients approach infinity as the specified terminal time is approached. In the present paper, it is shown that the optimal control for the above problem can be expressed in the form of a time-invariant non-linear control law. Certain parameters in the nonlinear control law are functions of the initial time and initial state of the system. The conventional time-varying linear control law can be obtained directly from the time-invariant nonlinear control law. The results of the present paper are applicable to a more general class of optimal control problems involving linear and nonlinear systems. Two examples are given to illustrate the method.

Device analyzes binary gas mixtures

We developed the novel control logic for a shock damper using particle-dispersion Electro-Rheological (ER) fluid. This is a high-powered means of shock attenuation for satellite instruments that are subjected to lift-off shock or pyrodevice ignition shock. The proposed method attenuates the shock so that the instrument's acceleration does not exceed the critical value, even when the shock is too large to be accepted. In contrast to the conventional linear shock controls, the proposed shock control does not attempt to attenuate a small shock in order to prepare for attenuating a coming large shock.