Showing papers on "Control theory published in 1978"

Feedback control of flexible systems

Abstract: Feedback control is developed for the class of flexible systents described by the generalized wave equation with damping. The control force distribution is provided by a number of point force actuators and the system displacements and/or their velocities are measured at various points. A feedback controller is developed for a finite number of modes of the flexible system and the controllability and observability conditions necessary for successful operation are displayed. The control and observation spillover due to the residual (uncontrolled) modes is examined and the combined effect of control and observation spillover is shown to lead to potential instabilities in the closed-loop system. Some remedies for spillover, including a straightforward phase-locked loop prefilter, are suggested to remove the instability mechanism. The concepts of this paper are illustrated by some numerical studies on the feedback control of a simply-supported Euler-Bernoulli beam with a single actuator and sensor.

Active control of flexible systems

Abstract: Since mechanically flexible systems are distributed-parameter systems, they are infinite-dimensional in theory and, in practice, must be modelled by large-dimensional systems. The fundamental problem of actively controlling very flexible systems is to control a large-dimensional system with a much smaller dimensional controller. For example, a large number of elastic modes may be needed to describe the behavior of a flexible satellite; however, active control of all these modes would be out of the question due to onboard computer limitations and modelling error. Consequently, active control must be restricted to a few critical modes. The effect of the residual (uncontrolled) modes on the closed-loop system is often ignored. In this paper, we consider the class of flexible systems that can be described by a generalized wave equation,u tt+Au=F, which relates the displacementu(x,t) of a body Θ inn-dimensional space to the applied force distributionF(x,t). The operatorA is a time-invariant symmetric differential operator with a discrete, semibounded spectrum. This class of distributed parameter systems includes vibrating strings, membranes, thin beams, and thin plates. The control force distribution $$F(x,t) = \sum\limits_{i = 1}^M { \delta (x - x_i )f_i (t)} $$ is provided byM point force actuators located at pointsx i on the body. The displacements (or their velocities) are measured byP point sensorsy i(t)=u(z j,t), oru t(z j,t),j=1, 2, ...,P, located at various pointsz j along the body. We obtain feedback control ofN modes of the flexible system and display the controllability and observability conditions required for successful operation. We examine the control and observation spillover due to the residual modes and show that the combined effect of spillover can lead to instabilities in the closed-loop system. We suggest some remedies for spillover, including a straightforward phase-locked loop prefilter, to remove the instability mechanism. To illustrate the concepts of this paper, we present the results of some numerical studies on the active control of a simply supported beam. The beam dynamics are modelled by the Euler-Bernoulli partial differential equation, and the feedback controller is obtained by the above procedures. One actuator and one sensor (at different locations) are used to control three modes of the beam quite effectively. A fourth residual mode is simulated, and the destabilizing effect of control and observation spillover together on this mode is clearly illustrated. Once observation spillover is eliminated (e.g., by prefiltering the sensor outputs), the effect of control spillover alone on this system is negligible.

Controller Design for a Manipulator Using Theory of Variable Structure Systems

Abstract: A new control algorithm is developed for manipulators using the theory of variable structure systems. The control is designed so that a new type of state space trajectories called sliding mode exists. Due to delays, neglected small time constants, and other idealizations, ideal sliding modes as predicted by the theory do not exist. We have verified through hybrid simulation that trajectories which are close to ideal sliding modes exist when the controller is designed according to theory. To illustrate the design procedures, a two-joint manipulator is considered.

Automatic generation control of an interconnected power system

Abstract: This paper investigates the stability and optimum settings of conventional automatic generation controllers for an interconnected power system having reheat steam plants. Effective application of the parameter-plane technique for obtaining optimal controller setting and sensitivity analysis has been demonstrated. Rigorous sensitivity analysis reveals that reserve of stability and optimum controller setting are sensitive to inertia constant, governor time constant, turbine time constant and reheat coefficient and barely sensitive to base load condition, synchronising coefficient and reheat time lag. The optimum controller setting, however, is hardly sensitive to the speed regulation parameter whereas reserve of stability is quite sensitive to it. A significant part of this paper highlights the condition for which it is possible to optimise the controller setting of an individual area, treating the rest of the system as having infinite inertia. Analysis reveals that a reheat system has a slower response, providing smaller generation rate and higher frequency and tie deviations when compared with a nonreheat system. Investigation reveals that in a reheat system the optimum controller setting achieved without considering generation rate constraint becomes unacceptable in the presence of generation rate constraint. Also, while accounting for generation rate constraint, a relatively large value of governor speed regulation parameter can be well acceptable without significantly affecting the quality of the system response.

The regulation of working methods as a function of work-load among air traffic controllers.

Abstract: A series of field studies among air traffic controllers is reviewed. It largely concentrated on regulatory aspects of operational behaviour, using a model based on the concept of ‘ economy ’ in the individual's selection of operating procedures. Attention is directed at processes involving reasoning, the receipt and transmission of information, and the division of tasks between controllers at the same station. The basic hypothesis, which is supported by numerous data, is that for a given task and a given controller certain operating procedures are less costly than others; that is, they generate lower levels of load. These procedures will therefore be more and more employed as work demand increases, together with the relaxation of certain, self-imposed, qualitative criteria. This regulatory feedback between work-load and operating methods is used by the controller to avoid the abrupt onset of overload conditions and to delay satiation. For the investigator, these progressive changes in operating p...

Application of the injected current model for the dynamic analysis of switching regulators with the new concept of LC 3 modulator

Abstract: A new generation of switching regulators inbedding an LC3 modulator (limit cycle conductance controller) is analysed and optimized from the point of view of dynamic performances. This is done by application of the current injected technique to the power stage model which is shown to behave like a first order system for low frequency perturbations. The optimization is carried out by specification of the desired closed loop modes of the system and calculation of the appropriate state variable feedback gains. The correctness of both the analytical model and optimisation procedure is verified by breadboard dynamic measurements.

A model for sensorimotor control and learning

Abstract: A model for motor learning, generalization, and adaptation is presented. It is shown that the equations of motion of a limb can be expressed in a parametric form that facilitates transformation of desired trajectories into plans. These parametric equations are used in conjunction with a quantized multidimensional memory organized by state variables. The memory is supplied with data derived from the analysis of practice movements. A small computer and mechanical arm are used to implement the model and study its properties. Results verify the ability to acquire new movements, adapt to mechanical loads, and generalize between similar movements.

Parallel process controller

Abstract: A parallel process controller capable of expandable, parallel operating multi-function control of processes without degradation of performance. The process controller comprises up to N (where N is a positive integer) programmable command memory modules, and also comprises data memory modules, an input/output system, a high speed data bus (N-bus) and a general timing and control unit. Each command memory module performs the functional equivalent of a central processing unit with storage of instruction lines designatable by a user via a programming panel. Each command memory module operates autonomously, without regard to the other command memory modules and cyclically solves each of the user instruction lines in a short, fixed length of time. Each data memory module supplements data storage in the command memory modules. The N-bus is a high speed data bus that cyclically interconnects for a fixed length of time each command memory module during one of N control signals generated by the general timing and control unit, to any of the data memory modules and to the input/output system. During this length of time, the selected command memory module may address, read, or write in any location in any data memory module. An interconnectable programming panel may monitor, program, or control line status indicators for any instruction line within any command module or any line within any data memory module. The programming panel communicates with the controller via a dedicated channel of the input/output system.

Inferential control of processes: Part II. The structure and dynamics of inferential control systems

Abstract: The static estimator of part I is incorporated into a dynamic control system. The system structure minimizes output feedback and thereby achieves stability even in the event of significant modeling errors. This inherent stability permits the use of simple and economical lead-lag compensation for the estimator and controller portions of the system. The overall system response to disturbances is similar to that of feed-forward control systems. The proposed control system structure is used to infer and control the overhead and bottoms product compositions of a simulated multicomponent distillation. Product compositions are inferred from selected stage temperature and process flow measurements. Inferential control system response to various disturbances is comparable or superior to that of a tuned composition feedback control system for both single product control and for simultaneus overhead and bottoms product control.

Automatic speed ratio control system for stepless transmission of automotive vehicles

Abstract: An automatic speed ratio control system of the integration servo mechanism type for a stepless transmission of an automotive vehicle. Speed ratio is controlled by a hydraulic pump motor of variable displacement type, which in turn is controlled by an actuator having a piston and a cylinder to which hydraulic oil is supplied. The system comprises a target value generator which produces a target value for an engine speed corresponding to a throttle opening or an output torque of an engine, or which produces a target value for an engine output torque corresponding to a throttle opening or an engine speed; a detector for producing a signal indicative of an engine speed or an output torque of an engine; a control signal generator for comparing the signal from the detector against the signal from the target value generator to produce a control signal in accordance with a deviation therebetween; and a controller responsive to the control signal to drive the actuator to change a speed ratio of the stepless transmission. The system is characterized by further comprising means for controlling a gain of the alteration rate of the speed ratio in response to a rotational speed of an output shaft of the stepless transmission to increase the alteration rate when the rotational speed of the output shaft is low and decrease the alteration rate when the rotational speed of the output shaft is high.

Relationships between digital signal processing and control and estimation theory

Abstract: The purpose of this paper is to explore several current research directions in the fields of digital signal processing and modern control and estimation theory. We examine topics such as stability theory, linear prediction, and parameter identification, system synthesis and implementation, two-dimensional filtering, decentralized control and estimation, and image processing, in order to uncover some of the basic similarities and differences in the goals, techniques, and philosophy of the two disciplines.

Modern Control System Theory and Application

Abstract: and the authors' work which it emphasizes is a deficiency of the simulation field-the book and the field need a conclusion, and none can yet be provided. The authors seem to suggest that steady efforts at simulation over several decades might provide greater understanding of the process of psychotherapy. I wonder if simulators are not "too smart by half" in their attempt to replace the complexity of human interaction with the uncertainty of probability. As a clinician, I expect we could proceed more rapidly by observing and recording clinicians' interactions with patients, then programming the computer to contain the therapist model and specific content and finally utilizing the computer as a simulated psychotherapist with actual psychotherapy patients presenting a range of problems. This simulated therapist will be far from perfect, but so are human psychotherapists who continue to provide the bulk of psychotherapy today. The computer can be tried and specific program modifications made until the program compares favorably with human therapists. There is a model for this approach in medicine, where Bleich has articulated a fluid and electrolyte-acid base abnormality program which surpasses virtually all physicians in management of those problems [1]. His has been a nine-year undertaking, but the result has clinical as well as educational utility and is also of interest to students of decisionmaking. My criticism is not of the presentation made in Simulation in Human Systems. That exposition is very well done and can be recommended to anyone interested in computer simulations and to psychotherapists who think critically about their craft. At a time when the psychotherapy field still lacks a dominant paradigm to guide it, this book is an important statement of the present role of simulation in psychotherapy. What is needed is a postscript to be written in the years ahead, in which the contributions of simulation to the understanding and perhaps even to the practice of psychotherapy will be manifest.

Gas well controller system

Abstract: A controller system for a flowing gas well utilizing battery powered solid state production and cycle time-out circuitry. In addition to expanded cycle interval capabilities, the system permits a broad range of automated controls over well production through the continuous monitoring of and reaction to such parameters as casing pressure, tubing string pressure, plunger elevation, sales line pressure and flow rate, as well as liquid level monitoring within separation and storage facilities. The solid state circuitry incorporates such features as liquid crystal readout, battery voltage level monitoring and automatic reset at the commencement of each timing cycle. Motor valve actuation is provided by electromagnetic actuation of a controller mounted shuttle piston valve.

Multilevel load-frequency control of interconnected power systems

Abstract: This paper presents a two-level optimal control for the load-frequency control of interconnected power systems using modern optimal control and multilevel system techniques. The controller minimises the deviations in frequency and scheduled tie-line power resulting from sudden disturbances. The interconnected power system considered in the paper is decomposed into subsystems each of which has a first level local controller. The local controller controls each subsystem according to the interaction variables provided by a second level controller (co-ordinator). The co-ordinator improves the interaction variables to satisfy interaction feasibility by means of an iteration technique. This paper differs from previous works in that the proposed controller is fast and simple and usually only a few iterations are required. Using the proposed controller the instability problem of subsystems is eliminated. Moreover, the proposed controller guarantees practically zero steady-state error in both frequency and tie-line power at the final time.

Load control processor

Abstract: A load control processor, for a programmable energy load controller system, includes a receiver-decoder section, a power supply section and a load switching section. The receiver-decoder section includes means for receiving an incoming data transmission encoded in a complementary-redundant error-detection code and for detecting the presence of errors in an initially transmitted address portion and a subsequently transmitted data portion of the data transmission. The power supply section includes means for recognizing the presence of a powersaver signal at the load control processor input, for removing power from the majority of the load control processor logic, when data reception and load change processing are not occurring, to reduce total power consumption of the load control processor.

Heat pump wrong operational mode detector and control system

Abstract: An improper or wrong operational mode fault detection and control system for a reverse cycle refrigeration system for detecting faulty operation, i.e., operation in the cooling mode when heating is desired or in the heating mode when cooling is requested, and for controlling the system in response to the detection of a fault by inhibiting the compressor and for providing a fault indication, the control system comprising a controller means receiving inputs indicative of the outdoor air temperature, the temperature of the outdoor heat exchanger coil refrigerant, and an output indicative of a demand from a building temperature sensing means for heating or cooling of the building. The controller means also includes timing means and means for comparing the value of the outdoor heat exchanger coil refrigerant temperature and the value of the outdoor air temperature. Further, the controller means has an operative connection to control means for controlling the operation of the compressor and functioning to inhibit any further operation of the compressor means unless the value of the difference between the temperature of the outdoor heat exchanger refrigerant and the temperature of the outdoor air is less than a first preselected value when the thermostat requests heating, and unless said difference exceeds a second preselected value when the thermostat requests cooling.

Decentralized robust control of unknown systems using tuning regulators

Abstract: The problem of determining a decentralized robust controller for a general servomechanism problem, in which the system to be regulated is unknown, is considered in this paper. In this problem, the unknown system is subject to disturbances and it is desired to find a decentralized controller so that the outputs track given specified reference inputs, independent of any disturbances occurring in the system, and such that this occurs for any perturbations in the parameters of the system (which do not cause instability). The only assumptions made regarding the system to be regulated are that 1) the system is described by a finite linear time-invariant multivariable model and 2) the system is stable. Note that the order of the system is not assumed to be known. The approach taken to solve the problem is in the same spirit of some results recently obtained on "multivariable tuning regulators" for centralized control systems [1]. In this problem formulation, the constraint is imposed that only one controller (at a given control station) may be adjusted at any time (and that when adjusted, this controller will remain fixed), and that the closed-loop system must remain stable at all times during the tuning procedure. It is shown that necessary and sufficient conditions for a solution to exist to the problem can be obtained by performing some simple experiments on the plant, and that a robust decentralized controller can then be synthesized using the results of these experiments in conjunction with a series of one-dimensional parameter searches performed on the closed-loop system. This later procedure is called "tuning the controller on line." The most interesting feature of this problem which differs from the centralized control problem is that the controller synthesis must be carded out in a certain preassigned order with respect to each controller agent (not necessarily unique); if this ordering is not carried out, then there may not exist a controller synthesis for the problem.

A State-Trajectory Control Law for DC-to-DC Converters

Abstract: Mathematical representations of a state-plane switching boundary employed in a state-trajectory control law for dc-to-dc converters are derived. Several levels of approximation to the switching boundary equations are presented, together with an evaluation of the effects of nonideal operating characteristics of converter power stage components on the shape and location of the boundary and the behavior of a system controlled by it. Digital computer simulations ions of d-to-dc converters operating in conjunction with each of these levels of control are presented and evaluated with respect to changes in transient and steady-state performance.

An example in decentralized control systems

Abstract: This correspondence provides an example of a system which cannot be stabilized by decentralized state feedback, even though the overall system and each local subsystem are completely controllable.

Digital control system with Boolean processor

Abstract: An eight-bit microprocessor sequentially reads controller type instructions from a memory and applies the operation codes of selected ones of the instructions to a hardwired Boolean processor. The microprocessor also couples status words between an I/O image table stored in the memory and the I/O interface racks which connect the programmable controller to the machine being controlled. In general, those controller type instructions which are word oriented are executed by the microprocessor and those which are single-bit oriented are executed by the Boolean processor. The Boolean processor is operable in combination with the microprocessor to examine selected status bits in the I/O image table and to set selected status bits therein to a logic state which is determined in part by the state of the examined status bits.

Discretizing continuous-data control systems

Abstract: A CAD method is presented for converting existing continuous-data control systems into digital control systems by means of a digital controller The digital controller is synthetized by matching the frequency response of the digital control system to that of the continuous-data system with a minimum weighted mean-square error A formula for computing the parameters of the digital controller is obtained as a result The design technique is illustrated with a numerical example and a comparison with previous methods is also presented

Decentralized control in packet switched satellite communication

Abstract: The problem of access control to a packet switched multi-access satellite broadcast channel is considered in the framework of nonclassical control theory. This viewpoint, with the simple model presented, gives us some interesting results. It is shown under certain assumptions, that because of the inherent delay in information, the optimal control law will be within the class of open loop control laws. By a result in Bayesion decision theory it is shown that randomized decisions will not be necessary. Given an additional minor restriction we find that for "new" pockets only two modes of operation of the channel could be optimal, namely, All Together (every station sends whenever it has a packet) or Round Robin (every station sends whenever it is turn and it has a packet), and an equation for the crossover arrival probability P 0 the channel would switch from All Together (P to Round Robin (P>P_{0}) is given. For collided packets we find that it is optimal to have predetermined assignments of groups of stations to time slots for retransmissions, and a dynamic programming algorithm for determining the optimal grouping is given.

On-line hierarchical control for steady-state systems

Abstract: This paper presents the basic principles and main properties of hierarchical control structures, which can be applied in steady-state optimization of complex systems. An essential feature of the structures considered in this paper is the use of feedback from the controlled system, along with the mathematical models. Suitable iterative procedures, preferably starting from the open-loop optimum, are proposed and investigated at some length. The stress of most of the discussion is on inequality constraints and on model-reality differences, which are unavoidable in any application of computer control.

Artificial endocrinal gland

Abstract: An artificial endocrinal gland comprises a blood dialyzer for transferring part of the blood to a measuring liquid in a separate circuit, an analyzer for quantatively determining this part and producing in the measuring liquid conversion products compatible to the patient's metabolism, a controller responsive to the analyzer and a device for supplying quantities of hormone to the patient's body under the control of the controller.