Showing papers on "Open-loop controller published in 1970"

Control system and method for machine or process having dead time

Abstract: A controller for a machine or process having a transportation lag is responsive to a signal sampled at time intervals less than the time required for the transportation lag. The sampled signal is fed to a controller which drives the machine prior to completion of the time required for the transportation lag. A negative feedback loop around the controller includes a transfer function indicative of the d.c., steady state response of the machine being controlled and a positive feedback loop indicative of the total transfer function of the machine being controlled, including the transportation lag thereof. A further negative feedback loop is provided between the machine output and the controller input. In a specifically disclosed embodiment, full corrections to errors of moisture and fiber content of a fibrous sheet are made within a transportation lag between a slurry input point of a headbox and scanning gauges located downstream of a dryer.

An approximate minimal time closed-loop controller for processes with bounded control amplitudes and rates

Abstract: This paper presents a method for designing an approximate minimal time closed-loop controller for linear systems with bounded control amplitudes and rates. The method is based on obtaining an approximate functional expression (explicitly in terms of the state variables) that describes the minimal time isochrones of the system. This expression is obtained by a series of least-squares fits to the computed system states on the various isochrones. The computation of the system states on the isochrones and the determination of the approximate expressions are achieved off-line. For on-line operation, it is only required to store a limited number of coefficients of the approximate expressions, and to compute the closed-loop control function by some algebraic manipulation. Consequently, the on-line computer storage requirement as well as the on-line computation requirement is relatively small. Thus, the method is feasible for high-order practical systems. To evaluate its usefulness in applications, the scheme is used to design a fourth-order Ranger Block III Attitude Control System. The results are compared to those obtained by applying the minimal time open-loop control.

Anti-Windup Scheme for Practical Control of Positioning Systems

Abstract: Positioning systems generally need a good controller to achieve high accuracy, fast response and robustness. In addition, ease of controller design and simplicity of controller structure are very important for practical application. For satisfying these requirements, nominal characteristic trajectory following controller (NCTF) has been proposed as a practical point-to-point (PTP) positioning control. However, the effect of actuator saturation can not be completely compensated for due to the integrator windup as the plant parameters vary. This paper presents a method to improve the NCTF controller for overcoming the problem of integrator windup using simple and classical tracking anti-windup scheme. The improved NCTF controller is evaluated through simulation using a rotary positioning system. The results show that the improved NCTF controller is adequate to compensate for the effect of integrator windup. Keywords: Positioning, point-to-point, integrator windup, compensation, controller, robustness.

Automatic control point adjustment system and method

Abstract: A system and method for automatically adjusting a control point including input circuits receiving arbitrarily selected control point values in engineering units and addresses of controllers to be adjusted, a memory storing conversion data for the controllers corresponding to a reset range and a curve of positioning of the controllers versus control point values, a calculator receiving the conversion data and the selected control point value for a controller and calculating a required position for the controller to provide the selected control point value, and a comparator receiving the required position and the actual position of the controller and providing output signals to move the controller to the required position

Traction motor control system

Abstract: There is disclosed a control system for vehicle traction motors. The system includes an ON and OFF chopper-type current controller and switching systems for connecting the motors and the current controller in either traction (motoring) configuration or braking (generating) configuration and for suppressing the ON mode of the current controller just prior to changing over from one configuration to the other and reactivating the ON mode of the controller after the switch from one to the other configuration is completed.

Bumpless-transfer control system

Abstract: A pneumatic controller has means for effecting bumpless-transfer between an automatic control mode of operation and a manual control mode; in the automatic mode, a pneumatic controller operates the process in a conventional manner, with the output signal to the process also being supplied to a follower device at an auto-manual station, positioning a mechanism continuously in accordance with the output signal to the process; upon transfer to the manual mode, the follower mechanism is placed into actuation by a manual set point, with the output signal to the process thereupon being provided from the manual-auto station; in addition, the output to the process is applied as a set point signal to a secondary pneumatic controller which is connected in a configuration with the primary pneumatic process controller such as will maintain the output bellows of the primary controller at the same pressure as the output signal to the process; to do this, the reset bellows of the primary process controller is supplied with a signal which will balance large deviations between measurement and set point supplied to the primary process controller; upon transfer from manual to automatic, the output of the primary process controller, being the appropriate pressure, is connected to provide the output signal to the process, and the secondary controller disconnected; deviation in output to the process from that demanded by the differential between measurement and set point is integrated in the normal pneumatic controller manner, according to the reset setting

Adaptive stochastic control for linear systems Part I: Solution method

Abstract: The problem considered in this two-part paper deals with the control of linear, discrete-time, stochastic systems with unknown (possibly time-varying and random) gain parameters. The philosophy of control is based on the use of an open-loop-feedback-optimal (O.L.F.O.) control using a quadratic index of performance. In Part I it is shown that the O.L.F.O. system consists of (1) an identifier that estimates the system state variables and gain parameters, and (2) by a controller described by an "adaptive" gain and correction term. Several qualitative properties of the overall system are obtained from an interpretation of the equations. Part II deals with the asymptotic properties of the O.L.F.O. adaptive system and with simulation results dealing with the control of stable and unstable third order plants. Comparisons are carried out with the optimal system when the parameters are known. In addition, the simulation results are interpreted in the context of the qualitative conclusions reached in Part I.

Hybrid design method for dead-beat regulators†

Abstract: Since the works of Kalman (1963) and Tou (1964) it is known that an nth-order sampled-data system needs n control signals to reach equilibrium if taken in an arbitrary initial state. These control signals may be applied either in open loop, through linear feedback channels when all the state variables are accessible or with a digital compensator if only the output is available. A computational procedure for solving this problem is described. This method uses the analogue simulation of the process in order to form a linear system which is then solved on a digital computer giving directly the open-loop control signals. Then, with the open-loop control signals one sees how the feedback coefficients or the digital compensator can be found in a very simple way in order to get dead-beet response. The method has the advantage of keeping all the tedious work (matrix integration and matrix multiplication) to a minimum by using the analogue computer, the digital computer only having to solve two linear systems. The...

Use of Models to Control Electroheat Processes

Abstract: Control of first-order thermal plants with inherent time lags by means of hystereitc ON?OFF controllers is investigated. Open-loop pulse-duration-modulation control of the same class of plants is briefly analyzed. A scheme is investigated where the plant is controlled on an open-loop basis by a controller which is included in a feedback loop containing a model of the plant. The parameters of the model can deliberately be made different than those of the process. By a suitable choice of these model parameters better performance criteria can be obtained, especially when they exist due to the distributed nature of thermal processes and to the location of temperature sensing units.

Application of combined optimum control and estimation theory to direct digital control

Abstract: This paper demonstrates methods for applying combined optimum control and estimation theory to serial systems with time delay. The case of serial linear systems with time delay is considered in detail; a result analogous to the separation theorem of linear systems is presented. Illustrative examples of serial chemical reactors, rolling mills, and second-order plus dead-time approximations of higher order systems are discussed. Numerical results for a second-order plus dead-time system are presented: these results are compared with a suboptimal feedback controller (modified Smith predictor) and the open-loop response. It is shown that, in this case, the optimum estimation and control gains may be approximated by constants which further simplify the DDC algorithm. In the second-order plus dead-time approximation to higher order overdamped systems, the optimum algorithm can be reduced to recursive estimation with constant gain and linear state variable feed forward control. This algorithm may be used as a direct replacement for digital controllers used in the process industries.