Showing papers on "Feedback loop published in 1973"

On Feedback Control of Linear Stochastic Systems

Abstract: Feedback control of linear continuous-time stochastic systems of general type is discussed. Various types of (classical) information patterns with both complete and partial observations (white and colored measurement noise) are considered. The cost functional is quadratic. A class of admissible control laws is defined which includes all linear and nonlinear control policies for which our problem makes sense, i.e., existence, uniqueness etc. are secured. Then, we determine the optimal control law by an imbedding procedure which amounts to solving a problem without a feedback loop. We investigate under what conditions the optimal control law is linear in the data.

Stability of systems with nonlinear feedback through randomly time-varying delays

Abstract: In a large class of multi-loop control systems, many feedback loops are "closed" through a timeshared digital computer, using algorithms which require information from sources which are sampled at a rate which is not synchronized with the sampling of the individual "Plants". This mis-synchronization, in conjunction with variations in the computer's task load caused by "interrupts", results in a randomly time-varying delay in the closing of the various feedback loops. Consequently, the dynamics of each controlled "plant" in such a system may be modeled by means of a stochastic delay-differential equation. This paper presents some new research resets concerning the sample stability (as opposed to statistical, or ensemble stability) of non-linear stochastic delay-differential equations.

Closed-loop speed control for step motors

Abstract: A closed-loop control system for a step motor which is started by a pulse from an external source, and then driven by feedback pulses from a transducer connected to the motor output. Each time the motor advances a step, the transducer generates a feedback pulse at a reference switching angle which determines the torque output of the motor and, therefore, the motor speed for any given load. An adjustable time delay is provided in the feedback loop for adjusting the effective switching angle at which the feedback pulses are applied to the drive unit of the motor, by delaying the feedback pulses. To automatically stabilize the motor at a selected speed, a signal representing the desired speed is compared with the actual motor speed, and an error signal is generated representing any difference between the actual and desired speeds. This error signal is then used to automatically select the magnitude of the time delay introduced into the feedback loop. The error signal may represent only the direction of the error, and the time delay means adjusted by a fixed unit of time after each motor step in the direction required to return the actual motor speed toward the desired motor speed. Alternatively, the error signal may represent both the magnitude and direction of the error, and the time delay adjusted in proportion to the magnitude of the error and in the direction required to return the actual motor speed to the desired motor speed. The system also includes means for automatically stopping the motor after a predetermined number of steps, and means for generating decelerating and/or damping pulses after termination of the feedback pulses.

Waveform generator including means for automatic slope calibration

Abstract: In a waveform generator such as a sawtooth wave generator, automatic slope calibration is provided. A variable resistance element is feedback-responsive and provides an input voltage which affects waveform shape. The shape of the waveform is controlled automatically by a time error signal through the use of a feedback loop which controls the input voltage. In one embodiment, the feedback loop measures the time at which waveform voltage reaches a predetermined level and compares the time span it takes for the value of the waveform to reach the predetermined level to a preselected time span to provide the time error signal. The time error signal is utilized in a closed loop to control the voltage supplied by the variable resistance element. In another embodiment, the feedback loop measures the voltage difference between a fixed reference and the generated waveform at a predetermined time to generate the time error signal and control the input voltage supplied from the variable resistance element.

Stabilizing system for an inverter-driven induction motor

Abstract: In a motor control system in which an induction motor is driven by an inverter and the motor tends to resonate, the resonant frequency of the motor and the extent of its damping are adjusted to desirable amounts by a local feedback circuit. An output signal of the local feedback circuit is algebraically added to a speed command voltage for the motor control system. A sum signal thus produced is connected to the input of the inverter to control the motor speed. The sum signal is also employed as one of two input signals to the local feedback circuit, the second input signal being proportional to the speed of the rotor of the motor and obtained from a sensor connected with the rotor shaft. The two input signals to the local feedback circuit are subtracted and their difference signal is processed through a lag circuit and a filter network to produce the output signal of the local feedback circuit. When the inverter and motor are thus stabilized by the local feedback circuit just described, it is much easier to stabilize a larger speed-control feedback loop in which the inverter and motor may be employed.

Regulation and stabilization in a switching power supply

Abstract: A switching-type power supply is provided in which switching transistors are switched off periodically in response to an oscillator to establish a basic operating frequency, but switched on at varying times during the basic period, in response to a signal from a first feedback loop, whenever the sensed output voltage level is less than a desired voltage level. When the duty cycle of the switching transistors is less than 50 percent, stability is provided by augmenting the sensed output voltage by an additional voltage with a parabolic waveform. In accordance with one embodiment of the invention, a second feedback loop responsive to slow variations in the load provides an input to the first feedback loop.

Measurement of CCD transfer efficiency by use of feedback to increase the effective number of transfers

Abstract: A technique is reported that permits accurate measurement of transfer efficiency in charge-coupled devices that have low overall transfer loss (/spl les/1 percent). By adding a feedback loop the signal is passed through the CCD many times, thus increasing the measured transfer loss. A detailed analysis is given that predicts the expected improvement in the minimum measurable transfer loss through the application of feedback. These predictions are then compared with experimental results on both three-phase and two-phase charge-coupled devices.

Feedback stabilization of a multimode two-stream instability

Abstract: Various theoretical schemes for the feedback stabilization of a multimode two-stream instability in a finite one-dimensional plasma are presented. The system under consideration is the fluid analog of the symmetric 'bump on the tail' Vlasov plasma. The most promising feedback scheme involves sensing the total density perturbation and feeding back an appropriate charge. It is shown that by proper choice of feedback parameters in a single feedback loop, all unstable modes can be stabilized without destabilizing any modes which were previously stable.

A negative hysteresis threshold circuit and its analysis

Abstract: It is well known that there is a hysteresis effect in the Schmitt trigger circuit. In the present paper, the author proposes a negative hysteresis threshold circuit which consists of a cathode-coupled trigger circuit with a CR delayed feedback loop. This circuit can be set to remove any hysteresis by adjusting the delayed feedback loop gain. A non-linear analysis is developed on the above circuit, using the phase-plane method together with the experimental results.

Process control system

Abstract: A process controller for controlling the operation of a particular process including an external control loop for combining an output signal from the process indicative of the operation thereof with a preselected reference signal and producing an output signal indicative of this combination. This output signal is then fed to an operational amplifier across a first two position switch which in the other position thereof open loops the input to the amplifier, connecting in an external signal source. The operational amplifier is arranged in a configuration of an integrator, including two capacitive feedback loops forming the internal loop of the controller, each feedback loop being respectively connected to the two switch positions. The capacitors in each feedback loop will therefore maintain identical initial outputs on either side of the switch, since in both instances they are referenced to a common reference, thus assuring transient-free switch over. At the output the operational amplifier is connected to control the process across a second two position switch, which, in its other position, connects the process directly to an externally powered manually controlled signal source, thus providing an alternate means for maintaining control over the process in case of power failure.

Linear regulators and observers

Abstract: The design of a regulator system using a constant gain observer in the feedback loop is discussed. By examining the poles of the closed-loop plant and observer, it is explicitly clear that the closed-loop response is jointly determined by the plant and observer poles and zeros.

Self calibrating digital to a.c. converter for multiple conversion

Abstract: Apparatus for performing multiple digital to a.c. conversions by using a self calibrating feedback loop. The conversions are performed accurately and without the need for a multiplicity of precision components.

Mechanical-electrical transducer gauge provided with a circuit for making linear the response of the gauge

Abstract: A circuit for making linear the response to a mechanicalelectrical transducer gauge having variable impedance means within an electrical detecting circuit including a compensating system comprising a feedback loop provided with an amplifier and a compensating impedance constituted by resistive and reactive components. The feedback loop generates an output electrical quantity equal in amplitude and opposed in phase to that absorbed by the undesired impedances. The amplifier includes a grounded collector transistor. The compensating impedance comprises a resistance and an inductance connected in parallel and connected at the input of the feedback loop. The inductance consists of the primary inductance of a transformer with the secondary of the transformer constituting the input of the feedback loop.

Time-varying system stability-interchangeability of the bounds on the logarithmic variation of gain

Abstract: A frequency-domain criterion for the L 2 -stability of systems containing a single time-varying gain in an otherwise time-invariant linear feedback loop is given. This is an improvement upon the earlier criteria presented by the authors in permitting an interchangeability of the allowable bounds on the logarithmic variation of the gain.