Feedback loop

About: Feedback loop is a research topic. Over the lifetime, 4441 publications have been published within this topic receiving 62638 citations.

The internal model principle for linear multivariable regulators

Abstract: Necessary structural criteria are obtained for linear multivariable regulators which retain loop stability and output regulation in the presence of small perturbations, of specified types, in system parameters. It is shown that structural stability thus defined requires feedback of the regulated variable, together with a suitably reduplicated model, internal to the feedback loop, of the dynamic structure of the exogenous reference and disturbance signals which the regulator is required to process. Necessity of these structural features constitutes the ‘internal model principle’.

Tracking control of a piezoceramic actuator

Abstract: The tracking control accuracy of piezoceramic actuators is limited due to their inherent hysteresis nonlinearity. This paper presents a computer-based tracking control approach for a piezoceramic actuator based on incorporating a feedforward loop with a PID (proportional-integral-derivative) feedback controller. The hysteresis nonlinearity of the piezoceramic actuator is modeled in the feedforward loop by using the classical Preisach model. Experiments were performed on a stacked piezoceramic actuator for tracking sinusoidal waveforms with signal frequencies ranging from 0.1-20 Hz. A comparison was made between a feedforward control scheme, a regular PID feedback control scheme, and a PID feedback control scheme with hysteresis modeling in the feedforward loop. The results show that the tracking control performance is greatly improved by augmenting the feedback loop with a model of hysteresis in the feedforward loop. The maximum error in tracking a sinusoidal waveform is about half that obtained using a regular PID controller.

A Use of Double Integration in Sigma Delta Modulation

Abstract: Sigma delta modulation is viewed as a technique that employs integration and feedback to move quantization noise out of baseband. This technique may be iterated by placing feedback loop around feedback loop, but when three or more loops are used the circuit can latch into undesirable overloading modes. In the desired mode, a simple linear theory gives a good description of the modulation even when the quantization has only two levels. A modulator that employs double integration and two-level quantization is easy to implement and is tolerant of parameter variation. At sampling rates of 1 MHz it provides resolution equivalent to 16 bit PCM for voiceband signals. Digital filters that are suitable for converting the modulation to PCM are also described.

Automatic control for electrosurgical generator

Abstract: In an ESV a control system responds to impedance and temperature as sensed between and at the electrodes (13) during desiccation each of such electrodes being provided separately and independently through a suitable multiplexer with a specifically controlled RF power. An instantaneous impedance monitor senses impedance variations and controls by means of specific derivative sensitive algorithm part of a feedback loop, the output power delivered through each electrode. A further temperature dependent feedback loop power control system is operative in a multiplexed mode in pair with the above impedance feedback system. Such second system uses an array of temperature sensors placed in the immediate proximity of the each tissue contacting electrode, and an appropriate derivative sensitive algorithm. Both systems are operated in a multiplex mode through a first multiplexer. A second multiplexer shifts the output power to the various electrodes independently and separately.

On the flexibility offered by state feedback in multivariable systems beyond closed loop eigenvalue assignment

Abstract: A characterization is given for the class of all closed loop eigenvector sets which can be obtained with a given set of distinct closed loop eigenvalues using state feedback. It is shown, furthermore, that the freedom one has in addition to specifying the closed loop eigenvalues is precisely this: to choose one set of closed loop eigenvectors from this class. Included in the proof of this result is an algorithm for computing the matrix of feedback gains which gives the chosen closed loop eigenvalues and eigenvectors. A design scheme based on these results is presented which gives the designer considerable freedom to choose the distribution of the modes among the output components. One interesting feature is that the distribution of a mode among the output components can be varied even if the mode is not controllable.