Open-loop controller: Difference between revisions

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An '''open-loop controller''', also called a '''non-feedback controller''', is a type of [[Controller (control theory)|controller]] that computes its input into a system using only the current [[state (controls)|state]] and its [[mathematical model|model]] of the system.

A characteristic of the open-loop controller is that it does not use [[feedback]] to determine if its output has achieved the desired goal of the input. This means that the system does not observe the output of the processes that it is controlling. Consequently, a true open-loop system can not engage in [[machine learning]] and also cannot correct any errors that it could make. It also may not compensate for disturbances in the system.

Advanced Open-Loop system based on Predefined Control methodology can be self-learning and adaptive.

== Examples ==

An open-loop controller is often used in simple processes because of its simplicity and low cost, especially in systems where feedback is not critical. A typical example would be a conventional [[washing machine]], for which the length of machine wash time is entirely dependent on the judgment and estimation of the human operator. Generally, to obtain a more accurate or more adaptive control, it is necessary to feed the output of the system back to the inputs of the controller. This type of system is called a [[Closed-loop_transfer_function|closed-loop system]].

For example, an [[irrigation sprinkler]] system, programmed to turn on at set times could be an example of an open-loop system if it does not measure [[soil]] [[moisture]] as a form of feedback. Even if rain is pouring down on the lawn, the sprinkler system would activate on schedule, wasting water.

Open-loop control is useful for well-defined systems where the relationship between input and the resultant state can be modeled by a mathematical formula. For example determining the [[voltage]] to be fed to an [[electric motor]] that drives a constant load, in order to achieve a desired [[speed]] would be a good application of open-loop control. If the load were not predictable, on the other hand, the motor's speed might vary as a function of the load as well as of the voltage, and an open-loop controller would therefore be insufficient to ensure repeatable control of the velocity.

An example of this is a conveyor system that is required to travel at a constant speed. For a constant voltage, the conveyor will move at a different speed depending on the load on the motor (represented here by the weight of objects on the conveyor). In order for the conveyor to run at a constant speed, the voltage of the motor must be adjusted depending on the load. In this case, a closed-loop control system would be necessary.

==See also==

*[[Control theory]]

*[[Controller (control theory)]]

*[[Feed forward (control)|Feed-forward]]

*[[Process control]]

==References==

* Kuo, Benjamin C. (1991). ''Automatic Control Systems'' (6th ed.). New Jersey: Prentice Hall. ISBN 0-13-051046-7.

* Ziny Flikop (2004). "Bounded-Input Bounded-Predefined-Control Bounded-Output" (http://arXiv.org/pdf/cs/0411015)

[[Category:Control theory]]

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