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Feed Forward Control

A feed forward, sometimes written feedforward, is an element or pathway within a control system that passes a controlling signal from a source in its external environment to a load elsewhere in its external environment. This is often a command signal from an external operator.

A control system which has only feed-forward behavior responds to its control signal in a pre-defined way without responding to how the load reacts; it is in contrast with a system that also has feedback, which adjusts the input to take account of how it affects the load, and how the load itself may vary unpredictably; the load is considered to belong to the external environment of the system.

In a feed-forward system, the control variable adjustment is not error-based. Instead it is based on knowledge about the process in the form of a mathematical model of the process and knowledge about, or measurements of, the process disturbances.

Some prerequisites are needed for control scheme to be reliable by pure feed-forward without feedback: the external command or controlling signal must be available, and the effect of the output of the system on the load should be known (that usually means that the load must be predictably unchanging with time). Sometimes pure feed-forward control without feedback is called 'ballistic', because once a control signal has been sent, it cannot be further adjusted; any corrective adjustment must be by way of a new control signal. In contrast, 'cruise control' adjusts the output in response to the load that it encounters, by a feedback mechanism.

from Feed Forward (Control) - Wikipedia

This topic includes the following resources and journeys:

 

 

Feedforward Control Intro

Vincent Stevenson
7 min
Beginner
Video
Theory

If we know how a disturbance will affect an output, we can proactively change our manipulated variable to counteract it.

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Peter Ponders PID - InputShaping

Peter Nachtwey
21 min
Beginner
Video
Theory
Input shaping is used by cranes and other applications where a load that vibrates or swings needs to be moved into position without vibrating or oscillating ... See More

Virtual Lab for a Two-tanks system

Jose Luis Guzman and Fatima Gonzalez
Beginner
Virtual Lab
Application

This is a virtual lab for a two-tank system that can be used for modelling and control learing/teaching purposes. Open-loop tests and closed-loop simulatons based on PI control or PI plus...

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Experimental evaluation of feedforward tuning rules

F. Garcia-Manas, J.L. Guzman, F. Rodriguez, M. Berenguel, T. Hagglund
Advanced
Peer Reviewed Paper
Demonstration

This paper presents a practical comparison for some of the most relevant tuning rules for feedforward compensators that have been published in the recent years. The work is focused on the...

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Feedforward Control Introduction

Vincent Stevenson
6 min
Beginner
Video
Theory

I introduce feedforward control (FFC) and describe how it can be used to minimize the difference between an output's setpoint and measured value (the error o...

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