Feed-forward , sometimes written feedforward , is a term describing elements or paths within a control system that pass controller signals from sources in their external environment, often a signal command from an external operator, to a charge elsewhere in its external environment. A control system that has only feed-forward behavior responds to its control signal in a pre-determined manner without responding to how the load reacts; it differs from a system that also has feedback, which adjusts the output to take into account how it affects the load, and how the load itself can vary unexpectedly; the load is considered to belong to the external environment of the system.
In the feed-forward system, the adjustment of control variables is not error-based. Rather it is based on knowledge of the process in the form of a mathematical model of the process and the knowledge of or measurement of process interruptions.
Some prerequisites are required for the control scheme to be reliable by pure feed-forward without feedback: an external command or control signal must be available, and the output effect of the system on the load should be known (which usually means that the load should be unpredictable unchanged with time). Sometimes a pure feed-forward control without feedback is called 'ballistic', because once a control signal has been sent, it can not be adjusted further; any corrective adjustment must be through a new control signal. In contrast, 'cruise control' adjusts output in response to the load it encounters, by feedback mechanism.
This system can relate to control theory, physiology computing.
Video Feed forward (control)
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With Feed-forward or Feedforward controls, interruptions are measured and accounted for before they have time to influence the system. In the home example, a feed-forward system can measure the fact that the door is opened and automatically turn on the heater before the house becomes too cold. The difficulty of feed-forward control is that the effects of interference on the system must be accurately predicted, and no unmeasured interference should be made. For example, if an unexpressed window opens, a feed-forward-controlled thermostat may let the house cool down.
This term has special meaning in the field of CPU-based automatic control. The discipline of "forward feeding" relating to modern, CPU-based automated controls is widely discussed, but is rarely practiced due to the difficulty and cost of developing or providing the mathematical model necessary to facilitate this type of control. Open loop control and feedback control, often based on the PID can control algorithm, are much more widely used.
There are three types of control systems: open loops, feedback-forward, and feedback. An example of a pure open-loop control system is a non-power-driven manual steering of a motor car; the steering system does not have access to additional resources and does not respond to any obstacles to turning the wheels of direction; the driver must make a response without the help of the steering system. For comparison, power steering has access to a controlled power source, which depends on engine speed. When the steering wheel is turned, the valve opens allowing the liquid under pressure to rotate the driving wheel. A sensor monitors that pressure so that the valve is only open enough to cause the correct pressure to reach the wheel rotation mechanism. It is a feed-forward control in which the output of the system, changes in the direction of vehicle travel, does not play a part in the system. See Model predictive controls.
If you include drivers in the system, then it provides a feedback path by observing the direction of travel and compensates for errors by turning the steering wheel. In this case you have a feedback system, and the block labeled "System" in Figure (c) is a feed-forward system.
In other words, systems of various types can be repeated, and the whole system is considered a black box.
The forward feed controls are very different from open-loop controls and teleoperator systems. The forward feed control requires the factory's mathematical model (controlled process and/or machine) and the factory relation for inputs or feedback that the system may receive. Both open loop control and teleoperator systems require the sophistication of a mathematical model of a physical system or a controlled installation. Controls based on operator inputs without integral processing and interpretation through the mathematical model of the system are teleoperator systems and are not considered feedforward controls.
Maps Feed forward (control)
History
Historically, the use of the term "forward bait" is found in works by D. M. MacKay as early as 1956. While MacKay's work is in the field of biological control theory, he only talks about the feedback system. MacKay does not mention "Feedforward Control" or offensive discipline "Feedforward Controls." MacKay and other early writers who use the term "feedforward" generally write about theories about how the human or animal brain works.
The discipline of "forward bait control" was largely developed by professors and graduate students at Georgia Tech, MIT, Stanford and Carnegie Mellon. Feedforward is usually not written in scientific publications. Meckl and Seering of MIT and Book and Dickerson of Georgia Tech embarked on the development of the concept of Feedforward Control in the mid-1970s. The discipline of Feedforward Controls is well defined in many scientific papers, articles and books in the late 1980s.
Benefits
The benefits of feedback control are very significant and can often justify the additional costs, time and effort required to apply the technology. The accuracy of controls can often be increased in order of magnitude if the mathematical model is of sufficient quality and the implementation of feedforward control laws is well thought out. Energy consumption by feedforward and driver control systems is usually much lower than with other controls. Stability is improved in such a way that controlled devices can be built at lower cost, lighter weight, temporary retention materials are still highly accurate and can operate at high speeds. Other benefits of feedforward control include reduced wear and tear on equipment, lower maintenance costs, higher reliability and substantial hysteresis reductions. Feedback controls are often combined with feedback controls to optimize performance.
Model
The mathematical model of the plant (machine, process or organism) used by the feedforward control system can be created and inserted by the control engineer or can be learned by the control system. Control systems that are able to learn and/or adapt their mathematical models have become more practical as the speed of the microprocessor has increased. The discipline of modern feedforward control itself is made possible by the invention of microprocessors.
Feedforward control requires the integration of mathematical models into control algorithms such as those used to define control actions based on what is known about the state of the system being controlled. In the case of controls for robotic arms that are light and flexible, this can be as simple as compensation between when the robot arm carries a payload and when not. The angle of the target joint is adjusted to place the charge in the desired position based on knowing the deflection in the arm of the mathematical model's interpretation of the interference caused by the payload. The system that plans the action and then forward the plan to a different system for implementation does not meet the feedforward control definition above. Unless the system includes means for detecting interference or accepting inputs and processes that input through a mathematical model to determine the necessary modifications to the control action, it is not properly feedforward control.
Open system
In system theory, the open system is a forward feed system that has no feedback to control its output. Instead, the closed system uses in the feedback loop to control the operation of the system. In an open system, the output of the system is not re-inserted into the input to the system for control or operation.
Apps
Physiologic feed-forward system
In physiology, feed-forward control is exemplified by the normal anticipatory regulation of heartbeat before actual physical deployment. The forward feed controls can be likened to the anticipated responses that have been studied for known instructions. The feedback setting of the heartbeat provides further adaptation to run the possibilities of physical activity.
The feedback system is also found in biological control by human and animal brains.
Even in the case of biological feed systems, as in the human brain, knowledge or mental models of plants (bodies) can be considered mathematical because their models are characterized by boundaries, rhythms, mechanics and patterns.
The pure feed-forward system differs from the homeostatic control system, which has the function of keeping the body's internal environment 'stable' or in a 'prolonged stable readiness condition'. The homeostatic control system mainly relies on feedback (mainly negative), in addition to the feedforward elements of the system.
Gene regulation and feed-forward
Gene cross regulation can be represented by a graph, in which the gene is a node and one node is connected to another if the first is a transcription factor for the second. A dominant motif appears in all known tissues (E. coli, Yeast,...) is A activates B, A and B activates C. This motif has proven to be an advanced feed system, detecting a non-transient environmental change. The themes of advanced feed controls are usually observed in the development of hematopoietic cell lines, where irreversible commitments are made.
Advanced feed system in computing
In computing, a forward feed usually refers to a perceptron network in which the output of all neurons goes to the following layer but not before, so there is no feedback loop. The connection is set during the training phase, which is basically when the system is a feedback system.
Remote phone
In the early 1970s, intercity coaxial transmission systems, including L-carriers, used advanced feed boosters to reduce linear distortion. This more complex method allows wider bandwidth than previous feedback systems. Fiber optics, however, make such a system obsolete before much built.
Automation and machine control
Feedback control is a discipline in the field of automated controls used in automation.
See also
- Black box
- Open loop controller
- Predictors Smith
References
Further reading
Source of the article : Wikipedia
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