【Control Version】One Question per Day 20180418
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What are the differences between feedforward and feedback? Answer: (1) Basis for control: The essence of feedback control is to \"eliminate deviations based on those deviations,\" while feedforward control aims to \"eliminate the impact of disturbances on the controlled variable based on those disturbances.\" (2) In terms of the timing of the control action: The operation of the feedback controller is always delayed relative to the occurrence of the disturbance, representing a form of \"delayed\" control ； After the disturbance occurs, the feedforward controller acts promptly. (3) In terms of control structure: feedback constitutes a closed-loop control system, and stability issues arise; even if each component within the closed-loop system is stable, it still needs further analysis to determine whether the entire system is stable as a whole ； Feedforward belongs to open-loop control; since each stage is stable, the system is necessarily stable. (4) In terms of the correction range: Feedback serves to correct various disturbances ； Feedforward only has a corrective effect on the feedforward perturbation being verified, and no effect on others. (5) In terms of control laws: feedback typically follows typical laws such as P, PI, PD, PID, etc ； The feedforward control law is relatively complex and difficult to master.
Feedforward control is a system that adjusts according to the change in disturbance. (1) Basis for control: The essence of feedback control is to \"eliminate deviations based on those deviations themselves\", while feedforward control aims to \"eliminate the impact of disturbances on the controlled quantity by acting on those disturbances\". (2) In terms of the timing of the control action: The operation of the feedback controller is always delayed relative to the occurrence of the disturbance, representing a form of \"delayed\" control ； After the disturbance occurs, the feedforward controller acts promptly. (3) In terms of control structure: feedback constitutes a closed-loop control system, and stability issues arise; even if each component within the closed-loop system is stable, it still needs further analysis to determine whether the entire system is stable as a whole ； Feedforward belongs to open-loop control; since each stage is stable, the system is necessarily stable. (4) In terms of the correction range: Feedback serves to correct various disturbances ； Feedforward only has a corrective effect on the feedforward perturbation being verified, and no effect on others. (5) In terms of control laws: feedback typically follows typical laws such as P, PI, PD, PID, etc ； The feedforward control law is relatively complex and difficult to master. .
Feedback refers to the process by which the controlled component sends information about its activity (a feedback signal) back to the control component. The control component then uses this feedback signal to adjust its own behavior in order to modify the instructions given to the controlled component, thereby regulating the activity of that component – this is known as feedback control. If the feedback signal causes the control unit to change its operation in the direction opposite to its original operation, this type of regulation is called negative feedback ； If the feedback signal strengthens the activity of the control section in its original direction of activity, it is called positive feedback. While the disturbance signal causes changes in the output variable by acting on the controlled part, it can also act directly on the control part through sensory devices, allowing the output variable to be corrected before any deviation occurs. This direct effect of the disturbance signal on the control part is known as feedback. Negative feedback plays a role in stabilizing the internal environment, while positive feedback disrupts the existing balance state, causing a certain physiological activity to intensify continuously and be completed rapidly. Therefore, the feedback is not predictive; it can only respond after being disturbed, resulting in a time lag in the response ； Feedforward is predictive, enabling adaptive responses in advance to prevent interference. Negative feedback exhibits certain volatility, that is, it gradually stabilizes during the recovery process ； Feedforward, on the other hand, has no volatility; it helps maintain homeostasis and reduces the lag and fluctuations that occur in negative feedback regulation. Furthermore, deviations can occur in both cases, but deviations in negative feedback are inevitable; it is only after a deviation occurs that correction becomes necessary ； The feedback error, on the other hand, is caused by potential forecasting mistakes.
Feedforward control is based on interference for regulation; the measurement signal of the controller is the interference signal, and the control action takes place before a deviation occurs； Feedback control operates based on the variation of the controlled variable; the controller’s measurement signal is the controlled variable itself, and the control action takes place after a deviation occurs ； Pure feedforward is open-loop control ； The feedforward control algorithm is derived based on the interference channel and the control channel ； Feedforward control can only overcome specific disturbances.
Feedforward control operates based on disturbances; it acts promptly, but its accuracy is low and implementation is difficult; it only helps to counteract certain disturbances. Feedback control acts on the basis of deviations; it is not timely, but it offers high accuracy and is easy to implement, and it can counteract all disturbances
Feedforward is a connection that goes directly from the input to the output, while feedback is an adder that connects from the output back to the input; one is from output to input, and the other is from input to output – the direction of signal flow is opposite in each case
A feedforward control system issues control commands before any deviation occurs in the activity of the controlled component. A feedback control system issues control commands only after detecting a deviation in the activity of the controlled component.
Answer: (1) Basis for control: The essence of feedback control is to \"eliminate deviations based on those deviations,\" while feedforward control aims to \"eliminate the impact of disturbances on the controlled variable based on those disturbances.\" (2) In terms of the timing of the control action: The operation of the feedback controller is always delayed relative to the occurrence of the disturbance, representing a form of \"delayed\" control ； After the disturbance occurs, the feedforward controller acts promptly. (3) In terms of control structure: feedback constitutes a closed-loop control system, and stability issues arise; even if each component within the closed-loop system is stable, it still needs further analysis to determine whether the entire system is stable as a whole ； Feedforward belongs to open-loop control; since each stage is stable, the system is necessarily stable. (4) In terms of the correction range: Feedback serves to correct various disturbances ； Feedforward only has a corrective effect on the feedforward perturbation being verified, and no effect on others. (5) In terms of control laws: feedback typically follows typical laws such as P, PI, PD, PID, etc ； The feedforward control law is relatively complex and difficult to master.
A feedforward control system issues control commands before any deviation occurs in the activity of the controlled component. A feedback control system issues control commands only after detecting a deviation in the activity of the controlled component.
A feedforward control system issues control commands before any deviation occurs in the activity of the controlled component, whereas a feedback control system issues control commands only after detecting a deviation in the activity of that component
Pre-feedback: The data acquisition point is located ahead of the control point; data feedback is used to adjust the control point, thereby ensuring stability of the data prior to that control point； Feedback: Since the data acquisition points are located after the control points, data feedback is used to adjust those control points, thereby ensuring stability of the data behind them.