A feedforward assessment can help employees learn new and effective methods to solve problems. Many organizations are making the switch and using feedforward assessments to improve the performance of their employees. A feedforward assessment can eliminate this risk as it removes negative connotations. Instead, employees should leave a feedforward assessment feeling motivated and supported.
Start a feedforward loop. Both participants will get a chance to give and receive a feedforward assessment. When performing a feedforward assessment loop, follow these steps:.
Feedforward assessments give insight into how a situation can be improved in the future rather than focusing on positive or negative feedback. Feedforward is not judgmental; it is empowering and eye-opening. It reinforces positive interpersonal relationships between employees. If you feel that your business, employees, or coworkers are stuck on a proverbial hamster wheel, feedforward can help you break through barriers and begin to make progress at a faster pace.
There is no feedback to see if the system is really in the desired state or "how far" it is from the desired state. If disturbances that are not measured cause the system's outputs to differ from the desired one, the controller will not react.
So to formulate it with "reactive" I would say that feedback control is reactive since it reacts to changes in the system's output while feedforward is proactive since it acts before the system's output change. The important factor in control theory is the controlled system output; that is probably why reactive is defined from the point of view of the change in the system's output.
Feedforward also reacts to something, but this something is not the system's output so from the point of view of the system's output it is not reactive. In feedforward control, the system's output can change without any reaction from the controller while in feedback control any change in the system output will provoke a reaction of the controller.
Since the important aspect is the system's output and the feedforward controller does not react to changes in the output it can be considered a non-reactive control method.
Illustration from Wikipedia , a open loop, b feedforward, c feedback. For a theoritical discussion, your pre-assumption is wrong. A feedforward control logic need not depend upon the sensor value. Rather it depnds on the desired value.
For example, If we have a simple rod hung like simple pendulum with a torsional spring at the pivot. Let's say we are operating this rod with a motor at the pivot. If we give 30 degree desire angle, then feedforward logic will send a duty, accordingly, to balance torsional spring rotated for 30 degree.
Whereas, feedback logic will take care the real world scenario of air resistance. The feedback controller uses the measured errors, computes changes to the inputs in order to squash those errors, and sends those inputs to the system. The idea is that all of the dynamics affecting a system won't be known in advance - friction values change, disturbances are encountered, payloads are not constant, etc. So we measure the error and eliminate it.
The feedforward controller usually wraps around the feedback controller. Although there are many types, they all generally estimate what the system's response will be for those changed inputs computed above. They then further "nudge" the inputs to account for the predicted additional errors in order to prevent those modeled errors from occurring. A good example is when the system knows that the payload changes when a device picks something up - the current to the motors can be increased to account for the additional torque required without waiting for the system to begin moving too slowly and seeing the errors occur.
Controllers are always reacting to something, so you're correct in thinking that "being reactive" is not the difference between the two. The key is what the controllers are reacting to. In feedback control, the controller acts to minimize an error signal. A system including feedback control would have:. In feed forward control, the controller acts without any direct knowledge of the system's response.
It may be reacting to a reference signal or output from a sensor as long as the sensor is not measuring system output - this would create a feedback loop or both.
This is also called "open-loop control. This is more than a semantic difference. Only a closed-loop controller has the ability to compensate for unknown parameters, modelling errors, etc. In your question, you refer to a situation where feed forward is used as a means to achieve disturbance rejection.
The idea would be that you measure the disturbance input, model the response of the system due to the this input, calculate the required control input to counteract this response, and then apply that control input. Since your control signal controller output is independent of system response, this is open-loop control.
It is not uncommon for controllers to be designed with both feedback and feed forward components. In this case, I usually think of the feedback component as the primary path, and the feed forward component as supplementary, to improve performance in some way.
For example, in motion control, a motor can be made to follow a velocity reference by using a PID controller that operates on the velocity error. Because the PID controller operates only on the error, without any knowledge of the reference signal, there must be some error before the controller responds, so there will be some amount of delay.
You can increase the gains to minimize the delay, but because real systems are flexible, there will be some point at which the system will become unstable as the gains are increased.
You can add a feed forward path, however, which operates on the derivative of the velocity reference so, the acceleration. If the system's inertia is constant, the feed forward controller can be a simple proportional gain times the acceleration signal, which would correspond to some additional torque. Now the motor will generate torque in response to changes in the velocity reference without waiting for the system to develop velocity error. Inst Tools. Feedback control. Feedback control is an important technique that is widely used in the process industries.
However, feedback control also has certain inherent disadvantages:. Feedforward Control.
0コメント