Feedforward compensators may be added for almost any disturbance, as shown by Figure 20.7. Physically each may be implemented, as discussed in Chapter 12, with an impulse function and a summer connected inside of the composition feedback controller reset circuit.
Individual feedforward compensator functions may be determined in a very simple fashion. Let us, for example, look at feedforward compensation for feed-rate changes, F. If the compensators do a perfect job, then yT(s) = 0 and xB(s) = 0, and there will be no contribution from the feedback controllers. Then, to make yT(s) = 0, we can see by inspection of Figure 20.7 that:
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