Move "Sensitivity to Process Varations" from Ch 12 to Ch 13?

[Richard Murray]

In Section 12.2 (feedforward design) you have put a new subsection titled Sensitivity to Process Varations that works through the sensitivity of the feedforward design to variations in the process model. This same type of material occurs in Chapter 13, where we do the same type of derivation, although for the “standard” controller design (rather than the more complex feedforward computations here). I was wondering if it makes sense to include the “robustness” analysis here in Chapter 12 rather than in Chapter 13 (titled “Robust Performance”).

I was thinking that an alternative would be to move this subsection into Chapter 13. The problem there is that we don’t really have the feedforward design discussion. One possibility would be to create an exercise in Chapter 13 in which we ask students to show that for the diagram in Figure 12.2 they obtain the properties listed in Table 12.2 (we could list the table, so that the results are explicitly given).

Let me know what you think. I am worried that the current (new) material introduces a topic that is really best handled in the next Chapter (specifically in Section 13.3, titled “Performance in the Presence of Uncertainty”).

[Richard Murray]

Karl's response:

Very good point! It does not make sense to talk about robustness in Chapter 12 the natural place is idefinitely in Chapter 13. The reason I introduced the new section was to emphasize how process uncertainty influences feedback and feedforward. The fact that feedforward reduces disturbance by subtraction while feedback reduces disturbances by multiplication with $S$ has a profound effect on process uncertainty. My preference would be your third alternative below; to remove the material from Chapter 12 and to make an exercise and have the table in the exercise. This also resolves another problem in the text in Chapter 12, namely that Figure 12.2 is quite far away from the table.

A good place to add it would be at the end of subsection 13.3 something along the lines of

Analysis of the sensitivity to small process perturbations can performed for many other system configurations. The analysis for the configuration in Figure 12.2 where the command signal response is improved by feedforward and the load disturbance response is improved by feedforward from measured disturbances in done in Exercise XXX.

[Richard Murray]

Fixed in commit b97b652