Another example of conflict

[From Richard Kennaway (20070124.1828 GMT)]

It seems to me that it is possible for conflict to arise even between control systems that have the same perceptual function, the same value of the reference, and the same output function.

Having two identical control systems operating together on the same perception amounts to a single control system with twice the gain (at least, when we're considering linear control systems). For systems that contain transport delays, doubling the gain of a controller can make it unstable.

For example, consider a version of the rubber band demo in which both parties are trying to keep the knot over the dot. (The standard rubber band demo has one party controlling the knot and the other controlling for producing an epiphany about PCT in the audience.) The transport delays in that setting are minimal. However, if the participants are operating and observing the rubber band remotely, with significant delays in the system, then they may find that together, they cannot control the knot, while if either of them kept their remote finger still, the other could easily manage the task.

The proverb about too many cooks comes to mind. Even if they're all trying to make the same soup, the dish may end up spoiled.


Richard Kennaway,,
School of Computing Sciences,
University of East Anglia, Norwich NR4 7TJ, U.K.