Re: Bound control system



Tim Wescott wrote:
Vladimir Vassilevsky wrote:


The classic closed loop system tries to minimize the error wrt some criteria. But what if the requirement is to limit the error to the bounds (-E,+E) ? So as long as the error is within the bounds, the control signal should be zero.

What's your goal, really? Are you trying to build a controller for a system where it just doesn't matter what the error is once it gets within the error bounds? Are you trying to build a controller for a system where it's expensive to keep the drivers turned on (making your desire to turn the drivers _off_ quite valid)?

The plant is a heavy push-pull thing which normally balances itself. Sometimes the external disturbance is too high, so the plant needs a little help from the servo to keep within the allowed limits. The plant is naturally slightly off zero because of the tolerances. So if I set the servo to keep the plant at exactly zero, then the servo will be fighting with the self balancing property of the plant. What is even worse in this case is that the servo has to compensate the full strength of the external disturbance rather then only helping to the plant when needed.

Synthesizing an appropriate controller from specifications and mathematical first principals can be a monumental, if not impossible task. Sometimes the best method to solve one of these corner cases is just apply a combination of common sense, intuition, and mathematical analysis of candidate controllers.

I got the system to work by the shamanistic methods. I was wondering if there is a good systematic approach to the problem. The compensation of the nonlinearities in the loop is a well developed area, however what I need seems to be the opposite.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com






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