Performance Limitations Arising from Sensor Delays in Feedback Systems

Motivated by a project involving the automation of radiotherapy, this talk
investigates the effect of sensor time delays on the performance of a
closed-loop feedback system. Existing results (not to mention intuition)
indicate that, for an open-loop unstable plant in the usual
one-degree-of-freedom feedback loop, closed-loop performance degrades
severely as the sensor delay increases. These standard results are
reviewed, then the following questions addressed: first, are there
performance limitations associated with a plant that is open-loop stable,
and, second, are there performance limitations associated with a
two-degree-of-freedom control topology? It turns out that there are
indeed performance limitations in both cases. Both discrete-time and
continuous-time results are presented.