Abstract
The place invariant method is well known as an elegant way to construct a Petri
net controller. It is possible to use the constraint for preventing forbidden states. But in
general case, there are many of the forbidden states, thus there is many control places. In
this paper is presented a systematic method to reduce the size and the number of
constraints. This method is applicable for safe and conservative Petri nets. By this method
we can construct a maximally permissive controller.
