Abstract: Based on invariants of Petri nets, an approach to the enforcement of fairness and liveness is presented for classic automated manufacturing systems. First of all, a fair net is obtained by adding some places that make the net have only one T-invariant. Then, a fair net is enforced to be live through controlling minimal siphons by P-invariants. Importantly, the concept of redundant strict minimal siphons is put forward, which can greatly simplify the synthesis and analysis of Petri net model of the system considered. Generally, the set of non-redundant strict minimal siphons is a much small subset of the set of strict minimal siphons in a Petri net, particularly in large-scale ones. The results show that all strict minimal siphons cannot be emptied if non-redundant strict minimal siphons are controlled. Examples are presented to illustrate these approaches. The results obtained can be applied to a larger class of flexible manufacturing systems and are of significance to Petri nets based scheduling problems for automated manufacturing systems.