This paper addresses specification and implementation of software for F.M.S. It introduces, based on an example of Flexible Assembly Cell, the complementary use of a formal specification tool: Petri nets, a formal concurrent specification language recently developed : LCS, and widely used implementation language : Modula2.

The control of FMS is now currently performed by means of distributed and hierarchical systems and Petri nets have been proved useful to specify such systems. In this paper, we propose to cope with monitoring by proposing a hierarchical structuration of monitoring functions and to use jointly Petri nets (for detection and handling purposes) and a knowledge based approach (for diagnosis and decision) in an integrated way.

Fail-safe sequential machines can be constructed in such a way that if a failure happens in the sequential part, the ulterior functioning must carry on outside the code chosen to represent the set of states. This paper presents a study of the failures in the input combinational circuit and of the feasibility conditions of sequential machines with states coded by a k-out-of-n code. The electronic circuit is realized in a classical way (on-set realization) and must obey two hypotheses, 1) no failure on clock line C, and 2) single fault (stuck at 0 or stuck at 1) on other connections than C.