CSP solver for Safe PLC Controller: Application to manufacturing systems

This paper presents an original approach of safe control synthesis for manufacturing systems controlled by Programmable Logic Controller (PLC) based on the use of a CSP (constraint satisfaction problem) solver. In this work, manufacturing systems are considered as Discrete Event Systems (DES) with logical Inputs (sensors) and logical Outputs (actuators). The proposed approach separates the functional control part from the safety control part. The methodology is based on the use of safety constraints in order to get from a CSP solver all the safe outputs vectors at each PLC scan time. The safe outputs vector is selected by choosing the one which minimizes the Hamming distance with the functional outputs vector. The approach is illustrated with a sorting boxes simulated process using the ITS PLC software from the Real Games Company (www.realgames.pt).