Synthesis of Restart States for Manufacturing Cell Controllers

In earlier work we presented a method for restart of manufacturing systems. After correction of an error, the system resumes normal production by returning to a certain restart state in the control function, and from there reexecuting parts of the work schedule. The current paper concerns automatically finding (synthesizing) the restart states. The control function is modeled by finite automata, and properties of the restart states are defined. The synthesis process finds all possible restart states, guaranteeing that the execution restrictions are fulfilled during a restart, and that the production goals can be maintained. The error and the corrective actions preceding the restart need not be modeled; neither is it necessary to know the exact physical states of the machines at the time of the error. The number of restart states is finally minimized to reduce the need for extensions to the control program.