Open-loop feedback control for hybrid manufacturing systems

We discuss a novel formulation for the optimal control of discrete-event dynamic processes representing manufacturing systems characterized by unreliable machines, finite buffers and time-varying predictable demands. We approximately represent the dynamics of the system with a hybrid model and derive an optimum control strategy for parts routing and machines scheduling embedded in a two-levels hierarchical control framework. At the higher level the discrete flows of parts are described by first-order fluid approximations and an optimum receding horizon control policy for the machines production rates is obtained by solving a sequence of linear programming problems. At the lower level a discrete-event real time dispatcher is used to track the solution of the upper level controller as closely as possible