A State-Space Model for Multiple-Input-Multiple-Output Manufacturing Systems

A state-space model for a class of multiple-input-multiple-output manufacturing systems is presented. This work is a generalization of a previous formulation for single-input-single-output systems. Buffers can receive or feed workpieces from multiple, instead of a single, machines in each machining stage. The coupling among buffer input processes, as well as cross-coupling among input and output processes, are explicitly modelled. A simple operating rule, which gives priority to the machine with the longest waiting time, is used to allocate workpiece or buffer space when there is a contention for it. Simulation results are included to show the dispatching of multiple channels of parts flow into and out of a general buffer, as well as blocking and starving due to full and empty buffers respectively. The model can be used to study the sensitivity of system performance to buffer size and machining rate. It can also be used to develop control strategies for minimizing work-in-process while maintaining, desired throughput.