A method for aligning serial batching decisions in a two-level organization of factory and distributed workstations

Large factories that manufacture high mixes of complex products are usually composed of a number of workstations and the manufacturing control function is divided between a factory and a workstation level. While the management of individual workstations tends to focus on efficient machine utilization, the top-level factory management is usually concerned with job flow control. Integration of operation decisions between the two organization levels can recover productivity loss stemming from disparate objectives. This paper presents a method for aligning the job batching decision for serial-batch machines that require machine setup to serve stochastic arrivals of multiple job types. The effect of batching on flow time is first analyzed and closed-form formulas for the probability of setup are derived for a time-based batching policy. The misalignment in batching decisions at the two organization levels is next illustrated. Finally, a state-based performance measure is designed for decision integration. Numerical simulation and regression are used to test the proposed method. The main contribution of this paper is on developing a distributed vertical alignment method which compliments the approaches of horizontal coordinated scheduling and vertical functional decomposition in architecture design of distributed manufacturing control.