On-Line Production Control of Tandem Systems with Finite Inter-Stage Storage, Using a Dynamic Maximum Cycle Time Algorithm

For a tandem manufacturing system with finite interstage storage and asynchronous operations, stage cycle times are allowed to vary from cycle to cycle and from stage to stage. Owing to the nature of the operation and the occurrences of blocking and starvation, the relationship between the time each stage spends on each job and the output rate of the system is not directly observable. In order to operate the system so that it meets the demand without over-producing or under-producing, it would be helpful to know the time limit available for each stage to operate on each job. This paper describes a method for calculating such cycle time limits for each stage at each cycle on a real-time basis. The calculated cycle time limits are always bounded below, approximately by the expected time between outputs of the system. The value of a cycle time limit is a function of the current system state, performance history of the stages and the interrelationship among the stages. Emulation examples (with 3-stage and 10- stage systems) will show that while cycle times are allowed to vary, as long as they do not exceed their calculated limits throughout the production, system output will be very close to a predefined expected amount.