Performance Evaluation and Optimization of Block Production Systems

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To increase flexibility of production, a variation of the assembly line has recently been introduced in which there are fewer workers than stations and workers walk to adjacent stations to continue work on an item. The system is called a U-shaped production system from its form. The U-shaped production system is, in effect, buffering itself against variation by altering the work assignments, which allows the system to operate with very low levels of work-in-process inventory (WIP). The control of the workers has some versions. One is Fixed Assignments in which each machine belongs to exactly one worker. Another is Free-floating System in which any worker can work on any machine. In this research, we have proposed the queueing model for U-shaped production systems, which includes both the fixed assignments and the free-floating systems as a special case. By the field work, we have observed the throughput, WIP, and the numbers of workers are important factor in U-shaped production systems. Then we have considered following optimization problems:(1) Under the restriction of the desired throughput, assign the fixed number of workers in order to minimize WIP(2) Under the restriction of the desired throughput, obtain the total number of workers and assign the workers in order to minimize the total cost for WIP and workersSince it is very difficult to solve the practical size of the problems using the traditional queueing theory, we apply the idea of sample-path optimization to the above optimization problems. The analytical results show that the coefficient of variation has a great influence on the optimal structure in the U-shaped production systems.