Pallet Input Control for a Closed Loop Production System.

Abstract

The number of pallets circulating in a closed loop production system is an important factor which affects the production rate. If the number is large, pallets stagnate in the system. If the number is small, an idling state occurs frequently in many stages. In both cases the production rate drops. Therefore, it is necessary to control the number of in-process pallets in the system according to the states of pallet flow and stages in order to maximize the production rate. In this paper, we study the effect of pallet input control for a closed loop production system with constant operation cycle time and stage breakdown. First, we model a pallet flow in the system by a Markov model, and analyze the maximum production rate yielded in the system and the optimum policy for pallet input control by a Markov decision process. Next, we present the effectiveness of pallet input control comparing with the uncontrolled system. Finally, in order to investigate the effect of the number of pallets on the production rate, we analyze the production rate and the number of in-process pallets under the optimum policy using the reward function which consists of the production rate and the number of in-process pallets. The main results are as follows. (1) There is the optimum policy for pallet input control which yields the maximum production rate. (2) The pallet control is effective to increase the production rate and decrease the number of in-process pallets. (3) The decrease of the number of pallets monotonously reduces the production rate. However, if the buffer capacity is large, the reduction is very small near the maximum production rate.