Comparison of DBR with CONWIP in a Production Line with Constant Processing Times

ABSTRACTWe compared a DBR(drum-buffer-rope) system with a CONWIP(constant work-in-process) system in a production line with constant processing times. Based on the observation that a WIP-controlled line production system such as DBR and CONWIP is equivalent to a m-node tandem queue with finite buffer, we applied a max-plus algebra based solution method for the tandem queue to evaluate the performance of two systems. Numerical examples with 6 workstations were also used to demonstrate the proposed analysis. The mathematical analyses support that CONWIP outperforms DBR in terms of expected waiting time and WIP. Unlike the CONWIP case, sequencing workstations in a DBR affects the performance of the system. Delaying a bottleneck station in a DBR reduces expected waiting time. Key words : CONWIP, DBR, tandem queue, max-plus linear system요 약이 연구는 상수 공정 시간을 갖는 라인생산시스템에서 CONWIP 과 DBR이 각각 max-plus 선형시스템의 특수형태임을 밝히고 max-plus 대수에 기반한 안정대기시간 연구결과를 이용하여 CONWIP 와 DBR의 성능을 비교 분석하였다 . CONWIP의 경우, 생산시스템 내의 체류시간은 DBR의 경우보다 항상 짧다는 사실이 수학적으로 규명되었고 예제를 통해 계산 , 비교되었다. 한편 두 경우에서 모두 , 애로공정이후 노드에서의 대기시간은 유한버퍼의 크기와 공정의 순서에 무관함을 확인하였다 . CONWIP에서는 시스템 내 평균 대기시간 또는 체류시간이 공정의 순서에 무관하지만 , DBR에서는 애로공정이 뒤로 갈수록 감소함을 확인하였다.주요어 : CONWIP, DBR, tandem queue, max-plus 선형 시스템

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