如何以TOC觀念設計生產系統之研究

Abstract

在過去的傳統思維是以平衡的觀念設計生產系統，但是這樣的設計往往無法應付生產系統所產生的變異，使產出達到理想的狀態。Goldrrat在1986年提出應該要平衡流量而不是平衡產能，主要是因為生產系統有相依性與變異性的存在。諷刺的是製造業者追求平衡產能，但是事實上在現實環境的生產系統都是不平衡的而且一定會有瓶頸存在，為何還是會有產出達不到理想的問題。此乃因生產系統的運作往往會因為保護性產能提供的不足夠，導致瓶頸機臺產生閒置，讓產品產出沒有如預期的目標。因此本研究建構生產模擬系統，模擬三種不同情境的產能組合，探討平衡產能與不平衡產能兩種生產模式。首先驗證Goldrrat提出的觀念是正確的，亦即在有變異的情況下，應該設計不平衡產能的生產系統。其次藉由這個模擬系統推論，非瓶頸工作站的保護性要多大才是合適的，並且評估以TOC觀念計算保護性產能方法的可行性。最後比較瓶頸站擺放在生產線的前面、中間、後面不同位置的效益。模擬研究結果得到以下的結論: 平衡產能在有變異的生產系統中是不適用的，而應該要設計不平衡產能的生產系統，因為不平衡產能有更多的彈性空間應付生產系統變異的狀況，並且運用TOC相依性相乘的觀念計算保護性產能方法是可行的，瓶頸在生產線中間的位置，成本效益是最佳的。

The traditional production system is designed based on the concept of balanced capacity; however, such design is hard to achieve ideal production because there are variations in the production system. Hence, Goldrrat proposed that production system should focus on the balanced flow instead of balanced capacity due to the existence of dependence and variation in the production system; yet, the manufacturers still pursue the balanced capacity. In practice, the production system is unbalanced and have bottleneck. Why the production system cannot reach the ideal production? This is because the protective capacity is insufficient; as a result, the bottleneck machine would be idle. That is, the throughput cannot reach the goal. Therefore, this research designs the production simulation system to simulate the combination of capacity in different scenarios and compare the balanced capacity production mode with the unbalanced capacity one. The simulation system has three main purposes. First, we conduct simulation to verify the theory proposed by Goldrrat. In other words, the production system should be designed as unbalance capacity mode when the variation exists in the system. Secondly, the simulation system helps us decide how much protective capacity in the non-bottleneck workstation is appropriate and analyze whether calculating the protective capacity based on the Theory of Constraints (TOC) is feasible or not. Finally, this research sets different scenarios which the bottleneck is in different position of the production line and uses the simulation system to evaluate the performance of the production system in each case. This research concludes the following statement based on the results of simulation experiment. First, the production system should be designed as unbalance capacity mode because this mode is able to handle the variations. In addition, it is feasible to calculate the protective capacity based on the concept of Theory of Constraints. Finally, when the bottleneck is in the middle of the production line, the performance of the production system is best.