Tham khảo tài liệu 'handbook of production management methods episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 110 Handbook of Production Management Methods can cause a fast machine to become the bottleneck from time to time high variance can cause the CONWIP line to become the bottleneck in the overall system. An analytical model computed bottleneck CBN was developed for predicting the mean and variance flow time. The concept of a virtual bottleneck machine was introduced that allowed the employment of analogies between deterministic and stochastic systems. This concept enables one to handle migrating bottlenecks an issue that is generally neglected. The results of simulation experiments show that the analytical model very accurately predicts the mean flow time and is sufficiently accurate at predicting the standard deviations of flow time. Simulation experiments also show that the analytical models are much quicker than simulations. Since simulation does not constrain the type of processing time distribution when developing models the influence of machine breakdowns can also be considered by including them in the processing time distributions. Since CONWIP systems can be viewed as closed queuing networks one may mistakenly view the system as a loop having no beginning nor end . This allows one to cut the line at any point in order to evaluate its performance. This approach as recognized by the model is valid for mean performance measures but very inaccurate for variance of performance measures. Bibliography 1. Burbidge J. 1990 Production control a universal conceptual framework Production Planning and Control 1 3-16. 2. Duenyas I. and Hopp . 1990 Estimating variance of output from cyclic exponential queuing systems Queuing Systems 7 337-354. 3. Duenyas I. Hopp . and Spearman . 1993 Characterizing the output process of a CONWIP line with deterministic processing and random outages Management Science 39 975-988. 4. Duenyas I. and Hopp . 1992 CONWIP assembly with deterministic processing and random outages IIE Transactions 24 97-109. 5. Hendricks K. and McClain .
