Effective process times for multi-server flowlines with finite buffers

An effective process time (EPT) approach is proposed for aggregate model building of multi-server tandem queues with finite buffers. Effective process time distributions of the workstations in the flow line are measured without identifying the contributing factors. A sample path equation is used to compute the EPT realizations from arrival and departure events of lots at the respective workstations. If the amount of blocking in the line is high, the goodness of the EPT distribution fits determines the accuracy of the EPT-based aggregate model. Otherwise, an aggregate model based on just the first two moments of the EPT distributions is sufficient to obtain accurate predictions. The approach is illustrated in an industrial case study using both simulation and analytical queueing approximations as aggregate models

Performance measurement and lumped parameter modelling of single server flowlines subject to blocking : an effective process time approach

The present paper extends the so-called Effective Process Time (EPT) approach to single server flowlines with finite buffers and blocking. The power of the EPT approach is that it quantifies variability in workstation process times without the need to identify each of the contributing disturbances, and that it directly provides an algorithm for the actual computation of EPTs. It is shown that EPT realizations can be simply obtained from arrival and departure times of lots, by using sample path equations. The measured EPTs can be used for bottleneck analysis and for lumped parameter modeling. Simulation experiments show that for lumped parameter modeling of flowlines with finite buffers, in addition to the mean and variance, offset is also a relevant parameter of the process time distribution. A case from the automotive industry illustrates the approach

Effective process times for multi-server tandem queues with finite buffers

An Effective Process Time (EPT) approach is proposed for the building of aggregate models to represent multi-server tandem queues with finite buffers. EPT distributions of the workstations in the flow line are measured without identifying the contributing factors. A sample path equation is used to compute the EPT realizations from arrival and departure events of lots at the respective workstations. If the amount of blocking in the line is high, the goodness of fits of the EPT distribution determines the accuracy of the EPT-based aggregate model. Otherwise, an aggregate model based on just the first two moments of the EPT distributions is sufficient to obtain accurate predictions. The approach is illustrated in an industrial case study using both simulation and analytical queueing approximations as aggregate models

Effective process times for multi-server flowlines with finite buffers

An effective process time (EPT) approach is proposed for aggregate model building of multi-server tandem queues with finite buffers. Effective process time distributions of the workstations in the flow line are measured without identifying the contributing factors. A sample path equation is used to compute the EPT realizations from arrival and departure events of lots at the respective workstations. If the amount of blocking in the line is high, the goodness of the EPT distribution fits determines the accuracy of the EPT-based aggregate model. Otherwise, an aggregate model based on just the first two moments of the EPT distributions is sufficient to obtain accurate predictions. The approach is illustrated in an industrial case study using both simulation and analytical queueing approximations as aggregate models

Lumped parameter modeling of the litho cell

Litho cells, are the most expensive equipment in a wafer fab. To support decision-making on this equipment, accurate simulation models for throughput and cycle time are helpful. The simulation models that are typically developed incorporate various shopfloor details. To properly model these details, they should be quantified, which is difficult and time-consuming.In this paper, a lumped parameter model is proposed for the litho cell. The model consists of two parts: a detailed representation of the processing inside the track and scanner, and an aggregate representation of the factory floor feeding the loadport.The track-scanner is modeled as a tandem flow line with blocking. The shop floor is represented by a delay distribution that incorporates all contributions outside the machine. Simulation results show that the suggested method provides a simple, yetaccurate approximation of the litho cell

Performance evaluation and lumped parameter modelling of single server flowlines subject to blocking : an effective process time approach

The present paper extends the so-called Effective Process Time (EPT) approach to single server flowlines with finite buffers and blocking. The power of the EPT approach is that it quantifies variability in workstation process times without the need to identify each of the contributing disturbances, and that it directly provides an algorithm for the actual computation of EPTs. It is shown that EPT realizations can be simply obtained from arrival and departure times of lots, by using sample path equations. The measured EPTs can be used for bottleneck analysis and for lumped parameter modeling. Simulation experiments show that for lumped parameter modeling of flowlines with finite buffers, in addition to the mean and variance, offset is also a relevant parameter of the process time distribution. A case from the automotive industry illustrates the approach

Performance measurement and lumped parameter modelling of single server flowlines subject to blocking : an effective process time approach

The present paper extends the so-called Effective Process Time (EPT) approach to single server flowlines with finite buffers and blocking. The power of the EPT approach is that it quantifies variability in workstation process times without the need to identify each of the contributing disturbances, and that it directly provides an algorithm for the actual computation of EPTs. It is shown that EPT realizations can be simply obtained from arrival and departure times of lots, by using sample path equations. The measured EPTs can be used for bottleneck analysis and for lumped parameter modeling. Simulation experiments show that for lumped parameter modeling of flowlines with finite buffers, in addition to the mean and variance, offset is also a relevant parameter of the process time distribution. A case from the automotive industry illustrates the approach