The Effect of Interaction Between the Production System (Ps) and a Looped Conveyor-based Material Handling System (Lcmhs) in a Manufacturing Facility

In this paper, we provide empirical evidence that shows the effect of the interaction between the production system (PS) and a looped conveyor-based material handling system (LCMHS) in a manufacturing facility. A rudimentary simulation model captures the interaction between the two systems. Varying several key factors, we test for a statistically significant difference in the work in process (WIP) of the production system with and without the LCMHS to find if the squared coefficient of variation (SCV) of the interarrival time distribution to the PS is affected. The results suggest the need to model the interaction between the two systems in order to obtain a more representative estimate of the WIP in a manufacturing facility

A Closed Queueing Network Approach To Analyzing Multi-Vehicle Material Handling Systems

This article models a multi-vehicle material handling system as a closed-loop queueing network with finite buffers and general service times, where the vehicles represent the jobs in the network. This type of network differs from other queueing systems, because the vehicles\u27 residence times on track segments (servers) depend on the number of jobs (vehicles) in circulation. A new iterative approximation algorithm is presented that estimates throughput capacity and decomposes the network consisting of S servers into S separate G/G/1 systems. Each subsystem is analyzed separately to estimate the work-in-process via a population constraint to ensure that the summation of the average buffer sizes across all servers equals the total number of vehicles. Numerical results show that the methodology proposed is accurate in a wide range of operating scenarios. Copyright © 2011 IIE

Analytical Approach to Estimating AMHS Performance in 300mm Fabs

This thesis proposes a computationally effective analytical approach to automated material handling system (AMHS) performance modeling for a simple closed loop AMHS, such as is typical in supporting a 300mm wafer fab bay. Discrete-event simulation can produce accurate assessments of the production performance, including the contribution by the AMHS. However, the corresponding simulation models are both expensive and time-consuming to construct, and require long execution times to produce statistically valid estimates. These attributes render simulation ineffective as a decision support tool in the early phase of system design, where requirements and configurations are likely to change often. We propose an alternative model that estimates the AMHS performance considering the possibility of vehicle-blocking. A probabilistic model is developed, based on a detailed description of AMHS operations, and the system is analyzed as an extended Markov chain. The model tracks the operations of all the vehicles on the closed-loop considering the possibility of vehicle-blocking. The resulting large-scale model provided reasonably accurate performance estimates; however, it presented some computational challenges. These computational challenges motivated the development of a second model that also analyzes the system as an extended Markov chain but with a much reduced state space because the model tracks the movement of a single vehicle in the system with additional assumptions on vehicle-blocking. Neither model is a conventional Markov Chain because they combine the conventional Markov Chain analysis of the AMHS operations with additional constraints on AMHS stability and vehicle-blocking that are necessary to provide a unique solution to the steady-state behavior of the AMHS. Based on the throughput capacity model, an approach is developed to approximate the expected response time of the AMHS to move requests. The expected response times are important to measure the performance of the AMHS and for estimating the required queue capacity at each pick-up station. The derivation is not straightforward and especially complicated for multi-vehicle systems. The approximation relies on the assumption that the response time is a function of the distribution of the vehicles along the tracks and the expected length of the path from every possible location to the move request location.Ph.D.Committee Chair: McGinnis, Leon; Committee Member: Billings, Ron; Committee Member: Foley, Robert; Committee Member: Paredis, Christiaan; Committee Member: Sharp, Gunte

Critical Tools Identification And Characteristics Curves Construction In A Wafer Fabrication Facility

The purpose of this research was to identify the factors in a wafer fabrication facility that significantly affect the cycle times of two main technologies that are currently in process and in demand for the next few years. Moreover, the goal was to construct the characteristics curves that would provide information about the different capabilities of a wafer fabrication facility for several improvement scenarios. A valid simulation model of the whole production line of the fabrication facility was built. The input factors in the fab that significantly affect cycle time, were identified through factor screening experiments. Based on these factors, several scenarios involving addition of tools, were identified and the characteristics curves were constructed for each scenario. These characteristics curves were used to relate cycle time to production volume capacities

Design Of A Manufacturing Facility Layout With A Closed Loop Conveyor With Shortcuts Using Queueing Theory And Genetic Algorithms

Most current manufacturing facility layout problem solution methods aim at minimizing the total distance traveled, the material handling cost, and/or the time spent in the system (based on distance traveled at a specific speed). The methodology proposed in this paper solves the looped layout design problem for a looped layout manufacturing facility with a looped conveyor material handling system with shortcuts by using the operational performance metric, i.e. the work-in-process on the conveyor in a manufacturing facility, as the design criterion. © 2011 IEEE

Throughput Performance Analysis For Closed-Loop Vehicle-Based Material Handling Systems

A computationally effective analysis of the throughput performance of a closed-loop multi-vehicle automated material handling system (AMHS) used in highly automated 300 mm wafer fabrication facilities (fabs) is presented. A probabilistic model is developed, based on a detailed description of AMHS operations, and the system is analyzed as an extended Markov chain. The model represents vehicle operations on the closed-loop considering the possibility of vehicle blocking. This analysis provides essential parameters such as the vehicle blocking probabilities and the throughput capacity of the AMHS. A numerical example is analyzed and simulated using AutoMod to demonstrate and validate the stochastic model

An Analytical Model Of Vehicle-Based Automated Material Handling Systems In Semiconductor Fabs

This research explores analytical models useful in the design of vehicle-based Automated Material Handling Systems (AMHS) to support semiconductor manufacturing. The objective is to correctly estimate the throughput and move request delay. This analysis proposes a computationally effective analytical approach to multi-vehicle AMHS performance modeling for a simple closed loop. A probabilistic model is developed, based on a detailed description of AMHS operations, and the system is analyzed as an extended Markov chain. The model tracks the operations of one vehicle on the closed-loop considering the possibility of vehicle-blocking. This analysis provides the essential parameters such as the blocking probabilities in order to estimate the performance measures. A numerical example is analyzed and simulated using Automod to demonstrate and validate the queuing model. © 2006 IEEE

Survey Of Research In Modeling Conveyor-Based Automated Material Handling Systems In Wafer Fabs

Automated material handling systems (AMHS) play a central role in modern wafer fabrication facilities (fabs). Typically, AMHS used in wafer fabs are based on discrete vehicle-based overhead systems such as overhead hoisted vehicles. Conveyor-based continuous flow transport (CFT) implementations are starting to gain support with the expectations that CFT systems will be capable of handling high-volume manufacturing transport requirements. This paper discusses literature related to models of conveyor systems in semiconductor fabs. A comprehensive overview of simulation-based models is provided. We also identify and discuss specific research problems and needs in the design and control of closed-loop conveyors. It is concluded that new analytical and simulation models of conveyor systems need to be developed to understand the behavior of such systems and bridge the gap between theoretical research and industry problems. © 2007 IEEE