1,721,028 research outputs found
Flow lines with regular service times: Evolution of delay, state dependent failures and semiconductor wafer fabrication
No full textOn the fidelity of the AX+B equipment model for clustered photolithography scanners in fab-level simulation
No full textRegular flow line models for semiconductor cluster tools: A case of lot dependent process times
No full textEquipment models for fab level proudction simulation: Practical features and computational tractability
No full textA Numerical Study on the Structure of Optimal Preventive Maintenance Policies in Prototype Tandem Queues
No full textWhile high levels of automation in modern manufacturing systems increase the reliability of production, tool failure and preventive maintenance (PM) events remain a significant source of production variability. It is well known for production systems, such as the M/G/1 queue, that optimal PM policies possess a threshold structure. Much less is known for networks of queues. Here we consider the prototypical tandem queue consisting of two exponential servers in series subject to health deterioration leading to failure and repair. We model the PM decision problem as a Markov decision process (MDP) with a discounted infinite-horizon cost. We conduct numerical studies to assess the structure of optimal policies. Simulation is used to assess the value of the optimal PM policy relative to the use of a PM policy derived by considering each queue in isolation. Our simulation studies demonstrate that the mean cycle time and discounted operating costs are 10% superior
Practical extensions to cycle time approximations.for the G/G/m-queue with applications
No full textApproximate closed form expressions for the mean cycle time in a G/G/m-queue often serve as practical and intuitive alternatives to more exact but less tractable analyses. However, the G/G/m-queue model may not fully address issues that arise in practical manufacturing systems. Such issues include tools with production parallelism, tools that are idle with work in process, travel to the queue, and the tendency of lots to defect from a failed server and return to the queue even after they have entered production. In this paper, we extend popular approximate mean cycle time formulae to address these practical manufacturing issues. Employing automated data extraction algorithms embedded in software, we test the approximations using parameters gleaned from production tool groups in IBM's 200 mm semiconductor wafer fabricator
Computational performance bounds for Markov chains with applications
No full textFor Markov chains exhibiting translation invariance of their transition probabilities on polyhedra covering the state space, we develop computational performance bounds for key measures of system performance. Duality allows us to obtain linear programming performance bounds. The Markov chains considered can be used to model multiclass queueing networks operating under affine index policies, a class of policies which subsume many that have been proposed
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