http://hdl.handle.net/1721.1/3653 Sat, 08 Jun 2013 14:02:24 GMT 2013-06-08T14:02:24Z http://dspace.mit.edu:80/bitstream/id/3315/sma_logo.gif http://hdl.handle.net/1721.1/3653 http://hdl.handle.net/1721.1/29837 Modeling and Analysis of Re-entrant Production Systems Jang, Young Jae; Gershwin, Stanley B. This paper presents a model and analysis of a re-entrant production line with finite buffers and unreliable machines. Semiconductor device and liquid crystal display (LCD) fabrication processes are characterized as a re-entrant process, in which a similar sequence of processing step is repeated several times. This re-entrant behavior of material flow with the stochastic nature of the system caused by machine failures or demand changes makes the system difficult predict and analyze. The decomposition method analyzes the behavior of the manufacturing systems by decomposing a long transfer line into small analytically tractable components, called two-machine line building blocks. Existing decomposition methods are limited to an in-linear production system without re-entrant flow. Since many manufacturing systems, particularly semiconductor and LCD production lines, consist of re-entrant flow paths, it is essential that models be developed to reflect this. The purpose of this paper is to present mathematical formulations and algorithms to analyze the material behavior of the re-entrant production system using the decomposition method. In developing equations for the two-machine building blocks for the re-entrant production line, we modify the existing decomposition model that has been created for the multiple-part type line. Two main performance measures are evaluated with the developed mathematical model: production rate and average inventory levels for each buffer space in the system. The qualitative behavior of the re-entrant production line under different machine parameters and demand scenarios is also described. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/1721.1/29837 2006-01-01T00:00:00Z http://hdl.handle.net/1721.1/29836 Modeling and Analysis of Manufacturing Systems with Multiple-Loop Structures Zhang, Zhenyu; Gershwin, Stanley B. Kanban and Constant Work-In-Process (CONWIP) control methods are designed to impose tight controls over inventory, while providing a satisfactory production rate. This paper generalizes systems with kanban or CONWIP control as assembly/disassembly networks with multiple-loop structures. We present a stochastic mathematical model which integrates the information control flows into material flows. Graph theory is used to analyze the multiple-loop structures. An efficient analytical algorithm is developed for evaluating the expected production rate and inventory levels. The performance of the algorithm is reported in terms of accuracy, reliability and speed. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/1721.1/29836 2006-01-01T00:00:00Z http://hdl.handle.net/1721.1/29835 Performance of a Serial-Batch Processor System with Incompatible Job Families under Simple Control Policies Tajan, John Benedict Cheng; Appa Iyer, Sivakumar; Gershwin, Stanley B. A typical example of a batch processor is the diffusion furnace used in wafer fabrication facilities (otherwise known as wafer fabs). In diffusion, silicon wafers are placed inside the furnace, and dopant is flown through the wafers via nitrogen gas. The higher the temperature, the faster the dopant penetrates the wafer surface. Then, a thin layer of silicon dioxide is grown, to help the dopant diffuse into the silicon. This operation can take 10 hours or more to finish processing, as compared to one or two hours for other wafer fab operations, according to Uzsoy [8]. Diffusion furnaces typically can process six to eight lots concurrently; we call the lots processed concurrently a batch. The quantity of lots loaded into the furnace does not affect the processing time. Only lots that require the same chemical recipe and temperature may be batched together at the diffusion furnace. We wish to control the production of a manufacturing system, comprised of a serial processor feeding the batch processor. The system produces different job types, and each job can only be batched together with jobs of the same type. More specifically, we explore the idea of controlling the production of the serial processor, based on the wip found in front of the batch processor. We evaluate the performance of our manufacturing system under several simple control policies under a range of loading conditions and determine which control policies perform better under which conditions. It is hoped that the results obtained from this small system could be extended to larger systems involving a batch processor, with particular emphasis placed on the applicability of such policies in wafer fabrication. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/1721.1/29835 2006-01-01T00:00:00Z http://hdl.handle.net/1721.1/29834 Generation of Dielectrophoretic Force under Uniform Electric Field Kua, C.H.; Yang, C.; Goh, S.; Isabel, R.; Youcef-Toumi, Kamal; Lam, Yee Cheong Effective dipole moment method has been widely accepted as the de facto technique in predicting the dielectrophoretic force due to the non-uniform electric field. In this method, a finite-particle is modeled as an equivalent point-dipole that would induce a same electric field under the external electric field. This approach is only valid when the particle size is significantly smaller than the characteristic length of interest. This assumption is often violated in a microfluidic device, where the thickness or width of the microchannel can be as small as the particle. It is shown in this numerical study that when the dimensions of the particle were in the same order of magnitude as the characteristic length of the device, dielectrophoretic force can be induced even in a uniform electric field. This force arises due to the disturbance of the particle and the bounding wall. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/1721.1/29834 2006-01-01T00:00:00Z