Modeling and Analysis of Manufacturing Systems with Multiple-Loop Structures

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.Singapore-MIT Alliance (SMA

Remanufacturing and product design: designing for the 7th generation

The following is taken directly from the research report. This report investigates Design for Remanufacture in terms of both detailed product design and the business context in which Design for Remanufacture may operate. Key Study Objectives • To understand the link between design and remanufacture • To understand how Design for Remanufacture can lead to increased innovation and Sustainable Development (SD) • To identify proactive strategies to further Design for Remanufactur

ret2spec: Speculative Execution Using Return Stack Buffers

Speculative execution is an optimization technique that has been part of CPUs for over a decade. It predicts the outcome and target of branch instructions to avoid stalling the execution pipeline. However, until recently, the security implications of speculative code execution have not been studied. In this paper, we investigate a special type of branch predictor that is responsible for predicting return addresses. To the best of our knowledge, we are the first to study return address predictors and their consequences for the security of modern software. In our work, we show how return stack buffers (RSBs), the core unit of return address predictors, can be used to trigger misspeculations. Based on this knowledge, we propose two new attack variants using RSBs that give attackers similar capabilities as the documented Spectre attacks. We show how local attackers can gain arbitrary speculative code execution across processes, e.g., to leak passwords another user enters on a shared system. Our evaluation showed that the recent Spectre countermeasures deployed in operating systems can also cover such RSB-based cross-process attacks. Yet we then demonstrate that attackers can trigger misspeculation in JIT environments in order to leak arbitrary memory content of browser processes. Reading outside the sandboxed memory region with JIT-compiled code is still possible with 80\% accuracy on average.Comment: Updating to the cam-ready version and adding reference to the original pape

Performance Evaluation of Remanufacturing Systems

Implementation of new environmental legislation and public awareness has increased the responsibility on manufacturers. These responsibilities have forced manufacturers to begin remanufacturing and recycling of their goods after they are disposed or returned by customers. Ever since the introduction of remanufacturing, it has been applied in many industries and sectors. The remanufacturing process involves many uncertainties like time, quantity, and quality of returned products. Returned products are time sensitive products and their value drops with time. Thus, the returned products need to be remanufactured quickly to generate the maximum revenue. Every year millions of electronic products return to the manufacturer. However, only 10% to 20% of the returned products pass through the remanufacturing process, and the remaining products are disposed in the landfills. Uncertainties like failure rate of the servers, buffer capacity and inappropriate preventive maintenance policy would be highly responsible the delays in remanufacturing. In this thesis, a simulation based experimental methodology is used to determine the optimal preventive maintenance frequency and buffer allocation in a remanufacturing line, which will help to reduce the cycle time and increase the profit of the firm. Moreover, an estimated relationship between preventive maintenance frequency and MTBF (Mean Time Between Failure) is presented to determine the best preventive maintenance frequency for any industry. The solution approach is applied to a computer remanufacturing and a cell phone remanufacturing industry. Analysis of variance and regression analysis are performed to denote the influential factors in the remanufacturing line, and optimization is done by using the regression techniques and ANOVA results

Analysis and design of manufacturing systems with multiple-loop structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 281-284).Kanban means card or token. A kanban-controlled production system is one where the flow of material is controlled by the presence or absence of a kanban, and where kanbans travel in the system according to certain rules. The study of kanban-controlled production systems can be traced back to the Toyota Production System in the 1950s. The classic kanban-controlled system was designed to realize Just-In-Time (JIT) production. Kanban-controlled production systems, though pervasively used in industry and studied for decades, are not well understood quantitatively yet. The essence of kanban-controlled production systems is to use single or multiple closed loops to provide information flow feedback using kanbans. By doing this, the systems keep tight controls over inventory levels, while providing satisfactory production rates. The goal of this research is to study the behavior of the class of manufacturing systems with multiple closed loop structures and explore the applications in design and operational control of production systems using multiple-kanban loops. To do so, stochastic mathematical models and effcient analytical methods for evaluating the performance of systems with complex structures are required.(cont.) In this thesis, we present an assembly/disassembly network model which integrates the control information flows with material flows. Blocking and starvation properties due to machine failures in a system are analyzed by establishing an effcient underlying graph model of the system. Based on the mathematical model and blocking and starvation properties, effcient and accurate algorithms are developed for evaluating the performance of systems with arbitrary multiple-loop structures. We study the behavior of multiple-loop structures and develop intuition for optimal design and operational control using multiple-kanban loops. Some practical guidelines for the design and control of production systems using multiple-kanban loops are provided at the end.by Zhenyu Zhang.Ph.D

Survey on assembly sequencing: a combinatorial and geometrical perspective

A systematic overview on the subject of assembly sequencing is presented. Sequencing lies at the core of assembly planning, and variants include finding a feasible sequence—respecting the precedence constraints between the assembly operations—, or determining an optimal one according to one or several operational criteria. The different ways of representing the space of feasible assembly sequences are described, as well as the search and optimization algorithms that can be used. Geometry plays a fundamental role in devising the precedence constraints between assembly operations, and this is the subject of the second part of the survey, which treats also motion in contact in the context of the actual performance of assembly operations.Peer ReviewedPostprint (author’s final draft

Modeling and Optimization of Disassembly Systems with a High Variety of End of Life States.

Remanufacturing is a promising product recovery method that brings new life to cores that otherwise would be discarded thus losing all value. Disassembly is a sub-process of remanufacturing where components and modules are removed from the core, sorted and graded, and directly reused, refurbished, recycled, or disposed of. Disassembly is the backbone of the remanufacturing process because this is where the reuse value of components and modules is realized. Disassembly is a process that is also very difficult in most instances because it is a mostly manual process creating stochastic removal times of components. There is a high variety of EOL states a core can be in when disassembled and an economic downside due to not all components having reuse potential. This thesis focuses on addressing these difficulties of disassembly in the areas of sequence generation, line balancing, and throughput modeling. In Chapter 2, we develop a series of sequence generation models that considers the material properties, partial disassembly, and sequence dependent task times to determine the optimal order of disassembly in the presence of a high variety of EOL states. In Chapter 3, we develop a joint precedence graph method for disassembly that models all possible EOL states a core can be in that can be used with a wide variety of line balancing algorithms. We also develop a stochastic joint precedence graph method in the situation where some removal times of components are normal random variables. In Chapter 4, we further advance the analytical modeling framework to analyze transfer lines that perform routing logics that result from a high variety of EOL states, such as a restrictive split routing logic and the possibility that disassembly and split operations can be performed at the same workstation.PhDIndustrial and Operations EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111570/1/robriggs_1.pd

Coping with disassembly yield uncertainty in remanufacturing using sensor embedded products

© 2011, Ilgin et al; licensee Springer.This paper proposes and investigates the use of embedding sensors in products when designing and manufacturing them to improve the efficiency during their end-of-life (EOL) processing. First, separate design of experiments studies based on orthogonal arrays are carried out for conventional products (CPs) and sensor embedded products (SEPs). In order to calculate the response values for each experiment, detailed discrete event simulation models of both cases are developed considering the precedence relationships among the components together with the routing of different appliance types through the disassembly line. Then, pair-wise t-tests are conducted to compare the two cases based on different performance measures. The results showed that sensor embedded products improve revenue and profit while achieving significant reductions in backorder, disassembly, disposal, holding, testing and transportation costs. While the paper addresses the EOL processing of dish washers and dryers, the approach provided could be extended to any other industrial product