Design of delayed reconfigurable manufacturing system based on part family grouping and machine selection

To improve the convertibility of reconfigurable manufacturing system (RMS), the concept of delayed reconfigurable manufacturing system (D-RMS) was proposed. RMS and D-RMS are both constructed around part family. However, D-RMS may suffer from ultra-long system problem with unacceptable idle machines using generic RMS part families. Besides, considering the complex basic system structure of D-RMS, machine selection of D-RMS should be addressed, including dedicated machine, flexible machine, and reconfigurable machine. Therefore, a system design method for D-RMS based on part family grouping and machine selection is proposed. Firstly, a part family grouping method is proposed for D-RMS that groups the parts with more former common operations into the same part family. The concept of longest relative position common operation subsequence (LPCS) is proposed. The similarity coefficient among the parts is calculated based on LPCS. The reciprocal value of the operation position of LPCS is adopted as the characteristic value. The average linkage clustering (ALC) algorithm is used to cluster the parts. Secondly, a machine selection method is proposed to complete the system design of D-RMS, including machine selection rules and the dividing point decision model. Finally, a case study is given to implement and verify the proposed system design method for D-RMS. The results show that the proposed system design method is effective, which can group parts with more former common operations into the same part family and select appropriate machine types.     

The philosophy of microscopic quantification

A large number of microscopic quantification procedures are now available. As a result, methodologies that have statistical and stereological rigor are available. However, which of them are likely to yield the most meaningful numbers is not immediately obvious to a potential user of these procedures. Accordingly, this overview takes an entirely philosophical approach. Rather than review all the procedures (well established and more recent), it looks at the solution of common problems in quantifying microstructures and, through a “worked example,” demonstrates the power and simplicity of a number of the more useful techniques.     

Technology and political philosophy

While a great many scientists and engineers feel that science and politics do not mix, political theorists feel completely free to talk about the influence of politics on science and technology. The author does not try to resolve this curious anomaly. Indeed, he simply assumes as background the body of literature by political theorists on science, technology and society. What the paper does is sort out that literature, picking out some of the principal types. A second aim of the paper is to urge scientists and engineeers not to ignore this body of literature; becoming familiar with it may even help them in practical efforts to deal with such issues as government regulation of science and technology.     

The Draper family material

Abstract

In 1972, John William Christopher Draper and James Christopher Draper wrote to the Smithsonian Institution informing us of the recent death of Dorothy Draper, in Yonkers, New York. A few weeks later, my colleague George Norton and I, together with the Draper brothers and their families, spent a long day in a large house owned by an elderly woman who had been loath to throw anything away. What we found ranged from the trivial to the terrific (from pieces of stale wedding cake and chains of annual dog-tags, to early daguerreotypes). The Drapers were very generous, and allowed us to put everything we deemed of historical interest into the Smithsonian van. When we returned to Washington and examined the collection, we found that we had a great deal of important material pertammg to the early development of photography and spectroscopy, and that some of this provided information that was not otherwise found in the historical record. ¹ Smithsornian Institution (SI) Accession 58,310.      

Risk-based grouping for checked baggage screening systems

With millions of bags checked at over 7000 baggage screening locations in US daily, the checked baggage screening system may be exploited by the terrorists to do harm to the homeland security. Due to such a huge amount of luggage, how to improve the effectiveness and efficiency of the screening system becomes a challenging task. In this paper, we propose a risk-based cost-effectiveness model where checked bags are classified into several risk classes according to their risk characteristics. According to their risk levels, bags from different classes may go through different device combinations sequentially. For a multiple-device screening system, we determine the optimal sequence of the screening devices and the separate grouping strategies for bags from different risk classes with the objective of minimizing the expected cost per bag. Based on a detailed numerical study, we compare our model with three other cost-effectiveness models (the first model assumes that there is only one risk class, the second model assumes that there is only one group for each risk class, and the third model assumes that all devices in a device combination need to be gone through). Our major conclusions are that our proposed model is beneficial compared with other three models and moreover, the relative benefit becomes larger when the authority commands a stricter upper bound for the probability of false clear.     

The creative design philosophy applied to the design of process plant

This paper describes a project based on design teaching at postgraduate level conducted in the Department of Mechanical Engineering at the University of Liverpool in conjunction with Pilkington Brothers plc. The co-operative project had two main aims: the education of a postgraduate design engineer employed by Pilkington Brothers plc to an adequate level to enable him to obtain a Master's Degree in Engineering Design; and the design of a specific item of process plant required by the Company. These two aims were complementary, as the student was introduced to many approaches to design thinking, while attempting to provide effective solutions to a specific design problem. The paper briefly describes the various steps involved in attempting to satisfy both requirements. It is indicated that, although there is no universal and all-sufficient design process, a creative and organized attitude of mind can result in the appropriate design procedure being adopted. This can then be justified by the performance of the end product.     

Where philosophy meets clinical science

Nowadays, there is a renewed interest in bone changes in experimental and clinical nephrology. However, the need for understanding the peculiarity of bone can be traced back to the 5th century BC, when Empedocles of Acragas put forward a theory of a world made of air, water, fire, and earth governed by love and hate. By observing the various body tissues, he strove to demonstrate that they consisted of 4 elements assembled with different mathematical ratios (logos). Blood is considered the most perfect tissue, because the ratio between elements is one. Bone is a very unusual tissue because it is made of 2 parts of earth, 2 parts of water, and 4 parts of fire. This kind of reasoning could be considered the first cry in the birth of quantitative chemistry.     

Models for machine-part grouping in cellular manufacturing

For cellular manufacturing strategies to succeed, the productive system first has to be divided into highly independent cells. This means that a partition of the machines into machine groups, a partition of the parts into part families, and a matching between the machine groups and the part families have to be simultaneously determined. Mathematically, this question can be expressed as the problem of finding a near block diagonal permutation of the machine-part incidence matrix. Research on such grouping problems has primarily concentrated on the design of heuristics. Different grouping efficiency criteria have been proposed to express the quality of the groupings proposed by these heuristics. This paper is concerned with mathematical programming approaches to the formation of production cells. Existing models are reviewed and their features are briefly discussed. An alternative model is proposed, which allows for the formulation of various constraints and grouping efficiency criteria. Finally, some test problems are used to support the claim that this model may be adequate for the solution to optimality of the cell formation problem.     

Optimal unit grouping in weighted voting systems

The voting system studied consists of n units that each provide a binary decision (0 or 1) or abstain from voting. Each unit has its own individual weight. System output is 1 if the cumulative weight of all 1-opting units is at least a pre-specified fraction τ of the cumulative weight of all non-abstaining units. Otherwise system output is 0.For a system consisting of voting units with given reliability characteristics one can maximize the entire system reliability by choosing proper unit weights and threshold values τ. In this paper it is shown that additional system reliability improvement can be achieved by grouping units in voting subsystems and tallying the weighted votes of these subsystems (groups) to make a final decision. An algorithm is suggested which finds the optimal element grouping as well as unit weights within each group, weights of the groups and corresponding system thresholds. The approach is based on using a universal generating function technique for evaluating system reliability. A genetic algorithm is used as the optimization tool. Examples are presented.     

The Perrego algorithm: a flexible machine-component grouping algorithm based on group technology techniques

The Perrego algorithm, which forms machining cells based upon the weighted importance of the parts which they produce, is presented. Classification and coding (C&C) and production flow analysis (PFA) were synthesized into one single algorithm using similarity coefficients and a cluster identification algorithm to combine the two methods. The resulting unique algorithm's advantage is the utilization of morphological information, such as manufacturing production quantity requirements, with the technological attributes of the parts: cells were formed with minimal amounts of parts travelling between cells. The algorithm also considers the economics of machine duplication for forming independent cells.     

Role of similarity measures in PCB grouping procedures

The problem of grouping printed circuit boards (PCBs) for simultaneous assembly on electronic assembly machines is an extension of the set-covering problem. A general approach based on cluster analysis and measure of similarity between PCBs is suggested as a basis of PCB grouping. The approach is independent of the specific similarity measure used. We show that, due to the analogy between this problem and the problem of machine cell formation in group technology, similarity measures developed for the second problem are useful as building blocks in a general framework that solves the PCB grouping problem.     

Three-dimensional spatial grouping affects estimates of the illuminant

The brightnesses (i.e., perceived luminance) of surfaces within a three-dimensional scene are contingent on both the luminances and the spatial arrangement of the surfaces. Observers viewed a CRT through a haploscope that presented simulated achromatic surfaces in three dimensions. They set a test patch to be approximately 33% more intense than a comparison patch to match the comparison patch in brightness, which is consistent with viewing a real scene with a simple lightning interpretation from which to estimate a different level of illumination in each depth plane. Randomly positioning each surface in either depth plane minimized any simple lighting interpretation, concomitantly reducing brightness differences to approximately 8.5%, although the immediate surrounds of the test and comparison patches continued to differ by a 5:1 luminance ratio.     

Item grouping effects on invariance of attitude items

The purpose of this study was to evaluate the effects of item grouping on local independence and item invariance, the characteristics of items scaled under the Rasch model that make them sample-free. Item fit and calibration for attitude items presented in a grouped versus random order were examined. It was hypothesized that grouping items to facilitate interpretation central to a construct may result in a failure of invariance. Data were 107 responses to a 40-item mail survey of teachers' opinions about the Ontario Ministry's grade 9 literacy test. Effects of grouping and item phrasing on invariance were found. Results, however, generally support the use of grouping of items to provide a higher person separation, and potentially higher quality data.     

Three perspectives for solving the job grouping problem

The production efficiency of printed circuit board (PCB) assembly depends strongly on the organization of the component placement jobs. This is characteristic, especially in a high-mix low-volume production environment. The present study discusses the problem of arranging the jobs of one machine into groups in such a way that the job change costs will be minimized when the costs depend on the number of the job groups. This problem is motivated by the practical case where the group utilizes a common machine set-up and the number of set-up occasions is the dominating factor in the production line optimization. The problem is well known and its large instances are hard to solve to optimality. We show how real-life problem instances can be solved by three different methods: efficient heuristics, 0/1-programming, and constraint programming. The first two of these are standard approaches in the field, whereas the application of constraint programming is new for the job grouping problem. The heuristic approach turns out to be efficient: algorithms are fast and produce optimal or nearly optimal groupings. 0/1-programming is capable of finding optimal solutions to small problem instances and it therefore serves as a benchmark to approximative methods. The constraint approach solves moderately large problem instances to optimality and it has the great advantage that changing the problem formulation is relatively easy one can add new constraints or modify the details of the existing ones flexibly.     

Robustness of the partitions in grouping multi-item inventories

A recent work obtained closed-form solutions to the.problem of optimally grouping a multi-item inventory into subgroups with a common order cycle per group, when the distribution by value of the inventory could be described by a Pareto function. This paper studies the sensitivity of the optimal subgroup boundaries so obtained. Closed-form expressions have been developed to find intervals for the subgroup boundaries for any given level of suboptimality. Graphs have been provided to aid the user in selecting a cost-effective level of aggregation and choosing appropriate subgroup boundaries for a whole range of inventory distributions. The results of sensitivity analyses demonstrate the availability of flexibility in the partition boundaries and the cost-effectiveness of any stock control system through three groups, and thus also provide a theoretical support to the intuitive ABC system of classifying the items.