Warren J. Boe

A CLOSE NEIGHBOUR ALGORITHM FOR DESIGNING CELLULAR MANUFACTURING SYSTEMS

The first step in creating a cellular manufacturing system is to identify machine groups and form part families. Clustering and data organization (CDR) algorithms (such as the bond energy algorithm) and array sorting (ARS) methods (such as the rank order clustering algorithm) have been proposed to solve the machine and part grouping problem. However, these methods do not always produce a solution matrix that has a block diagonal structure, making visual identification of machine groups and part families extremely difficult. This paper presents a ‘close neighbour algorithm’ to solve this problem. The algorithm overcomes many deficiencies of the CDR and ASM methods. The algorithm is tested against ten existing algorithms in solving test problems from the literature. Test results show that the algorithm is very reliable and efficient.

DESIGNING CELLULAR MANUFACTURING SYSTEMS: BRANCH-AND-BOUND AND A∗ APPROACHES

In this paper, heuristic and optimal algorithms for solving the group technology problem are presented. The heuristic algorithm is based on a branch-and-bound concept. A quadratic programming model for the machine grouping problem is formulated. The A∗ algorithm is developed for optimal solving of the machine grouping problem. The performance of the heuristic branch-and-bound method and the A∗ algorithm is compared with several existing heuristics.

An experimental investigation of FMS scheduling rules under uncertainty

Abstract This article reports the results of an experimental investigation of scheduling decision rules for a dedicated flexible manufacturing system (FMS) with variable performance times and machine break-downs. An existing FMS was modeled using the actual performance times obtained from the systems transaction log. The performance of six heuristic scheduling rules were tested under differing uncertainty conditions. The simulation model included three types of uncertainty, namely: minor breakdowns, which averaged two hours and occurred once every two shifts; major breakdowns, which averaged ten hours and occurred once every ten shifts; and operation time deviations, which ranged from 0% to 20% of standard time. The runtime for the simulation approximated the work to be done over a ten-week period of time, or 7,590 parts. Six different part loading rules were used to determine whether they could produce different performance results. The smallest proportion of jobs launched and the next empty pallet rule worked appreciably better than the rest of the rules in obtaining the highest FMS utilization.

Bond Quality Rating Changes for Electric Utilities: A Multivariate Analysis

Most bond issues of large utility companies are rated for quality by at least two of the three rating agencies. Bond investors individuals and institutions are concerned not only with original ratings of an issue but also with future ones. Since a rating change will affect prices of the outstanding bonds as well as interest rates and marketability of new issues, it may be a cause of portfolio readjustment for investors as well as a reason for the utility to reconsider its capital budgeting policies. Each rating agency maintains that models based on financial statements or data bases cannot replicate its ratings [4, 7]. Nevertheless, studies have explained bond quality ratings by using financial statement data [9, 19, 21, 25] and related bond quality ratings to systematic risk [15], prices [10], bond yield [26], and market-determined risk measures [22]. Several scholars have examined the impact of rating changes on borrowing cost [11] and on price adjustments [8, 12, 20]. No work has been uncovered, though, that centers upon forecasting rating changes by the various rating agencies. The purpose of this paper, therefore, is to investigate whether or not a multivariate discriminant model that incorporates the recent levels, past trends, and instability of financial ratios can explain and predict the quality rating changes of electric utility bonds. We used 1971 as a starting point because bond rating changes were rare before then. In 1971, there were no quality rating changes announced by Moodys for industrial or utility bonds graded B or above. With rising interest rates and the environmental problems

Examining the use of dedicated and general purpose pallets in a dedicated flexible manufacturing system

This research describes one example of how the failure to understand the relationships between the flexibility associated with all resources within an FMS can be critical to overall performance. The need for such understanding is clearly spelled out by Jaikumar (1986). This research illustrates that even in situations where the demands placed upon the system are very well defined, tooling resources, such as pallets, may constrain overall system flexibility and subsequent system performance. In this paper, we simulate the operational performance of an existing FMS designed to manufacture a relatively small set of agricultural equipment components (only eight part types) over a known planning horizon using general purpose pallets and dedicated pallets. The simulation model is run under experimental conditions that include levels of: demand mix variability, number of each type pallet available to the system, and incremental loading time and scrap rate when general purpose pallets are used. In most cases, the...

Database operating efficiency in fragmented databases in mainframe, mini, and micro system environments

Abstract Vertical fragmentation in database design is the process of assigning attributes to physical segments to improve the database performance. Experiments were conducted to measure the performances of four Fragmentation design methods in the three hardware environments with six transaction mixes, using simulation and quantitative modelling. Some hypotheses are laid down regarding database performance and are validated. The MRGB design method which considered the hardware characteristics produced highest fragmentation in micro (IBM AT), and lowest in mini (Prime), with mainframe (IBM) in between. MRGB design performed the best in the three systems. The Hammer & Niamirs design did its best in mini (61%), and better in mainframe (50%) than in mini (41%) in low update environment. While the fully fragmented design performed the best in micro and the worst in mainframe, the unfragmented design performed the best in mini and the worst in micro.

What's in a change in an industrial bond rating?

Abstract Bond quality rating changes (BQRC) for industrial bonds are analyzed using both univariate statistical methods and discriminant analysis to find significant variables and their relationship with the changes. The single most important explanatory variable is found to be the rate of return on assets (ROA), followed by the trend in the return on assets (ROATREND). The univariate analysis found six of the seven proposed explanatory variables significant beyond the 0.01 level. The two-group discriminant analysis model achieved a correct classification rate of over 77%. The paper shows how the results of the two-group discriminant analysis can be used for a three-way prediction (upgrade, downgrade, or no change of bond ratings). The results of this study show that models based on financial statement data can predict rating changes with good accuracy and therefore may be a useful tool for rating agencies, at least as an initial screening device.

Effect of schema size on fragmentation design in multi-relational databases

Abstract Vertical fragmentation in database design is aimed at improving database performance. In shared databases, referential integral constraints are maintained to ensure the consistency of database. The database fragment design differences and operating cost differences between large and small databases, in which differential levels of integral constraints exist, are presented. Experiments are conducted with database schema size ranging from 4 to 20 relations with six transaction environments and four fragment design methods. A total of 150 database design problems were solved. Statistically significant optimum design differences between small and large databases were observed. It is shown that the MRGB design is recommended in small and large database fragmentations. The other designs recommended are: unfragmented design in larger databases, trivially fragmented design in smaller databases and Hammer and Niamirs design in large databases with low updates and in smaller databases with medium updates.

Periodic reconfiguration of general-purpose fixtures in a dedicated FMS

Fixtures dedicated to a given part type in an FMS can sometimes become bottlenecks to some FMSs as demand variability increases. Past research indicates that the increased operating flexibility associated with general-purpose fixtures may be a key to the efficient scheduling of even those FMSs dedicated to producing a small number of part types over a known planning horizon. However, the increased time required to reconfigure general-purpose fixtures to meet current demand may also create a bottleneck in the loading area. Increases in the defect rate associated with improper fixture assembly and part alignment are also possible. One solution may be to reconfigure general-purpose fixtures off line according to specific demand schedules for the period, and then to treat them as “pseudo-dedicated” fixtures until the next period. This would utilize some of the flexibility associated with general-purpose fixtures, while reducing the negative drawbacks associated with incremental loading time and alignment errors.The research reported in this article simulates an existing FMS, using fixtures dedicated to individual part types, and compares the results to those collected using a group of general-purpose fixtures that are reconfigured each week, based on current demand for each part type, and used in a pseudo-dedicated fashion. Three simulation experiments are run with increasing coefficients of variation in the input distributions used to generate demand.Performance is measured by system throughput, proportion of parts tardy, and average tardiness. The simulation results show that while overall system performance decreases as the level of demand mix variability increases, this negative impact is significantly less severe when using pseudo-dedicated, general-purpose fixtures.