Yavuz A. Bozer

Tandem Configurations for Automated Guided Vehicle Systems and the Analysis of Single Vehicle Loops

Abstract Automated Guided Vehicle (AGV) systems continue to play a significant role in many low to medium flow manufacturing operations, including Flexible Manufacturing Systems (FMS) and other applications. The relatively inexpensive guidepath, coupled with the high degree of flexibility and control offered in vehicle routing, has made AGV systems a proven and viable handling technology for the 90s. Traditionally, AGV systems have been implemented and analyzed assuming that every vehicle is allowed to visit any pick up/deposit point in the system. We introduce a conceptually simple and intuitive approach where the system is decomposed into non-overlapping, single-vehicle loops operating in tandem. In this paper, we also develop an analytical model to study the throughput performance of a single vehicle loop. The resulting expressions are the first closed form analytical expressions that have been obtained to determine the throughput capacity of a single vehicle operating under a specific dispatching rul...

A new simulated annealing algorithm for the facility layout problem

In this paper we present an application of simulated annealing to facility layout problems with single and multiple floors. The facility layout problem is highly combinatorial in nature and generally exhibits many local minima. These properties make it a suitable candidate for simulated annealing. Using a new candidate layout generation routine and spacefilling curves, we develop an improvement-type layout algorithm based on simulated annealing that considers an expanded set of department exchanges. The resulting algorithm achieves low-cost solutions that are much less dependent on the initial layout than other approaches. We compare the performance of the simulated-annealing based algorithm with both steepest-descent and randomized approaches from the literature. Unlike other simulated annealing papers which typically present a statistical experiment to evaluate the effect of numerous control settings, all the experiments presented in this paper were conducted with control settings that are constant or e...

Kitting versus line stocking: A conceptual framework and a descriptive model☆

Abstract In this paper, based on a number of site visits we performed, we present certain fundamental differences between kitting and line stocking (i.e., no kitting), and we develop definitions which are intended to serve as a framework to study most kitting operations. We also develop a descriptive model which can be used to quantify the trade-offs in material handling, space requirements, and work-in-process between kitting and line stocking at an early decision stage. We present a numerical example to demonstrate the model and some of the insight we gained. Lastly, we discuss new research directions to further explore kitting and its impact on the shop floor.

Tandem AGV systems: A partitioning algorithm and performance comparison with conventional AGV systems

In an earlier paper, Bozer and Srinivasan introduced the tandem concept for automated guided vehicle (AGV) systems and presented an analytical model to evaluate the throughput performance of a basic component of the system; namely, a single vehicle serving a set of workstations under the First-Encountered-First-Served rule. In this study, using the above analytical model and certain column generation techniques, we present a heuristic partitioning scheme to configure tandem AGV systems. The partitioning scheme is based on a variation of the well-known set partitioning problem. It is aimed at evenly distributing the workload among all the AGVs in the system. We demonstrate the procedure with two numerical examples. Using simulation, the performance of the tandem configuration obtained for each example is compared to that of the corresponding conventional AGV system.

Optimizing inbound and outbound door assignments in less-than-truckload crossdocks

This study is concerned with inbound and outbound trailer-to-door assignments in crossdocks, which are used by many transportation companies as a redistribution point. A Simulated Annealing (SA)-based heuristic procedure to determine the door assignments in order to minimize the overall material handling workload in a rectangular crossdock is presented. The SA heuristic addresses congestion concerns as well as robustness concerns in a worst-case sense. Using internally generated data, and square versus narrow shapes, the SA heuristic is evaluated against optimal solutions (with up to 20 doors) and solutions obtained from a pairwise exchange, steepest-descent procedure (with up to 96 doors). The SA heuristic performs well in all problems tested. A linear mixed-integer program formulation for the general rectilinear-quadratic assignment problem is also presented. Lastly, the SA heuristic is applied at a 118-door crossdock operated by Con-way. The door assignment obtained with the SA heuristic outperforms the current door assignment by approximately 35% on data sets provided by Con-way.

TRIP-BASED MATERIAL HANDLING SYSTEMS: THROUGHPUT CAPACITY ANALYSIS

Abstract In this paper we present a general-purpose analytical model to compute die approximate throughput capacity of a trip-based material handling system used in a manufacturing setting. A wide variety of handling systems, including freight elevators, cranes, microload automated storage/retrieval (AS/R) systems, industrial lift trucks, and automated guided vehicle (AGV) systems can be modeled as trip-based handling systems. To our knowledge, this model is one of the few analytical models that explicitly considers an empty device dispatching rule. The model is first developed for a single-device system (such as a crane) and subsequently, with a simple modification, it is extended to multiple-device systems (such as lift trucks and AGVs). Using this model one can rapidly evaluate a wide range of handling and layout alternatives for given flow data. Hence, die model would be most effective when used early in the design phase to narrow down die set of alternative handling systems and configurations prior t...

Geometric Approaches to Solve the Chebyshev Traveling Salesman Problem

Abstract: Several heuristic procedures based on geometric concepts have been developed for the Chebyshev (or too) Traveling Salesman Problem (CTSP),which has numerous applications in materials handling and information storage-retrieval. The following study is concerned with evaluating the performance of geometric approaches as a function of the shape of the service region and the number of points to be sequenced. A new approach, the band insertion heuristic, is also introduced and compared with existing procedures. Trade-offs in tour quality and solution effort are the primary focus of the study, which is empirical in nature; however, the results generally apply to a wide range of configurations.

Order batching in walk-and-pick order picking systems

This paper investigates the order-batching problem both as a theoretical problem, including its special variants, and as a practical problem, with possible heuristic solution procedures. It shows that certain special cases or variants of the order batching problem are solvable, while other cases of the problem are NP-hard. It also develops a new Mixed-Integer Programming (MIP) model to obtain near-exact solutions to the problem. The MIP provides good lower and upper bounds to the problem, which prove useful in the investigation of the heuristic solution procedures. The paper identifies and modifies slightly the order batching heuristic, which shows the strongest results in the numerical experiments. Although good solutions are obtained with this particular heuristic, the results indicate that it is computationally intensive. Furthermore, solutions obtained through the MIP model suggest there is still room to obtain even better solutions to the problem via heuristic procedures, although the challenge is to do so without further increasing the computational burden.

A reexamination of the distance-based facility layout problem

In this paper we qualitatively and numerically compare basic modeling approaches to the distance-based facility layout problem and the types of result obtained from them. In the process we observe that when the facility layout problem is modeled as a QAP, one will not necessarily obtain an optimal solution to the layout problem even if the QAP is solved to optimality. We also propose an alternative distance measure, namely, EDIST, which is based on the expected distance between two departments. We illustrate how the EDIST measure addresses some of the well-known shortcomings associated with the centroid-to-centroid distance measure.

A generalized design and performance analysis model for end-of-aisle order-picking systems

In this paper we present an analytical design algorithm to determine the near-minimum number of pickers required in an end-of-aisle order-picking operation based on a miniload automated storage/retrieval system. The algorithm is based on an approximate analytical model we developed to estimate the expected picker utilization (and the storage/retrieval machine utilization) for general system configurations with two or more pick positions per aisle and/or two or more aisles per picker. For systems with two pick positions, we also investigate the possibility of improving the picker utilization by sequencing container retrievals within each order.