A review of design and control of automated guided vehicle systems <s> Transfer point <s> 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 90's. 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... <s> BIB001 </s> A review of design and control of automated guided vehicle systems <s> Transfer point <s> 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. <s> BIB002 </s> A review of design and control of automated guided vehicle systems <s> Transfer point <s> Automated guided vehicle (AGV) systems provide the flexibility and integration required for flexible manufacturing systems. Previous AGV system studies have attempted to reduce the controlling complexities commonly encountered in these systems. However, this has not been accomplished without additional resources (e.g., automated guided vehicles) and lower system flexibility. The primary objective of this study is to compare the performance of AGV system configurations that reduce controlling and modification complexities (i.e., tandem configurations) to traditional AGV system configuration. Three AGV system configurations were tested under 16 experimental conditions. Performance metrics considered were AGV utilization, mean flowtime, mean tardiness, and percent tardy. The results of this study extend the findings of the previous studies in demonstrating the viability of tandem configurations, in that the tandem configurations match the performance of traditional configuration across all performance metrics, without sacrificing ease of control and system flexibility. Finally, the cost tradeoffs inherent in selecting a particular configuration are discussed. <s> BIB003 </s> A review of design and control of automated guided vehicle systems <s> Transfer point <s> A new design concept of materialtransportation system is proposed on the basis of tandem automated guided vehicle (AGV) systems. The first design stage is to find the one and only one optimal transfer point for each traffic zone. All in-process parts to be moved into and out of a zone must go through the specified transfer point and parts can be moved directly to their destinations. The second design stage is to link all transfer points as a 'transportation centre' by several bidirectional tracks. This design concept can simplify material transportation system and provides accurate estimation of traffic load in a zone. <s> BIB004 </s> A review of design and control of automated guided vehicle systems <s> Transfer point <s> The partitioning of a tandem layout for an automated guided vehicle (AGV) system directly affects the system performance. Determining the location of the transfer points between zones is another important issue in the design of a tandem layout. In this paper, a heuristic partitioning algorithm for a tandem AGV system based on the concept of variable path routing within a zone is developed. Transfer points are simultaneously determined during the network partitioning process. The algorithm assumes the prior existence of a conventional and unidirectional layout. The problem of interest is one of converting the existing, conventional layout to a variable path based tandem AGV system layout. A comparison between the conventional and the tandem AGV system with respect to system performance under the same operating conditions is presented. The results show that the variable path based tandem layout requires a smaller number of vehicles in most situations than the equivalent conventional layout. In addition, the total vehicle use time of a tandem layout is smaller than that of the conventional layout. <s> BIB005
Figure 2 A tandem guide-path system with three zones (one loop and two segments) The tandem guide-path system was first introduced by BIB001 . The tandem guide-path system contains multiple zones. Only one vehicle serves each zone and transfer stations are used to interface between zones (Figure 2 ). In case zones are loops, we have a tandem-loop configuration. A number of non-overlapping single-loop paths provide transportation possibilities. In tandem guide-path systems, a job may require more than one vehicle to transport it to its destination. Vehicle blocking and interference problems are totally eliminated. BIB001 also propose an analytical model to study the throughput of a single vehicle loop. BIB002 introduce an algorithm based on a set-partitioning approach to decompose a system into non-overlapping, single-vehicle zones operating in tandem. The procedure starts by generating promising subsets of workstations. A vehicle must have enough capacity to serve a subset (with workload ω). After that, the feasibility of each subset is checked. These subsets (columns) are fed into a set-partitioning model, which is used to identify the best tandem layout. The set-partitioning model is given below: minimize z subject to: The first constraint ensures the workload in any zone does not exceed z (maximum workload). The second constraint ensures that each workstation is assigned to only one column (zone) and the last constraint forces the resulting partition to have exactly L zones. The objective of the set-partitioning problem is to avoid generating bottleneck zones by evenly distributed the overall workload among the zones as much as possible. This model was solved using LINDO, however to solve big problems, a more efficient algorithm is proposed. In BIB002 , a vehicle in the tandem guide-path system does not need to use FEFS, but it can use other dispatching rules as well. BIB004 introduces a variation of tandem configurations with an additional transportation center. This particular tandem configuration serves transportation jobs quicker and needs smaller number transfer stations between loops. However, the transportation center needs more space and requires higher investment. His procedure allocates a transfer point in each zone and constructs a transportation center to connect them for a given tandem system. BIB005 introduce a variable-path tandem system based on partitioning a conventional guide-path into non-overlapping tandem zones. A dedicated vehicle serves each partition (sub-network) and additional transfer points provide interfaces between adjacent networks. Each sub-network is not necessarily a loop, so the dedicated vehicle has a greater flexibility in routing. BIB003 compare the performance (AGV utilization, mean flow time, mean tardiness, mean percent tardy) of the tandem and conventional systems for specific configurations. They show that the tandem system performs as efficient as the conventional system. In comparison with the conventional system, the tandem system is simpler to control, has no congestion problem and is easier to expand. However, the tandem system requires additional transfer buffers which are costly and increase the handling time. This disadvantage may reduce the system throughput. The tandem system also has other disadvantages such as less tolerance to system failures.