A review of design and control of automated guided vehicle systems <s> The segmented guide-path system (segmented flow topology -SFT) <s> Due to increases in versatility and the complexity of demands in modern manufacturing systems a growing need has evolved t0 simplify the control of these systems while maintaining a high degree of efficiency and flexibility in operation. The segmented flow approach (SFT) suggested in this paper is a possible solution to these needs. This structure simplifies the control task by reducing the need for dispatching and by eliminating the need for routeing material handling devices and scheduling traffic at intersections. Each task involves only one material handling device and one possible route. This structure maintains a high degree of efficiency by operating material handling devices in a bidirectional mode and eliminates congestion and blocking by operating them on mutually exclusive tracks. This paper introduces a design procedure for an SFT implemented system using a minimum cost objective, and compares the throughput and time in system performance of this system to a conventional system and a tandem ty... <s> BIB001 </s> A review of design and control of automated guided vehicle systems <s> The segmented guide-path system (segmented flow topology -SFT) <s> In this paper, both the single pick-up and delivery station (SPDS) and the multiple pick-up and delivery station (MPDS) cases of the segmented flow topology (SFT) system configuration are presented. These system's configurations serve as the backbone of a heuristic design procedure for SFT. This design procedure consists of an upper and lower bound calculation and a search procedure that minimizes the total system cost (transportation, setting up pick-up and/or delivery stations, and material handling devices). Two examples of the implementation of the procedure are given. <s> BIB002 </s> A review of design and control of automated guided vehicle systems <s> The segmented guide-path system (segmented flow topology -SFT) <s> Guided vehicles (GVs) are commonly used for the internal transportation of loads in warehouses, production plants and terminals. These guided vehicles can be routed with a variety of vehicle dispatching rules in an attempt to meet performance criteria such as minimizing the average load waiting times. In this research, we use simulation models of three companies to evaluate the performance of several real-time vehicle dispatching rules, in part described in the literature. It appears that there is a clear difference in average load waiting time between the different dispatching rules in the different environments. Simple rules, based on load and vehicle proximity (distance-based) perform best for all cases. The penalty for this is a relatively high maximum load waiting time. A distance-based rule with time truncation, giving more priority to loads that have to wait longer than a time threshold, appears to yield the best possible overall performance. A rule that particularly considers load-waiting time performs poor overall. We also show that using little pre-arrival information of loads leads to a significant improvement in the performance of the dispatching rules without changing their performance ranking. <s> BIB003
Sinriech and Tanchoco (1995) describe a specific type of guide-path systems: the segmented flow topology (Figure 2 ). The SFT system contains one or more zones, each of which is separated into non-overlapping segments served by a single vehicle. Transfer buffers are situated at both ends of each segment and serve as interface devices between the segments (Figure 2 ). A SFT system may be not fully connected, depending on logical material flow requirements. Considering the SFT system carefully, it appears to be very similar to a general tandem system. Even in the case when the SFT system is not fully connected, we may interpret it as a combination of several tandem sub-systems. BIB001 propose a procedure to solve the segmented flow-path layout design problem. According to their results, the SFT system outperforms the conventional system in many criteria. However, even a small problem requires a large amount of time to solve. In BIB002 , a more efficient procedure was developed for the SFT design problem, which can be implemented for real-life problems. The main disadvantage of the SFT system is that it requires additional transfer stations. To summarize this guide-path system section we describe some characteristics of guide-path systems in Table 2 and Table 3 . Table 3 Advantages and disadvantages of guide-path systems Many modern AGV systems do not use fixed guide-paths (induction tracks). The guide-paths may, for example, be computer-programmed and uploaded to the vehicles' controllers. These vehicles are free-ranging and find their way using optical (laser), magnetic, odometer, gyroscope, vision, or radio-frequency techniques  . In order to make full use of the flexibility capabilities of such systems, smart AGVs are needed. The flexibility of changing guide-paths demands a capability to adapt the guide-path system satisfying new system requirements. In this case, obtaining the optimal guide-path system as a first objective becomes less important, however the system's flexibility becomes crucial. An emerging problem in the guide-path design is selecting an appropriate type of guide-path system, but a guideline to select a suitable guide-path system is not available yet. The conventional guide-path system can be seen regularly in warehouses and distribution centers BIB003 , the single-loop system is used, for example, in cross-dock centers. The tandem configuration may be more appropriate for manufacturing environments where workstations are grouped into manufacturing cells.