A review of design and control of automated guided vehicle systems <s> Zone planning <s> Abstract One of the advances in computer-aided production is the application of computer control to automated material handling systems. Computer control is especially important to Automated Guide Vehicles (AGVs) since their control problems are more complicated than those of traditional automated material handling systems, e.g., conveyors. Of the many design and control issues of AGVs, an important one is the prevention of vehicle collision. Many traditional vehicle-collision prevention strategies are the so-called zone strategies that divide guide paths into several non-overlapping zones, and restrict the presence of at most one vehicle in any zone at any time. In this paper, the concept of a new vehicle-collision prevention strategy called “dynamic-zone strategy” will be introduced. Detailed procedures based on this new strategy will be proposed for an AGV system with a single-loop guide path. Traditional zone strategies are fixed-zone strategies in which the zone assigned to each vehicle cannot be changed and vehicles are not allowed to help each other. As a result, fixed-zone strategies often have the disadvantage of not being able to satisfy the transportation demand whenever there is a load imbalance between vehicles. The objective of this paper is to develop a strategy that not only can prevent the collision of vehicles but also can avoid the disadvantage of fixed-zone strategies. To accomplish this, the proposed strategy relies on two procedures — Zone Adjustment Procedure and Zone Assistance Procedure. With Zone Adjustment Procedure, the area of each zone will be changed according to the current production demand. On the other hand, with Zone Assistance Procedure, vehicles are allowed to help each other so that the workload of every vehicle is balanced all the time. The methods of these two procedures will be developed in this paper. In addition, a Simulated Annealing (SA)-based zone-division design method that can find near-optimal zone-division designs will also be proposed in this paper. Experiments are then conducted to show that the proposed dynamic-zone strategy and the proposed zone-division design method are indeed beneficial to the throughput performance of production systems. <s> BIB001 </s> A review of design and control of automated guided vehicle systems <s> Zone planning <s> Currently, conflict-free routing in AGV systems is established by means of one of the following three approaches: (i) the problem elimination through the adoption of a segmented path flow or tandem queue configuration; (ii) the identification of imminent collisions through forward sensing and their aversion through vehicle backtracking and/or rerouting; or (iii) the imposition of zone control and extensive route pre-planning, typically based on deterministic timing of the vehicle traveling and docking stages. Among these three approaches, the segmented path flow-based approach presents the highest robustness to the system stochasticities/randomness, but at the cost of restricted vehicle routings and the need for complicated handling operations. This paper proposes an alternative conflict resolution strategy that will ensure robust AGV conflict resolution, while maintaining the operational flexibility provided by free vehicle travel on arbitrarily structured guidepath networks. Specifically, the approach advocated in this paper also employs zone control, but it determines vehicle routes incrementally, one zone at a time. Routing decisions are the result of a sequence of safety and performance considerations, with the former being primarily based on structural/logical rather than timing aspects of the system behavior. The resulting control problem is characterized as the AGV structural control. After defining the notion of AGV structural control, the paper proceeds to the formal characterization and analysis of the problem, and to the development of a structural control policy appropriate for the class of AGV resource allocation systems. The paper concludes with some discussion on the accommodation of emerging AGV operational features in the proposed modeling and analysis framework, and the integration of AGV structural control with the broader control of material-flow among the shop-floor workstations. <s> BIB002
Zone planning is an important method to avoid deadlock. There are two types of zoning systems: static zoning and dynamic zoning. In case of a static zoning, the guide-paths are divided into several zones. When a vehicle arrives at a zone, the controller checks for the presence of another vehicle in this zone. If a vehicle is already traveling in this zone, then the vehicle intended to enter that zone has to wait until the other has passed. In case of a dynamic zoning strategy, zones are not fixed; they can be changed according to the traffic flow in the system. BIB001 presents a dynamic-zone strategy for vehicle-collision prevention. His method relies on two procedures: the Zone Adjustment Procedure and the Zone Assistance Procedure. With the Zone Adjustment Procedure, the area of each zone changes according to the current production demand. The Zone Assistance Procedure allows vehicles to help each other so that the workload of every vehicle is balanced over time. BIB002 proposes a zone control strategy that determines vehicle routes incrementally, one zone at a time. Routing decisions are the results of a sequence of safety and performance considerations, with the former being primarily based on structural/ logical rather than timing aspects of the system behavior. In general, the conflict resolution task is much simpler in systems using smart AGVs, since smart AGVs can handle most parts of collision avoidance tasks.