A review of design and control of automated guided vehicle systems <s> Forward sensing <s> This research project investigates and develops techniques for automatically detecting potential vehicle conflicts in an automated guided vehicle (AGV) system. Three activities are involved: (1) construction of a set of formal definitions of Petri nets for modelling AGV systems; (2) development of procedures for detection of vehicle routeing conflicts; (3) development of a simulation program of the procedure. In this paper the first two activities are discussed in detail, and examples are provided. <s> BIB001 </s> A review of design and control of automated guided vehicle systems <s> Forward sensing <s> The paper presents a control-based Petri net (PN) modeling method that translates a high-level automated guided vehicle system (AGVS) flowpath net model into a low-level on/off control model systematically. The relation between a high-level AGVS flowpath net model and the equivalent low-level control net model is uniquely defined by introducing certain I/O control functions and station control macros into the net model. To ensure the uniqueness of the translation, the AGVS flowpath layout is first decomposed into constituent basic PN flowpath modules. By employing a modular concept, the wiring layout of each basic flowpath module is established. Proper I/O control functions and station control macros are introduced and incorporated into basic flowpath net modules to generate basic control net modules. The union of constituent basic control net modules systematically leads to a complete AGVS control PN model. A laboratory AGVS is used to verify the effectiveness of the proposed modeling method. The results indicate that the proposed method is capable of generating a control model directly from a given flowpath layout. Many by-products are generated by the method: wiring layout, minimum size and specification of the controller, scanning time of the control program, and so on. These features allow a designer to quickly conduct cost estimation and performance evaluation on any given flowpath layout. <s> BIB002
AGVs can be equipped with sensors which they can use to detect if they are too close to other vehicles BIB001 . A vehicle stops when the distance between it and the vehicle in front of it, is less than a threshold value. This technique however is not effective for systems with many curved guide-paths. BIB001 use Petri nets to detect conflicts in AGV systems. A Petri-net approach seems to be a promising direction to detect and prevent conflicts in AGV systems BIB001 BIB002 .