A REAL-TIME TRAFFIC CONTROL SCHEME OF MULTIPLE AGV SYSTEMS FOR COLLISION-FREE MINIMUM-TIME MOTION - A ROUTING TABLE APPROACH

A two-staged traffic control scheme, in which sets of candidate paths are prepared off-line prior to overall motion planning process, has be en widely adopted for motion planning of mobile robots, but relatively little attention has been given to the application of the two staged scheme to multiple automated guided vehicle systems (MAGVS's). In this paper, a systematic two-staged traffic control scheme is presented to obtain collision-free minimum-time motions of AGV's along loopless pa ths. The overall structure of the controller is divided into two tande m modules of off-line routing table generator (RTG) and an on-line tra ffic controller (OTC). First, an induced network model is established considering the configurational restrictions off guide-paths. With thi s model and a modified k-shortest path algorithm, RTG finds sets of k candidate paths from each station nodes to all the other station nodes off-line and stores them in the form of routing tables. Each time a d ispatch command for an AGV is issued, OTC utilizes these routing table s to generate a collision-free minimum-time motion along a loopless pa th. Realtime computation is guaranteed in that time-consuming graph se arching process is executed off-line by RTG, and OTC looks for the min imum time motion among the k candidate paths. The traffic control sche me proposed is suitable for practical application in centralized MAGVS with zone blocking technique.