Using existing workstations as transfer stations in tandem AGV systems

Abstract

Tandem AGV systems, which were introduced by Bozer and Srinivasan, are based on dividing all the stations in a system into non-overlapping, single-vehicle zones with transfer stations connecting adjacent zones. Although tandem AGV systems offer flexibility and simplicity, the transfer stations, that is, the additional pickup/deposit (P/D) points and the conveyors connecting the P/D points, generally increase the cost and floor space requirements of the system. Furthermore, the transfer conveyors may interfere with other material handling functions and make it more difficult to reconfigure the zones. This paper considers the elimination of conveyros by using an existing station as a transfer point. Depending on how the vehicles access the station, however, such an approach may lead to blocking between vehicles. An analytical model is developed and an iterative algorithm is presented to evaluate the performance of two vehicles under possible blocking scenarios at the transfer station. A numerical example illustrates the accuracy of the analytical model. The proposed algorithm converges under the most realistic blocking scenario.