Concurrent specification of unit load sizes and automated guided vehicle fleet size in manufacturing system

Even though many subproblems related to the design of automated guided vehicle (AGV) systems interact with one another, current design approaches of AGV systems tend to focus on solivng one subproblem at a time. Piecemeal solution leads to suboptimal design. What is required is a concurrent engineering design approach that integrates two or more subproblems into a design model which, when solved, yields the optimal design parameters for the entire system. Three areas that are amenable to integrated design for AGV systems are unit load size specification, vehicle size selection, and fleet size determination. Even though the size and number of unit loads to be moved per period constitute major factors in the determination of vehicle requirements and the specification of vehicle size for AGV based systems, there is very little research done in the specification of load sizes to optimize on total vehicle requirements. In this paper, a procedure is presented for the selection of the best unit load sizes for all part types manufactured in a shop that employs AGVs for handling. The problem is modeled as a mathematical program and solved by a hybrid algorithm that includes numerical search, computer simulation, and statistical analysis. The decision criterion is based on the minimization of expected total manufacturing cost.