Automatic guided vehicles (AGV) based material handling systems have become the most widely used method of transporting pallets and parts between workstations in flexible manufacturing systems. Their primary advantages include increased routing flexibility, space utilization, safety, and reduced overall operational cost. Key issues to address during the design of an AGV system include selection of AGV platform, flow path design, and fleet size determination. During run time AGV system functionality includes: system management, (AGV allocation), navigation (establishing conflict free routes), and load transfer (material pick up and deposit mechanisms). Autonomous AGV systems offer numerous advantages in comparison to traditional systems. The following chapter will discuss the state-of-the-art in AGV systems concentrating on AGV run time functionality and AGV system performance measurement.
TopIntroduction
Manufacturing flexibility is the ability of a manufacturing system to respond, at a reasonable cost and appropriate speed, to planned or unplanned changes in external or internal environments. It is accomplished by multidimensional attributes of the manufacturing system. In the global, rapidly changing modern market conditions manufacturing flexibility becomes a necessity in many industrial environments (Tsouveloudis & Phillis, 1998; Roll et al., 1998; Gustavsson, 1984; Zelenovic, 1982). In flexible manufacturing environments product mix, processing requirements, arrival and due times, and job priorities may continuously vary.
The flow of parts, mobile resources (e.g., tools), and wastes (e.g., machined chips), throughout the manufacturing facility is implemented by the material handling system. The cost of material handling is a significant part of total product cost (Groover, 1987). Therefore, optimization of the material handling system can lead to substantial cost reductions. Material transport is achieved by systems such as conveyors, monorails, hoists, cranes, and industrial vehicles. Material handling flexibility is an important layer of overall manufacturing flexibility.
Automatic guided vehicles (AGVs) are driverless, steerable, wheeled industrial vehicles driven by electric motors using storage batteries. Some of their primary advantages include increased routing flexibility, space utilization, safety, and reduced overall operational cost (Ganesharajah et al., 1998). An AGV system is material handling system based on several AGVs operating concurrently. An AGV system is highly suited for flexibly manufacturing environments and such systems have become the most widely used method of transporting pallets and parts between workstations in flexible manufacturing systems (Reveliotis, 2000; Hwang & Kim, 1998).
Key issues to be addressed during the design level of an AGV system are: the selection of the AGV platform, flow path design, and fleet size determination. During run time AGV system functionality includes: system management (AGV allocation), navigation (establishing conflict free routes), and load transfer (material pick up and deposit mechanisms). Load transfer between the AGV and the workstation commonly takes place at a designated place next to the station termed the load port or Pick/delivery station. AGV system navigation includes navigation (determining the designated route) and traffic management (conflict resolution between AGVs) (Koff, 1987).