Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering
Transport Technology / Logistic Engineering

B.R.C. Herijgers Simulation model of dynamic AGV dispatching.
Computer program, Report 2001.LT.5493, Transport Technology, Logistic Engineering.

Automatic Guided Vehicle systems have found a wide range of application. The design of an AGV system affects the performance of the system and the design can be very complicated. A number of interrelated decisions must be made in order to exploit the full benefits of the system. An important aspect is vehicle dispatching, selecting the right vehicle for performing the transportation task.

In this report a bid-based dynamic dispatching process of move requests in a simulation model is presented. The Bid-Based Dynamic Dispatching Rule is a dynamic task assignment rule. As soon as a transportation task is received, all the AGVs in the system are allowed to 'bid' for this move request even when they are still busy performing another task. After receiving all the bids the AGV with the shortest travel distance will get the move request in its 'joblist'.

The AGV system has a network layout. In a network AGV system, each vehicle is allowed to orbit in any track and each station can be pickup or delivery point. The distance between two nodes situated next to each other is the same for every two nodes. The lanes are perpendicular to each other and have the same length. The path layout of this model consists of multiple lanes. Every arc consists of two lanes and every lane has its own direction The location of the pickup and delivery points is at the nodes. Every node can be a pickup or delivery point of a move request.

The performance indicators implemented in this model are related to the execution of the move requests and the performance of the AGVs. The performance indicators are: Several input parameters can be used to evaluate the performance of the system. The three major input parameters are: Simulation runs have been made by using different seeds for the uniform distribution the define the starting nodes and end nodes of the move requests and different seeds for the exponential distribution that is used to define the time between two generated move requests. This resulted in the conclusion that the system is very sensitive for deadlocks. Therefore experimental runs with different threshold values and amount of returns could not be not be properly evaluated.

In this simulation model only the Bid-Based Dynamic Dispatching rule is implemented. The results of this dispatching rule should be compared with the results that can be obtained by other dispatching rules. These other dispatching rules should be first implemented before interesting evaluations of the performance of the dispatching rules can be made.

This simulation model can be expanded with the implementation of a deadlock recovery procedure, more dispatching rules and more detailed system information.

Reports on Logistic Engineering (in Dutch)
Modified: 2001.08.04; , TU Delft / 3mE / TT / LT.