  In this paper we propose a control scheme based on coloured Petri net (CPN)
for a flow-rack automated storage and retrieval system. The AS/RS is modelled
using Coloured Petri nets, the developed model has been used to capture and
provide the rack state. We introduce in the control system an optimization
module as a decision process which performs a real-time optimization working on
a discrete events time scale. The objective is to find bin locations for the
retrieval requests by minimizing the total number of retrieval cycles for a
batch of requests and thereby increase the system throughput. By solving the
optimization model, the proposed method gives according to customers request
and the rack state, the best bin locations for retrieval, i.e. allowing at the
same time to satisfy the customers request and carrying out the minimum of
retrieval cycles.
