Modular Warehouse Control: Simultaneous Rectilinear Movement of Multiple Objects within a Limited Free Space Environment.

摘要

A public logistics network (PLN) has been proposed as an alternative to private logistics networks for the ground transport of parcels using the analogy between the packages transported in the network and the packets transmitted through the Internet. An integral part of such a network is a large number of fully automated modular warehouses functioning similar to routers in the Internet. In this dissertation, the algorithms to control the movement of packages in such a modular warehouse have been developed. Precisely, the main purpose of this dissertation is to develop efficient algorithms to control the simultaneous movement of objects of various sizes within an area with limited free space and to apply the developed algorithms for modular warehouse control. The details of the developed algorithms are as follows.;First, algorithms are developed for a simpler version of the control problem where all objects (packages) are unit squares. The developed algorithm is a combination of centralized and decentralized approaches and is based on a unique priority level assigned to each individual object. The basic algorithm is comprised of three main parts, namely, main control, route planning and the tagging process. The main control portion controls the movement of all objects at each time step and detects deadlocks, which indicate that some objects are blocked and cannot move to their destinations. Route planning is used by each active object to find a path from its current location to its destination. When conflicts occur, a tagging process is used by a higher priority object to tag each lower priority object in its way in order to move it out of the path to its destination.;Next, the use of priority assignment to prevent or resolve deadlocks in the movement of unit-size objects is explored. In addition, two extensions to the basic algorithm are implemented to improve performance, where the objectives considered are either to minimize the maximum traversal time or to minimize the total/weighted average traversal time of the objects in the system.;Finally, various simulations and experiments for unit-size algorithm are conducted to examine the efficiency of the algorithm and identify the relations among parameters in the system. Based on experiments, the algorithm for unit-size objects works efficiently even at a 95% utilization level of the available space in the warehouse.;For future work, the algorithm designed for the movement of unit-size objects can be extended to that of multi-size objects. The main difficulty here is that an object can occupy multiple modules. Therefore, the relationship between object and module is not one-to-one as in the case of square unit-size objects. Consequently, the tagging process can grow exponentially. In order to cope with this difficulty, the tagging process has to be implemented sequentially, not simultaneously.