New Paper: GridStore—a Grid-Based Storage and Retrieval System

After many years of development and testing, we finally have a completed and accepted paper on GridStore: A Puzzle-Based Storage System with Decentralized Control. The paper, which will appear in IEEE Transactions on Automation Science and Engineering, was written with my colleague and friend Kai Furmans from Karlsruhe Institute of Technology and with two of our students, Zäzilia Seibold and Onur Uludağ.

For those familiar with this work from presentations gone by, you will notice that the name of the system has changed from GridFlow to GridStore. We are beginning to use the term GridFlow to refer to the class of systems that uses a grid-based movement architecture, rather than to a specific instance. GridFlow, GridPick, and GridSequence are all instances of the GridFlow way of thinking.

Below is an example of GridStore at work. Gray cells contain an item, such as a tote or pallet.  Black cells represent requested totes trying to make their way to the southern boundary, where they are removed from the system by a conveyor or other means. Gray cells with a black circle represent totes returning to their “home rows.” When a replenishing totes reaches its home row, it turns gray until requested, after which it turns black. White cells are empty.

At each iteration conveyor cells determine their current state and then engage their neighbors in two rounds of “negotiations,” in which cells with competing interests try to reconcile. After negotiations are complete, cells convey in the appropriate direction. Voilà—GridStore!

The main feature of this paper is a detailed description of the decentralized controls rules that effect the nice global behavior of GridStore. Describing these rules was no easy task, so feel free to contact us if the paper doesn’t make sense.


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