Warehouse optimizer by Kees Jan Roodbergen

The warehouse optimizer can determine the best layout for an order picking area. It determines the optimal number of aisles and blocks. Furthermore, it can be used to calculate average travel distances for order picking applications. More information in the white paper An explanation of some rack layout concepts for warehouses.

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Short instructions

Explanation of terminology

Total aisle length - The total aisle length is the desired sum of all aisle lengths. It is one of the prime design parameters. For example, when entering a total aisle length of 400 meters, the program will find the optimal configuration from all possibilities ranging from a warehouse with just one aisle of 400 meters long, up to 400 aisles of 1 meter each. If a certain warehouse system has 2 pick locations per meter aisle (one pallet on each side of the aisle), then a total aisle length of 400 meters is equivalent to a storage requirement of 800 pick locations. (Rack height is ignored here. If, for example, racks are 4 pallets high, then total capacity would amount to 3200 positions.) Assuming a location size of 1 meter, the warehouse in the picture on the right has a total aisle length of 42 meters (3 aisles of each two segments having each a length of 7 locations of 1 meter).

Number of aisles - This is the number of aisles in which one picker collects items. This means that this picker is allowed to pick anywhere in these aisles. This number cannot be entered when optimizing the layout (after all, part of the goal of layout optimization is to determine the optimal number of aisles). The warehouse in the picture on the right has 3 aisles.

Number of blocks - A cross aisle is an aisle which is perpendicular to the storage aisles in which the items can be picked (the pick aisle). Its main function is to enable aisle changing. A block is consists of partial aisles between adjacent cross aisles. Thus, the number of blocks is by definition equal to the number of cross aisles minus one. This number cannot be entered when optimizing the layout (after all, part of the goal of layout optimization is to determine the optimal number of blocks). The warehouse in the picture on the right has 2 blocks.

Number of picks per route - This the number of order lines. Or in other words, the number of stops that have to be made in one route before returning to the depot. The warehouse in the picture on the right has 6 picks (indicated with black squares).

Aisle width - This is equal to the center-to-center distance between aisles. Or in other words, it equals the width of the pathway within an aisle plus the depth of the racks on both sides of the aisle. The total width of the warehouse is the number of aisles multiplied by the aisle width. The aisle width is indicated graphically in the picture on the right.

Cross aisle width - The distance between the last location of one subaisle and the first location of the next subaisle. No part of the racks is included in this number. The cross aisle width is indicated graphically in the picture on the right.

Model Assumptions

Depot location - the depot is assumed to be located in the lower left corner. This cannot be changed. Other depot locations may potentially require a different layout, however, experiments have shown that the depot location typically has only a very small influence on travel distances.

Storage method - All products are assumed to be stored according to the random storage policy. This means that for each incoming load an empty storage location is selected from all eligible locations with equal probability. Other storage assignment policies (such as ABC storage or dedicated storage) likely require a different layout than generated with this program.

Routing method - The layout optimization method is developed for the S-shape routing method (also called Transversal method). Research has shown that the layout optimization method also works quite well for the Combined and Largest gap routing methods. An explanation of routing methods can be found here. An interactive way to explore routing issues in warehouses can be found in the Interactive Warehouse.

Simulation - When the program is used in the "calculate average travel distance" mode, simulation results will be given based on 2000 replications.

Further reading

This program is based on the scientific article "Designing the Layout Structure of Manual Order-Picking Areas in Warehouses".

Notification

The author cannot be held responsible for the functionality of this software nor for the quality of the resulting layouts. Usage of this software is at your own risk. Please contact the author if you have any questions or would like to have more information.

 

by dr. Kees Jan Roodbergen