## 3 Case Description  
In order to achieve the distribution process at the national and foreign level of its finished products, the bakery company has a DC to consolidate all of its products. All products are handled on pallets.  
This DC is composed of four zones: receiving, storage, picking and shipping. The problem is located in the picking zone. This zone is where special orders are picked. Additionally, these orders are sent to the shipping zone. Next, the handling and arrangement of spaces in the DC are described.  
The picking zone is divided into four areas, shown in Figure 2. Areas A and B are intended to store high-demand products; Area C is for medium-low-demand products; and Area D is for low-demand products. Orders are built onto pallets with the respective items (each pallet is a part of the order, consisting of a type of product and its quantity in boxes) requested by the customer. Each product occupies a unique space, but not necessarily all spaces must store products. The area is located on a second floor and is fed by the suppliers who allocate the pallets onto the racks with forklifts. Retrieval is done under the picker-to-parts low-level system.  
Area A can store 32 different types of products and each can have five pallets available. In Figure 2 are the spaces from 1 to 32. Area B has 26 spaces (from 33 to 58) with the capacity to store seven pallets of the product. Area B1 is composed of spaces 59-61, and its storage capacity is five pallets each; see Figure 2.  
Area C has 30 spaces on each side of the aisle, with a storing capacity of 60 different types of products. In Figure 2 are the spaces from 66 to 121. In area D, there are shelves on both sides of the aisle, and unlike other areas, the product is stored in boxes. Each shelf is eight spaces long by four high, giving a total capacity of 32 on each side, in which only 64 types of different products can be stored. In Figure 2 are the spaces from 122 to 185.  
The company has a warehouse management system (WMS) that indicates the route that employees must take to collect the products in the picking area, a route that is established according to the location  
Figure 2: Layout of the warehouse in our case study.  
of the products; but the average time taken to collect the items of the order is greater than that established by the company, because when products are picked--the employees consider alternate routes, and take care of stowing, making sure the weight of the item that is located on top does not affect the one below it--thereby generating extra personnel costs and decreased productivity such that they do not align to non-fulfilled orders. In a comprehensive study of travel time by [42], they found that decreasing travel time is an important factor in reducing costs and delays.  
In line with [43], the order picking is carried out by the WMS. This system has the capability of being able to determine the correct location and quantity of each product to be collected, and then indicate the route. However, for [44] a WMS was used to improve warehouse efficiency and maintain accurate inventory by recording transactions. Another advantage of using WMS is to reduce inventory discrepancies. That is mentioned in [7], and was based on comments from professionals. Even so, the algorithms used in this system are not advanced, because they often need a large amount of accurate data that is generally not available in practice. The professionals prefer to keep solutions based on very simple logic to make sure they work in reality. Additionally, these authors and [45] show that the tool most frequently used in the order picking process is mathematical programming, although some professionals disagree with its use. In contrast, in this research, the use of mathematical models in the improvement of this and other processes within the company is viable for professionals.