Controlling the Material Flow System (MFS)

While SAP EWM mainly automates the strategic and planning functions in the warehouse, the material flow system (MFS) manages and controls the physical movements. Along with complete integration, the advantage of MFS in SAP EWM is that it removes the need for interfaces to external systems or additional warehouse control units because SAP EWM communicates directly with the control level.

Incoming or outgoing handling units (HUs) are physically moved on conveyor belts, or automatic storage or retrieval systems. They pass on their way to different communication points, where they are identified and moved to further destinations, for example:

• A high-rack storage bin
• A pick point (if only a partial quantity of a HU is to be delivered)

The physical transportation on conveyor technology is controlled by an underlying controller called the programmable logic controller (PLC). The PLC also controls the communication between SAP EWM and the MFS. The PLC evaluates signals from the connected automatic storage or retrieval system, conveyor system, or other systems, and activates or deactivates the connected motors, appliances, sensors, readers, and so on.

When setting up a material flow system (MFS), you need to define a warehouse layout for MFS. The MFS requires common warehouse objects such as:

• Storage Types
• Storage Bins
• Resources (even in MFS, a HU is located in a storage bin or on a resource)

As well as these requirements, an MFS requires additional objects. The point where EWM and PLC communicate is called the communication point, and it is assigned to a PLC. Common communication points are I-points (identification point) or scanner points. If a HU arrives at an I-Point, it is scanned and the PLC sends a message with the relevant information to SAP EWM. This message is called a telegram.

Based on the information received in the telegram, SAP EWM can start the next action (for example, storage bin determination) and SAP EWM returns a telegram to the PLC to transport the HU to the next communication point. Based on this telegram, the PLC controls the MFS to move the HU to the respective destination. Arriving at this communication point, the HU is identified again and depending on the communication point type, the next telegram and a resulting action is triggered.

Configuring the MFS ensures that the telegrams are sent in the correct sequence. This is to avoid a situation where, for example, the system tries to execute step 2 before step 1. At least one communication channel must be defined for each PLC. This communication channel is for telegram-transmission between MFS and the PLC. It controls the length of a message, the time and number of recurrences, and the Handshake-mode (which defines if a PLC confirms the receipt of a telegram and how it does so). If a communication point cannot identify a HU, that HU should be transferred to a Clarification Point where a warehouse employee can resolve the problem.

The distance between two communication points can be modeled as a conveyor segment (conveyor element). This is where HUs are transported physically. As in the settings of the communication points and resources, you can define the capacity limit per conveyor segment, for example, you define the number of HUs that are currently transported on this segment. If the capacity limit is exceeded, SAP EWM holds further orders for this element. To transport the HU from one communication point to another, resources may be required. If the distance between two communication points requires a stacker crane (to transport that HU), then that stacker crane can be modeled as a resource.

To transport HUs, SAP EWM generates warehouse tasks and warehouse orders and sends them in a respective queue. In the MFS, each warehouse order has one warehouse task assigned.

Putaway and Picking with MFS

As in the example, one could set up layout-oriented storage control and MFS to process the inbound deliveries as follows:

1. A handling unit (HU) arrives and the goods receipt is posted.
2. SAP EWM determines the final storage bin and creates the correspondent warehouse task and warehouse order. Layout-oriented storage control is taken into account and substitutes the determined storage bin by the first communication point.
3. The HU is moved to the communication point, in this case, the I-Point.
4. At the I-Point, the HU is scanned and the system determines (again) the final storage bin.

As before, layout-oriented storage control intervenes and determines that the HU is to be transported to another communication point. At this communication point, the HU must be moved to a transfer car that takes the HU to the next communication point. At the last communication point, layout-oriented storage control determines that the HU is to be moved to the final storage bin and therefore a stacker crane is required. The warehouse task for putaway is re-activated and assigned to the respective queue for the stacker crane. The HU is moved to the stacker crane and put away in the storage bin in the high-rack storage area. By confirming this warehouse task, the process is finished.