Integrating a Material Flow System

If you use SAP EWM to manage an automatic warehouse, you can use the following functions:

• Configurable paths through storage control

• Automatic identification of HUs using scanners on the automatic storage retrieval facility

• Automatic diversion of HUs that cannot be stored (incorrect contours, excessive weight, unidentified)

• Full automatic putaway of HUs in the storage bin using any number of interim steps; these interim steps are represented by communication points

• Malfunctions reported by the controls taken into account

• Configurable capacity limits for communication points, conveyor segments, and vehicles taken into account

• Reduction in empty traveling paths for stacker cranes through interleaving

• Goods-to-man picking principle

• Stocks are also available for deliveries during transportation within the system

• Stable telegram communication between EWM and the PLC using parallel, bidirectional communication channels

• Monitoring and troubleshooting as part of the regular warehouse management monitor

These devices are usually controlled by means of a real-time system, called a programmable logic controller (PLC) that monitors and switches the sensors and actuators (light barriers, switches, motors, and so on). These real-time systems obtain their orders from the superordinate warehouse control level, which derives them from the warehouse requests.

In SAP ERP Warehouse Management, the connection to a PLC required separate, third-party software. Information between this software and WM was sent using IDocs.

With SAP Extended Warehouse Management no additional software is required anymore.

The following differences exist between automated warehouses and warehouses operated manually or by radio frequency:

• The resources are passive (as in the case of stacker cranes).
• Capacity bottlenecks must be watched and controlled much more closely.
• Technical malfunctions must be taken into consideration.
• Logistical malfunctions must not block the material flow (for example, occupied bin or an unknown HU on the automatic storage retrieval system).

In the MFS, the warehouse to be controlled is mapped with the following components:

• Programmable logic controller (PLC):

  The PLC is the underlying real-time system controlling the physical transportation of HUs on conveyor systems and their components. It evaluates signals from the connected automatic storage retrieval or conveyor system, or other controls, and activates or deactivates motors, appliances, sensors, readers, and so on. Each control that communicates with the SAP EWM system must be defined as a PLC. In larger installations, head controls may be in use, which regulate local controls. The SAP EWM system communicates with the head controls, so in that scenario you only define the head controls.

  At least one communication channel must be defined for each PLC.

• Communication channel:

  The communication channel is the connection for transmission of messages between MFS and a control facility, defined by an IP address and a port. You can define certain properties, such as the length of the messages and whether telegram confirmations are to be used. Using the application menu, you also create the settings for the IP address and the port through which the PLC can be reached. You can use several channels to communicate with the same PLC. Each of these must use a separate port. You can specify that certain telegrams are to be sent on a particular port and other messages on a different port. Messages from a communication channel are communicated sequentially. One communication channel per control is sufficient.

Communication Points:

SAP EWM maps the system to be controlled by means of communication points. Communication points are stations in the automatic storage retrieval system from which SAP EWM communicates with the PLC. Here, the PLC registers HUs (on the basis of scanner information or material flow tracking) and awaits new destination specifications. More communication points lead to closer material flow tracking in SAP EWM, but also to more intensive communication and consequently more load on the SAP EWM system. For each stage between communication points, a warehouse task is created. Every communication point is also a storage bin, but only the storage bins on the automated storage retrieval system are also communication points, whereas the storage bins in the actual warehouse are not.

Conveyor segments:

Conveyor segments physically transport handling units (HUs) from one communication point to the next. You can define a capacity limit for conveyor segments. As in the case of communication points, the capacity relates to the number of HUs that can simultaneously be transported using the relevant conveyor segment. If the capacity of a conveyor segment is full, SAP EWM restricts further orders. You assign conveyor segments to your start and end points in layout-oriented storage control. You can combine conveyor segments to form a conveyor segment group, which in turn is assigned a conveyor segment group type. This can be used, for example, to set several conveyor segments inactive at the same time, by setting this for the conveyor segment group type in case of a malfunction. The system then holds back orders for these conveyor segments. You only need to define conveyor segments if you want to check their status (readiness, capacity) in SAP EWM. In many cases, it is enough to record capacity and status at communication points.

Resources:

In the MFS, a resource is a vehicle that transports an HU from one communication point (or storage bin) to another. A resource moves to the pickup point in an empty state, takes on the load, and then discharges the load at its destination. To reduce the number of empty travel paths, you must optimize the sequence of the orders.

SAP EWM contains an interleaving strategy for stacker cranes that have the following:

• Just one load handling attachment (which means that only one HU can be loaded)

• Putaway and removal bin at the same end of the aisle

• To optimize the movements of stacker cranes from within SAP EWM, the stacker cranes must be mapped in SAP EWM as resources. Conveyor lines are not mapped as resources. To transport HUs, SAP EWM generates WTs and WOs and arranges them in queues. In the MFS, each warehouse order is assigned one WT only. To execute warehouse tasks, the SAP EWM system generates telegrams and sends these to the appropriate PLC.

For systems such as those previously described, the routing of the MFS movements is done using the layout oriented storage control and creates warehouse tasks for every single movement. With MFS for case conveyor systems, SAP EWM offers routing decisions based on the current location of a handling unit (HU) and context information related to the HU (such as general information regarding putaway or picking destination data).

Handling unit (HU) movements in MFS for case conveyor systems are not immediately modeled as warehouse tasks. Instead, the initial routing decision is made based on HU information, location information, and warehouse tasks or warehouse orders that might exist for final putaway or picking. As a result, a telegram is created and sent to the PLC. This telegram has no direct connection to a warehouse task. Nevertheless, the HU movement, which is based on the routing decision, can be modeled as a warehouse task in the system. You can do this in the following ways:

• The PLC executes the movement after it receives the routing decision from the EWM system. After this, it sends a new telegram with the actual routing information for the HU to EWM. EWM creates a warehouse task for this movement. This warehouse task is immediately confirmed.

• If the PLC is not able to send the actual routing information for the HU to EWM, it can trigger an asynchronous posting to the location of the routing decision.

Case conveyor systems use a different routing logic to other conveyor systems, which use layout-oriented storage control. With this routing logic you can enter different destinations for the following:

• Activity areas

• HUs without an MFS error

• HUs with an MFS error

• Empty HUs without a warehouse order (WO) or warehouse task (WT)

• HUs containing content without a WO or WT

• HUs that do not fit any of the previous criteria

  You can specify a default direction. The system uses the default direction if no appropriate entry has been customized. For example, two entries have been customized, one for HUs without an error and one default. If a HU has an error or no WT exists, the system chooses the default entry.