In dynamic production environments, time pressure is always at the forefront. Efficient warehousing is essential for smooth processes, reliable quality and maximum sustainability. To ensure this, the software experts at Artschwager + Kohl (A+K) recently worked with the automation specialists at Heitec to successfully replace the local material flow and warehouse management system at the plant of a major vehicle manufacturer.

The customer's group management wanted to replace the warehouse management system (WMS), which was based on proprietary software from a provider, with an SAP EWM MFS system, as this could be seamlessly integrated into the company's SAP landscape. There was also the risk of the previous solution being cancelled. The container warehouse was to be secured for the future and the control software seamlessly integrated into the group structure. Once this project phase has been completed, the next step will be to modernise the plant's Siemens control systems.

The plant produces several thousand vehicles a year for the international market. The demands on warehousing and material flow are correspondingly high and complex. Millions of small parts have to be stored in the central warehouse, picked and supplied to the assembly lines and workstations.

Gap management in the centralised container warehouse is carried out using SAP EWM

In the centralised tote warehouse for small parts, there are two loading points from which the totes are transported together with the returns from the picking stations to the three storage and retrieval machines (SRMs). Each SRM can pick up either two large or four small containers at the same time and store up to four containers deep. In addition to the telescopic forks, the SRMs have a grouping station that enables individual containers that are further back in the compartment to be removed and the remaining containers to be placed back in the compartment, taking the gaps into account.

These gaps are managed in SAP EWM, with the new linking software controlling the SRMs accordingly when bins are stored in these gaps. Containers that have been removed from storage are transported to three picking stations via a picking carousel. There, the goods are picked manually and the bins are then put back into storage. Thanks to the picking carousel, SAP EWM can feed containers that are required for several orders directly to a picking station again, thus saving time.

Although the previous WMS software had an intelligent structure, it was proprietary, meaning that customisations or updates were not possible. There was also a lack of comprehensive technical documentation, which would not only have made operation more difficult in the future, for example in the event of staff changes, but also made technology transfer a challenge. The previously existing system visualisation could no longer be used due to its integration into the old warehouse management system.

Control of conveyor technology and storage and retrieval machines in the container warehouse via SAP EWM MFS

For further standardisation in the company, the control of the conveyor technology and stacker cranes in the container warehouse was to be converted to SAP EWM MFS. To do this, it was necessary to remove the software no longer required for communication with the old LVR from the PLCs and to integrate new coupling software.

Such brownfield projects often lack complete and correct documentation of the control software and communication interfaces. Although some documentation was available for this plant, it was not sufficient to define a reliable new interface to SAP EWM MFS together with the SAP team.

In order to fill the gaps in the documentation regarding control processes, technical interfaces, time sequences and error handling, monitor switches were installed on site at important communication nodes. The monitoring tool "Wireshark" was used to record data traffic in real time.

The A+K team worked together with their colleagues from Heitec on a complete reengineering of the control software for the conveyor technology and the stacker crane controls. At the same time, the communication experts from A+K analysed the recorded telegrams between all controllers and the existing WMS. The aim was to achieve a complete inventory of the current status - one of the biggest challenges for the company.

At the same time, the communication experts from A+K analysed the recorded telegrams between all controllers and the existing WMS. The aim was to achieve a complete inventory of the current status - one of the biggest challenges when modernising systems.

In short: the entire warehouse with all control systems and data exchange was to be comprehensively recorded and documented in order to make the system transparent.

Seamless integration of SAP EWM MFS

The next challenge was to seamlessly integrate the new SAP EWM MFS into the system. To achieve this, the experts from SAP and A+K developed a new interface between the controllers and SAP EWM. Although the telegrams were based on a predefined SAP EWM schema, they had to be specially adapted to the individual system with its dialogue points and control processes. The new telegram sequences covered all possible conveyor movements: From goods receipt to the tote warehouse, from the tote warehouse to the picking stations, from the picking stations back to the tote warehouse or to goods issue. Errors such as full compartments during storage, empty compartments during retrieval or the failure of an SRM were also taken into account.

stacker crane were also taken into account.

A+K used its tried-and-tested SAP EWM coupler to connect the SAP EWM with the existing control systems. This coupler was originally developed in 2006 for the world's first SAP EWM warehouse in pure PLC code and has been perfected over the years with each subsequent warehouse modernisation. Thanks to the use of this proven SAP-EWM-MFS coupler, all development goals were achieved. The programme changes in the control systems were carried out in such a way that quick adaptations were possible, but unnecessary interventions in the existing software were avoided. The A+K SAP EWM coupler contains a logger that logs all processes within the system and all data traffic between the controllers involved and SAP EWM. This creates a logbook that documents all processes in the system over the last 14 days. The logbook can be analysed directly in MS Excel.

Four days for the complete tests

Only four days were available for the complete tests of the control systems and SAP EWM on the real plant.

To make this possible without any problems, the control software and the SAP EWM programme were thoroughly tested in advance. To this end, the various centres involved, including the SAP server location at the customer's company headquarters, its production facility and Heitec in Erlangen, were directly connected to each other for the planned "site-to-site" simulation. Identical control systems for conveyor technology and storage and retrieval machines were then set up in the Heitec AG Erlangen office. A digital twin developed by Heitec was connected to these control systems according to the "hardware in the loop" principle. 

This digital twin simulated the real system, including all elements such as motors, sensors, switches etc. and their behaviour over time. On this basis, the finished control software for the conveyor technology and the storage and retrieval equipment as well as the SAP EWM test system were tested in Heitec's office in Erlangen and the SAP EWM test system at the head office.

Thanks to this procedure, the actual commissioning tests on the real system could be carried out in the shortest possible time and with the utmost reliability. The new visualisation was checked on site during the comprehensive tests and optimised based on customer requirements. All teams from the SAP and PLC units worked closely and efficiently together. The actual test phase lasted just two and a half days, and a week of company holidays could be used for the installation, which meant that the production flow was not affected. The tests were successfully completed within a week. This optimal process was achieved thanks to the continuous dialogue and close, cooperative partnership between the service providers and the customer.

Conclusion

The customer's plant now benefits from a simplified, optimised and clear warehouse management system that is integrated into the SAP enterprise software and can be operated from a central access point. All processes can be organised and comprehensively logged, enabling traceability at all times. The data can be conveniently sorted, filtered and analysed. The conveyor technology is now fully documented and ready for future SAP customisations and updates. Instead of a proprietary structure with the risk of discontinuation, the entire SAP ecosystem is now open to the customer.

This technical article was published in the Retrofit and Maintenance 2023 magazine (HUSS MEDIEN). www.technische-logistik.net

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