Troubleshooting in a pick-by-light system

Where can malfunctions occur in a pick-by-light system?

A pick-by-light system consists of a control computer with a host connection (usually a Windows server), controllers, and pick-by-light compartment displays. This also includes cabling, connection terminals, mounting rails, and extensions (such as scanners, scales, and RFID).
You can find out more about the physical structure in the main article: Pick-by-Light & Pick-to-Light.

The system therefore consists of complex hardware and software components, which can also cause malfunctions.

Our system is fundamentally very professionally developed, has been tried and tested for many years, and is very stable. However, there are important prerequisites that must be met to ensure trouble-free operation.

Cabling and potential interference

All wiring below the controller is implemented as a BUS. All compartment displays of a controller are connected in parallel and are addressed directly by the controller.

This means that the cabling is very clear and generally unproblematic. It is of course possible to swap the 4-wire cables, but this affects installation or commissioning rather than productive operation.

Mechanical damage is the most common cause of faults in connection terminals and cabling.

The use of heavy order picking trolleys and shelves can lead to collisions that cause damage. In this case, the defective cables and connection terminals must be replaced immediately.

Network connection and firewalls

In large systems, the on-site networks are often very complex. In some cases, multiple switches and even firewalls are in use. To ensure proper operation, the network parameters must be correct. It is therefore not enough to simply check the ping to the controllers.

Changes or updates to switches or firewalls are among the possible causes of malfunctions, but these occur very rarely in practice.

The elimination of these errors is one of the tasks of the on-site IT department. According to the documentation, the appropriate ports and addresses must be set correctly.

Failure of individual pick-by-light compartment indicators

The specialist displays are very well secured and electronic failures are virtually unheard of. A zone test allows all displays in a picking zone to be checked visually and electrically very quickly. The internal test mechanisms and error messages immediately register any irregularities.

Mechanical damage to the displays is possible due to the application of high forces.

The errors can be corrected by simply replacing the compartment indicators.

Malfunctions at the interfaces of warehouse management

Data is usually supplied to the pick-by-light system via various software interfaces (SAP via RFC, databases, TCP/IP sockets, REST, etc.). Some systems also function as stand-alone solutions and have no connection to the warehouse management software. We have also supplied pick-by-light systems in which all the information relating to the picking order was contained in a QR code.

Depending on the system, this topic is naturally very complex and not straightforward. Our system has several mechanisms for maintaining a stable interface to warehouse management (auto-connect mechanisms, data format checks, telegram repetitions, etc.).

The most common cause of malfunctions at the HOST interfaces is incorrect master data and incorrectly implemented automation mechanisms after a system restart.

We have extensive experience in developing interfaces and pay particular attention to automating mechanisms for restarting. Unfortunately, customer systems are often not prepared for such scenarios. In some cases, it is not possible to simulate such exceptions during commissioning and testing (e.g., restarting SAP).

Problems with master data are easy to find and fix. We have particularly well-developed log file systems for this purpose, which allow our own technicians or the LUCA hotline to find such errors very quickly. Our data transfer processes can also automatically identify and report some errors very quickly (e.g., incorrect storage compartment names).

The emergency strategy

Even though all system components are very secure and professional, there is always a residual risk that an entire system will not function correctly.

For this reason, an emergency strategy should always be drawn up for the eventual failure of a picking system and tested during maintenance work. In some cases, these are simple picking lists in paper form, which should be printed by the warehouse management system.

Conclusion

There are many possible causes and reasons for malfunctions in a pick-by-light system. Professional LUCA training for customer personnel, up-to-date documentation, and LUCA hotline contracts are essential for finding faults as quickly as possible. The more important the system is in the process chain, the shorter the response time and fault rectification must be. Nevertheless, emergency strategies in the event of a total failure are also very important and crucial to us.
More about order picking: What is order picking?