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Troubleshooting in a Pick-to-Light system

Faults in a Pick-to-Light system must be found and rectified quickly. In this article, we explain the possible causes and methods for eliminating faults.

Where can faults occur in a Pick-to-Light system?

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

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

Basically, our system is very professionally developed, has been tried and tested for many years and is very stable. However, there are important requirements that must be met for trouble-free operation.

Cabling and possible faults

The entire cabling 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.

The cabling is therefore very clear and basically unproblematic. It is of course possible to swap the 4-core cables, but this is more a matter of installation or commissioning and not productive operation.

Mechanical destruction is the most common cause of faults in the connection terminals and wiring.

When using heavy order picking trolleys and shelves, a collision can occur that causes destruction. 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, several switches and even firewalls are in use. To ensure operation, the network parameters must be correct. It is therefore not enough to just check a ping to the controllers.

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

Eliminating these errors is one of the tasks of the on-site IT department. The appropriate ports and addresses must be set correctly in accordance with the documentation.

Failure of the individual Pick-to-Light displays

The compartment displays are very well protected and electronic failures are virtually unknown. With a zone test, all displays in a picking zone can be checked visually and electrically very quickly. The internal test mechanisms and error messages immediately register any irregularities.

Mechanical destruction of the displays is possible due to the effect of high forces.

The faults can be rectified by simply replacing the compartment displays.

Malfunctions at the warehouse management interfaces

Data is usually supplied to the Pick-to-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-to-Light systems in which all the information about the picking order was contained in a QR code.

Depending on the system, the issue is of course very complex and not the same. Our system has several mechanisms to maintain a stable interface to warehouse management (auto-connect mechanisms, data format checks, telegram repetitions, etc.).

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

We have a great deal of experience with the development of interfaces and pay particular attention to the automation of mechanisms in the event of a restart. Unfortunately, the customer's systems are often not prepared for such scenarios. In some cases, it is not possible to simulate such exceptions during the commissioning and test phase (e.g. SAP restart).

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

The emergency strategy

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

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

Conclusion

Faults in a Pick-to-Light system can have many causes and reasons. Professional LUCA training for customer personnel, up-to-date documentation and the conclusion of LUCA hotline contracts are the basic prerequisites for finding faults as quickly as possible. The more important the system is in the process chain, the shorter the response time and troubleshooting 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?

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