Standard connection to a pick-by-light system
In this article, you will learn how to implement a standard connection to a pick-by-light system. We will not only explain the general mechanisms, but also show you the details and examples of the connection. After registering by email, we will gladly send you complete documentation on our standard pick-by-light interface.
How is the standard connection of a pick-by-light system implemented?
The connection of a pick-by-light system is implemented via two separate channels with TCP/IP sockets. The connection is established via software that is installed on a server or PC. A channel is set up in each communication direction. The first connection is responsible for switching on the displays. The second interface reports back the acknowledgements of the removals, the quantity corrections, and the special keys.
The two channels operate independently (asynchronously). The higher-level warehouse management system can activate or deactivate the displays at any time, or change the content or colors displayed. Feedback is provided exclusively on the second channel.
Securing data transmission
To secure data transmission, a confirmation of receipt is sent by the receiver on each data channel (short acknowledgment). If the sender receives the confirmation of receipt from the receiver correctly, the telegram is considered to have been transmitted.
If the sender does not receive a confirmation of receipt, the data channel is closed, reestablished, and the telegram is repeated.
The telegram counter
Each data telegram is identified by the sender in the telegram header with a four-digit telegram counter (0001-9999). The telegram counter is used to synchronize the transmission and reception confirmation of the data telegrams. The receiver always confirms receipt of a data telegram with the same telegram counter.
After the system starts up, the transmitter generates a telegram counter with the number 0001. The telegram counter is incremented with each data telegram and increased by +1.
After an overflow above 9999, the telegram counter is reset to 0001 by the sender.
Live telegrams
To check the status of the connection, the transmitter sends the receiver a live telegram (special telegram) without content. The telegram counter is always 0000.
The live telegram is only sent if no active telegrams have been sent in the channel within a certain period of time (usually approx. 30 seconds). The live telegram is acknowledged by the recipient in the normal way (confirmation of receipt).
If the sender does not receive confirmation of receipt from the receiver, the connection is closed by the sender and reopened. If the receiver does not receive live telegrams from the sender, it also reinitializes its connection channel.
Who establishes the TCP/IP connection?
As a rule, the transmitter always establishes the connection. From this perspective, the first data channel (activation and updating of the displays) is established by the warehouse management system as a TCP/IP client. In this case, the pick-by-light system is a TCP/IP server.
For feedback, the pick-by-light system actively establishes a connection to the warehouse management system as a TCP/IP client. In this case, the warehouse management system is a TCP/IP server.
The two connections are kept open permanently and are only closed in the event of interface malfunctions or system shutdowns.
In some situations, connection to a warehouse management system is only possible as a TCP/TP client. In this case, the pick-by-light system operates on both channels as a TCP/IP socket server. The type of connection can be configured in our pick-by-light system.
What does the standard interface control?
A warehouse management system (WMS) can switch the pick-by-light displays on, update them, and switch them off via the standard connection. The picker's confirmations are reported back to the higher-level system.
With the standard interface, the entire logic of order control, functionality, and process flow is controlled by the warehouse management system.
The response times of the warehouse management system are crucial here. Response times should not exceed 500 milliseconds.
If the process is controlled directly by the pick-by-light system, data transfer is implemented differently. Read more about this in a separate article on the customer-specific connection of the pick-by-light system.
