Standard connection to a Pick-to-Light system
In this article you will learn how a standard connection to a Pick-to-Light system is realised. We not only explain the general mechanisms, but also show the details and examples of the connection. After an email registration we will gladly send you a complete documentation of our standardPick-to-Light interface.
How is the standard connection of a Pick-to-Light system realised?
The connection of a Pick-to-Light system is realised via two separate channels with TCP/IP sockets. The connection is made via software that is installed on a server or PC. One channel is established in each communication direction. The first connection is responsible for switching on the displays. The second interface reports back the acknowledgements of the withdrawals, the quantity corrections and the special keys.
The two channels work independently (asynchronously). The higher-level warehouse management system can activate or switch off the displays at any time or change the displayed contents or colours. Feedback is provided exclusively on the second channel.
Securing the data transmission
In order to secure the data transmission, an acknowledgement of receipt is sent by the receiver on each data channel (short acknowledgement). If the sender receives the receiver's acknowledgement correctly, the telegram is considered transmitted.
If the transmitter does not receive an acknowledgement of receipt, the data channel is closed, reestablished and the telegram is repeated.
The telegram counter
Each data telegram is identified by the transmitter in the telegram header with a four-digit telegram counter (0001-9999). The telegram counter is used to synchronise 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 start, 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 transmitter.
The live telegrams
To check the status of the connection, the sender 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 time (usually approx. 30 seconds). The live telegram is acknowledged normally by the receiver (acknowledgement of receipt).
If the transmitter does not receive an acknowledgement of receipt from the receiver, the connection is closed by the transmitter and reopened. If the receiver does not receive any live telegrams from the transmitter, it also reinitialises its connection channel.
Who establishes the TCP/IP connection?
As a rule, the sender always establishes the connection. From this point of view, the first data channel (activation and updating of the displays) is established by the warehouse management system as a TCP/IP client. In that case, the Pick-to-Light system is a TCP/IP server.
For the feedback, the Pick-to-Light system actively establishes the 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 case of malfunctions of the interface or system shutdown.
In some situations, the connection of a warehouse management system is only possible as a TCP/TP client. In that case, the Pick-to-Light system works as a TCP/IP socket server on both channels. The type of connection is configurable in our Pick-to-Light system.
What does the standard interface control?
Via the standard connection, a warehouse management system (WMS) can switch on, update and switch off the Pick-to-Light displays. The order picker's acknowledgements are reported back to the higher-level system.
With the standard interface, the entire logic of order control, operation and sequence is controlled by the warehouse management system.
Here, the response times of the warehouse management system are crucial. The response times here should not exceed 500 milliseconds.
If the process is to be controlled directly by the Pick-to-Light system, the data transfer is realised differently. Read more about this in a separate article on the customised connection of the Pick-to-Light system.
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