TL;DR
WCS-to-PLC communication faults almost always come from a failed network switch port, a damaged Ethernet cable, or a PLC that has faulted and stopped scanning. Check the network first before calling IT.
What you might see
- WCS showing all carriers in unknown state
- PLC heartbeat alarm on the WCS communication status screen
- system reverts to manual mode or halts
- network switch error LED active near the system panel
Likely causes
Failed or overloaded network switch port breaking the WCS-to-PLC Ethernet path
Damaged Ethernet cable from equipment movement or mechanical damage in the cable track
PLC major fault condition stopping the scan cycle and breaking the communication heartbeat
IP address conflict or VLAN configuration error following a recent network change
Required tools
- Network switch management access (if available)
- Laptop with ping capability or WCS workstation
- Replacement Ethernet cable (CAT5e or better)
- PLC programming terminal (if major fault clear is required)
Safety first
- Do not clear a PLC major fault without first understanding the fault code. Clearing a fault that indicates a mechanical problem can allow the machine to restart in an unsafe state.
- Network changes in a warehouse automation environment can affect multiple systems. Coordinate with IT and system integrators before modifying switch or IP settings.
Procedure
- 1
Check the network switch error LEDs in the system panel. A flashing or amber port LED on the WCS or PLC port confirms a link problem.[1]
- 2
Ping the PLC IP address from the WCS workstation. If there is no response, the problem is at the network layer.
Warning: Changes to network switch configurations or PLC IP settings should only be made by personnel who are authorized to work on the system controls network. Unauthorized changes can affect other production systems on the same network. - 3
Trace the Ethernet cable from the WCS server to the PLC. Inspect the cable for visible damage, especially in cable track sections. Replace any damaged cable with a CAT5e or higher-rated cable.
- 4
Check the PLC processor fault light. A major fault (red fault light) stops the scan and breaks the heartbeat. Refer to the PLC fault log to identify the fault code before clearing it.
- 5
If the cable and switch port are functional, check the WCS server's network adapter for errors and restart the WCS communication service if the WCS software allows it.
- 6
After restoring communication, verify all carriers report their correct positions to the WCS before releasing the system to auto mode.
Sources
Dematic (KION) Dematic Multishuttle AS/RS (Automated Storage) general technical documentation, Dematic (KION)
AS/RS warehouse control system networking, PLC communication fault diagnosis, general material handling references (general)
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