On site support - Labelling Machine
Yesterday we were called out to our customer in the beverage packaging industry who had a high speed labelling machine that had been down for over 24 hours with a servo motor communication fault. They getting ready to replace all the CAN cables when we arrived.
The machine uses a large slip ring to transmit power and signals from the static section to the rotating section. The rotating section has 60 servo motors with integrated drives that rotate the bottles as the labels are applied. These servo motors are controlled over 6 seperate CAN networks back to a central controller at the top of the labeller. They also have no indication of life or fault making this job extremely difficult.
The machine was reporting a complete loss of communication to all 60 motors. We hoped it would be a simple cable damage issue but things wern't quite as simple. Disconnecting the 6 CAN lines at the controller revealed shorts across the CAN and Vcc lines on all networks which explained why nothing was communicating. A good reading should be 120 ohms which is due to the terminating resistor at the end of each network.
We started by disconnecting and verifying the master cables, then the painful process of disconnecting each of the 60 motors in turn which was extremely difficult due to access under the machine. Slowly resistances returned to healthy readings. The entire process took the best part of 6 hours, and in the end 11 bad motors were removed with various low resistances across the connector. We put this down to a possible spike on the CAN network or a failed motor that had sent high voltage across to the communication circuitry.
We ended the day having got 2/3 of the system back online, with a further 3 motors to change out by the next shift, bringing the full system back online ready for production.
£2000 an hour loss, over a day being down already, but with the right approach and electronic knowledge we were able to go straight to the fault. It was a long process after this but saved many hours of fruitless cable swapping which would have landed them back in the same position a day later.
We have now returned 11 motors to the workshop as well as a master controller PCB for repair.
If you are needing support on site, sometimes a fresh pair of eyes on a problem can help get straight to an issue.
