I am helping trouble shoot a machine that has not run in years. It has an AC servo system with resolvers, not encoders. We suspected there was an issue with an axis due to an alarm when trying to bring the machine online. We invoked a diagnostic test called a phase test in which each phase of the servo is sequentially powered and held at position for a few seconds. It basically jolts the ballscrew with a small bit of motion, then holds it firm. You can feel and hear it. One phase of that test is completely MIA, and you can hear the servo motor completely let go.
The cables were all swapped with another axis to troubleshoot if this was a motor/resolver issue, or the amp/feedback card.
We found that the problems follow the electronics but no one isolated the amp from the axis card. The card functions as a ADC converter from the resolver and sends that data to the control unit as well as takes digital motion command from the control and relays that to the amplifier.
I have the amp opened up now and there is no simple indication of failure. Usually when they fail, they let the smoke out, and the IGBT pack is blown. In this case, it seems to test good. As well, I simply cannot get my head around how only ONE phase of the test can be missing? If you drop out one phase of a 3 phase system, you should lose two of the phases!! I think that detail may be key in understanding what is going on here.
The system basically works with a logic control board inside the amp that further sends command to the 3 phase IGBT module. There are also current monitors in the board and one of them has corroded traces. I am not sure if the feedback from this device would cause complete shutdown of a phase or not but it seems to at least have continuity in the board for now.
The cables were all swapped with another axis to troubleshoot if this was a motor/resolver issue, or the amp/feedback card.
We found that the problems follow the electronics but no one isolated the amp from the axis card. The card functions as a ADC converter from the resolver and sends that data to the control unit as well as takes digital motion command from the control and relays that to the amplifier.
I have the amp opened up now and there is no simple indication of failure. Usually when they fail, they let the smoke out, and the IGBT pack is blown. In this case, it seems to test good. As well, I simply cannot get my head around how only ONE phase of the test can be missing? If you drop out one phase of a 3 phase system, you should lose two of the phases!! I think that detail may be key in understanding what is going on here.
The system basically works with a logic control board inside the amp that further sends command to the 3 phase IGBT module. There are also current monitors in the board and one of them has corroded traces. I am not sure if the feedback from this device would cause complete shutdown of a phase or not but it seems to at least have continuity in the board for now.