[EPTech]

Hi there,

I have an injection mold machine with a weird acting spindle that drives the extruder. The motor will slowly turn counter-clockwise for a quarter turn, then do half a turn clockwise a couple of times and then start turning but it will vibrate. After turning weird for a while and a whole lot of turning the motor off and on, it will suddenly start working like a charm.
The motor is a Siemens 1PH6163 with ERN1387 Heidenhain incremental sin/cos 1Vpp encoder controlled by a Simodrive 611HSA with 6SN1121 controller. I already replaced the encoder with a new one. I marked the shaft and the body of the motor before replacing the encoder so it should be in the same position. But replacing the encoder did not help the problem. The cable is OK from encoder plug to drive.
I checked the phase voltages and currents. When the motor is turning badly and vibrating, the voltages and currents are out of balance. Phase W seems to be off. By coincidence, the current in this phase is not measured by the power module , so the condition goes without error. I measured the phases with a scope with HV differential probe. There is an obvious difference in the picture when the motor is turning badly or nicely. When the motor is turning OK, you see these nice positive and negative going blocks of pulses but when the motor acts weirdly, the pictures are quite erratic. When the motor jerks before starting you can even see only positive going pulses, so the drive is reconstructing anything but a sine wave.

To proceed with debugging, I need to rule out the motor. My main question is: Do you need to adjust the encoder on an asynchronous servo motor, which is in fact a squirrel cage induction motor? I cannot find the procedure anywhere. To my knowledge only synchronous motors use the encoder for commutation. Is this a correct assumption?
This an older drive so I suspect a bad opto coupler in the IGBT driver board or dried out capacitors in the switching supplies of the controller board. It seems like the error fixes itself after the drive has warmed up and the next morning, same error. Has anyone seen this with these Simodrives before?

Your advice is much appreciated.

[Al_The_Man]

I think I came across these PWM drives years ago, but they are similar to VFD but with feedback giving them the appearance of a DC servo.
AFAIK there is not 'tuning' required of the encoder.
Sounds like a component heating up, it may be possible to trace with a heat gun and a can of Artic Air freezer to pin point it.
Al.

[EPTech]

Thanks Al,

The manager already decided to go for another drive. This machine has been defective for to long and he will not wait for a component level repair.

greetings,
Pascal.