How to readjust the Master/Slave motors safely ina gantry operation?

[Jamie Cho]

We are using FlexMotion, NI7344-FW, two stepper motors and .5 micron linear encoders to control a gantry over two stages. The steppers are usually geared in a 1:1 Master/Slave operation.

To help ensure that the master and slave are completely "in-sync" we typically disable the gearing between each move, re-adjust the slave, and then re-enable gearing.

This usually works perfectly, but periodically (less than .1% of moves) the slave loses 16mm of counts. This is about 32000 ticks that become lost.

Has anyone else experienced this problem? Can they suggest any work arounds?

[dmp]

Hi, Jamie,

I recommend checking the amount of torque that your motor is designed to produce vs. the amount of load that is being applied to it. If the load exceeds the torque, this might explain why you are occasionally missing counts.

Best regards,
Dawna P.
Applications Engineer
National Instruments

[Jamie Cho]

It's the encoders (our position sensors whose ticks the ni controller accumulates counts) that spontaneously lose 16mm of counts. Physically, the master and slave are in the position predicted by the master's encoder.
It is always the slave that has the wrong value and it always seems off by the same amount.

It is not physically possible for the Master and Slave to be apart by that much without something breaking.

We poll the master and slave encoders while they are in motion - is there a race condition in the NI controller that would cause the slave encoder to become corrupted?

[dmp]

Hi, Jamie,

What version of the NI-Motion driver are you using? There was a similar issue with master/slave gearing in previous versions of the driver, but this was resolved in NI-Motion 6.1. If you are not currently using this version of the driver, you can upgrade to it.


Best regards,
Dawna