Motion Instruction Enable flag stuck on

[JRoss 84]

Has anybody seen anything like this? I was called out to a customer site tonight because their motion axis (Kinetix 6000 with ControlLogix PLC) hit the hard overtravel. They got the axis moved off the overtravel sensor, but when they tried to restart, the servo would not enable. When I came in, I could enable the servo with a motion direct command, but when they would stop and restart, the servo would disable but not re-enable. I added a test bit to manually trigger the MSO instruction in the code, but that didn't work. I finally noticed that the enable bit of the MSO instruction stayed on even when the input conditions were false. So I manually reset the enable bit, and things started working. Only time I've seen behavior like that before is when the motion instruction tag was used multiple times instead of just once, but that wasn't the case as far as I could tell.

[lostcontrol 23]

Not 100% sure, but is the rung edge triggered, or conditional? From memory, I had similar issues, so just un-latched the Done, Error & Enable flags always (I think), due to similar issues.

[JRoss 84]

The rung with the MSO instruction is conditional. So it sounds like you've experienced similar behavior.

[kaiser_will 65]

I have not made it to the Motion Advanced class, yet, but have fumbled often with motion status bits that are not in the proper state after certain events. What I have added is a rung at the top of the motion logic routine that unlatches all motion status bits, such as EN & DN, when an alarm condition is present and the alarms are reset. This seems to work well in that the code always puts the motion commands in their proper state on startup. I have run into similar situations before that are difficult to test and verify working properly, such as running past the end of travel sensor.

[JRoss 84]

Yeah, that's probably what I'll have to do. Thanks.