Moves not getting to position

Moves not getting to position

We have an odd situation with an MC4N running EtherCAT drives.
The issue is that axis 1 is not getting to the commanded position via MOVEABS.

The command MOVEABS is where we are hanging because the move seems to cancel.

We did a the test with all programs stopped, and issuing commands at the Terminal #0 prompt.

DPOS at 7.5.
Then I do a MOVEABS(0), and DPOS gets to and stops at 5.7.
Then I do a MOVEANS(-0.75). DPOS gets to -0.559 and the move stops.
After a few manual MOVEABS(1), MOVEABS(4.5), MOVEABS(0)…all seems ok again.

Note this does not happen consistently, and may take several dozen cycles to show up (this is a pick and place system).
Also, as far as I know, this is only happening on axis 1 of the 2 axis system. What could be causing it?

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We checked the program and axis settings and noticed that there are limit sensors allocated to FWD_IN and REV_IN. We suggested to check that the sensors are giving a solid signal and not intermittently going off during the moves.

An engineer visited the site and disabled the overtravel limit switches for the suspect axis. It ran for 1.5hrs with no issues!
The conclusion is that the limit sensors were triggering the FWD_IN and REV_IN inputs and cancelling the moves.

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