Using MAX 1d interactive motion (just to recreate what is happening during normal stepper operation), I set up one axis of my motion system to cycle between two counts, with a 1 second pause between cycles. The stepper is attached to a butterfly valve, and the forward motion opens it about 45 degrees, and the reverse motion close it completely, actuating the reverse limit.
Most (99%) of the time, motion works as expected. Occasionally, when the reverse limit transitions from high to low during a forward move off of the limit, forward motion stops. I have attached an image that shows two screen caps of a VI that I used to monitor the limit switch and the voltage command. As can be seen in the image, when motion fails, the control voltage goes to zero at the same moment as the reverse limit goes low.
Servo drive: Kollmorgen MMC-SD-2.0-230
UMI: NI-7764
Motion Controller: PCI-7340
Software: NI-Motion 8.4, using MAX
OS: Windows XP
Thank You,
Rick Howard