Stepper picks it own directtion

[mwchildress]

I am using t100md888 to control a stepper drive on an index table.  In my program I need to home the unit first. To do this I tell the drive to make on revolution about 36000 steps to find the home sensor. The problem is the drive seems to choose its own direction to get to home sometimes it rotates clockwise and sometimes counterclockwise.  In simulation mode it always works correctly.  Depending on which direction the motor comes from the point it shuts off at can be 1/8" different.  When I index the drive it always travels the right direction regardless of which direction the drive tried to find home with.

[support]

Are you using the stepmoveabs command? If that is the case the PLC needs to know where its current location is and it will then move in the direction to go to where stepcountabs=0. If the current location is lost then it could be moving in different direction from where you think it should go. Perhaps it will be good to put a limit switch at one end of the travel so that the motor will always move in the direction that goes to the correct end. If your homing sensor is somewhere in the middle then it is hard for the PLC to know which direction to turn if it loses its current location for whatever reason (power down, manual move etc).