Re : Cannot set home position using reference move

[ajfaul]

I am controlling a servo motor using a NI 7350.  I have two inductive proximity switches connected as the forward and reverse limits.  I have set the following in Motion Assistant in order to execute a reference move:
Reference type: Home
Initial direction: Reverse
Final direction: Forward
Edge to stop on: Reverse
Offset postion: -200 counts.
If I understand the help correctly, I should be able to set a home position using this configuration.  However, when I do the reference move, the motor stops after reaching the forward limit switch, do not go to the offset position, and gives the following error: Limit switch is active.
Anybody with ideas on how to resolve this?

[JB]

The HOME reference function expects also a signal on the Home Switch Input of the NI-Motion controller. Therefore, you need 3 proximity switches (forward limit, reverse limit and home). This document may share some light.

[Jochen]

You also could wire the limit switch to the HOME input. If activated, the HOME switch acts exactly like any other limit switch, so you don't loose safety. If you wire the the limit switch to the HOME input, please make sure, that the SMART ENABLE option for the HOME switch is disabled. Otherwise the HOME switch input is only activated during a find home sequence and the axis wouldn't stop if the HOME switch is hit during a normal move.

Regards,

Jochen Klier
National Instruments

[ajfaul]

Thanks Jochen.  That will help.  I had it wired like that also, but did not disable the Smart Enable.
Regards
Andre

[ajfaul]

Jochen,
I connected the limit switch as you suggested, and disabled the SMART ENABLE in MAX, but the motor moves beyond the home limit switch when a REFERENCE move is activated.  I then connected the limit switch to the FORWARD limit input and get the same error as previously.  According to the HELP in MOTION ASSISTANT, it should be possible to use two limit switches and still define a home position:

Physical end-of-travel limit switches

A home reference move can run on a motion system that does not have a physical home switch, but has forward and reverse end-of-travel limit switches. An example of this is a stage, where length of travel is limited by the physical dimensions of the stage. The following figure diagrams the behavior of the home reference move in this situation:

The home search begins searching in the initial direction selected. The direction of search reverses when the first end-of-travel limit switch is found. The search continues until the second end-of-travel limit switch is found. The home reference move ends when the second limit is found, and offset moves and counter resets are performed.

What am I missing here?
Thanks
Andre

[Jochen]

André,

the limit switches are used successfully in almost every motion control application that I know. To get a better idea about what's going on, could you please provide some more information?

1. Which NI-Motion version are you using?
2. What's the type of your drive?
3. How do you connect the drive to the motion control board? Are you using an UMI? Which type of UMI are you using?
4. What about the proximity switches? Could you please provide a data sheet?
5. Do you see the correct status of the switches in MAX (1D-Interactive)

Thanks,

Jochen

[ajfaul]

Jochen,
I am using Labview 8.5 and Motion Assistant 2.2 with an Applied Motion BluAC-S drive.  I now have the reverse limit switch connected to the reverse switch input on the NI7350 and the forward limit switch connected to the "home" input in the NI7350 through a SCB-68 connector block.  I found out that the "edge to stop on" for the home reference move must be set to "reverse" in order for the limit switch and the home offset to function correctly.  It seems that things are sorted out now.
Thanks again for your help.
Andre