RTSI for Additional Limit Switches?

[ksakaki]

Hi,

BACKGROUND:
I have to hook up additional limit switches which will alert me to specific positions on an XYZ linear motor stage. I have currently hooked up several limit switches to the digital I/O ports on a UMI-7774 board which is connected to the NI-7350 (8 Axis) controller.

My goal is to have the controller recognize when a digital I/O line has been activated and to halt the motor from proceeding any further which may damage expensive equipment. I unfortunately require the factory installed limits as homing indicators, and therefore can't wire the additional limit switches into the ports provided on the UMI-7774.

From reading the documentation online and some of the forum posts it seems like the RTSI acts like a hardware interrupt that will signal the controller that a condition on an external device has occured. 

QUESTION:
Would a proper method, to achieve my goal, be to route a digital i/o pin to a RTSI port which (configure in MAX) which I'm able to setup in the labview programming environment? I take it that the high-speed capture (RTSI) ccts are virtual.

I don't necessarily need directions how to do this. I would just like to know if I'm heading in the right direction. I'm pretty new to the LabVIEW environment but can usually figure how to do things on the LabVIEW interface on my own.

Thanks for your help!

[Luke H]

Kelly,

You should be able to continually poll a digital line on the motion board using Read I/O Port.flx by putting it inside of a while loop.  You could then a case structure with Enable Limits.flx to enable the software limits whenever Read I/O Port.flx returned a high value for the line you were interested in.  These will of course not be as deterministic as the limits in hardware, but it would probably be the most straightforward way to suddenly activate an additional set of limits on your axis.  This document, Axis Settings for Motion Controllers, will provide you with additional information about software limits.

Regards,
Luke H

[ksakaki]

Hi Luke,

Since the velocity will be kept relatively low, I'm going to try it your way first. If it doesn't work out I'll implement it in hardware. Thanks for your help again!

K.