Host Engineering Forum

General Category => CTRIO and CTRIO2 => Topic started by: rgbarr on August 10, 2011, 02:48:58 PM

Title: H2-CTRIO Reloading Position
Post by: rgbarr on August 10, 2011, 02:48:58 PM

I have an application where the dynamic positioning profile may be interrupted by "Suspending the Output" - sort of an emergency stop. The problem is when taking it out of this condition it continues the profile at the point in the profile where it was suspended i.e. it can restart with the velocity at it's highest set value. This causes the stepper motor to slip and lose position. I need to ramp the velocity up like a normal trapezoidal profile but start from the count I stopped at. I tried modifying the simulated retentive counter example but once the output is enabled the counter resets to zero. Is there a way around this problem?

Title: Re: H2-CTRIO Reloading Position
Post by: BobO on August 10, 2011, 03:48:38 PM

Yes...but sadly it isn't available just yet. The CTRIO2 due out in a couple of months does this beautifully, at up to 250k.

In the meantime, I honestly don't know of any good way to fix it. The CTRIO was not really designed for pulse output, and it was no small feat to make it work as well as it does. The suspend function is admittedly dang near useless. How's that for honesty?

Title: Re: H2-CTRIO Reloading Position
Post by: Greg on August 10, 2011, 03:59:02 PM

There is not a graceful way of doing this with the current CTRIO. It is a feature we added to the CTRIO2 that is very near official release. Unfortunately, that doesn't help you at this time. Here is what you will have to do to get this to work with the current CTRIO.

• Run the Dynamic Position Profile.
• SET Suspend whenever your e-stop occurs.
• Use a System Command to Read your Output Position.
• RESET Enable Output. (This keeps the following Suspend Output from turning the Output back ON yet.
• RESET Suspend Output.
• SET Enable Output. (This will zero out the Output Position as you stated).
• Use a System Command to Write back the Output Position you read above.
• TOGGLE the Goto Position bit.

The problem here is if your stepper motor cannot handle the sudden accel back when you were RESETTING Suspend Output, is it also intolerable to the sudden stop caused by SETTING Suspend Output? Because SETTING Suspend Output causes instant decel; it doesn't ramp down to zero speed. Thus this method may not work if the decel causes slippage on the machine's position.

Title: Re: H2-CTRIO Reloading Position
Post by: rgbarr on August 11, 2011, 09:22:17 AM

Thanks! That worked. I just need to make sure I'm not not slipping on the sudden stop. I'll probably switch to the CTRIO2 once it's available.