What input should I use for a probe fault.

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08 Jul 2020 23:56 #174042 by oldtech
I'm building an experimental probe that will have the ability to fault if too much force is applied to it. So I need a way to halt motion when this occurs in order to limit damage to the probe. Any suggestions?

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09 Jul 2020 07:55 #174065 by tommylight
What type of output will it have for overload ? Analogue or digital?
Digital is easy to do in hal, analogue would require some type of Mesa or analogue to digital converter.

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09 Jul 2020 09:40 #174078 by rodw
If you connect your probe to motion.probe−input , it will halt motion when its triggered. If you want to measure force, thats a different kettle of fish!

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09 Jul 2020 16:23 #174105 by oldtech
Thanks. I should have added more details. I'm using Linux Mint with a Mesa 5i25/7i76 and I'm still the process of building out my control box and adding new features. I should also add that I'm connecting to a cnc router (a Millrightcnc Power Route). I'm retired with a background in system and application software mostly on Windows.

The probe will only have analog inputs and outputs. Yes, I know that the probe will stop on contact but since there is always some overshoot I'm adding an internal limit signal. If successful, I'm planning on mounting the probe to a sub-z-axis so that it is always available and does not require a tool change.

So it sounds like I simply need to connect the internal limit signal to a custom analog input and then connect that pin to E-Stop.

I should emphasize that the probe is very much in a conceptual state with a goal to have an accuracy of 0.01mm.

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09 Jul 2020 21:17 - 09 Jul 2020 21:18 #174141 by rodw
A couple of problems.

Linuxcnc does not really have a method to receive an analog input. If the the 7i76 is like the 7i76e there is a mode to enable some analog voltage inputs but its not particularly accurate.

With Plasma machines we use the encoder input with a bit file that converts the mesa encoder input into 3 x Encoder A inputs which then support 3 x THCAD voltage to frequency boards that is decoded from the encoder count back to a voltage. But you need the encoder for your spindle. You might be able to use the software encoder component.

Estop will need a bit output pin not a float. You might like to look at the sourcecode for the ohmic component in master branch for inspiration.
linuxcnc.org/docs/devel/html/man/man9/ohmic.9.html
It might work for you as is. Its purpose is to take a voltage from a THCAD and generate a probe output with hysteresis.
Last edit: 09 Jul 2020 21:18 by rodw.
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09 Jul 2020 21:33 #174142 by tommylight
This should do just fine for that
www.ti.com/product/LM331
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09 Jul 2020 21:46 #174145 by oldtech
The 7i76 has 8 analog inputs and I'm successfully using 3 for limit/home switches.

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09 Jul 2020 22:05 #174148 by tommylight

oldtech wrote: The 7i76 has 8 analog inputs and I'm successfully using 3 for limit/home switches.

7i76 should have 4 analogue inputs when set to mode 2, not 8, but in any case double check that.
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09 Jul 2020 22:11 #174149 by tommylight

oldtech wrote: The 7i76 has 8 analog inputs and I'm successfully using 3 for limit/home switches.

That reminds me, you should have mentioned you have an 7i76 in the first post, wasted 10 minutes looking where did i put those LM331 chips as i have 3 of them in a box waiting for some quality time ..... :)

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09 Jul 2020 22:20 #174150 by rodw

oldtech wrote: The 7i76 has 8 analog inputs and I'm successfully using 3 for limit/home switches.


Yes, you need to change modes to use as analog inputs. If you don't they are normal digital inputs. I use them for home/limits too.

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