G38.2 randomly stops

Hello all,

I need some help. I am working on a series of tutorials on making a touch off plate and configuring it under LinuxCNC. I am running AXIS GUI and v2.6.7 of LinuxCNC.

I am using parallel port pin 15 for the input pin, it is pulled low normally. My other wire is 5V.

The pin is netted to probe-in. When watching the pin with Hal Meter, it is false when not making contact, and true when it does make contact. This seems to be all working fine.

When I go to MDI and issue the command

G38.2 Z-5.5 F2.5

The command starts to run then will stop before making contact. I am getting no errors. When I rerun the command it will continue. The length that it runs seems to be random. Sometimes it stops as nearly as soon as I press the button. Other times it will run longer. Once in a while it will run to completion.

I have made a video demonstrating what I am talking about. Does anyone have any suggestions? I will try to link the file but I am not sure how. The youtube video is located here:



Joe

I would use halscope to see if there are false triggers on the pin. halmeter won't always show fast triggers.

Ultimately what I would be checking for is induced noise in the probe wires.

Chris M

I done this before I read your post Chris, but I made some changes.\

I changed the input pin on the BOB from being pulled LOW to pulling it HIGH.

Changed the PIN in the hal file to parport.0.pin-15-in-not, and brought out a ground wire from the 5V power supply. Tested it with Hal Meter to make sure it was detecting it. The started running the command again.

This time, I could probe from any location on the Z-Axis ant several different feed rates, so maybe running it the other way was the issue, but either way it should work shouldn't it?

I will say this, when probing at slow speeds, it would stop and Hal Meter would read false, but running the command again only moved it one step. So I guess it is catching some bounce. I guess HAL Scope would confirm this? Also, sometimes when it is true and I go to retract, I get an error that says "Probe tripped during non probe MDI command. Again I suspect this is from bounce.

I think using hal scope may be the solution here (but I need to learn how to use it), The BOB I have will pull the input pins either high or low by moving a jumper. They are pulled with a 4.7K resistor either up or down.

For what it is worth, the BOB I have is the CNC4PC C10, you can find the manual here: cnc4pc.com/Tech_Docs/C10R10_USER_MANUAL.pdf

And the manual shows a touch off plate with the input pulled high and a ground wire.

Anyway, suggestions are welcome.

Joe

Probes are notorious for interference based false readings.

If you are probing slowly you have quite a bit of scope for using a higher debounce value if necessary and not traveling any appreciable distance extra in the ms that might take.

Another options is screening and grounding one end of the lead.

My favorite, use a 12v plus low wattage plugin PSU to power the probe line and have this activate a SSR which switches a 5v / 3.3v feed to the BOB.

I have used this a few times, especially with limits, the switches are completely noise immune and the SSRs make and break so rapidly there is no lag.

regards

JoeHildreth wrote: Anyway, suggestions are welcome.

A standard touch-probe is short-circuit when not tripped, and tends to be fairly noise-immune because of that.

There is a software debounce component that can help in your situation. I think that probe inputs are monitored in the servo-thread so a software debounce running in the base thread won't introduce a delay.
www.linuxcnc.org/docs/html/man/man9/debounce.9.html

ArcEye wrote: Probes are notorious for interference based false readings.

If you are probing slowly you have quite a bit of scope for using a higher debounce value if necessary and not traveling any appreciable distance extra in the ms that might take.

I will take a look at the HAL debounce.

ArcEye wrote: Another options is screening and grounding one end of the lead.

That would explain why it worked so much better when I changed the input to a high and brought a ground wire from the PSU. Although, I am not sure what you mean by screening.

ArcEye wrote: My favorite, use a 12v plus low wattage plugin PSU to power the probe line and have this activate a SSR which switches a 5v / 3.3v feed to the BOB.

I have used this a few times, especially with limits, the switches are completely noise immune and the SSRs make and break so rapidly there is no lag.

regards

Is this to keep your signal wires as short as possible? Is there a supplier of specific brand or type SSR that you recommend?

Thanks again,

Joe