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Author Topic: Probe not retracting  (Read 899 times)

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Probe not retracting
« on: January 01, 2022, 05:35:07 PM »
Using Mach4 and CNC4PC Smoothstepper with Touch Sensor. I'm completely new to CNC so struggling to figure this out. Using G31.0 to probe and the plasma tip as the conductive touch sensor. I have been using the TouchOff UI and it does the touch off as set in the parameters but it will not retract. The log shows the probe touches but then errors that the probe touch is lost and doesn't retract. The touch sensor trips off once it detects touch and that seems to cause an error for Mach4. How do I get Mach4 to understand that it just need to go up the retract distance after the Plasma Touch Sensor triggers and not continue to look for a signal?
Re: Probe not retracting
« Reply #1 on: January 10, 2022, 05:29:57 PM »
it sounds like your probe circuit has noise on it. The torch lowers until it touches but with contact bounce may make and break contact many times within
milliseconds....and that will screw up the G31 move up and thereafter the ESS will issue a <Cycle Stop> and so the torch will not retract.

Try on the Port&Pins tab of the ESS adding a value, say 5000, as filtering to your probe circuit.

You may also try reading some of the posts about troubles various users have had with the Probing module. If the ESS detects a fault during a G31 move it will error out and issue a <Cycle Stop> by default.
You can change that behaviour if you think it warranted......and some recent posts cover it.

'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Probe not retracting
« Reply #2 on: January 11, 2022, 11:23:58 AM »
Thanks Craig. I am probably not using the correct terminology here but this is what is happening. The probe is wired to the Probe Touch Sensor with is only activated when probing. When the probe touches during probing it acts like a relay trips, the touch sensor is deactivated and signal s send to the controller that it has touched. So there is no noise since it simply trips the sensor. I did try putting in 5000 for a noise filter but nothing changed in the operation.

It really acts like Mach4 is wanting a constant probe sensor signal once it touches but that is not possible with the Touch Sensor that I have. I cannot find a setting that allows to change that. Could this be the problem?
Re: Probe not retracting
« Reply #3 on: January 11, 2022, 02:29:00 PM »
I think the problem lies in the manner in which you are sensing.

I probe PCB blanks many hundred of times a day. The tip of the tool is earthed and when it touches the PCB surface the contact is detected by the probe circuit.
The controller must decelerate the axis, come to a stop and report its axis positions back to Mach. This will happen quickly but not instantly, I would guess several
milliseconds. I'm not sure, but if the report to Mach is made during the regular cycle of the motion controller as I suspect, then there could be an additional 10-25ms delay in the comms.
Once Mach gets the axis still report AND the axes positions from the motion controller then it is at liberty to issue another move, usually a g0 retract move.

From your description the motion controller/Mach is expecting the probe contact to be made continuously during that period, lets say 50ms. That comports with what I observe
with the on-screen LED that reflects the probe circuit.

May I suggest you experiment with a very simple probe circuit such as I have described and see if it works. All you need is some metallic tool in the spindle tool holder,
an endmill for instance, with a clip to ensure that is earthed and a flat piece of metal lying flat on the bed of the machine but insulated from earth with a sheet of plastic.
The probe circuit sense wire would be connected to the metal plate....it would be earthed or 'pulled low' on probe contact. With the tip of the tool 2mm above the plate,
zero the Z axis and issue this MDI:

g31 z-1
g0 z10

If this move is successful the tool will lower until it touches the surface, wait the appropriate 50ms or whatever for Mach and motion controller to do their thing
and then retract to 10mm above the surface.

That would confirm my hypothesis that the probe contact must be held while Mach and motion controller communicate.

'I enjoy sex at 73.....I live at 71 so its not too far to walk.'