All_surface scanning z-probe
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@fcwilt Well assuming this is mounted alongside a nozzle (if it is not then you have an entirely different set of "deployment" methods), what's going to happen when print something? To enable the ball to touch the print surface it will need to be lower then the nozzle tip (unless you want the nozzle to be dragging along the bed as well). Won't the ball constantly be hitting whatever is being printed?
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@gloomyandy I'd probably consider something a little more like the Euclid probe where you can pick up and drop off. Would be neat to see especially for folks who use glass/mirror beds.
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Also a ball is not necessarily the optimal contact shape. even a relatively large radius ball is going to have minimal contact area so you are either going to have to scan many close together lines, miss areas, or have a huge ball. probably a roller is better as scanning only needs to be on one axis. Manufacturing and mounting a smooth and concentric roller is its own challenge!
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@Sindarius Euclid is how I do it
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Thanks for the interesting replies. They made me think...
IMHO a small contact area would be best to find the lowest valley in the surface. A roller or cylinder would average out what's underneath.
OTOH a ball might miss the highest point, but that's less of a problem when it comes to 1st layer adhesion.Retracting the ball is a thing I haven't thought about. It would be like a BLtouch, but here the sensor board would need an actor to lift the ball.
Maybe a parking macro for the probe could retract/unretract the probe. Like with the oldfashioned allen key switch probes.If we'd use a capacitive sensor the ball could be made of POM, which is lighter. And has less impact, if we don't retract it and it bumps into the print.
A magnetic sensor (*) would need a mechanic to translate the vertical motion into rotational. (maybe backlash problems)
*) the new MT6835 has a super high resolution of 21 bit = 0,00017 degree/step and has an SPI clock of 16MHz -
@T3P3Tony
I just read the discussion in the official thread about the need of a separate Z-probe for calibration...
What if outside of the coil are two protruding contacts and the steel washer is used to close the contact? Voilá, z=0 datum set -
@o_lampe You could retract/deploy the ball with an electromagnet. Altough I wouldn't use a ball but a rod with a spherical end. I don't think this kind of zprobe needs a "rolling" element.
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@o_lampe I was considering mechanical devices that could be used for non-metallic build plates, like glass.
You could use a FSR or a load cell on a ballpoint pen style roller, this would probably cause issues with heat drift.
You could use some style of linear potentiometer/hall effect. This would probably drift with temp also.
You could use an optical gauge with a slider. This would probably drift with temp too.
I think the biggest issue is eliminating the temp drift.
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@Surgikill Temp drift can be an issue, but when we scan the bed really fast and contact material has a low thermal conductivity (ceramic ball or POM) it won't matter.
The inductive probe is especially sensitive, but some other sensors just expand a tiny bit. The range of motion we have to deal with is so small, their thermal expansion is below the radar.
Other issues like AD-conversion noise and interface delay can also mess up the result. -
What about adapting a digital dial gauge? Something like https://github.com/stawel/dialIndicatorToSerial ... I assume the challenges are a) getting readings fast enough, and b) finding a digital dial gauge that's precise enough without costing an arm and a leg.
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@oliof There are linear hall sensors, but I don't know how sensitive they are. Passing a small magnet along the sensor would act like the rotary mag-sensors, but without the need of a motion translation.
