Duet 3 Scanning Z probe

gtj0

Folks have been talking about magnets but what about a bed heater? I've got a 500x500x6.5mm aluminum bed with a full coverage 1600 watt heater on the bottom and PrintBite on top. As the probe passes over the heater wires, especially if they're energized (not to mention with PWM active), is there going to be an issue? I would think that 6.5mm of aluminum would help to dampen any variance but I'm curious if that was tested.

fcwilt

@gtj0

There is an option to turn off bed heaters during probing.

Reference M558 parameter B

Bn If 1, turn off all heaters while probing, default (B0) leaves heaters on.

Frederick

gtj0

@fcwilt said in Duet 3 Scanning Z probe:

@gtj0

There is an option to turn off bed heaters during probing.

Reference M558 parameter B

Bn If 1, turn off all heaters while probing, default (B0) leaves heaters on.

Frederick

Ah yeah, I forgot about that. I never used it because probing currently takes long enough that, even with all that mass, the bed cools down a bit during the probe with the heater off. Shouldn't be an issue at this speed though, and de-energized, the wires aren't going to make a difference through 6.5mm of aluminum.

droftarts

@gtj0 as far as I’m aware, the SZP is not affected by bed heaters. I’m pretty sure @dc42 told me that at the show.

Ian

zapta

Here is an idea, a Klicky like probe that first picks a switch for a reference Z data and then a coil for fast scanning of the entire bed.

(Don't ask me how to do that).

o_lampe

@zapta I guess you could have a combination of switch and analog sensor in one housing. That would eliminate the time for double tool-pickup.
Just have to config the zprobe to be digital for the first probe point, then switch over to the analog sensor.

zapta

@o_lampe, when the switch is pressed, it can change the characteristics of the sensor, e.g. disconnect it. This way there is not need to switch sensors. Just an idea.

Notepad

Brain dump regarding using the probe as the only probe.

In theory it would be possible to use the probe as the only sensing equipment as it includes the only variable you need. which is an amplitude reading from the probe (which is then converted to distance)

The issue is there is no datum point, as depending on the scanned surface material, the activation distance could vary.
HOWEVER, assuming there is no minimum distance to the sensing coils, you could put the probe directly against the print surface and take a measurement to create a "zero" reference measurement and store that for later use.
In reality you may want to take various zero point measurements at different coil temperatures and create a look up table of sensitivity vs temperature.

Then once the coils are mounted you would need to set a single Z-offset and that should be good enough.

There is another way off the top of my head, but I cannot remember the algorithms name where you can repeatedly move a reference plate (in this case the bed) up and down a known amount (say 1mm and 2mm) and then you can work out the differences in measurements to gain a pretty accurate depth to probe value. The math was complex the last time I checked, but once I find the name of it, ill post it here as it may be helpful.

o_lampe

@Notepad said in Duet 3 Scanning Z probe:

you could put the probe directly against the print surface

I see a problem here with the probes mounting screw heads. Are they countersunk or protruding? How accurate are they made.
It might be easier to use the nozzle as contact probe on a blank metall surface and use that height as reference.

Harish2811

RRF.3.5.0 is not working for me and I got the error as "make" does not found path I was using eclipse ide for this. Msys2 file doesn't have make.exe in it. Can someone help me with this.

jay_s_uk

@Harish2811 please start a new thread

A Former User

This post is deleted!

ofliduet

Is the STL / STEP for the probe holder availalbe that I see in the picture of the Revo toolboard?

edsped

What's the maximum distance the probe can be from the bed and still be effective? I need at least 4mm preferably more for my mount.

T3P3Tony

@edsped 4mm should be fine. We are doing more testing to establish maximums, including with different temperatures

edsped

@T3P3Tony Perfect thank you for answering.

zapta

Lowering the max working distance of the probe, may allow to reduce the probe size, to simplify the integration.

Regarding the temperature affect, is it dominated by hotend or bed temperature?

jlipavsky79

@T3P3Tony I would love to follow the progress on this because TAMV is good and works really well when it works but sometimes it's really bad, the nozzle has to be pristine and with the coil sensing the metal only would be great, it would just need a macro similar to prusa pinda measuring the magnets in the bed to find their center

dc42

@zapta said in Duet 3 Scanning Z probe:

Regarding the temperature affect, is it dominated by hotend or bed temperature?

We are doing research to determine whether the predominant effect is the temperature of the coil (which is affected by the temperature of the hot end) or the temperature of the bed plate. We have sensors for both. If it proves necessary, we will extend RRF to provide compensation for both.

zapta

@dc42, I was thinking about the Z probe and meshing issue.

Since you control also the Z while scanning in X,Y, instead deducing height in mm from the probe, you can just pick a certain probe measurement value and then, while scanning in X,Y, dynamically adjust the Z to maintain that level.

This will equal-height surface that is well calibrated to mm by the accuracy of the Z steps, and will still be must faster than the stop-and-probe approach of BL Touch.

BTW, the same approach can possibly also be used with your IR sensor, assuming that its differential mechanism can give you a on-target/above/below indication.

Does this make sense?