Question about scanning Z probe

fcwilt

Hi,

I am trying to update one of my printers with the Duet Scanning Z Probe.

It seems to be work as expected but I have a couple of questions.

One:

I'm getting this warning:

Warning: obsolete object model field sensors.probes^.diveHeight queried

Why does this happen?

Two:

Since the probe is analog, and there is no "on/off" trigger height, what exactly does the G31 Z param do?

Thanks.

Frederick

dc42

@fcwilt said in Question about scanning Z probe:

I'm getting this warning:

Warning: obsolete object model field sensors.probes^.diveHeight queried

Why does this happen?

Because you have a macro that refers to sensors.probes[N].diveHeight for some N. Use sensors.probes[N].diveHeights[0] instead, or diveHeights[1] if you want the dive height for the second and subsequent probes at the same point.

@fcwilt said in Question about scanning Z probe:

Since the probe is analog, and there is no "on/off" trigger height, what exactly does the G31 Z param do?

If you use the probe with a G30 command and you don't switch it to the experimental touch mode, then it behaves like a regular probe and G31 Z sets the trigger height as usual.

fcwilt

@dc42

Thank you for the reply.

So the change from firmware 3.4.6 to 3.5.4 was the cause of the change from diveHeight to diveHeights?

I overlooked that subtle change and missed it every time I looked at my code.

I'm blaming it on lack of sleep.

Regards the G21 Z param - it plays no role in scanning mode?

Frederick

gloomyandy

@fcwilt The trigger height set by G31 is used as the basis for the calibration performed by M558.1, which is typically required for scanning. So yes it is (indirectly) used for scanning mode. The trigger height is also used as the scanning height during the actual scan.

fcwilt

@gloomyandy

Thanks very much.

So if value was G31 Z4, what object would be at Z=4 during scanning?

Frederick

droftarts

@fcwilt said in Question about scanning Z probe:

So if value was G31 Z4, what object would be at Z=4 during scanning?

Usually, the nozzle, but can be any other point your use as Z datum. See https://docs.duet3d.com/User_manual/Tuning/Defining_tool_and_Z_probe_offsets

If your SZP is 2mm above the nozzle (or Z datum point), and you're scanning at Z4, it will mean that your probe is 6mm above the bed. This is a little out of the SZP ideal range, which is ideally 4mm. When I was doing SZP testing I created a graph of height vs reading, and sensitivity is best below this height.

Ian

fcwilt

@droftarts

Thank you very much.

That makes it all quite clear. Sometimes the documentation tells us what to do but not why.

Frederick

droftarts

@fcwilt said in Question about scanning Z probe:

Sometimes the documentation tells us what to do but not why.

It's a difficult balance. Explaining everything in minute detail can make the documentation far to long, and most people don't want or need the extra info.

Ian