Stow probe after raising Z when homing

[ldursw]

Description

This is a follow-up for PR #21124 where it was identified in the discussion that a BLTouch sensor may collide when homing.

Homing sequence before the PR:

1. Raise Z
2. Home X and Y
3. Stow the probe
4. Home Z

Homing sequence after the PR:

1. Raise Z
2. Stow the probe
3. Home X, Y, and Z

Requirements

BLTouch

Benefits

The PR may reduce probe damage caused by collision.

Related Issues

PR #21124

[VanessaE]

Is there some way to disable this change? It adds unnecessary delays.

On my machines, the bed lowers by 10 mm before homing, and the probe pin always gets stowed after homing (not to mention if it's about to print something 😄), so it's never at risk of hitting anything during the X/Y move.

[ldursw]

@VanessaE The pin always gets stowed because if for some reason the pin gets pulled manually the firmware won't notice and the pin may collide with bed clips possibly damaging the probe. This was discussed in more detail in #21124.

[VanessaE]

That seems unnecessary?

The probe wire/Z end stop reflects the state of the probe pin anyway, whether the BLtouch moved it or the user pulled it out/pushed it in, at least mine seems to.

But like I said, on setups like mine, it's impossible for the probe pin to hit anything during homing -- my bed is flat, there are no binder clips or clamps sticking up, and the bed gets lowered by 10 mm before the X/Y move happens.

In fact, there's so much clearance at the moment the X/Y move starts, that it could deploy the probe mid-flight, eliminating the usual pause just before the Z move starts.

[ManuelMcLure]

The probe wire/Z end stop reflects the state of the probe pin anyway, whether the BLtouch moved it or the user pulled it out/pushed it in, at least mine seems to.

That’s only the case if the BLTouch is in SW mode. If it’s in the default “pulse” mode it will always be read as “open” except for a very short pulse when triggered.
It might make sense to avoid the retract if you have explicitly set the BLTouch to SW mode, though.

[VanessaE]

That’s only the case if the BLTouch is in SW mode.

I've just now checked, and M119 tracks the up/down position of the probe (in the "z_probe" field) whether I pull/push it by hand, or deploy/stow it via the menu, and it seems to read steady even after several minutes in either position.

BLTOUCH_FORCE_SW_MODE is commented out in my configs (I think that's the default), but maybe my probe always operates in SW mode regardless of the state of that flag? It's a Trianglelab 3DTouch, should be equivalent to BLTouch v3.1.

[ManuelMcLure]

Who knows what the clones do. I know that the genuine BLTouch behaves as I describe. It’s possible that different instances of “3DTouch” work very differently. I know that a lot of the complications in the BLTouch code are specifically to work around clone bugs.

[VanessaE]

All I can say is mine's always been reliable, so while this change probably helps on some setups, on mine it just adds delays and brings no benefit. Please add a setting to restore the previous homing behavior.