Conditional homing and z-height fine adjustment

fcwilt

Hi,

I was wondering why you home to Z max.

Thanks.

Frederick

GuidoP

@fcwilt said in Conditional homing and z-height fine adjustment:

Hi,

I was wondering why you home to Z max.

Thanks.

Frederick

I have had several considerations for implementing the z-max switches:

When the axis home they drop down a couple of mm. If the bed is max down it would crash into the hard mechanical endstops, offsetting the mesh and creating a terrible noise. Creating endstops and adjusting the homeing files eliminated this problem
After the print i want the bed to drop down so i have easy access to the print and don't have to move something manual. Now i can simply home the Z-axis, and don't need to worry abbout the previous issue
Additional benefit is having 2 z-max switches is that i can easily have a fixed reference point without much adjustment and home both z motors individually without much hassle.

There are a couple of downsides aswell:

Starting a print can take considrable longer as the bed needs to travel from z-max to z-min.
You have to carefully need to measure the Z-max to get your mesh leveling to work niceliy. Also you need something in your start g-code to do some z-level fine adjustments, (Hence above script).

To reduce the total time before the print starts i want to check the homing status to prevent a unnessecairy homing cycle in case the z-axis is already homed. And i wanted to test out the meta commands to see what would be possible.

fcwilt

@GuidoP said in Conditional homing and z-height fine adjustment:

I have had several considerations for implementing the z-max switches: ...

Thank you for the reply.

All of my printers home to Z min and it seems to me all of the reasons you stated for using Z max apply to Z min.

The crash scenario is the same for min versus max.
Most slicers will execute some user defined code on print completion. One of the things my "printing complete" macro does is move down to a bit - it could just as easily move to Z max.
I don't understand the fixed reference issue. You are referencing the frame when using either min or max - correct?

Thanks for the help in understanding.

I don't know if this makes any difference but I eliminated multiple Z steppers in favor a single stepper, belt driven setup which naturally keeps both Z axis lead screws in sync.

Frederick

GuidoP

@fcwilt Thanks for sharing your thoughts and considerations.
An alternative to my current setup would indeed be using a z-min homing scenario and just use the endstops as safetystops so the bed wont crash when is full down when the machine starts. (This is actuatlly my backuo scenario if i don't get the macro running).

The crash scenarion in a z-min homing situation is higher imho:

Machine starts, axis are not homed. The machine has no clue where the different axis are located
Homing is initiated. X and Y homing will initiate (in the default g-code) a Z move in the z-max direction. Regardless if z-max or z-min is used
If the bed is at or near the z-max position, with z-min endstops the machine has no way of knowing it will run out of bed travel and will crash to the mechanical limits. In a z-max endstop configuration the z-max endstop will trigger, stopping the move gracefully. With to independend z-motors you'll need to re-perform the bed leveling again due to the unknown shift between the two leadscrews. I'm not sure what would happen in your setup with a single stepper for 2 leadscrews. Does the belt slip or does the stepper skip steps?

I have two optical endstops bolted to the frame between steppermotor and linear rod. As the frame is square and level these switches are in the same position horizontally. I use a single 25mm aluminium angle profile bolted directly to the 2020 profiles of the bed as endstop flag. So basically there are no manual adjustments and everything is referenced to a fixed point resulting in a repeatable fixed horizontal level.
An alternative to this procedure on the z-min side would be using the z-probe to probe near the leadscrews and let the duet calculate how to level things out. This is a bit more straight forward without extra probing time. (Or use a single steppermotor which drives 2 leadscrews.... )

There are a lot of differnt approaches and sollutions to solving a single problem. These are my solutions now, which i might (or might not) change in the future... That's the beauty of learning and progressing...

Anyway, i'm getting a bit off-topic... Sorry...

fcwilt

@GuidoP said in Conditional homing and z-height fine adjustment:

Homing is initiated. X and Y homing will initiate (in the default g-code) a Z move in the z-max direction. Regardless if z-max or z-min is used

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Frederick

Phaedrux

@fcwilt said in Conditional homing and z-height fine adjustment:

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Maybe he means the small lift before homing x and y for clearance?

fcwilt

@Phaedrux said in Conditional homing and z-height fine adjustment:

Maybe he means the small lift before homing x and y for clearance?

What small lift? I must do things backwards. I home Z first and then move to Z=5 before I home Y & X.

Frederick

Phaedrux

@fcwilt For instance in homeall.

G1 Z5 F100 S2 ; Lower bed 5mm to ensure it is below the trigger height

fcwilt

@Phaedrux said in Conditional homing and z-height fine adjustment:

@fcwilt For instance in homeall.

G1 Z5 F100 S2 ; Lower bed 5mm to ensure it is below the trigger height

What would you do that?

Consider when homing to Z min:

G1 Z-999 H1
G1 Z20
G1 Z-999 H1

When the first G1 executes if the endstop is already triggered no movement takes place and the next G1 executes which is safe.

Am I overlooking something?

Frederick

Phaedrux

@fcwilt said in Conditional homing and z-height fine adjustment:

Am I overlooking something?

Yes, when using a probe you must position the probe first, so X and Y must be homed first, and by default the configurator includes a short lift of the Z axis to give clearance for the X Y move and to lift the probe above trigger height.

But I was just speculating on what he might have been meaning.

fcwilt

@Phaedrux said in Conditional homing and z-height fine adjustment:

Yes, when using a probe you must position the probe first, so X and Y must be homed first, and by default the configurator includes a short lift of the Z axis to give clearance for the X Y move and to lift the probe above trigger height.

Ah... I see.

I use a Z min endstop switch setup for homing in relation to the frame so I never encountered that issue.

I only use the Z probe for setting Z=0 and mesh comp probing, things which only occur after the ZYX homing has been done.

Thanks.

Frederick

GuidoP

@Phaedrux said in Conditional homing and z-height fine adjustment:

@fcwilt said in Conditional homing and z-height fine adjustment:

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Maybe he means the small lift before homing x and y for clearance?

Thats correct

GuidoP

Thanks all for the input, but unfortunately it does not bring me closer to an answer to the original question: Why does the conditional gcode not work as intended? Where is the bug in the code??

GuidoP

I finally got the macro working with following code:

; Source: https://forum.duet3d.com/topic/4202/homing-to-z-max-when-also-using-a-z-probe/19
; Start g-code: G28, M98 P"0:/macros/Leveling/SetZ" ; run z fine tuning

; If the printer hasn't been homed, home it

;M291 P"checking homing status" R"Homing status" S1			; Report status

if !move.axes[0].homed || !move.axes[1].homed || !move.axes[2].homed  	; Check if axis are not homed
  ;If axis are not homed, home axis
  echo "Axis are not homed, performing homing"
  M98 P"0:/sys/homeall.g"
else
  ;If axis are already homed, home only the X and Y axis
  echo "axis are homed, re-homing x and Y"
  M98 P"0:/sys/homex.g"											; Run the Home X macro
  M98 P"0:/sys/homey.g"											; Run the Home Y macro
  ;G1 X100 Y100 H0 F1800											; move to be centre slowly.
  
;End homeing check
M291 P"Axis homed" R"Homing status" S1							; Report status
;echo "start fine tuning z-level"
G1 X100 Y100 H0 F1000											; move to be centre slowly.
G1 Z15 H1 F8000	 	 											; Raise the bed to start probing
G30 															; probe for z=0
G1 Z10 H1 F1000 												; raise nozzle
G30 S-1 														; check z gap
G1 Z10 H1 F1000 												; raise nozzle

M400															; Wait until all moves are completed

I changed and tested several different thing, but i think the trick that did it was removing the empty line between the end of the "If" block and the start of the "else" block.