3D printer - Piezo Z probing

[tekkydave]

I think you connect it to the z endstop connector not the probe connector. Config should be same as for x & y endstops I think.

[Gina]

That's what I thought but it doesn't work.  If I manually adjust the bed to be the thickness of a piece of paper from the nozzle and start a print run (having disabled Z homing and bed probing).  It prints one layer then drops the bed to 100mm!  I'll have a Google and see if I can find anything.

Edited March 18, 2019 by Gina

[Gina]

I may have the answer here if I can work it out but I think my brain is suffering from overload ATM.  Guess I need a break.

[Gina]

From that thread it seems that this is covered in the Duet instructions but I haven't found it!!

Quote

If you home Z using a microswitch instead, then you can use a pattern similar to homex,g and homey.g. However, if you use a low-end homing switch that triggers a little before Z=0, then you can't use M208 to define the homing position, because it would prevent you moving below the trigger height. You can use a G92 command after homing instead. Here is an example, for the case where you have a low-end homing switch that triggers at Z=0.3mm:

G91 ; relative mode
G1 Z4 F200 ; raise head 4mm to ensure it is above the switch trigger height
G90 ; back to absolute mode
G1 X0 Y0 F2000 ; put head wherever you want it to be when you home Z (omit this line if it doesn't matter)
G91 ; relative mode
G1 Z-200 S1 F100 ; move Z down until the switch triggers
G90 ; back to absolute mode
G92 Z0.3 ; tell the firmware that we are at Z=0.3mm

This G code stuff can be a bit tricky it seems.  Easy when you know how, of course.

[Gina]

I fell foul of this :-

Quote

However, if you use a low-end homing switch that triggers a little before Z=0, then you can't use M208 to define the homing position, because it would prevent you moving below the trigger height.

This then is pretty much what I need in homez.g and the Z part of homeall.g

G91 ; relative mode
G1 Z4 F200 ; raise head 4mm to ensure it is above the switch trigger height
G1 Z-350 S1 F100 ; move Z down until the switch triggers
G90 ; back to absolute mode
G92 Z0.3 ; tell the firmware that we are at Z=0.3mm (or whatever the nozzle height is when the X endstop triggers)

Changed the second G1 line to allow for the bed being at  Z = 350, the printing height of the Concorde.

Edited March 18, 2019 by Gina

[Gina]

Put the above in homez.g but with 1.3mm offset as determined by lifting the bed in 0.1mm steps until the Z endstop triggered then further lifting in same steps until paper just stopped from moving under the nozzle.  However, homing Z fives an error :-

Quote

Error: Bad command: G92 Z1.3

Nothing found by Googling!  Any suggestions please?

[Gina]

I don't know what's wrong with G92 but I've got round it by adjusting the Z endstop (or rather the operating lever).  Nozzle is at about 0.2 - 0.3mm which is alright for PETG which is what I'm printing.  Why things appear to work for others but not me I don't know - but I'm not going to let it get me down.  I could get paranoid!!!

[tekkydave]

1 hour ago, Gina said:

Put the above in homez.g but with 1.3mm offset as determined by lifting the bed in 0.1mm steps until the Z endstop triggered then further lifting in same steps until paper just stopped from moving under the nozzle.  However, homing Z fives an error :-

Nothing found by Googling!  Any suggestions please?

Have you executed a G90 first to put it in absolute position mode? That's all I can think of

 

[Gina]

Yes.

Here's the latest try where I had over-corrected the endstop adjustment.

; homez.g
; called to home the Z axis
;
G91 ; relative mode
G1 Z4 F200 ; raise head 4mm to ensure it is above the switch trigger height
G1 Z-350 S1 F100 ; move Z down until the switch triggers
G90 ; back to absolute mode
G92 Z-0.2 ; tell the firmware that we are at Z=0.3mm (or whatever the nozzle height is when the X endstop triggers)

Error :-

Quote

12:14:54

G28 Z
Error: Bad command: G92 Z-0.2

 

[Gina]

Had a thought...  I've come across situations in the past where non-printing characters have crept into code and stopped it working.  Think I'll just try deleting the line and rewriting it.

[Gina]

Though I replied to that!!!  Amazingly I was right!  That cured the error. Evidently an invisible character in the command string.  After a few more sillies corrected, I now have the Concorde printing. 

Bed heating is a lot better but the heater is still a fair bit hotter than the top of the glass.  I think I'll add a thermistor to the top of the glass plate to see what the real bed temperature is.  I can wire that up to Heater 2 and display it on the web page.

[Gina]

Back here because I'm having a spot of bother again.

Having had reliability problems with the bare piezo discs and the little amplifier board and seeing Precision Piezo had a new "Orion Kit" that used a specially made PCB rather than a disc with a hole in it, I decided to try it in the hope of getting better reliability.  Bought the kit and assembled it and put it between E3D Titan extruder and hotend on my Concorde printer.  I have the LEDs changing when I tap the nozzle with my finger and same when manually bringing the bed up to touch the nozzle but Z homing doesn't work and it seems the Duet board isn't seeing it.  The probe is connected to the Z probe connector same as with my Mini printer.

This is the section of config.g concerned.

; Endstops
M574 X1 Y1 S0                            ; Set active low endstops
M574 Z1 S2                               ; Set endstops controlled by probe

;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
; Z Probe & Mesh Grid
;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
M558 P8 I1 R0.5 H3 F420 T15600 A5 S0.05   ; P8 = Digital mode (unfiltered), I1 = Active Low, R0.5 = 500mS delay before probing	
                                          ; F420 = 420mm/min probe speed (7mm/sec)
                                          ; T15600 = Travel between probe points at 15600mm/min (260mm/sec)
                                          ; A5 = Max No of touches, S0.03 = Tolerance for multi-touch (mm)
                                          ; H3 = Dive Height 3mm

G31 X0 Y0 Z-0.2 P100                      ; X, Y, Z offsets, debounce interval

M557 X20:280 Y20:280 S130                  ; Define mesh grid (3x3)	
;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

homez.g

; homez.g
; called to home the Z axis
;
G91                ; relative positioning
G1 Z5 F6000        ; lift Z relative to current position
G90                ; absolute positioning
G1 X150 Y150 F6000 ; go to first probe point  **********************************
G30                ; home Z by probing the bed

homeall.g

; homeall.g
; called to home all axes
;
; generated by RepRapFirmware Configuration Tool on Wed Jan 31 2018 10:30:18 GMT+0000 (GMT)
G91                     ; relative positioning
G1 Z7 F6000             ; lift Z relative to current position
G1 S1 X-400 Y-400 F7200 ; move quickly to X and Y axis endstops and stop there (first pass)
G1 X5 Y5 F6000          ; go back a few mm
G1 S1 X-400 Y-400 F360  ; move slowly to X and Y axis endstops once more (second pass)
;
G91 ; relative mode
G1 Z4 F200 ; raise head 4mm to ensure it is above the switch trigger height
G90 ; back to absolute mode

G1 X150 Y150 F6000      ; go to first bed probe point and home Z
G30                     ; home Z by probing the bed
;G1 Z5 F100             ; uncomment this line to lift the nozzle after homing

Any suggestions as to what might be wrong would be most welcome.  TIA

Edited June 16, 2019 by Gina

[Gina]

On ideas anyone?

[tekkydave]

If nothing is happening when you press the 'Home Z' button you need to home x and y first.  What versions of firmware do you have on the Duet. The later ones require an extra parameter on the G1 in your homing files in order to allow z movement in the homex.g, homey.g and homeall.g before z is homed. 

It is S2 or H2 depending on the version

My homex.g:

G91                    ; relative positioning
G1 Z5 F600 H2          ; lift Z relative to current position
G1 H1 X-320 F4000      ; move quickly to X endstop and stop there (first pass)
G1 X5 F1800            ; go back a few mm
G1 H1 X-320 F360       ; move slowly to X axis endstop once more (second pass)
G90                    ; absolute positioning

See Duet G-code

 

[tekkydave]

Its worth reading the notes Here to pick up any differences between versions.

[Gina]

The Z homing operates in that it moves the nozzle to the middle of the bed and raises the bed.  When the bed touches the nozzle the blue LED lights and the red goes out briefly but the bed continues to rise lifting the X carriage.  IOW  the piezo probe is triggered but the Duet doesn't respond.  I've checked the signal levels and the logic "1" is +1.6v - I wondered if this was a bit low.  Anyway, I'' read up on the links you gave and see if I can see anything.  Thank you.

[Gina]

Firmware Version:	1.20 (2017-12-23)

[tekkydave]

Worth upgrading at some point but not the cause of your homing issue.

If you tap the nozzle with something during homing can you get it to trigger? If not I would check the wiring of the probe. It should show in the 'Probe' section of the UI when you trigger the nozzle manually.

[Gina]

I see there have been new versions since I last updated which may fix or improve things but my current version is same as before when it was working but unreliable due to mechanics.  It's also the same version as in my Mini printer and that works (though not reliable due to hardware).  I copied the code over from the Mini to the Concorde with adjustment for bed size.

[Gina]

Crossed posts.  I'll check as you suggest.

[Gina]

It doesn't stop raising the bed when homing if I tap the nozzle - just flashes the LEDs.

[Gina]

Where is the 'Probe' section of the UI ?  Can't see it.

Unless you mean here, in which case nothing showing when tapping nozzle and triggering piezo.

 

Edited June 17, 2019 by Gina

[Gina]

When Z probing the the XYZ values are 150, 150, -0.2.  The Z-Probe stays on 0.

[tekkydave]

Look for 'Z-Probe' in the status section. It shows a number 0-1000. When triggered it should go to 1000 if you have it in a digital mode.

[tekkydave]

Just now, Gina said:

When Z probing the the XYZ values are 150, 150, -0.2.  The Z-Probe stays on 0.

The Duet is not getting the signal for some reason.