4. Precision Piezo z probes guide for duet users reference

Precision Piezo z probes guide for duet users reference


  • If you have a Precision Piezo Z-Probe and want to connect it to your duet wifi/ethernet board here's how to do it. Tuning and other aspects of the probe's operation are dealt with in the manuals at http://www.precisionpiezo.co.uk/documents

    Electrical connection:
    The Piezo20 module or Universal Z-Probe Kit PCB comes with a standard DuPont 3 pin endstop cable attached with correct wiring at the piezo pcb. The other end has three wires red (VCC), black (GND) and green/blue (SIG/TRG). A 4 pin DuPont connector housing is supplied.

    Insert the red wire at one end of this housing, ensure the crimp is inserted so the spring clip retains it in the housing. Leave a gap of one pin, then connect black, then green/blue. Insert the plug into the duet z probe connector with the red wire end facing toward the long expansion socket and the green/blue SIG wire facing towards the end of the duet board with the LEDs and sd card slot.

    Config.g

    You need to define a probe there are two options:
    Analogue:
    This enables you to adjust the fine sensitivity of the probe on the fly, the coarse sensitivity is adjusted from the pcb. If using a Piezo20 module the signal must be NO (active high) and therefore use the I0 parameter. If using universal kit PCB you can set up the PCB with a NO - active high (I0) or NC - active low (I1) signal. It's your choice but NC -active low offers failsafe operation.

    Add
    M558 P1 I0(or I1) R0.4 F300 X0 Y0 Z0
    (analogue mode, NO/NC, delay, speed, not used as axis endstop)

    And

    G31 X0 Y0 Z-0.1 P600
    (X, Y, Z offsets, sensitivity/threshold)

    To reduce mechanical noise from the frame or axis vibration, the R parameter is the delay before probing in seconds, set a longer delay if the probe triggers before contacting the bed.

    Probing speed F parameter (in mm/min). A value from 300-420 is recommended. Slower can give more accuracy but too slow may not trigger, as the probe generates a signal on a change (compression or flexing in the piezo disc.

    The z probe analogue value is from 0 to 1000. If you get a lot of false triggering increase this value, a firmer bed contact will be needed to trigger. This value can be seen on Duet Web Control in the "z-probe" box. It is normal for this value to bounce around during head movement and printing moves, its only required for it to be stable just before and during probing dives.

    Digital:
    which is simpler and works as it would on an 8 bit board.

    Add
    M558 P5 I0( or I1) R0. 4 F300 X0 Y0 Z0
    (digital mode, NO/NC, delay, speed, not used as axis endstop)

    and
    G31 X0 Y0 Z-0.1 P100
    (X, Y, Z offsets, debounce interval)

    The debounce interval in ms smoothes the signal.

    Please note as of RRF version 1.20 you can use M558 P8 instead (other parameters are the same) which is a digital probe but without filtering or smoothing of the signal. This increases accuracy, as it takes less time to react to a trigger.

    The Z offset accounts for the compliance in the sensor and is usually -0.1mm as effectively the trigger point is just below the bed (this is opposite with inductive/IR sensors which trigger above the bed). If you have to babystep your first layer lower by 0.1mm, for example, then reverse the sign and add it to your G31 offset or vice versa if you have to babystep higher subtract the value from G31. Example, G31 Z-0.1 is set in config.g, probe/level/home/calibrate then print, if you babystep up 0.1mm then subtract 0.1mm from G31 Z change the value in config.g, power cycle/reset the machine, when your print finishes and you are ready for consistent first layers from now on.

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  • @DjDemonD

    Thanks for the guide. I will be installing my kit this week - would you recommend config in digital or analog?
    I'm unaware of the benefits of each so wondering what you use since you're one of the minds behind this all…

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  • I use digital its simpler but relies more on having the tuning of the piezo sensor system right. For Piezo20 read made units I've done this for you, digital is best. You can still monitor analogue "ripples" as the analogue value will still change in DWC/Paneldue as the probe moves around.

    If you've built one, especially if the design is a novel one, analogue gives you another layer of fine tuning which might help to get the most out of a design where the "tuning window" is very narrow.

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  • @DjDemonD

    I like this guide..thx but i do have a question. in this section:

    M558 P1 I0(or I1) R0.4 F300 X0 Y0 Z0
    (analogue mode, NO/NC, delay, speed, not used as axis endstop)

    shouldn't it be Z1, as the probe is used as an endstop for z axes?

    -curtis

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  • Depends. I have a corexy with a mechanical z max endstop switch at the bottom of the machine. I home x y and then z to the mech switch. Then I heat the bed to 1st layer temp, then nozzle to 130 then move to be centre, z=10 and do G30. This sets the fine z point.

    So in this case I'm not using my probe as z endstop.

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  • Can the 3-piezo under-heatbed setup be directly attached to the silicone heater? And wont the heat damage the piezo speakers? The temperature is quite high, up to 140 degrees.

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  • @Zerogee
    I have the system set up without setting the probe as a Z Endstop and without a mechanical Z Endswitch.

    My homez and homeall config files jsut contain the following:

    G91
    G1 Z5 F6000
    G90
    G1 Y10 X10 F6000
    G30
    G1 Z2
    G1 Y0 X0 F6000
    G1 Z0.05

    In my start gcode I tell the printer to heat the nozzle to 130c then home the axis, then heat the nozzle to the desired temp:
    M572 D0 S0.01
    M190 S[bed0_temperature];
    M109 S130;
    G28 ; home axes
    M109 S[extruder0_temperature];

    This works perfectly for me, as the G30 will set the Z to 0 when its triggered.

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  • @krzaku:

    Can the 3-piezo under-heatbed setup be directly attached to the silicone heater? And wont the heat damage the piezo speakers? The temperature is quite high, up to 140 degrees.

    No that won't work. The way I do it is make bed mounts which contain the Piezos and attach your bed to the mounts. I've tried using mounts which just support the bed at the sides, and mounts with screws to attach the bed to which are also adjustable. The Piezos can take a little temperature rise but not more than 60 degrees C approximately.

    Here's something to you started https://www.thingiverse.com/thing:2461746

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  • I think there's something wrong with the link you posted.

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  • Nope opens thingiverse to my design for a possible underbed piezo mount.

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  • Shows a 404 error for me.

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  • @krzaku:

    Shows a 404 error for me.

    +1, link doesn't work

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  • That's weird when I click it it loads the page I linked to maybe because it's cached on my phone.

    Try this https://www.thingiverse.com/DjDemonD/designs

    It's about the 4th or 5th one down.

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  • I've had no luck getting mine to act as a z endstop and may be confused what I need to do.

    On my corexy I have a mechanical z switch and have the piezo on my Titan Aero bracket (my own design, flexes/lights the led easily).

    What do I need to do, do away with the switch and just use the piezo for endstop and mesh bed leveling or some combination?

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  • Yes no switch need, use the probe for homing.

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  • So home x, then home y, move to bed centre and send G30.

    That should do it.

    The only time this is not going to just work is if the motion required to bring nozzle and bed into contact is triggering the probe. If so lower acceleration and jerk for Z, and make sure you are using the R parameter in M558, such as M558 R0.4 to allow the frame/axis to settle before probing.

    Also make sure M558 has X0 Y0 Z1 in it which means probe is used for homing Z. Although probably not necessary, as you can instead change your homez.g and probably your homeall.g file, to have the move to bed centre and G30 commands instead of the G1 S1 xxxx commands you would have been using before.

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  • Ah, now I finally figured it out after some confidence from your post. I had it all configured but when I was issuing G30 earlier after already doing it once, I'd get Error: Z probe was not triggered during probing move which means I needed to override the Z position.

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  • A bit of interest.
    https://www.facebook.com/groups/makerbot/permalink/1442086032575563/

    Thanks DJ for helping me out so quickly.

    Now I just have to implement it into my printing.

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  • Hi,
    I have a D-BOT coreXY (30x30x30cm), i've purchased the precise piezo last week and it is on its way.
    While i'm waiting for it i want to prepare the firmware.
    So in Z probe section of config.g i've put the digital code:

    M558 P5 I0 R0.4 F300 X0 Y0 Z1        ; Digital Z probe, also used for homing the Z axis
G31 X0 Y0 Z-0.1 P100				 ; Set the probe height

    i would like to use the piezo also for the z home in z min so i put "Z1 in M558".

    These are my homez.g and homeall.g:

    ;**********************************
;homeall.g
;homing using a x-MIN, Y-MAX and z-MIN endstops
;**********************************

G91                       ; relative mode
G1 Z4 F400 	          ; lowers bed 4mm to avoid dragging nozzle over the bed
G1 S1 X-340 Y340 F2000    ; move 340/340mm in -X (x endstop is MIN) and +Y(y endstop is MAX)
G1 S1 X-340               ; course home X
G1 S1 Y340                ; course home Y
G1 X4 Y-4 F500             ; move away from the endstops
G1 S1 X-10                ; fine home X
G1 S1 Y10                ; fine home Y

G1 Z4 F200                ; lowers bed 4mm to avoid dragging nozzle over the bed
G90                       ; back to absolute mode
G1 X150 Y150 F4000        ; put head over the centre of the bed, or wherever you want to probe
G30                       ; probe
G91                       ; relative mode
G1 Z4 F50                 ; move slowly 4mm in the +Z direction
G90                       ; back to absolute mode
G30                       ; probe


    ;**********************************
; homez.g
;homing using a z-MIN endstop
;**********************************

G91                       ; relative mode
G1 Z4 F200                ; lowers bed 4mm to avoid dragging nozzle over the bed
G90                       ; back to absolute mode
G1 X150 Y150 F4000        ; put head over the centre of the bed, or wherever you want to probe
G30                       ; probe
G91                       ; relative mode
G1 Z4 F50                 ; move slowly 4mm in the +Z direction
G90                       ; back to absolute mode
G30                       ; probe

    and in my starting code i put this to perform the bed leveling/compensation:

    M561                      ; Cancel any existing bed compensation by sending 
M557 X10:290 Y10:290 S40  ; Define the probing grid
G29                       ; Probe the bed and save height map to SD
;M190 S[70]               ; i don't have a bed heater 
M109 S130          ; set 130 extruder temp
G28                       ; home axes

    Is this correct or i have to change something?
    Any advice and suggestions will be greatly appreciated

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  • Looks okay to me, but then I'm not so good at just eyeballing it and spotting errors, just use low motor current at first so any crashes just stall the z motor, not do any damage. And tune the piezo carefully, so that a gentle tap up triggers it, and you see the trigger on DWC screen in Z-probe box goes red and says 1000.

    The do G30 with nozzle way above the bed, tap up with your finger or a tool, to make sure the firmware registers triggered and reacts to it before trying it on your bed.

    Then hit home all and go from there. But I'd say you are well prepared.

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