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3D printer - Piezo Z probing


Gina

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My Concorde printer definitely has Z drive problems.  I'm already using NEMA23 motors driving single start threaded rods (trapezoidal tooth cross-section) and the maximum speed I can get is just above 300mm/m before I get step skipping.  Using 2A setting for motor current.

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; Configuration file for Duet WiFi (firmware version 1.20 or newer)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool on Wed Jan 31 2018 10:30:18 GMT+0000 (GMT)

; General preferences
M111 S0                                  ; Debugging off
G21                                      ; Work in millimetres
G90                                      ; Send absolute coordinates...
M83                                      ; ...but relative extruder moves
M555 P1                                  ; Set firmware compatibility to look like RepRapFirmare
; Automatic saving after power loss is not enabled
M667 S1                                  ; switch to CoreXY mode *** Gina added
M208 X0 Y0 Z0 S1                         ; Set axis minima
M208 X400 Y400 Z350 S0                   ; Set axis maxima

; Endstops
M574 X1 Y1 S0                            ; Set active low endstops
M574 Z1 S2                               ; Set endstops controlled by probe
;M558 P4 H2 F300 T6000 I1                 ; Set Z probe type to unmodulated and the dive height + speeds
;G31 P500 X35 Y0 Z2.6                    ; Set Z probe trigger value, offset and trigger height
;M557 X35:400 Y20:400 S365            ; Define mesh grid

;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
; Z Probe & Mesh Grid
;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
M558 P8 I1 R0.5 H3 F420 T15600 A5 S0.03   ; 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 X20:180 Y20:180 S160                 ; Define mesh grid (2x2)	
M557 X0:399 Y20:398 S133:380              ; Define mesh grid (3x3)	
;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

; Drives
M569 P0 S0                               ; Drive 0 goes backwards
M569 P1 S1                               ; Drive 1 goes forwards           *************************      
M569 P2 S0                               ; Drive 2 goes backwards         
M569 P3 S1                               ; Drive 3 goes forwards
M350 X16 Y16 Z16 E16 I1                  ; Configure microstepping with interpolation
M92 X80 Y80 Z3200 E418.5                 ; Set steps per mm                                   ******************* 80 microsteps/mm XY and 3200 microsteps/mm Z for Concorde ************************
M566 X900 Y900 Z50 E120                  ; Set maximum instantaneous speed changes (mm/min)
M203 X6000 Y6000 Z300 E1200              ; Set maximum speeds (mm/min)                              ******************* mm/minute Z for Concorde ************************
M201 X800 Y800 Z50 E250                  ; Set accelerations (mm/s^2)                              ******************* Z acceleration 1/10 for Concorde ************************
M906 X1000 Y1000 Z2000 E1000 I30           ; Set motor currents (mA) and motor idle factor in per cent1010  ******************* 100omA Z for Concorde ************************
M84 S30                                  ; Set idle timeout

; Heaters
M305 P0 T100000 B3950 C7.060000e-8 R4700 ; Set thermistor + ADC parameters for heater 0
M143 H0 S150                             ; Set temperature limit for heater 0 to 150C
M305 P1 T100000 B4725 C7.060000e-8 R4700 ; Set thermistor + ADC parameters for heater 1
M143 H1 S350                             ; Set temperature limit for heater 1 to 300C

; Tools
M563 P0 D0 H1                            ; Define tool 0
G10 P0 X0 Y0 Z0                          ; Set tool 0 axis offsets
G10 P0 R0 S0                             ; Set initial tool 0 active and standby temperatures to 0C

; Network
M550 PGinaRep Concorde                   ; Set machine name
M552 S1                                  ; Enable network
M587 S"Ubiquity" P"********"           ; Configure access point. You can delete this line once connected
M586 P0 S1                               ; Enable HTTP
M586 P1 S0                               ; Disable FTP
M586 P2 S0                               ; Disable Telnet

; Fans
M106 P0 S0.3 I0 F500 H-1                 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
M106 P1 S1 I0 F500 H1 T45                ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
M106 P2 S1 I0 F500 H1 T45                ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

; Custom settings are not configured

 

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To be fair, I can barely feel the vibration from the Z drive on the X carriage when raising the bed at full speed.  Though maybe that's still too much compared with the light tap on the nozzle.

Edited by Gina
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To be fair, 5mm/s should be fast enough to trigger the piezo. I was managing on 4.3mm/s before upgrading from 2 to 3 motors. I can get 10mm/s if I really push it. I started using plum couplers between the motor and screw - made it quieter and also fewer binding issues due to marginal screw misalignment.

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Yes, they could help.  One of my rods wobbles a little bit but both sides seem to stall at higher speeds though not at the same time.  I could increase the motor current from 2A to 2.4A if I fan cool the Duet board but I think I'll order a couple of plum couplers - 6.35mm x 8mm for NEMA23s.

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Mini printer is working fine again but I decided to make sure by increasing the Z speed to 8mm/s when piezo probing.  Max Z speed on the Mini is 900mm/m - no speed limitation due to threaded rods - this printer uses cord.

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Back to Concorde, I increased the Z motor current to 2.2A and max Z speed to 330mm/m and the Z Homing worked - once.  Mesh Grid Compensation didn't.  So I think I'm getting close to getting this going.

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Increased maximum Z speed to 350mm/m and one Z motor skipped steps but the Z homing worked a couple of times.  MGC didn't because the bed was tilted too much.  So yes, it's close to working.

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FWIW Gina I have an iPhone app I very occasionally use called VibSensor which enables vibration and tip/tilt logging using the inbuilt accelerometers. It operates across a decent frequency range and does power spectrum analysis, automatic resonant frequency ID'ing etc. Sensitivity (with recent iPhone) is quite good and span with most smartphones will be 0-2G. By comparison of power spectrum before/after treatments such as the torsional damper, this might help you get to the bottom of any resonance issues with your Z motor mounting and coupling, as well as help you quantify bending stiffness of your printbed and the print carriage on its linear ways. If you decide to try this, I'd recommend fixing the accelerometers (smartphone) to the structure you are interested in using 3 bits of Blu-tac.

Those larger frame size steppers can be installation-sensitive. Other treatments I've used myself to try and tame resonant behaviour and loss of steps include clamping a heavy steel annulus around the motor body (round motors obviously) and mounting the motor flange using purpose-made hard elastomer motor mounts like these: https://www.ebay.co.uk/itm/Nema-23-Stepper-Motor-Damper-Pad-Anti-Vibration-CNC-3D-Printer-Mill-/151856260838

Tony Owens

PS: Credit where credit is due: The tip about coupling the accelerometers to the structure was from Es Reid in a different engineering context but it works well for this too!

Edited by tonyowens_uk
Afterthought
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The plum type flexible shaft couplers arrived today and I've fitted them but the difference if any is minor - still triggering the sensor.  No reduction in noise either.

Edited by Gina
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The noise seems to come from the motors so maybe I shall have to look at anti-vibration mounting.  I have some rubber grommets I can try.  OTOH if I can avoid dragging the printer out and turning it on its back...

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Been tackling the problem of getting piezo Z probing to work on the Concorde still without any joy.  It looks like either going back to inductive probe or adding the piezo between extruder and hotend.  The latter would mean a complete redesign of almost all the parts of the X carriage to accommodate it.  looks like this project is a failure.  I hate to give up on anything but there comes a time when all the time and effort involved is just not worth it.  So it's back to inductive probing ?

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The Mini printer has a piezo sensor that's working fine.  It's a bit different from the Concorde in that it uses a pancake motor with 0.9° step angle and the hotend is a V6 whereas the Concorde uses a Volcano hotend and standard NEMA17 1.8° step 40mm motor.  I thought of changing the extruder motor on the Concorde to a pancake type but the one on the Mini gets pretty hot so with higher throughput on the Concorde I doubt it could cope.

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I found the pancake motor supplied with the Titan to be underpowered. Once I replaced it with one of the motors from my old Prusa (1.8 deg, 42Ncm) I had no issues.

Piezo probing can be a bit hit and miss. I had good results with the Precision Piezo PP20 and Orion modules but they fit between extruder and hotend. When I switched to using the Titan Aero I needed a different solution. I now have a 27mm piezo mounted in a specially designed part between the Titan body and motor. This is specific to the D-Bot though but it might give you some ideas.

2124697846_2019-03-0610_43_02.thumb.jpg.e053d0db595b7cde5f0eb3f178eff48c.jpg

2035080256_2019-03-0610_44_46.thumb.jpg.962eb81f0129752cf2ea3bfdfa9d4ee1.jpg

1445649193_2019-03-0610_44_57.thumb.jpg.db2dd2aec83c98a979fdc68ccd59f877.jpg

Precision Piezo also have a Part on Thingiverse which might help.

 

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Thanks Dave, I wondered if I might do something like that.  Hadn't thought of using the bigger sort with a hole to go over the motor shaft but between extruder and motor seems a good place.  Certainly food for thought :thumbsup:

Yes, I've seen that part on Thingiverse.

Edited by Gina
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Hey, folks. If I understood correctly, the original goal was  to improve the printing accuracy? But, imho, the Z sensor is not for that, it's to eliminate the need to level the bed often as it gets randomly misaligned with use. It is indeed crucial for mass-production. However for the fine printing accuracy it's more beneficial to just take care of good manual bed leveling (including the orthogonality) each time and better yet always print on the raft. The original construction of commercially available printers could be custom tailored to the expected printing dynamics, i.e. adding weight or drag may easily lead to various strange issues without the firmware correction or/and mechanical re-calibration.

I'm playing with my 3d printer (Rigidbot) since 2014. Glad there are more and more astronomers in that hobby too around!

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