Duet 0.8.5 - "Z-Probe Problem"

Hi,

I am Duet 0.8.5 user and I use it in cartesian 3d printer type. I modified g-codes for Z-Probe with Capacitive Proximity Sensor (LJC18A3-B-Z/BX).

However, sometimes nozzle is so close glass bed, sometimes about 5mm above although bed is same position. This difference btw bed and nozzle changes. Where do I make mistake? G-Codes are below:

bed.g

M561
G1 Z10 F200

G1 X0 Y100 F2000
G30 P0 Z-100000

G1 X160 Y160 F2000
G30 P1 Z-100000

G1 X160 Y0 F2000
G30 P2 S Z-100000


G1 X0 Y0 F2000

G4 P1500 ; Leave the probe there to give the web interface time to report the plane points
G1 Z10 F200

config.g

; Configuration file for RepRap Mendel 3
; RepRapPro Ltd
;
; Copy this file to config.g if you have a Mendel 3
; If you are updating a config.g that you already have you
; may wish to go through it and this file checking what you
; want to keep from your old file.
; 
; For G-code definitions, see [reprap.org]
; 
M111 S0                             ; Debug off
M550 xxx           ; Machine name (can be anything you like). With DHCP enabled connect to (example) [reprappromendel3] (machine name with no spaces).
M551 Preprap                        ; Machine password (currently not used)
M540 P0xBE:0xEF:0xDE:0xAD:0xFE:0x14 ; MAC Address
;M552 P0.0.0.0                       ; Un-comment for DHCP
M552 P192.168.1.21                  ; IP address, comment for DHCP
M553 P255.255.255.0                 ; Netmask
M554 P192.168.1.1                   ; Gateway, comment for DHCP
M555 P2                             ; Set output to look like Marlin
G21                                 ; Work in millimetres
G90                                 ; Send absolute corrdinates...
M83                                 ; ...but relative extruder moves
M906 X1400 Y1400 Z1400 E800           ; Set motor currents (mA)
M305 P0 R4700                       ; Set the heated bed thermistor series resistor to 4K7


M305 P1 R4700                       ; Set the hot end thermistor series resistor to 4K7
M305 P2 R4700

M569 P0 S0                          ; no Reverse the X motor

M569 P2 S0

M569 P3 S1                          ; Reverse the extruder motor (T0)
M569 P4 S0                          ; Reverse the extruder motor (T1)
M569 P5 S0                          ; Reverse the extruder motor (T2)

M92 X161 Y160 Z1280
M574 X2 S1
M574 Y2 S1
M574 Z2 S1


M92 E110                            ; Set extruder steps per mm
M558 P1 X0 Y0 Z1   H5 F100                        ; 
G31 X3 Y-48 Z3.32 P600                       ; Set the probe height and threshold (deliberately too high to avoid bed crashes on initial setup)
M556 S75 X0 Y0 Z0                   ; Put your axis compensation here
M201 X350 Y350 Z20 E500           ; Accelerations (mm/s^2) 
M203 X8000 Y8000 Z250 E3600       ; Maximum speeds (mm/min)
M566 X200 Y200 Z30 E20              ; Minimum speeds mm/minute    

M563 P0 D0 H1                       ; Define tool 0
;G10 P0 S-273 R-273                  ; Set tool 0 operating and standby temperatures
M563 P1 D1 H2                       ; Define tool 1, uncomment if you have a dual colour upgrade
;G10 P1 S-273 R-273                  ; Set tool 1 operating and standby temperatures, uncomment if you have a dual colour upgrade
M563 P2 D2 H3                       ; Define tool 2, uncomment if you have a tri colour upgrade
;G10 P2 S-273 R-273                  ; Set tool 2 operating and standby temperatures, uncomment if you have a dual colour upgrade
M563 P3 D3 H4

Edited 1 time(s). Last edit at 01/21/2016 10:29AM by usen.

There may be nothing wrong with your configuration. Capacitive sensors are very susceptible to atmospheric moisture and temperature. They are not a good choice for 3D printers, especially when used with non-conducting bed surfaces such a glass. Cheap capacitive sensors are designed for detecting that something is close, not for precise height detection.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Which sensor do you suggest?

I am biased because I make and sell a differential infrared sensor - the one used by T3P3 in their Kossel kits and by E3D in their BigBox kit. But here is my take anyway. There is no perfect height sensor for 3D printers. Different sensors have their own advantages and disadvantages. Here is a summary:

Plain IR (e.g. original RepRapPro sensor used on the Ormerod 1: avoid. Too sensitive to ambient IR, also very sensitive to reflectivity of the bed.

Modulated IR (e.g. RepRapPro Ormerod 1/Mendl/Huxley sensor): less sensitive to ambient IR than a plain IR sensor (by a factor of 15 in my tests), but still very sensitive to bed surface. Only suitable for use with special targets on the bed, or on a special bed surface (the white version of BuildTak might work well, but I haven't tried it).

Differential modulated IR (the one I make): completely insensitive to ambient IR unless the IR is so strong as to saturate the sensor (e.g. if bright sunlight reflects off a highly-reflective bed surface directly into the photo receptor). Works on most opaque bed surfaces, except for bright aluminium which reflects too strongly. When used with transparent bed surfaces (e.g. glass or PEI), a black or dull backing should be used so that the reflection from the top surface is not swamped by a brighter reflection from the surface below the transparent material. Trigger height is slightly affected by the bed surface material, but much less than for other types of IR sensor.

Inductive: has very short range when used with a non-ferrous target. OK if you print directly on aluminium, but no good if you use glass on top of aluminium. Would probably be OK with thin PEI sheet on top of aluminium. Larger and heavier than infrared sensors.

Force sensitive resistor(s), either mounted in the print head support, or under the bed supports of a delta printer, using the nozzle itself as the probe: main advantage is that the trigger height is not affected by varying tilt of the print head as it translates in the XY plane (delta printers commonly suffer from this). If you probe cold then the trigger height may be affected by filament stick to the tip of the nozzle; but if you probe hot then this is bad for some bed materials such as BuildTak and PEI.

Microswitch - the probe itself is simple and the switch may give reproducible results, but it needs a deployment mechanism, which may be heavy and/or cumbersome and may affect reproducibility.

Capacitive - sensitive to temperature and humidity. Probably OK with a plain aluminium bed, but inductive is probably better for that application.

Ultrasonic - I used to sell an ultrasonic height sensor. It worked quite well with the bed cold, but when the bed was heated, the convection currents disturbed the reading.

More details of my IR sensor are at [escher3d.com].

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Some additional words:

The differences between the plain IR and the modulated IR may be present, but I cannot confirm this. The plain IR is light dependent, but this is most a problem with direct sunlight. The bigger problem in my eyes is the surface dependency. Here I can add that even the bed level can affect the sensor readings. If the alignment of the bed is really wrong you get totally wrong readings. The sensors only work properly when the bed is nearly leveled.

Inductive sensor: Failed in my pre-test. I have a standard one with a nominal distance of 4mm. It is triggered by my Aluminium bed at a distance of less than 1mm. That is too close for proper bed leveling.

A microswitch gives indeed reproducible results as I use this method with my Ormerod 2 at the moment, but it is heavily dependent from the mechanical solution. For example the tilt method failed (nozzle hits bed and tilts towards the X-arm), because at high X-values the bed was pushed down first as there is no direct support. I will test this method with my Ormerod 1 as it could have a more stable bed support. You probably will have the same disadvantages like the FSR method. I cannot use BuildTak with my Ormerod 2.

However my own printer design probably will use a rebuild of dc42's Mini sensor board. The price is more than okay for the sensor. My own design will probably use a BuildTak surface so I need a contactless probing.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

I change my board. I test Mega 2560 and Ramps 1.4 and I measure capacitive from multimeter:

Input: 11.64 Volt
Signal: 3.80 Volt
Sensor Output: 9.72 Volt

Is there any problem?



Edited 2 time(s). Last edit at 01/27/2016 02:23PM by usen.

Deleted bad reply

Edited 1 time(s). Last edit at 01/27/2016 03:40PM by dc42.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Capacitive sensors with PNP outputs like yours produce output voltages too high to suit the 3.3V inputs of the Duet or the 5V inputs of Arduino/RAMPS. So you need to connect two resistors.configured as a potential divider to drop the output voltage to a safe level. There are many posts on other forums about this. If you connected the output directly to a Duet or a RAMPS, you may have damaged that electronics board.

I may be biased because I sell an infrared height sensor board, but I can't recommend cheap capacitive sensors because their trigger heights are too sensitive to temperature, humidity and supply voltage.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I watched this video: [www.youtube.com] and I use 15k and 10k resistors like below:

What's the max output voltage from your sensor? With the resistor values you show, the input to the Duet will reach 3.3V when the sensor output is at 8.25V. If the sensor output voltage gets higher than that, you risk blowing the Duet CPU. I would assume that the output of the sensor could be almost as high as its supply voltage, which erring on the side of caution I would take to be 14V. To divide this down to a max of 3.3V you should replace your 15K resistor with 33K

I would also fit a 3V zener diode across the 10K resistor (anode to ground) - it really is not worth risking the CPU.

Dave

When it is not triggered;

11,82V (Sensor Output) and 0,62V (Signal Output from Sensor)
11,84V (Sensor Output Reach to Ramps 1.4) and 0,92V (Signal Reach to Ramps 1.4)

When it is triggered;

9,31V (Sensor Output) and 2,66V (Signal Output from Sensor)
11,97V (Sensor Output Reach to Ramps 1.4) and 3,81V (Signal Reach to Ramps 1.4)