Tuning of Sensorless Homing

BenNorton01

Hi All

I am trying to set up the sensor-less homing on my Duet 2/Duex5 controlled printer and am so far have had some issues in that the bed drives into the ends of the Z-Axis assemblies and skips steps but does not sense them.

I am wanting to use the sensor-less homing to do a 'gross' homing of the ball-screw driven Z-Axis actuators which are prone to falling under the weight of the bed when the motors are idled which leaves the bed on a bad angle. This does not cause any damage as the bed is mounted with ball and socket joints. After this gross homing is completed, the printer will then use the BL-Touch probe and the independently driven Z-Axis actuators to to the more accurate bed levelling (G32).

I have setup a testing macro that is essentially a modified 'homeall' sequence. The G32 would be added in later.

G91                                  ; relative positioning
G1 Z10 F6000 S2                      ; lift Z relative to current position
G1 S1 X480 Y475 F9000                ; move quickly to X and Y axis endstops and stop there (first pass)
G1 X-5 Y-5 F6000                     ; go back a few mm
G1 S1 X480 Y475 F360                 ; move slowly to X and Y axis endstops once more (second pass)
M400                                                   ; make sure everything has stopped before we make changes
M915 P2:5:6 S-30 F0 H250 R0                            ; Configure Z-Axis Stall Detection
M584 X0 Y1:7 Z2 U5 V6 E3 P5                            ; Separate Z-Axis Lead screws and drive independently
M913 Z50 U50 V50                                       ; Lower motor current by 50%
M574 Z1 U1 V1 S3                                       ; Configure Z-Axis stall detection homing
G91                                                    ; relative positioning
G1 S1 Z-650 U-650 V-650 F500                           ; Home Z-Axis actuators independently
M400                                                   ; make sure everything has stopped before we make changes
M913 Z100 U100 V100                                    ; Reset motor current
M584 X0 Y1:7 Z2:5:6 U5 V6 E3 P3                        ; Reset drive mapping
M574 Z1 S2                                             ; Reset Z-Axis to be controlled by probe
G90                                  ; absolute positioning
G1 Z10 F6000 S2                      ; lift Z relative to current position
G1 X220 Y197.5 F9000                 ; go to first bed probe point
M558 F400                            ; adjust first probe speed
G30                                  ; home Z by probing the bed
M558 F120                            ; reset probe speed
G30                                  ; home Z by probing the bed

My config configures the rest of the U and the V axes:

; Drives
M569 P0 S0                                           ; X drive goes backwards
M569 P1 S0                                           ; Y1 drive goes backwards
M569 P2 S0                                           ; Z1 drive goes backwards
M569 P3 S1                                           ; E0 drive goes forwards
M569 P5 S0                                           ; Z2 drive goes backwards
M569 P6 S0                                           ; Z3 drive goes backwards
M569 P7 S1                                           ; Y2 drive goes forwards

M584 X0 Y1:7 Z2:5:6 U5 V6 E3 P3                      ; Apply custom drive mapping, U is a dummy Axis and P3 is setting the number of visible axes
M671 X222:-10:520 Y581:25:25 S10.0                   ; leadscrews at rear middle, front left and rear right

M350 X16 Y16 Z16 U16 V16 E16 I1                                 ; Configure microstepping with interpolation
M92 X160 Y80 Z320.00 U320.00 V320.00 E946.00                    ; Set steps per mm
M566 X900.00 Y900.00 Z12.00 U12.00 V12.00 E120.00               ; Set maximum instantaneous speed changes (mm/min)
M203 X10000.00 Y10000.00 Z400.00 U400.00 V400.00 E1200.00       ; Set maximum speeds (mm/min)
M201 X1000.00 Y1000.00 Z20.00 U20.00 V20.00 E250.00             ; Set accelerations (mm/s^2)
M906 X1000.00 Y1500.00 Z1500.00 U1500.00 V1500.00 E1200.00 I100 ; Set motor currents (mA) and motor idle factor in per cent

M84 S0                                                          ; Set idle timeout (0 is disable a time out, always on ) 

; Axis Limits
M208 X0 Y0 Z-0.5 U-0.5 U-0.5 S1                      ; Set axis minima
M208 X470 Y465 Z650 U650 V650 S0                     ; Set axis maxima

; Endstops
M574 X2 Y2 S1                                        ; Set active high endstops

; Z-Probe
M574 Z1 S2                                           ; Set endstops controlled by probe
M307 H3 A-1 C-1 D-1                                  ; Disable heater on PWM channel for BLTouch
M558 P9 H5 F120 T9000 X0 Y0 Z1                       ; Set Z probe type to bltouch and the dive height + speeds
G31 P500 X25.4 Y0.2 Z0.847                           ; Set Z probe trigger value, offset and trigger height
M557 X25.4:435 Y10.2:440 P5                          ; Define mesh grid

Any help would be greatly appreciated

BenNorton01

Is anyone able to weigh in on this issue?

Phaedrux

What is the lead of your ball screws?

Stall detection on the Z axis is difficult even under ideal circumstances.

There needs to be enough back EMF to trigger the stall so the dive speed needs to be frighteningly high.

You may have better luck with RRF3 as it has an additional multi motor stall option.

https://duet3d.dozuki.com/Wiki/Gcode#Section_M574_RepRapFirmware_Num_3

Try lowering the motor current even further than 50%. Lower is as low as you can go and still get reliable movement.

Increase the dive speed from 500mm/min you have now.

And play with the sensitivity.

zapta

@BenNorton01 said in Tuning of Sensorless Homing:

After this gross homing is completed, the printer will then use the BL-Touch probe

Since you have BLTouch, have you considered using it for Z homing?

You can still do dual speed homing since the BLTouch extends and is thus triggered before the bed hits the nozzle.

pro3d

Hi Ben. This is an old post, but did you solve your homing? I try to do the same as you did