Autocalibration probe radius and endstop signal duration
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Probing starts by moving the nozzle to the dive height (M558 H parameter) plus trigger height unless it is negative. Then there is a pause as specified by the M558 R parameter to allow the probe to settle. The nozzle is then moved down at the speed given by the M558 F parameter. The probe output is sampled every 1ms and a running average of the last 8 output values is maintained. For a digital-output probe, the output value is taken as 1000 when triggered and 0 when not triggered.
When average reaches or exceeds 90% of the threshold given in the G31 P parameter, the probing speed is reduced by two thirds. When it reaches or exceeds 100%, probing stops and a hit is recorded.
If the probe is already triggered at the start of a probing move when the pause ends, this counts as a failure. If the probe has not been triggered after moving the probe down by twice the dive height, that also counts as a failure.
HTH David
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Awesome, thanks. Sounds like I can increase dive speed with M558 F, and inscrease the pause with M558 R. That should allow me to figure out what is going on.
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This seems to work better now, with increased dive speed and a 1 second delay between probe attempts.
However, at the very beginning, the nozzle comes straight down to the center of the plate (which is not the first point specified), hits the plate, and grinds across it towards the edge. The hit sensors are triggering during this time (between 30 and 35 times as the nozzle scrapes/skips across the plate), but the nozzle essentially never leaves the plate (it might come up slightly – hard to see and hard to tell what is vibration versus planned movement -- but certainly doesn't come up to my setting of H20 between strikes). Only after that does it seem like the "real" autocalibration begins (but by this time I don't think it actually knows where the nozzle is -- perhaps grinding it into the plate causes the motors to skip steps).
Any idea what this first odd phase is?
====== bed.g ======
; Auto calibration routine for delta printers
; Before running this, you should have set up your zprobe Z offset to suit your build, in the G31 command in config.g.M561 ; clear any bed transform, otherwise homing may be at the wrong height
G31 X0 Y0 P100 ; don't want any probe offset for this, P is probe activation threshold, should not matter for digital, which should always count as 1000 when "on" but this lowering because web control panel does not always show 1000
G28 ; home the printer; Reduce the motor current for bed leveling in case the tip crashes into the bed
; Normally current is 1000, presumably will revert to main config.g value when done
M906 X600 Y600 Z600 I60 ; Set motor currents (mA, 1000 is default), Idle = I60 is default; Change the default M558 dive height (H, mm), dive speed (F, mm/min),
; pause between probes (R in secs, default 0), and T, travel speed between points (mm/min)
M558 H20 F1200 R1 T1200; Probe the bed
; Changed from original, just using a square for testing
; To generate circular parameters see http://escher3d.com/pages/wizards/wizardbed.php
; setting H to small negative value since in theory a piezo needs to move to signal
G30 P0 X-50 Y-50 H-0.2 Z-9999 ; upper left
G30 P1 X0 Y-50 H-0.2 Z-9999 ; upper middle
G30 P2 X50 Y-50 H-0.2 Z-9999 ; upper right
G30 P3 X-50 Y0 H-0.2 Z-9999 ; middle left
G30 P4 X0 Y0 H-0.2 Z-9999 ; middle middle
G30 P5 X50 Y0 H-0.2 Z-9999 ; middle right
G30 P6 X-50 Y50 H-0.2 Z-9999 ; bottom left
G30 P7 X0 Y50 H-0.2 Z-9999 ; bottom middle
G30 P8 X50 Y50 H-0.2 Z-9999 ; bottom right; Note S7 includes diagonal rod length but requires oversize bed. See:
; https://duet3d.com/wiki/Configuring_RepRapFirmware_for_a_Delta_printer
G30 P9 X0 Y0 Z-99999 S6 ; center, and auto-calibrate 6 factorsG1 X0 Y0 Z150 F15000 ; get the head out of the way of the bed
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It sounds to me that some of the M665 or M666 parameters in config.g are a very long way off the correct value. It's probably the M665 H parameter. With the carriages up against the endstops, measure how high the nozzle tip is from the bed, and compare that with what you have H set to.
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M665 H is within a millimeter of exact. I think I have M92 set incorrectly so that it is not moving the distance it thinks. Using 0.9 degree motors = 400 steps per revolution x 16X microstepping / 36mm per revolution (for 18 teeth) = 177.78 steps/rev, meaning that M92 should be:
M92 X177.78 Y177.78 Z177.78
Is that correct? I assume you have to account for microstepping per the sample calculations I see, although it seems like it would be simpler to always enter M92 by whole step and allow microstepping to be calculated from that.
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That fixed it– I had use the wrong number of teeth in my calculation for M92. Uggghhh.
Anyway, this is what I get now:
"Calibrated 6 factors using 10 points, deviation before 7.591 after 1.077"
Running again, I got:
"Calibrated 6 factors using 10 points, deviation before 2.104 after 0.941"
Is that flat enough? If that's mm, seems like it might be too much error.
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16 tooth pulleys with GT2 belts and 0.9deg motors works out as 200 steps/mm, so your figure of 177.78 looks about right for 18 tooth.
I agree, it would be more logical to enter mm per whole step or vice versa, but 3D printing has used microsteps/mm for too long to change it now. At least RRF adjusts the steps/mm automatically when you change microstepping.
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How high a deviation after calibration is acceptable? Can you also then use bed mapping (I assume that autocalibration figures out the geometry, while bed mapping assumes the geometry is correct and corrects for bed deviations)?
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High deviation errors are caused by geometrical errors in your build, which will cause print distortions. So the deviation you can accept depends on how accurate you need your prints to be. I used to have around 100um deviation, but after the rebuild it is down to 20um.
You can use mesh bed compensation after auto calibration.
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20um?!? Sh*t. Well, I just ordered a larger caliper and a digital protractor. I'm guessing that play in the rod ends is important too at this level. I need to change those. Hopefully in a few days I'll get the error down. Thanks!
