Statistically-based Bed Compensation and Calibration
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Hello,
Had an interesting experience with the Smart Effector the other day. I ran bed calibration and got something like this:
(Shamelessly stolen from TLeTorneau in another thread)
[https://forum.duet3d.com/assets/uploads/files/1542436419111-bed_level_001_mesh_11172018.pngWhat's interesting is that this shows some real mechanical drift of the sensor over time. I had the same problem on the Smart Effector. I doubt that this is an artifact of the print bed, especially since when I changed directions, the lines appeared in the other direction.
I think an ideal bed probe system would be to implement the following:
- Randomly determine the probe point order.
- This would help eliminate sensor drift from the final results.
- Alternatively, you could probe in reverse directions (although randomly would be better)
- Perform 3+ measurements at the same point (at random points in time)
- This gives you mean standard error reduction
- Implement a localized flatness smoothing
- Sharp bumps are more likely to be errors than real changes.
- False sharp bumps can produce problems / deformations in the final print
Bottom line is that with the statistical methods mentioned above, I think it's possible to achieve a 3X decrease in calibration sensor error. For mechanically based sensors, this could be a real boon and help achieve the accuracy needed for printing.
- Randomly determine the probe point order.
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Have you checked out the A and S parameters of set probe type?
https://duet3d.dozuki.com/Wiki/Gcode#Section_M558_Set_Z_probe_type
On the upside for the current method testing in a specific order does give you a fighting chance of driving out sources of error. Randomising the order could potentially hide these patterns giving the false impression of it just being a noisy measurement?
