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3.9.3 Firmware for MK3, MK3S, MK3S+, MK2.5 and MK2.5S
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@DRracer DRracer released this 07 Jan 12:24
· 57 commits to MK3_3.9.3 since this release
v3.9.3
603d704

Summary

  • Redesigned XYZ calibration

This is the final release of the firmware 3.9.3 introducing redesigned XYZ calibration. There are no changes compared to the previous release 3.9.3-RC1.

Redesigned XYZ calibration

Starting with the release of the Original Prusa i3 MK3S+ printer there is a new induction sensor called SuperPINDA, which is temperature-independent, features a much higher quality sensor and better quality components overall, plus, it does not need a thermistor. This sensor is a successor to the P.I.N.D.A. v2 (with thermistor) and is compatible with the following printers:

  • Original Prusa i3 MK3/MK3S/MK3S+
  • Original Prusa i3 MK2.5/MK2.5S

In order to use the full potential of both sensors, this firmware brings a significantly redesigned XYZ calibration. Previously, the data during the calibration were measured in one direction and approximated. Now, for both P.I.N.D.A. v2 and SuperPINDA the new algorithm measures 1024 points (32x32 bitmap) on the heatbed for each calibration point and utilizes z-hop on the Z-axis (multiple distances from the surface). The reason for multiple measurements is to mitigate the effect of the hysteresis* of the sensor. A similar method is used in the Mesh Bed Levelling (MBL).

*Every measurement sensor has its own hysteresis, which can be explained as a memory effect from the previous measurement. If you measure the first point, some of the energy remains in the sensor and affects the value in the second measured point. This effect has to be eliminated to provide accurate data.

Calibration_point_FW393

Calibration point on the heatbed "as seen" by the printer

From the measured data, the printer now performs a subpixel processing of the scanned 32x32 bitmap and detects very precisely the center of each calibration point. More precise data of the printer's overall geometry (e.q. axis skew) helps the printer to apply appropriate adjustments resulting in a better print accuracy. Note that this new XYZ calibration requires more time (around 20-25 minutes) to scan and evaluate all the calibration points.

This new method also replaces the last step of the older process, where the exact center of each calibration point was iteratively searched using a cross-search technique. The previous “whole-pixel” search was providing an accuracy of about 0.6 mm. Now, it is less than 0.1 mm thanks to the sub-pixel analysis.

Performing this new XYZ calibration on a calibrated printer is not necessary unless you are experiencing issues with your prints. Note that 3D printers from the MK3 family recognize this new sensor automatically. However, in the case of MK2.5/MK2.5S, the user needs to toggle a switch in the settings menu (LCD Menu -> Settings -> HW settings -> SuperPINDA -> ON/OFF) to inform the printer that the SuperPINDA sensor is present as the printer cannot recognize it automatically.

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