Nozzle Offset Calibration Tool

The purpose of this tool is to reduce the time needed to calibrate Nozzle offset for 3D printers that have multiple extruders and/or tool changing capabilities, by using a modified webcam as inspection microscope.

It utilizes OctoPrint to communicate with the printer and camera.

Current State

I consider the tool be in a serious alpha state, not ready for the masses, contributions (documentation, bug reports, patches) are welcome. I released the code mostly as a “technology demonstration”, and I’m happy to support anyone who wants to take this idea and integrate it into eg. OctoPrint as a plugin (I tried but failed, too steep of a learning curve for me :)) MIT License was specifically chosen to have as little as possible legal hurdles with taking code/ideas out of this project.

How it works

An upwards facing camera/microscope, mounted to the bed of the printer is used to get an high magnification (~5µm/pixel) image of a nozzle and moved to the center of the image using the XY carriage of the printer, thus the XY offset between all nozzles/tools can be determined from the carriage position. Z offset is determined by maximizing the contrast between two rings.

This video shows the whole process in detail.

Further details about how it evolved and how the camera is built can be found here:

https://hackaday.io/project/26053-tool-switching-multi-extrusion/log/67725-update-cameras-and-calibration-tool

https://hackaday.io/project/26053-tool-switching-multi-extrusion/log/66799-wip-offset-calibration-tool

https://hackaday.io/project/26053-tool-switching-multi-extrusion/log/66200-wip-offset-calibration-camera

https://hackaday.io/project/26053-tool-switching-multi-extrusion/log/64076-nozzle-offset-calibration

Setup

The very basic setup step (OctoPrint host/port/api-key) should be self explaining.

Setting up the tool changer is a bit more tricky, and might involve some knowledge of python. In short, parameters is evaluated using eval and must return a dictionary, which is than used to format Tool load and Tool unload gCode sequences. As OctoPrint provides no way to determine the printer position. Load end position and Unload end position need to be given instead.

If this sounds complicated, it is, but on the other hand imposes gives a lot of freedom to calculate/specify the commands needed to load/unload tools.

Example:

parameters:

{
  'x_enter': 157 + tool * 60,
  'x': 150 + tool * 60,
  'x_leave': 143 + tool * 60,
  'y_safe': 250,
  'y_fast': 288,
  'y': 290,
  'fast': 15000,
  'slow': 1000
}

Note: tool is a variable and indicates the number of the tool to be loaded/unloaded

unloadCmds:

G0 X{x} Y{y_safe} F{fast}
G0 Y{y}
G0 X{x_leave} F{slow}
G0 Y{y_safe} F{fast}

unloadEndPos:

(x, y_safe, Z)

Note: this is a python tuple, the values need to match the position after the previous gCode is executed. X, Y and Z are injected variables, refer to the printer position from before. In the given example unload doesn't move the printer in Z.

loadCmds:

G0 X{x} Y{y_safe} F{fast}
G0 Y{y}
G0 X{x_leave} F{slow}
G0 Y{y_safe} F{fast}

loadEndPos:

(x_leave, y_safe, Z)

Dependencies

The tool is written in Python and requires the following dependencies

sudo pip3 install opencv-python-headless
sudo apt-get install python3-pyqt4
sudo apt-get install python3-yaml
sudo apt-get install python3-matplotlib

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.