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Marlin's Collision Sensing

Info

This feature requires a BD sensor firmware version (you can obtain this version by sending the M102 S-1 command, not the hardware version on the sensor)
of V1.1b, greater than V1.2b, or purchased after March 2024; otherwise, you need to flash the firmware into the BD sensor using an external hardware tool (such as STlink).

How It Works

  • Automatic Z-axis offset calibration when executing G28: it can be triggered during homing (after the nozzle contacts the platform) – then slowly move upward until the nozzle just leaves the platform – set this position as the Z-axis zero point.

Advantages

  • Automatic Z-axis offset calibration.
  • You can still manually adjust the Z-axis offset for different filaments.
  • Overcomes temperature drift.
  • Temperature drift changes the Z-axis offset, but it does not affect the range of the bed mesh height map with the BD sensor. This means that even with different temperatures, the bed mesh remains the same.
Tip

The code for this feature is in the pull request list of the official Marlin GitHub: https://github.com/MarlinFirmware/Marlin/pull/27243
So please use the following Marlin code: https://github.com/markniu/MarlinPULL/tree/bugfix-2.1.x

How to Use

Enable BD_SENSOR and add #define BD_SENSOR_CONTACT_PROBE in configuration.h
It should look like this:

#define BD_SENSOR
#if ENABLED(BD_SENSOR)
  #define BD_SENSOR_PROBE_NO_STOP // Probe bed without stopping at each probe point
  #define BD_SENSOR_CONTACT_PROBE // it uses nozzle collision sensing to probe while homing
#endif

  • Increase the probe speed in configuration.h.

  • Sensitivity depends on speed, so you need to adjust the Z-axis speed.

  • homing_speed and second_homing_speed should be in the range of 3 to 10, here is the Z-axis probe feed rate.

  • For example:

 #define Z_PROBE_FEEDRATE_FAST  (5*60)
 #define Z_PROBE_FEEDRATE_SLOW  (5*60)
  • Increase the Z-axis homing lift to greater than 4 mm in Configuration_adv.h.
#define HOMING_BUMP_MM      { 5, 5, 5 }

Testing Homing

  • Send the G28 Z command about 10 times, or use the M48 command, to check if it is stable.
Demo Video
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