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Marlin Collision Sensing

Info

This feature requires the BD sensor firmware version (you can obtain it by sending M102 S-1, not the hardware version on the sensor) to be V1.1b, greater than V1.2b, or purchased after March 2024. Otherwise, you need to use external hardware tools (such as STlink) to flash the firmware into the BD sensor.

How It Works

  • Automatically performs Z-axis offset calibration during G28: It triggers when homing (after the nozzle contacts the bed)—then slowly moves upward until the nozzle just leaves the bed—and sets this position as the Z-axis zero point.

Benefits

  • 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 not the range of the bed mesh height map with the BD sensor. This means the bed mesh remains the same even at different temperatures.
Tip

The code for this feature is in the official Marlin GitHub pull request list: 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, which 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 }

Test Homing

  • Please 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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