docs: Add a new Eddy_Probe.md document

Signed-off-by: Kevin O'Connor <[email protected]>

docs/Eddy_Probe.md

@@ -0,0 +1,56 @@
+# Eddy Current Inductive probe
+
+This document describes how to use an
+[eddy current](https://en.wikipedia.org/wiki/Eddy_current) inductive
+probe in Klipper.
+
+Currently, an eddy current probe can not be used for Z homing. The
+sensor can only be used for Z probing.
+
+Start by declaring an [eddy_current config
+section](Config_Reference.md#eddy_current) in the printer.cfg file. It
+is recommended to set the `z_offset` to 0.5mm. It is typical for the
+sensor to require an `x_offset` and `y_offset`. If these values are
+not known, one should estimate the values during initial calibration.
+
+The first step in calibration is to determine the appropriate
+DRIVE_CURRENT for the sensor. Home the printer and navigate the
+toolhead so that the sensor is near the center of the bed and is about
+20mm above the bed. Then issue an `LDC_CALIBRATE_DRIVE_CURRENT
+CHIP=<config_name>` command. For example, if the config section was
+named `[eddy_current my_eddy_probe]` then one would run
+`LDC_CALIBRATE_DRIVE_CURRENT CHIP=my_eddy_probe`. This command should
+complete in a few seconds.  After it completes, issue a `SAVE_CONFIG`
+command to save the results to the printer.cfg and restart.
+
+The second step in calibration is to correlate the sensor readings to
+the corresponding Z heights. Home the printer and navigate the
+toolhead so that the nozzle is near the center of the bed. Then run an
+`EDDY_PROBE_CALIBRATE CHIP=my_eddy_probe` command. Once the tool
+starts, follow the steps described at ["the paper
+test"](Bed_Level.md#the-paper-test) to determine the actual distance
+between the nozzle and bed at the given location. Once those steps are
+complete one can `ACCEPT` the position. The tool will then move the
+the toolhead so that the sensor is above the point where the nozzle
+used to be and run a series of movements to correlate the sensor to Z
+positions. This will take a couple of minutes. After the tool
+completes, issue a `SAVE_CONFIG` command to save the results to the
+printer.cfg and restart.
+
+After initial calibration it is a good idea to verify that the
+`x_offset` and `y_offset` are accurate. Follow the steps to [calibrate
+probe x and y
+offsets](Probe_Calibrate.md#calibrating-probe-x-and-y-offsets). If
+either the `x_offset` or `y_offset` is modified then be sure to run
+the `EDDY_PROBE_CALIBRATE` command (as described above) after making
+the change.
+
+Once calibration is complete, one may use all the standard Klipper
+tools that use a Z probe.
+
+Note that eddy current sensors (and inductive probes in general) are
+susceptible to "thermal drift". That is, changes in temperature can
+result in changes in reported Z height. Changes in either the bed
+surface temperature or sensor hardware temperature can skew the
+results. It is important that calibration and probing is only done
+when the printer is at a stable temperature.

docs/Overview.md

@@ -99,3 +99,4 @@ communication with the Klipper developers.
     troubleshooting CAN bus.
 - [TSL1401CL filament width sensor](TSL1401CL_Filament_Width_Sensor.md)
 - [Hall filament width sensor](Hall_Filament_Width_Sensor.md)
+- [Eddy Current Inductive probe](Eddy_Probe.md)

docs/_klipper3d/mkdocs.yml

@@ -138,4 +138,5 @@ nav:
     - CANBUS_Troubleshooting.md
     - TSL1401CL_Filament_Width_Sensor.md
     - Hall_Filament_Width_Sensor.md
+    - Eddy_Probe.md
   - Sponsors.md