z_thermal_adjust: Add Z thermal adjuster module (#4157)

Use a frame-coupled temperature probe to compensate for thermal
expansion in real-time.

Signed-off by: Robert Pazdzior <robertp@norbital.com>

docs/Config_Reference.md

@@ -1205,6 +1205,45 @@ the nature of skew correction these lengths are set via gcode. See
 [skew_correction]
 ```
 
+### [z_thermal_adjust]
+
+Temperature-dependant toolhead Z position adjustment. Compensate for vertical
+toolhead movement caused by thermal expansion of the printer's frame in
+real-time using a temperature sensor (typically coupled to a vertical section
+of frame).
+
+See also: [extended g-code commands](G-Codes.md#z_thermal_adjust).
+
+```
+[z_thermal_adjust]
+#temp_coeff:
+#   The temperature coefficient of expansion, in mm/degC. For example, a
+#   temp_coeff of 0.01 mm/degC will move the Z axis downwards by 0.01 mm for
+#   every degree Celsius that the temperature sensor increases. Defaults to
+#   0.0 mm/degC, which applies no adjustment.
+#smooth_time:
+#   Smoothing window applied to the temperature sensor, in seconds. Can reduce
+#   motor noise from excessive small corrections in response to sensor noise.
+#   The default is 2.0 seconds.
+#z_adjust_off_above:
+#   Disables adjustments above this Z height [mm]. The last computed correction
+#   will remain applied until the toolhead moves below the specified Z height
+#   again. The default is 99999999.0 mm (always on).
+#max_z_adjustment:
+#   Maximum absolute adjustment that can be applied to the Z axis [mm]. The
+#   default is 99999999.0 mm (unlimited).
+#sensor_type:
+#sensor_pin:
+#min_temp:
+#max_temp:
+#   Temperature sensor configuration.
+#   See the "extruder" section for the definition of the above
+#   parameters.
+#gcode_id:
+#   See the "heater_generic" section for the definition of this
+#   parameter.
+```
+
 ## Customized homing
 
 ### [safe_z_home]

docs/G-Codes.md

@@ -1281,6 +1281,24 @@ print.
 #### SDCARD_RESET_FILE
 `SDCARD_RESET_FILE`: Unload file and clear SD state.
 
+### [z_thermal_adjust]
+
+The following commands are available when the
+[z_thermal_adjust config section](Config_Reference.md#z_thermal_adjust)
+is enabled.
+
+#### SET_Z_THERMAL_ADJUST
+`SET_Z_THERMAL_ADJUST [ENABLE=<0:1>] [TEMP_COEFF=<value>] [REF_TEMP=<value>]`:
+Enable or disable the Z thermal adjustment with `ENABLE`. Disabling does not
+remove any adjustment already applied, but will freeze the current adjustment
+value - this prevents potentially unsafe downward Z movement. Re-enabling can
+potentially cause upward tool movement as the adjustment is updated and applied.
+`TEMP_COEFF` allows run-time tuning of the adjustment temperature coefficient
+(i.e. the `TEMP_COEFF` config parameter). `TEMP_COEFF` values are not saved to
+the config. `REF_TEMP` manually overrides the reference temperature typically
+set during homing (for use in e.g. non-standard homing routines) - will be reset
+automatically upon homing.
+
 ### [z_tilt]
 
 The following commands are available when the

docs/Status_Reference.md

@@ -484,6 +484,19 @@ object is always available):
 - `state_message`: A human readable string giving additional context
   on the current Klipper state.
 
+## z_thermal_adjust
+
+The following information is available in the `z_thermal_adjust` object (this
+object is available if [z_thermal_adjust](Config_Reference.md#z_thermal_adjust)
+is defined).
+- `enabled`: Returns True if adjustment is enabled.
+- `temperature`: Current (smoothed) temperature of the defined sensor. [degC]
+- `measured_min_temp`: Minimum measured temperature. [degC]
+- `measured_max_temp`: Maximum measured temperature. [degC]
+- `current_z_adjust`: Last computed Z adjustment [mm].
+- `z_adjust_ref_temperature`: Current reference temperature used for calculation
+  of Z `current_z_adjust` [degC].
+
 ## z_tilt
 
 The following information is available in the `z_tilt` object (this