probe_eddy_current: Support new tap_z_offset config parameter

Theoretically a "tap" probe should detect the exact point that the
nozzle contacts the bed.  In practice, however, there can be a
systemic bias that one may wish to account for.  This bias may be due
to backlash, thermal expansion, a detection bias, or similar issues.

Add a new tap_z_offset config parameter to allow users to specify an
offset.

Also, update the Z_OFFSET_APPLY_PROBE command to support modifying
this value.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Config_Reference.md

@@ -2348,6 +2348,12 @@ sensor_type: ldc1612
 #   the bed. If this value is specified then one may override its
 #   value at run-time using the "TAP_THRESHOLD" parameter on probe
 #   commands. The default is to not enable support for "tap" probing.
+#tap_z_offset: 0.0
+#   The Z height (in mm) of the nozzle relative to the bed at the
+#   contact point detected during "tap" probing. Nominally this would
+#   be 0.0 to indicate the contact point has zero distance, but one
+#   may set this to account for backlash, thermal expansion, a
+#   systemic probing bias, or similar. The default is zero.
 ```
 
 ### [axis_twist_compensation]

docs/G-Codes.md

@@ -1251,6 +1251,14 @@ additional parameters if a `[probe_eddy_current]` section is defined:
   specified in the `[probe_eddy_current]` config section when probing
   using `METHOD=tap`.
 
+The `Z_OFFSET_APPLY_PROBE` command is also extended to support a
+`METHOD=tap` parameter. When no METHOD parameter is provided, the
+`Z_OFFSET_APPLY_PROBE` command alters the probe calibration to apply
+the current Z G-Code offset to future `scan`, `rapid_scan`, and
+default probes. If `METHOD=tap` is specified then the command instead
+applies the change to `tap_z_offset` so that future `tap` probes are
+updated to use the current Z G-Code offset.
+
 #### PROBE_EDDY_CURRENT_CALIBRATE
 `PROBE_EDDY_CURRENT_CALIBRATE CHIP=<config_name>`: This starts a tool
 that calibrates the sensor resonance frequencies to corresponding Z

klippy/extras/probe_eddy_current.py

@@ -260,6 +260,19 @@ class EddyCalibration:
         cal_contents.pop()
         configfile = self.printer.lookup_object('configfile')
         configfile.set(self.name, 'calibrate', ''.join(cal_contents))
+    def _save_tap_z_offset(self, gcmd, homing_z):
+        eventtime = self.printer.get_reactor().monotonic()
+        configfile = self.printer.lookup_object('configfile')
+        cstatus = configfile.get_status(eventtime)
+        csettings = cstatus.get('settings', {}).get(self.name, {})
+        tap_z_offset = csettings.get('tap_z_offset', 0.)
+        new_calibrate = tap_z_offset - homing_z
+        gcmd.respond_info(
+            "%s: tap_z_offset: %.3f\n"
+            "The SAVE_CONFIG command will update the printer config file\n"
+            "with the above and restart the printer."
+            % (self.name, new_calibrate))
+        configfile.set(self.name, 'tap_z_offset', "%.3f" % (new_calibrate,))
     cmd_EDDY_CALIBRATE_help = "Calibrate eddy current probe"
     def cmd_EDDY_CALIBRATE(self, gcmd):
         self.probe_speed = gcmd.get_float("PROBE_SPEED", 5., above=0.)
@@ -273,6 +286,9 @@ class EddyCalibration:
         if offset == 0:
             gcmd.respond_info("Nothing to do: Z Offset is 0")
             return
+        if gcmd.get("METHOD", "").lower() == "tap":
+            self._save_tap_z_offset(gcmd, offset)
+            return
         cal_zpos = [z - offset for z in self.cal_zpos]
         z_freq_pairs = zip(cal_zpos, self.cal_freqs)
         z_freq_pairs = sorted(z_freq_pairs)
@@ -488,6 +504,7 @@ class EddyTap:
         self._z_min_position = probe.lookup_minimum_z(config)
         self._gather = None
         self._filter_design = None
+        self._tap_z_offset = config.getfloat('tap_z_offset', 0.)
         self._tap_threshold = config.getfloat('tap_threshold', 0., above=0.)
         if self._tap_threshold:
             self._setup_tap()
@@ -572,7 +589,8 @@ class EddyTap:
         self._validate_samples_time(measures, start_time, end_time)
         pos_time = self._pull_tap_time(measures)
         trig_pos = self._lookup_toolhead_pos(pos_time)
-        return manual_probe.create_probe_result(trig_pos)
+        return manual_probe.create_probe_result(trig_pos,
+                                                (0., 0., self._tap_z_offset))
     # Probe session interface
     def start_probe_session(self, gcmd):
         self._prep_trigger_analog_tap(gcmd)