probe: Added truncated mean averaging capability

Added a new 'samples_trunc_count' configuration attribute to the
'[probe]' section that will cause the 'samples_trunc_count' number of
highest and lowest samples to be removed and then the average of the
remaining samples is returned.

Signed-off-by: Nick Weedon <[email protected]>

docs/Config_Reference.md

@@ -1929,6 +1929,17 @@ z_offset:
 #   not obtained in the given number of retries then an error is
 #   reported. The default is zero which causes an error to be reported
 #   on the first sample that exceeds samples_tolerance.
+#samples_trunc_count: 0
+#   Setting this to a non-zero value effectively enables a 'truncated mean' algorithm
+#   which removes 'samples_trunc_count' number of highest and lowest probe values
+#   before taking an average. The number which are removed is specified by this configruation value.
+#   This averaging option gives the best of both worlds between the median and the mean (average)
+#   since it is resistant to outliers but still averages the remaining results.
+#   This option is useful when you are taking 5 or more samples (using a
+#   samples_trunc_count of 2 for example).
+#   Note that if this option is configured such that there is less than 3 samples remaining
+#   after removing the truncated samples (i.e. samples_trunc_count) then this is considered a
+#   configuration error since this is the same as simply taking a median.
 #activate_gcode:
 #   A list of G-Code commands to execute prior to each probe attempt.
 #   See docs/Command_Templates.md for G-Code format. This may be
@@ -1997,6 +2008,7 @@ control_pin:
 #samples_result:
 #samples_tolerance:
 #samples_tolerance_retries:
+#samples_trunc_count:
 #   See the "probe" section for information on these parameters.
 ```
 
@@ -2048,6 +2060,7 @@ z_offset:
 #samples_result:
 #samples_tolerance:
 #samples_tolerance_retries:
+#samples_trunc_count:
 #activate_gcode:
 #deactivate_gcode:
 #deactivate_on_each_sample:
@@ -2088,6 +2101,7 @@ sensor_type: ldc1612
 #samples_result:
 #samples_tolerance:
 #samples_tolerance_retries:
+#samples_trunc_count:
 #   See the "probe" section for information on these parameters.
 ```
 

docs/G-Codes.md

@@ -999,7 +999,7 @@ see the [probe calibrate guide](Probe_Calibrate.md)).
 #### PROBE
 `PROBE [PROBE_SPEED=<mm/s>] [LIFT_SPEED=<mm/s>] [SAMPLES=<count>]
 [SAMPLE_RETRACT_DIST=<mm>] [SAMPLES_TOLERANCE=<mm>]
-[SAMPLES_TOLERANCE_RETRIES=<count>] [SAMPLES_RESULT=median|average]`:
+[SAMPLES_TOLERANCE_RETRIES=<count>] [SAMPLES_TRUNC_COUNT=<count>] [SAMPLES_RESULT=median|average]`:
 Move the nozzle downwards until the probe triggers. If any of the
 optional parameters are provided they override their equivalent
 setting in the [probe config section](Config_Reference.md#probe).

klippy/extras/probe.py

@@ -4,6 +4,7 @@
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import logging
+import math
 import pins
 from . import manual_probe
 
@@ -14,12 +15,23 @@
 """
 
 # Calculate the average Z from a set of positions
-def calc_probe_z_average(positions, method='average'):
+def calc_probe_z_average(positions, method='average', trunc_count=0):
+
     if method != 'median':
         # Use mean average
-        count = float(len(positions))
-        return [sum([pos[i] for pos in positions]) / count
+        count = len(positions)
+
+        # Perform truncated mean if required
+        if trunc_count > 0:
+            z_sorted = sorted(positions, key=(lambda p: p[2]))
+            start_index = trunc_count // 2
+            end_index = count - math.ceil(trunc_count)
+            return calc_probe_z_average(
+                z_sorted[start_index:end_index], 'average', 0)
+
+        return [sum([pos[i] for pos in positions]) / float(count)
                 for i in range(3)]
+
     # Use median
     z_sorted = sorted(positions, key=(lambda p: p[2]))
     middle = len(positions) // 2
@@ -259,6 +271,19 @@ def __init__(self, config, mcu_probe):
                                                  minval=0.)
         self.samples_retries = config.getint('samples_tolerance_retries', 0,
                                              minval=0)
+        self.samples_trunc_count = config.getint('samples_trunc_count', 0,
+                                             minval=0)
+
+        if self.samples_trunc_count > 0:
+            if self.samples_result != 'average':
+                raise config.error("samples_trunc_count is only "
+                                   "valid with samples_result=average")
+
+            if not self.sample_count - self.samples_trunc_count > 2:
+                raise config.error(
+                    "samples_trunc_count must be either zero or "
+                    "such that: sample_count - samples_trunc_count > 2")
+
         # Session state
         self.multi_probe_pending = False
         self.results = []
@@ -299,13 +324,27 @@ def get_probe_params(self, gcmd=None):
                                            self.samples_tolerance, minval=0.)
         samples_retries = gcmd.get_int("SAMPLES_TOLERANCE_RETRIES",
                                        self.samples_retries, minval=0)
+        samples_trunc_count = gcmd.get_int("SAMPLES_TRUNC_COUNT",
+                                       self.samples_trunc_count, minval=0)
         samples_result = gcmd.get("SAMPLES_RESULT", self.samples_result)
+
+        if samples_trunc_count > 0:
+            if samples_result != 'average':
+                raise gcmd.error("samples_trunc_count is only "
+                                   "valid with samples_result=average")
+
+            if not samples - samples_trunc_count > 2:
+                raise gcmd.error(
+                    "samples_trunc_count must be either zero or "
+                    "such that: sample_count - samples_trunc_count > 2")
+
         return {'probe_speed': probe_speed,
                 'lift_speed': lift_speed,
                 'samples': samples,
                 'sample_retract_dist': sample_retract_dist,
                 'samples_tolerance': samples_tolerance,
                 'samples_tolerance_retries': samples_retries,
+                'samples_trunc_count': samples_trunc_count,
                 'samples_result': samples_result}
     def _probe(self, speed):
         toolhead = self.printer.lookup_object('toolhead')
@@ -355,7 +394,8 @@ def run_probe(self, gcmd):
                     probexy + [pos[2] + params['sample_retract_dist']],
                     params['lift_speed'])
         # Calculate result
-        epos = calc_probe_z_average(positions, params['samples_result'])
+        epos = calc_probe_z_average(positions, params['samples_result'],
+                                    params['samples_trunc_count'])
         self.results.append(epos)
     def pull_probed_results(self):
         res = self.results