z_thermal_adjust: Add Z thermal adjuster module (Klipper3d#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

@@ -1309,6 +1309,25 @@ times, with two different weights. It is suggested to have one of the
 calibration weights be zero and the other near the maximum weight for your
 load cell.  SAVE_CONFIG must be used to save the calibration.
 
+### [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

@@ -493,6 +493,19 @@ calibrated.
 measurement, adjusted for tare.  Absent if calibration has not been
 performed.
 
+## 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

klippy/extras/z_thermal_adjust.py

@@ -0,0 +1,183 @@
+# Z Thermal Adjust
+#
+# Copyright (C) 2022  Robert Pazdzior <robertp@norbital.com>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+
+# Adjusts Z position in real-time using a thermal probe to e.g. compensate
+# for thermal expansion of the printer frame.
+
+import threading
+
+KELVIN_TO_CELSIUS = -273.15
+
+class ZThermalAdjuster:
+    def __init__(self, config):
+        self.printer = config.get_printer()
+        self.gcode = self.printer.lookup_object('gcode')
+        self.lock = threading.Lock()
+        self.config = config
+
+        # Get config parameters, convert to SI units where necessary
+        self.temp_coeff = config.getfloat('temp_coeff', minval=-1, maxval=1,
+            default=0)
+        self.off_above_z = config.getfloat('z_adjust_off_above', 99999999.)
+        self.max_z_adjust_mm = config.getfloat('max_z_adjustment', 99999999.)
+
+        # Register printer events
+        self.printer.register_event_handler("klippy:connect",
+                                            self.handle_connect)
+        self.printer.register_event_handler("homing:home_rails_end",
+                                            self.handle_homing_move_end)
+
+        # Setup temperature sensor
+        self.smooth_time = config.getfloat('smooth_time', 2., above=0.)
+        self.inv_smooth_time = 1. / self.smooth_time
+        self.min_temp = config.getfloat('min_temp', minval=KELVIN_TO_CELSIUS)
+        self.max_temp = config.getfloat('max_temp', above=self.min_temp)
+        pheaters = self.printer.load_object(config, 'heaters')
+        self.sensor = pheaters.setup_sensor(config)
+        self.sensor.setup_minmax(self.min_temp, self.max_temp)
+        self.sensor.setup_callback(self.temperature_callback)
+        pheaters.register_sensor(config, self)
+
+        self.last_temp = 0.
+        self.measured_min = self.measured_max = 0.
+        self.smoothed_temp = 0.
+        self.last_temp_time = 0.
+        self.ref_temperature = 0.
+        self.ref_temp_override = False
+
+        # Z transformation
+        self.z_adjust_mm = 0.
+        self.last_z_adjust_mm = 0.
+        self.adjust_enable = True
+        self.last_position = [0., 0., 0., 0.]
+        self.next_transform = None
+
+        # Register gcode commands
+        self.gcode.register_command('SET_Z_THERMAL_ADJUST',
+                                    self.cmd_SET_Z_THERMAL_ADJUST,
+                                    desc=self.cmd_SET_Z_THERMAL_ADJUST_help)
+
+    def handle_connect(self):
+        'Called after all printer objects are instantiated'
+        self.toolhead = self.printer.lookup_object('toolhead')
+        gcode_move = self.printer.lookup_object('gcode_move')
+
+        # Register move transformation
+        self.next_transform = gcode_move.set_move_transform(self, force=True)
+
+        # Pull Z step distance for minimum adjustment increment
+        kin = self.printer.lookup_object('toolhead').get_kinematics()
+        steppers = [s.get_name() for s in kin.get_steppers()]
+        z_stepper = kin.get_steppers()[steppers.index("stepper_z")]
+        self.z_step_dist = z_stepper.get_step_dist()
+
+    def get_status(self, eventtime):
+        return {
+            'temperature': self.smoothed_temp,
+            'measured_min_temp': round(self.measured_min, 2),
+            'measured_max_temp': round(self.measured_max, 2),
+            'current_z_adjust': self.z_adjust_mm,
+            'z_adjust_ref_temperature': self.ref_temperature,
+            'enabled': self.adjust_enable
+        }
+
+    def handle_homing_move_end(self, homing_state, rails):
+        'Set reference temperature after Z homing.'
+        if 2 in homing_state.get_axes():
+            self.ref_temperature = self.smoothed_temp
+            self.ref_temp_override = False
+            self.z_adjust_mm = 0.
+
+    def calc_adjust(self, pos):
+        'Z adjustment calculation'
+        if pos[2] < self.off_above_z:
+            delta_t = self.smoothed_temp - self.ref_temperature
+
+            # Calculate Z adjustment
+            adjust = -1 * self.temp_coeff * delta_t
+
+            # compute sign (+1 or -1) for maximum offset setting
+            sign = 1 - (adjust <= 0)*2
+
+            # Don't apply adjustments smaller than step distance
+            if abs(adjust - self.z_adjust_mm) > self.z_step_dist:
+                self.z_adjust_mm = min([self.max_z_adjust_mm*sign,
+                    adjust], key=abs)
+
+        # Apply Z adjustment
+        new_z = pos[2] + self.z_adjust_mm
+        self.last_z_adjust_mm = self.z_adjust_mm
+        return [pos[0], pos[1], new_z, pos[3]]
+
+    def calc_unadjust(self, pos):
+        'Remove Z adjustment'
+        unadjusted_z = pos[2] - self.z_adjust_mm
+        return [pos[0], pos[1], unadjusted_z, pos[3]]
+
+    def get_position(self):
+        position = self.calc_unadjust(self.next_transform.get_position())
+        self.last_position = self.calc_adjust(position)
+        return position
+
+    def move(self, newpos, speed):
+        # don't apply to extrude only moves or when disabled
+        if (newpos[0:2] == self.last_position[0:2]) or not self.adjust_enable:
+            z = newpos[2] + self.last_z_adjust_mm
+            adjusted_pos = [newpos[0], newpos[1], z, newpos[3]]
+            self.next_transform.move(adjusted_pos, speed)
+        else:
+            adjusted_pos = self.calc_adjust(newpos)
+            self.next_transform.move(adjusted_pos, speed)
+        self.last_position[:] = newpos
+
+    def temperature_callback(self, read_time, temp):
+        'Called everytime the Z adjust thermistor is read'
+        with self.lock:
+            time_diff = read_time - self.last_temp_time
+            self.last_temp = temp
+            self.last_temp_time = read_time
+            temp_diff = temp - self.smoothed_temp
+            adj_time = min(time_diff * self.inv_smooth_time, 1.)
+            self.smoothed_temp += temp_diff * adj_time
+            self.measured_min = min(self.measured_min, self.smoothed_temp)
+            self.measured_max = max(self.measured_max, self.smoothed_temp)
+
+    def cmd_SET_Z_THERMAL_ADJUST(self, gcmd):
+        enable = gcmd.get_int('ENABLE', None, minval=0, maxval=1)
+        coeff = gcmd.get_float('TEMP_COEFF', None, minval=-1, maxval=1)
+        ref_temp = gcmd.get_float('REF_TEMP', None, minval=KELVIN_TO_CELSIUS)
+
+        if ref_temp is not None:
+            self.ref_temperature = ref_temp
+            self.ref_temp_override = True
+        if coeff is not None:
+            self.temp_coeff = coeff
+        if enable is not None:
+            if enable != self.adjust_enable:
+                self.adjust_enable = True if enable else False
+                gcode_move = self.printer.lookup_object('gcode_move')
+                gcode_move.reset_last_position()
+
+        state = '1 (enabled)' if self.adjust_enable else '0 (disabled)'
+        override = ' (manual)' if self.ref_temp_override else ''
+        msg = ("enable: %s\n"
+               "temp_coeff: %f mm/degC\n"
+               "ref_temp: %.2f degC%s\n"
+               "-------------------\n"
+               "Current Z temp: %.2f degC\n"
+               "Applied Z adjustment: %.4f mm"
+               % (state,
+                  self.temp_coeff,
+                  self.ref_temperature, override,
+                  self.smoothed_temp,
+                  self.z_adjust_mm)
+        )
+        gcmd.respond_info(msg)
+
+    cmd_SET_Z_THERMAL_ADJUST_help = 'Set/query Z Thermal Adjust parameters.'
+
+def load_config(config):
+    return ZThermalAdjuster(config)