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pid_calibrate: Add some comments on the calibration methodology 

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2018-10-19 21:30:15 -04:00
parent e30053f2a9
commit 7efbc021a5
1 changed files with 7 additions and 2 deletions
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9
klippy/extras/pid_calibrate.py
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@ -75,6 +75,8 @@ class ControlAutoTune:
self.heater.set_pwm(read_time, value) self.heater.set_pwm(read_time, value)
def temperature_update(self, read_time, temp, target_temp): def temperature_update(self, read_time, temp, target_temp):
self.temp_samples.append((read_time, temp)) self.temp_samples.append((read_time, temp))
# Check if the temperature has crossed the target and
# enable/disable the heater if so.
if self.heating and temp >= target_temp: if self.heating and temp >= target_temp:
self.heating = False self.heating = False
self.check_peaks() self.check_peaks()
@ -83,6 +85,7 @@ class ControlAutoTune:
self.heating = True self.heating = True
self.check_peaks() self.check_peaks()
self.heater.alter_target(self.calibrate_temp) self.heater.alter_target(self.calibrate_temp)
# Check if this temperature is a peak and record it if so
if self.heating: if self.heating:
self.set_pwm(read_time, self.heater_max_power) self.set_pwm(read_time, self.heater_max_power)
if temp < self.peak: if temp < self.peak:
@ -110,9 +113,11 @@ class ControlAutoTune:
def calc_pid(self, pos): def calc_pid(self, pos):
temp_diff = self.peaks[pos][0] - self.peaks[pos-1][0] temp_diff = self.peaks[pos][0] - self.peaks[pos-1][0]
time_diff = self.peaks[pos][1] - self.peaks[pos-2][1] time_diff = self.peaks[pos][1] - self.peaks[pos-2][1]
Ku = 4. * (2. * self.heater_max_power) / (abs(temp_diff) * math.pi) # Use Astrom-Hagglund method to estimate Ku and Tu
amplitude = .5 * abs(temp_diff)
Ku = 4. * self.heater_max_power / (math.pi * amplitude)
Tu = time_diff Tu = time_diff
# Use Ziegler-Nichols method to generate PID parameters
Ti = 0.5 * Tu Ti = 0.5 * Tu
Td = 0.125 * Tu Td = 0.125 * Tu
Kp = 0.6 * Ku * heater.PID_PARAM_BASE Kp = 0.6 * Ku * heater.PID_PARAM_BASE