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Switch PID implementations to seemingly more stable and one that is a…
… better match for our C++ implementation
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| #!/usr/bin/python | ||
| # | ||
| # This file is part of IvPID. | ||
| # Copyright (C) 2015 Ivmech Mechatronics Ltd. <bilgi@ivmech.com> | ||
| # | ||
| # IvPID is free software: you can redistribute it and/or modify | ||
| # it under the terms of the GNU General Public License as published by | ||
| # the Free Software Foundation, either version 3 of the License, or | ||
| # (at your option) any later version. | ||
| # | ||
| # IvPID is distributed in the hope that it will be useful, | ||
| # but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| # GNU General Public License for more details. | ||
| # | ||
| # You should have received a copy of the GNU General Public License | ||
| # along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
|
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||
| # title :PID.py | ||
| # description :python pid controller | ||
| # author :Caner Durmusoglu | ||
| # date :20151218 | ||
| # version :0.1 | ||
| # notes : | ||
| # ============================================================================== | ||
|
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| """Ivmech PID Controller is simple implementation of a Proportional-Integral-Derivative (PID) Controller in the Python Programming Language. | ||
| More information about PID Controller: http://en.wikipedia.org/wiki/PID_controller | ||
| """ | ||
| import time | ||
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| class PID: | ||
| """PID Controller | ||
| """ | ||
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| def __init__(self, P=0.2, I=0.0, D=0.0): | ||
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| self.Kp = P | ||
| self.Ki = I | ||
| self.Kd = D | ||
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| self.sample_time = 0.00 | ||
| self.current_time = time.time() | ||
| self.last_time = self.current_time | ||
|
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| self.clear() | ||
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| def clear(self): | ||
| """Clears PID computations and coefficients""" | ||
| self.SetPoint = 0.0 | ||
|
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| self.PTerm = 0.0 | ||
| self.ITerm = 0.0 | ||
| self.DTerm = 0.0 | ||
| self.last_error = 0.0 | ||
|
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| # Windup Guard | ||
| self.int_error = 0.0 | ||
| self.windup_guard = 20.0 | ||
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| self.output = 0.0 | ||
|
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| def update(self, feedback_value): | ||
| """Calculates PID value for given reference feedback | ||
| .. math:: | ||
| u(t) = K_p e(t) + K_i \int_{0}^{t} e(t)dt + K_d {de}/{dt} | ||
| .. figure:: images/pid_1.png | ||
| :align: center | ||
| Test PID with Kp=1.2, Ki=1, Kd=0.001 (test_pid.py) | ||
| """ | ||
| error = self.SetPoint - feedback_value | ||
|
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| self.current_time = time.time() | ||
| delta_time = self.current_time - self.last_time | ||
| delta_error = error - self.last_error | ||
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| if (delta_time >= self.sample_time): | ||
| self.PTerm = self.Kp * error | ||
| self.ITerm += error * delta_time | ||
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| if (self.ITerm < -self.windup_guard): | ||
| self.ITerm = -self.windup_guard | ||
| elif (self.ITerm > self.windup_guard): | ||
| self.ITerm = self.windup_guard | ||
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| self.DTerm = 0.0 | ||
| if delta_time > 0: | ||
| self.DTerm = delta_error / delta_time | ||
|
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| # Remember last time and last error for next calculation | ||
| self.last_time = self.current_time | ||
| self.last_error = error | ||
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| self.output = self.PTerm + (self.Ki * self.ITerm) + (self.Kd * self.DTerm) | ||
|
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| def setKp(self, proportional_gain): | ||
| """Determines how aggressively the PID reacts to the current error with setting Proportional Gain""" | ||
| self.Kp = proportional_gain | ||
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| def setKi(self, integral_gain): | ||
| """Determines how aggressively the PID reacts to the current error with setting Integral Gain""" | ||
| self.Ki = integral_gain | ||
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| def setKd(self, derivative_gain): | ||
| """Determines how aggressively the PID reacts to the current error with setting Derivative Gain""" | ||
| self.Kd = derivative_gain | ||
|
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| def setWindup(self, windup): | ||
| """Integral windup, also known as integrator windup or reset windup, | ||
| refers to the situation in a PID feedback controller where | ||
| a large change in setpoint occurs (say a positive change) | ||
| and the integral terms accumulates a significant error | ||
| during the rise (windup), thus overshooting and continuing | ||
| to increase as this accumulated error is unwound | ||
| (offset by errors in the other direction). | ||
| The specific problem is the excess overshooting. | ||
| """ | ||
| self.windup_guard = windup | ||
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| def setSampleTime(self, sample_time): | ||
| """PID that should be updated at a regular interval. | ||
| Based on a pre-determined sampe time, the PID decides if it should compute or return immediately. | ||
| """ | ||
| self.sample_time = sample_time |