text: #!/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/>.
  
  # title           :PID.py
  # description     :python pid controller
  # author          :Caner Durmusoglu
  # date            :20151218
  # version         :0.1
  # notes           :
  # python_version  :2.7
  # ==============================================================================
  
  """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
  """
  
  class PID:
      """PID Controller
      """
  
      def __init__(self, P=0.2, I=0.0, D=0.0,sample_time=0.01):
  
          self.Kp = P
          self.Ki = I
          self.Kd = D
  
          self.sample_time = sample_time
  
          self.clear()
  
      def clear(self):
          """Clears PID computations and coefficients"""
          self.SetPoint = 0.0
  
          self.PTerm = 0.0
          self.ITerm = 0.0
          self.DTerm = 0.0
          self.last_error = 0.0
  
          # Windup Guard
          self.int_error = 0.0
          self.windup_guard = 20.0
  
          self.output = 0.0
  
      def update(self, set_point, 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)
  
          """
          self.SetPoint = set_point
          error = self.SetPoint - feedback_value
  
          delta_time = self.sample_time
          delta_error = error - self.last_error
  
          self.PTerm = self.Kp * error
          self.ITerm += error * delta_time
  
          if (self.ITerm < -self.windup_guard):
              self.ITerm = -self.windup_guard
          elif (self.ITerm > self.windup_guard):
              self.ITerm = self.windup_guard
  
          self.DTerm = 0.0
          if delta_time > 0:
              self.DTerm = delta_error / delta_time
  
          # Remember last time and last error for next calculation
          self.last_error = error
  
          self.output = self.PTerm + (self.Ki * self.ITerm) + (self.Kd * self.DTerm)
  
          return self.output;
  
  
      def setKp(self, proportional_gain):
          """Determines how aggressively the PID reacts to the current error with setting Proportional Gain"""
          self.Kp = proportional_gain
  
      def setKi(self, integral_gain):
          """Determines how aggressively the PID reacts to the current error with setting Integral Gain"""
          self.Ki = integral_gain
  
      def setKd(self, derivative_gain):
          """Determines how aggressively the PID reacts to the current error with setting Derivative Gain"""
          self.Kd = derivative_gain
  
      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
  
      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
  
      def setSetPoint(self, set_point):
          self.SetPoint = set_point
  