PID.py

'''PID for F651
 
  Copyright (C) 2018 Patrik Karlsson. All rights reserved.
 
  BSD license:
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.
  3. Neither the name of the copyright holder nor the names of
     contributors to this software may be used to endorse or promote
     products derived from this software without specific prior written
     permission.
 
  THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS''
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
  HOLDER OR THE CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY
  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 '''
#!/usr/bin/env python
import rospy

class PID:
    def __init__(self, Kp=0.2, Ki=0.001, Kd=0.001, maxI=0.1, maxOut=3.0):
        self.Kp = Kp
        self.Ki = Ki
        self.Kd = Kd

        self.target = 0
        self.output = 0
        self.error = 0
        self.maxI = maxI
        self.maxOut = maxOut
        self.reset()
        self.lastTime = rospy.get_time()

    def update(self, target, state, time):
        # u(t) = K_p e(t) + K_i \int_{0}^{t} e(t)dt + K_d {de}/{dt}
        self.target = target
        self.state = state
        self.error = self.target - self.state

        self.time = time
        dTime = self.time - self.lastTime
        dError = self.error - self.lastError
        #print("DTime: {}, dError: {}".format(dTime, dError))

        p = self.error
        self.intError += self.error * dTime
        if (dTime > 0):
            d = dError / dTime
        else:
            d = 0
            rospy.logdebug("Change in time is zero.")
        # Make sure I does not exceed maximum windup
        if (self.maxI is not None and self.intError > self.maxI):
            i = self.maxI
        elif (self.maxI is not None and self.intError < -self.maxI):
            i = self.maxI
        else:
            i = self.intError

        # Remember last time and last error for next calculation
        self.lastTime = self.time
        self.lastError = self.lastError

        output = self.Kp * p + self.Ki * i + self.Kd * d
        # Make sure output does not exceed maximum
        if (self.maxOut is not None and output > self.maxOut):
            output = self.maxOut
        elif (self.maxOut is not None and output < -self.maxOut):
            output = -self.maxOut

        return output

    def setKp(self, Kp):
        self.Kp = Kp

    def setKi(self, Ki):
        self.Ki = Ki

    def setKd(self, Kd):
        self.Kd = Kd

    def setMaxI(self, maxI):
        self.maxI = maxI
    def setMaxO(self, MaxO):
        self.maxOut = MaxO

    def reset(self):
        self.target = 0.0
        self.error = 0.0
        self.state = 0.0
        self.intError = 0.0
        self.lastError = 0.0
        self.output = 0.0