Diff: PID.cpp

Revision:

0:6e12a3e5af19

Child:

1:227ce995f635

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PID.cpp	Thu Sep 02 16:48:10 2010 +0000
@@ -0,0 +1,324 @@
+/**
+ * @author Aaron Berk
+ *
+ * @section LICENSE
+ *
+ * Copyright (c) 2010 ARM Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @section DESCRIPTION
+ * 
+ * A PID controller is a widely used feedback controller commonly found in
+ * industry.
+ *
+ * This library is a port of Brett Beauregard's Arduino PID library:
+ *
+ *  http://www.arduino.cc/playground/Code/PIDLibrary
+ *
+ * The wikipedia article on PID controllers is a good place to start on
+ * understanding how they work:
+ *
+ *  http://en.wikipedia.org/wiki/PID_controller
+ *
+ * For a clear and elegant explanation of how to implement and tune a
+ * controller, the controlguru website by Douglas J. Cooper (who also happened
+ * to be Brett's controls professor) is an excellent reference:
+ *
+ *  http://www.controlguru.com/
+ */
+
+/**
+ * Includes
+ */
+#include "PID.h"
+
+PID::PID(float Kc, float tauI, float tauD, float interval) {
+
+    usingFeedForward = false;
+    inAuto           = false;
+
+    //Default the limits to the full range of I/O: 3.3V
+    //Make sure to set these to more appropriate limits for
+    //your application.
+    setInputLimits(0.0, 3.3);
+    setOutputLimits(0.0, 3.3);
+
+    tSample_ = interval;
+
+    setTunings(Kc, tauI, tauD);
+
+    setPoint_             = 0.0;
+    processVariable_      = 0.0;
+    prevProcessVariable_  = 0.0;
+    controllerOutput_     = 0.0;
+    prevControllerOutput_ = 0.0;
+
+    accError_ = 0.0;
+    bias_     = 0.0;
+    
+    realOutput_ = 0.0;
+
+}
+
+void PID::setInputLimits(float inMin, float inMax) {
+
+    //Make sure we haven't been given impossible values.
+    if (inMin >= inMax) {
+        return;
+    }
+
+    //Rescale the working variables to reflect the changes.
+    prevProcessVariable_ *= (inMax - inMin) / inSpan_;
+    accError_            *= (inMax - inMin) / inSpan_;
+
+    //Make sure the working variables are within the new limits.
+    if (prevProcessVariable_ > 1) {
+        prevProcessVariable_ = 1;
+    } else if (prevProcessVariable_ < 0) {
+        prevProcessVariable_ = 0;
+    }
+
+    inMin_  = inMin;
+    inMax_  = inMax;
+    inSpan_ = inMax - inMin;
+
+}
+
+void PID::setOutputLimits(float outMin, float outMax) {
+
+    //Make sure we haven't been given impossible values.
+    if (outMin >= outMax) {
+        return;
+    }
+
+    //Rescale the working variables to reflect the changes.
+    prevControllerOutput_ *= (outMax - outMin) / outSpan_;
+
+    //Make sure the working variables are within the new limits.
+    if (prevControllerOutput_ > 1) {
+        prevControllerOutput_ = 1;
+    } else if (prevControllerOutput_ < 0) {
+        prevControllerOutput_ = 0;
+    }
+
+    outMin_  = outMin;
+    outMax_  = outMax;
+    outSpan_ = outMax - outMin;
+
+}
+
+void PID::setTunings(float Kc, float tauI, float tauD) {
+
+    //Verify that the tunings make sense.
+    if (Kc == 0.0 || tauI < 0.0 || tauD < 0.0) {
+        return;
+    }
+
+    //Store raw values to hand back to user on request.
+    pParam_ = Kc;
+    iParam_ = tauI;
+    dParam_ = tauD;
+
+    float tempTauR;
+
+    if (tauI == 0.0) {
+        tempTauR = 0.0;
+    } else {
+        tempTauR = (1.0 / tauI) * tSample_;
+    }
+
+    //For "bumpless transfer" we need to rescale the accumulated error.
+    if (inAuto) {
+        if (tempTauR == 0.0) {
+            accError_ = 0.0;
+        } else {
+            accError_ *= (Kc_ * tauR_) / (Kc * tempTauR);
+        }
+    }
+
+    Kc_   = Kc;
+    tauR_ = tempTauR;
+    tauD_ = tauD / tSample_;
+
+}
+
+void PID::reset(void) {
+
+    float scaledBias = 0.0;
+
+    if (usingFeedForward) {
+        scaledBias = (bias_ - outMin_) / outSpan_;
+    } else {
+        scaledBias = (realOutput_ - outMin_) / outSpan_;
+    }
+
+    prevControllerOutput_ = scaledBias;
+    prevProcessVariable_  = (processVariable_ - inMin_) / inSpan_;
+
+    //Clear any error in the integral.
+    accError_ = 0;
+
+}
+
+void PID::setMode(int mode) {
+
+    //We were in manual, and we just got set to auto.
+    //Reset the controller internals.
+    if (mode != 0 && !inAuto) {
+        reset();
+    }
+
+    inAuto = (mode != 0);
+
+}
+
+void PID::setInterval(float interval) {
+
+    if (interval > 0) {
+        //Convert the time-based tunings to reflect this change.
+        tauR_     *= (interval / tSample_);
+        accError_ *= (tSample_ / interval);
+        tauD_     *= (interval / tSample_);
+        tSample_   = interval;
+    }
+
+}
+
+void PID::setSetPoint(float sp) {
+
+    setPoint_ = sp;
+
+}
+
+void PID::setProcessValue(float pv) {
+
+    processVariable_ = pv;
+
+}
+
+void PID::setBias(float bias){
+
+    bias_ = bias;
+    usingFeedForward = 1;
+
+}
+
+float PID::compute() {
+
+    //Pull in the input and setpoint, and scale them into percent span.
+    float scaledPV = (processVariable_ - inMin_) / inSpan_;
+
+    if (scaledPV > 1.0) {
+        scaledPV = 1.0;
+    } else if (scaledPV < 0.0) {
+        scaledPV = 0.0;
+    }
+
+    float scaledSP = (setPoint_ - inMin_) / inSpan_;
+    if (scaledSP > 1.0) {
+        scaledSP = 1;
+    } else if (scaledSP < 0.0) {
+        scaledSP = 0;
+    }
+
+    float error = scaledSP - scaledPV;
+
+    //Check and see if the output is pegged at a limit and only
+    //integrate if it is not. This is to prevent reset-windup.
+    if (!(prevControllerOutput_ >= 1 && error > 0) && !(prevControllerOutput_ <= 0 && error < 0)) {
+        accError_ += error;
+    }
+
+    //Compute the current slope of the input signal.
+    float dMeas = (scaledPV - prevProcessVariable_) / tSample_;
+
+    float scaledBias = 0.0;
+
+    if (usingFeedForward) {
+        scaledBias = (bias_ - outMin_) / outSpan_;
+    }
+
+    //Perform the PID calculation.
+    controllerOutput_ = scaledBias + Kc_ * (error + (tauR_ * accError_) - (tauD_ * dMeas));
+
+    //Make sure the computed output is within output constraints.
+    if (controllerOutput_ < 0.0) {
+        controllerOutput_ = 0.0;
+    } else if (controllerOutput_ > 1.0) {
+        controllerOutput_ = 1.0;
+    }
+
+    //Remember this output for the windup check next time.
+    prevControllerOutput_ = controllerOutput_;
+    //Remember the input for the derivative calculation next time.
+    prevProcessVariable_  = scaledPV;
+
+    //Scale the output from percent span back out to a real world number.
+    return ((controllerOutput_ * outSpan_) + outMin_);
+
+}
+
+float PID::getInMin() {
+
+    return inMin_;
+
+}
+
+float PID::getInMax() {
+
+    return inMax_;
+
+}
+
+float PID::getOutMin() {
+
+    return outMin_;
+
+}
+
+float PID::getOutMax() {
+
+    return outMax_;
+
+}
+
+float PID::getInterval() {
+
+    return tSample_;
+
+}
+
+float PID::getPParam() {
+
+    return pParam_;
+
+}
+
+float PID::getIParam() {
+
+    return iParam_;
+
+}
+
+float PID::getDParam() {
+
+    return dParam_;
+
+}