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Version 1.15rc3

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Improved PID tuning
This commit is contained in:
David Crocker 2016-08-20 21:13:44 +01:00
parent 84a274f748
commit 8d47fe8791
7 changed files with 44 additions and 43 deletions
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2
src/Configuration.h
View file

@ -26,7 +26,7 @@ Licence: GPL
// Firmware name is now defined in the Pins file
#ifndef VERSION
# define VERSION "1.15-rc2"
# define VERSION "1.15-rc3"
#endif
#ifndef DATE

10
src/GCodes/GCodes.cpp
View file

@ -3206,7 +3206,7 @@ bool GCodes::HandleMcode(GCodeBuffer* gb, StringRef& reply)
if (!success)
{
error = true;
platform->MessageF(GENERIC_MESSAGE, "Setting pin %d to %d is not supported\n", pin, val);
reply.printf("Setting pin %d to %d is not supported\n", pin, val);
}
}
}
@ -4216,9 +4216,13 @@ bool GCodes::HandleMcode(GCodeBuffer* gb, StringRef& reply)
{
// When reporting the PID parameters, we scale them by 255 for compatibility with older firmware and other firmware
const PidParams& spParams = model.GetPidParameters(false);
reply.catf("\nSetpoint change: P%.1f, I%.2f, D%.1f", 255.0 * spParams.kP, 255.0 * spParams.kI, 255.0 * spParams.kD);
const float scaledSpKp = 255.0 * spParams.kP;
reply.catf("\nSetpoint change: P%.1f, I%.2f, D%.1f",
scaledSpKp, scaledSpKp * spParams.recipTi, scaledSpKp * spParams.tD);
const PidParams& ldParams = model.GetPidParameters(true);
reply.catf("\nLoad change: P%.1f, I%.2f, D%.1f", 255.0 * ldParams.kP, 255.0 * ldParams.kI, 255.0 * ldParams.kD);
const float scaledLoadKp = 255.0 * ldParams.kP;
reply.catf("\nLoad change: P%.1f, I%.2f, D%.1f",
scaledLoadKp, scaledLoadKp * ldParams.recipTi, scaledLoadKp * ldParams.tD);
}
}
}

21
src/Heating/FOPDT.cpp
View file

@ -57,26 +57,13 @@ bool FopDt::SetParameters(float pg, float ptc, float pdt, float pMaxPwm, bool pU
void FopDt::CalcPidConstants()
{
const float timeFrac = deadTime/timeConstant;
#if 1
loadChangeParams.kP = 0.7/(gain * timeFrac);
loadChangeParams.kI = loadChangeParams.kP/(deadTime * 2.0);
loadChangeParams.kD = loadChangeParams.kP * deadTime;
loadChangeParams.recipTi = 1.0/(deadTime * 2.0); // Ti = 2 * deadTime
loadChangeParams.tD = deadTime * 0.7;
setpointChangeParams.kP = 0.7/(gain * timeFrac);
setpointChangeParams.kI = setpointChangeParams.kP/max<float>(deadTime * 2.0, timeConstant);
setpointChangeParams.kD = setpointChangeParams.kP * deadTime;
#else
// Calculate the PID parameters for responding to changes in load, using ITAE-load
loadChangeParams.kP = (0.77902/gain) * pow(timeFrac, -1.06401);
loadChangeParams.kI = loadChangeParams.kP/((1.0/1.14311) * timeConstant * pow(timeFrac, 0.70949));
loadChangeParams.kD = loadChangeParams.kP * 0.57137 * timeConstant * pow(timeFrac, 1.03826);
// Calculate the PID parameters for responding to changes in the setpoint using IAE-setpoint
setpointChangeParams.kP = (0.65/gain) * pow(timeFrac, -1.04432);
setpointChangeParams.kI = setpointChangeParams.kP * (0.9895 + 0.09539 * timeFrac)/timeConstant;
setpointChangeParams.kD = setpointChangeParams.kP * 0.50814 * timeConstant * pow(timeFrac, 1.08433);
#endif
setpointChangeParams.recipTi = 1.0/max<float>(deadTime * 2.0, timeConstant); // Ti = time constant unless dead time is very long
setpointChangeParams.tD = deadTime * 0.7;
}
// End

6
src/Heating/FOPDT.h
View file

@ -12,9 +12,9 @@
struct PidParams
{
float kP;
float kI;
float kD;
float kP; // controller (not model) gain
float recipTi; // reciprocal of controller integral time
float tD; // controller differential time
};
class FopDt

1
src/Heating/Heat.cpp
View file

@ -134,6 +134,7 @@ Heat::HeaterStatus Heat::GetStatus(int8_t heater) const
return (pids[heater]->FaultOccurred()) ? HS_fault
: (pids[heater]->SwitchedOff()) ? HS_off
: (pids[heater]->IsTuning()) ? HS_tuning
: (pids[heater]->Active()) ? HS_active
: HS_standby;
}

2
src/Heating/Heat.h
View file

@ -31,7 +31,7 @@ class Heat
{
public:
// Enumeration to describe the status of a heater. Note that the web interface returns the numerical values, so don't change them.
enum HeaterStatus { HS_off = 0, HS_standby = 1, HS_active = 2, HS_fault = 3 };
enum HeaterStatus { HS_off = 0, HS_standby = 1, HS_active = 2, HS_fault = 3, HS_tuning = 4 };
Heat(Platform* p);
void Spin(); // Called in a tight loop to keep everything going

41
src/Heating/Pid.cpp
View file

@ -257,26 +257,30 @@ void PID::Spin()
if (usingPid)
{
// Using PID mode
float kP, kI, kD, gain;
float kP, recipTi, tD, gain;
bool inSetPointMode;
if (useModel)
{
const PidParams& params = model.GetPidParameters(fabs(error) < 1.0);
inSetPointMode = fabs(error) > 1.0; // use modified PID when the error is large
const PidParams& params = model.GetPidParameters(!inSetPointMode);
kP = params.kP;
kI = params.kI;
kD = params.kD;
recipTi = params.recipTi;
tD = params.tD;
gain = model.GetGain();
}
else
{
kP = pp.kP/255.0 * pp.kS;
kI = pp.kI/255.0 * pp.kS;
kD = pp.kD/255.0 * pp.kS;
inSetPointMode = false; // use standard PID always
kP = (pp.kP * pp.kS) * (1.0/255.0);
recipTi = pp.kI/pp.kP;
tD = pp.kD/kP;
gain = 255.0/pp.kT;
}
// If the P term still has full authority, preset the I term to the expected PWM for this temperature
// and turn the heater full on or full off
const float pPlusD = (kP * error) - (kD * derivative);
const float errorMinusDterm = error - (tD * derivative);
const float pPlusD = kP * errorMinusDterm;
const float expectedPwm = constrain<float>((temperature - NormalAmbientTemperature)/gain, 0.0, maxPwm);
if (pPlusD + expectedPwm > maxPwm)
{
@ -290,7 +294,12 @@ void PID::Spin()
}
else
{
iAccumulator = constrain<float>(iAccumulator + (error * kI * platform->HeatSampleInterval() * MillisToSeconds), 0.0, maxPwm);
// In the following we use a modified PID when the temperature is a long way off target.
// During initial heating or cooling, the D term represents expected overshoot, which we don't want to add to the I accumulator.
// When we are in load mode, the I term is much larger and the D term doesn't represent overshoot, so use normal PID.
const float errorToUse = (inSetPointMode) ? errorMinusDterm : error;
iAccumulator = constrain<float>(iAccumulator + (errorToUse * kP * recipTi * platform->HeatSampleInterval() * MillisToSeconds),
0.0, maxPwm);
lastPwm = constrain<float>(pPlusD + iAccumulator, 0.0, maxPwm);
}
}
@ -549,7 +558,6 @@ void PID::DoTuningStep()
timeSetHeating = tuningPhaseStartTime = millis();
lastPwm = tuningPwm; // turn on heater at specified power
tuningReadingInterval = platform->HeatSampleInterval(); // reset sampling interval
active = true;
mode = HeaterMode::tuning1;
return;
}
@ -580,10 +588,10 @@ void PID::DoTuningStep()
DisplayBuffer("At phase 1 end");
}
tuningTimeOfFastestRate = index * tuningReadingInterval * MillisToSeconds;
tuningPhaseStartTime += index * tuningReadingInterval;
tuningFastestRate = (tuningTempReadings[index + 1] - tuningTempReadings[index - 1]) / (tuningReadingInterval * 2 * MillisToSeconds);
tuningFastestRate = (tuningTempReadings[index + 2] - tuningTempReadings[index - 2]) / (tuningReadingInterval * 4 * MillisToSeconds);
// Move the readings down so as to start at the max rate index
tuningPhaseStartTime += index * tuningReadingInterval;
tuningReadingsTaken -= index;
for (size_t i = 0; i < tuningReadingsTaken; ++i)
{
@ -599,7 +607,7 @@ void PID::DoTuningStep()
{
// In the following, the figure of 2.75 was chosen because a value of 2 is too low to handle the bed heater
// with embedded thermistor on my Kossel (reservoir effect)
if (ReadingsStable(tuningReadingsTaken/2, (temperature - tuningTempReadings[0]) * 0.269)) // if we have been going for ~2 time constants
if (ReadingsStable(tuningReadingsTaken/2, (temperature - tuningTempReadings[0]) * 0.2)) // if we have been going for ~2.75 time constants
{
// We have been heating for long enough, so we can do a fit
FitCurve();
@ -643,13 +651,14 @@ bool PID::ReadingsStable(size_t numReadings, float maxDiff) const
}
// Return the index in the temperature readings of the maximum rate of increase
// In view of the poor resolution of most thermistors at low temperatures, we measure over 4 time intervals instead of 2.
/*static*/ size_t PID::GetMaxRateIndex()
{
size_t index = 1;
size_t index = 2;
float maxIncrease = 0.0;
for (size_t i = 1; i + 1 < tuningReadingsTaken; ++i)
for (size_t i = 2; i + 2 < tuningReadingsTaken; ++i)
{
const float increase = tuningTempReadings[i + 1] - tuningTempReadings[i - 1];
const float increase = tuningTempReadings[i + 2] - tuningTempReadings[i - 2];
if (increase > maxIncrease)
{
maxIncrease = increase;