diff options
author | David Crocker <dcrocker@eschertech.com> | 2016-08-20 23:13:44 +0300 |
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committer | David Crocker <dcrocker@eschertech.com> | 2016-08-20 23:13:44 +0300 |
commit | 8d47fe8791fb6a69e81ca6a7522ef10b5ef0b239 (patch) | |
tree | c20d913bda3d049c4cfe42af4f0a68ea961b0aa9 /src | |
parent | 84a274f7484fb2436733d500e597cf1a8d42baab (diff) |
Version 1.15rc3
Improved PID tuning
Diffstat (limited to 'src')
-rw-r--r-- | src/Configuration.h | 2 | ||||
-rw-r--r-- | src/GCodes/GCodes.cpp | 10 | ||||
-rw-r--r-- | src/Heating/FOPDT.cpp | 21 | ||||
-rw-r--r-- | src/Heating/FOPDT.h | 6 | ||||
-rw-r--r-- | src/Heating/Heat.cpp | 5 | ||||
-rw-r--r-- | src/Heating/Heat.h | 2 | ||||
-rw-r--r-- | src/Heating/Pid.cpp | 41 |
7 files changed, 44 insertions, 43 deletions
diff --git a/src/Configuration.h b/src/Configuration.h index c75a98b6..def6e1f9 100644 --- a/src/Configuration.h +++ b/src/Configuration.h @@ -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 diff --git a/src/GCodes/GCodes.cpp b/src/GCodes/GCodes.cpp index 93885324..371fe517 100644 --- a/src/GCodes/GCodes.cpp +++ b/src/GCodes/GCodes.cpp @@ -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); } } } diff --git a/src/Heating/FOPDT.cpp b/src/Heating/FOPDT.cpp index 2682c20f..6515cb12 100644 --- a/src/Heating/FOPDT.cpp +++ b/src/Heating/FOPDT.cpp @@ -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 diff --git a/src/Heating/FOPDT.h b/src/Heating/FOPDT.h index 82688076..d174da53 100644 --- a/src/Heating/FOPDT.h +++ b/src/Heating/FOPDT.h @@ -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 diff --git a/src/Heating/Heat.cpp b/src/Heating/Heat.cpp index 53fb0220..49ca6c67 100644 --- a/src/Heating/Heat.cpp +++ b/src/Heating/Heat.cpp @@ -134,8 +134,9 @@ Heat::HeaterStatus Heat::GetStatus(int8_t heater) const return (pids[heater]->FaultOccurred()) ? HS_fault : (pids[heater]->SwitchedOff()) ? HS_off - : (pids[heater]->Active()) ? HS_active - : HS_standby; + : (pids[heater]->IsTuning()) ? HS_tuning + : (pids[heater]->Active()) ? HS_active + : HS_standby; } void Heat::SetActiveTemperature(int8_t heater, float t) diff --git a/src/Heating/Heat.h b/src/Heating/Heat.h index 00fb9ed5..49dff9df 100644 --- a/src/Heating/Heat.h +++ b/src/Heating/Heat.h @@ -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 diff --git a/src/Heating/Pid.cpp b/src/Heating/Pid.cpp index 2b49dcf0..bf13b219 100644 --- a/src/Heating/Pid.cpp +++ b/src/Heating/Pid.cpp @@ -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; |