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/*
* FOPDT.cpp
*
* Created on: 16 Aug 2016
* Author: David
*/
#include "FOPDT.h"
#if HAS_MASS_STORAGE
# include "Storage/FileStore.h"
#endif
#if SUPPORT_CAN_EXPANSION
# include <CanMessageFormats.h>
#endif
// Heater 6 on the Duet 0.8.5 is disabled by default at startup so that we can use fan 2.
// Set up sensible defaults here in case the user enables the heater without specifying values for all the parameters.
FopDt::FopDt() noexcept
: gain(DefaultHotEndHeaterGain), timeConstant(DefaultHotEndHeaterTimeConstant), deadTime(DefaultHotEndHeaterDeadTime), maxPwm(1.0), standardVoltage(0.0),
enabled(false), usePid(true), inverted(false), pidParametersOverridden(false)
{
}
// Check the model parameters are sensible, if they are then save them and return true.
bool FopDt::SetParameters(float pg, float ptc, float pdt, float pMaxPwm, float temperatureLimit, float pVoltage, bool pUsePid, bool pInverted) noexcept
{
if (pg == -1.0 && ptc == -1.0 && pdt == -1.0)
{
// Setting all parameters to -1 disables the heater control completely so we can use the pin for other purposes
enabled = false;
return true;
}
// DC 2017-06-20: allow S down to 0.01 for one of our OEMs (use > 0.0099 because >= 0.01 doesn't work due to rounding error)
const float maxGain = max<float>(1500.0, temperatureLimit + 500.0);
if (pg > 10.0 && pg <= maxGain && pdt > 0.099 && ptc >= 2 * pdt && pMaxPwm > 0.0099 && pMaxPwm <= 1.0)
{
gain = pg;
timeConstant = ptc;
deadTime = pdt;
maxPwm = pMaxPwm;
standardVoltage = pVoltage;
usePid = pUsePid;
inverted = pInverted;
enabled = true;
CalcPidConstants();
return true;
}
return false;
}
// Get the PID parameters as reported by M301
M301PidParameters FopDt::GetM301PidParameters(bool forLoadChange) const noexcept
{
M301PidParameters rslt;
const PidParameters& pp = GetPidParameters(forLoadChange);
const float reportedKp = pp.kP * 255.0;
rslt.kP = reportedKp;
rslt.kI = pp.recipTi * reportedKp;
rslt.kD = pp.tD * reportedKp;
return rslt;
}
// Override the PID parameters. We set both sets to the same parameters.
void FopDt::SetM301PidParameters(const M301PidParameters& pp) noexcept
{
loadChangeParams.kP = setpointChangeParams.kP = pp.kP * (1.0/255.0);
loadChangeParams.recipTi = setpointChangeParams.recipTi = pp.kI/pp.kP;
loadChangeParams.tD = setpointChangeParams.tD = pp.kD/pp.kP;
pidParametersOverridden = true;
}
#if HAS_MASS_STORAGE
// Write the model parameters to file returning true if no error
bool FopDt::WriteParameters(FileStore *f, size_t heater) const noexcept
{
String<ScratchStringLength> scratchString;
scratchString.printf("M307 H%u A%.1f C%.1f D%.1f S%.2f V%.1f B%d\n",
heater, (double)gain, (double)timeConstant, (double)deadTime, (double)maxPwm, (double)standardVoltage, (usePid) ? 0 : 1);
bool ok = f->Write(scratchString.c_str());
if (ok && pidParametersOverridden)
{
const M301PidParameters pp = GetM301PidParameters(false);
scratchString.printf("M301 H%u P%.1f I%.3f D%.1f\n", heater, (double)pp.kP, (double)pp.kI, (double)pp.kD);
ok = f->Write(scratchString.c_str());
}
return ok;
}
#endif
/* Re-calculate the PID parameters.
* For some possible formulas, see "Comparison of some well-known PID tuning formulas", Computers and Chemical Engineering 30 (2006) 1416–1423,
* available at http://www.ece.ualberta.ca/~marquez/journal_publications_files/papers/tan_cce_06.pdf
* Here are some examples, where r = td/tc:
* Cohen-Coon (modified to use half the original Kc value):
* Kc = (0.67/G) * (r + 0.185)
* Ti = 2.5 * td * (tc + 0.185 * td)/(tc + 0.611 * td)
* Td = 0.37 * td * tc/(tc + 0.185 * td)
* Ho et al, best response to setpoint changes:
* Kc = (1.086/G) * (r^-0.869
* Ti = tc/(0.74 - 0.13 * r)
* Td = 0.348 * tc * r^0.914
* IAE-setpoint:
* Kc = (0.65/G) * r^-1.04432
* Ti = tc/(0.9895 + 0.09539 * r)
* Td = 0.50814 * tc * r^1.08433
* Ho et al, best response to load changes:
* Kc = (1.435/G) * r^-0.921
* Ti = 1.14 * tc * r^0.749
* Td = 0.482 * tc * r^1.137
* ITAE-load:
* Kc = (0.77902/G) * r^-1.06401
* Ti = (tc/1.14311) * r^0.70949
* Td = 0.57137 * tc * r^1.03826
* However, none of these works well in this application. The setpoint-based methods have integral times comparable to the process time
* constant. This makes them very slow to reach that target temperature. Typically, the power is reduced too soon, so the temperature
* flattens out too soon it and then it takes a very long time for the integral term to accumulate to the required value. The load-based
* ones tend to have massive overshoot when the setpoint is changed, and even in the steady state some of them have marginal stability.
*/
void FopDt::CalcPidConstants() noexcept
{
const float timeFrac = deadTime/timeConstant;
loadChangeParams.kP = 0.7/(gain * timeFrac);
loadChangeParams.recipTi = (1.0/1.14)/(powf(timeConstant, 0.25) * powf(deadTime, 0.75)); // Ti = 1.14 * timeConstant^0.25 * deadTime^0.75 (Ho et al)
loadChangeParams.tD = deadTime * 0.7;
setpointChangeParams.kP = 0.7/(gain * timeFrac);
setpointChangeParams.recipTi = 1.0/(powf(timeConstant, 0.5) * powf(deadTime, 0.5)); // Ti = timeConstant^0.5 * deadTime^0.5
setpointChangeParams.tD = deadTime * 0.7;
pidParametersOverridden = false;
}
#if SUPPORT_CAN_EXPANSION
void FopDt::SetupCanMessage(unsigned int heater, CanMessageUpdateHeaterModel& msg) noexcept
{
msg.heater = heater;
msg.gain = gain;
msg.timeConstant = timeConstant;
msg.deadTime = deadTime;
msg.maxPwm = maxPwm;
msg.standardVoltage = standardVoltage;
msg.enabled = enabled;
msg.usePid = usePid;
msg.inverted = inverted;
msg.pidParametersOverridden = pidParametersOverridden;
msg.kP = setpointChangeParams.kP;
msg.recipTi = setpointChangeParams.recipTi;
msg.tD = setpointChangeParams.tD;
}
#endif
// End
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