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ardupilot/libraries/APM_Control/AP_AutoTune.cpp

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/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
The strategy for roll/pitch autotune is to give the user a AUTOTUNE
flight mode which behaves just like FBWA, but does automatic
tuning.
*/
#include "AP_AutoTune.h"
#include <AP_Common/AP_Common.h>
#include <AP_HAL/AP_HAL.h>
#include <AP_Logger/AP_Logger.h>
#include <AP_Math/AP_Math.h>
#include <AC_PID/AC_PID.h>
#include <AP_Scheduler/AP_Scheduler.h>
#include <GCS_MAVLink/GCS.h>
extern const AP_HAL::HAL& hal;
// step size for changing FF gains, percentage
#define AUTOTUNE_INCREASE_FF_STEP 12
#define AUTOTUNE_DECREASE_FF_STEP 15
// limits on IMAX
#define AUTOTUNE_MIN_IMAX 0.4
#define AUTOTUNE_MAX_IMAX 0.9
// ratio of I to P
#define AUTOTUNE_I_RATIO 0.75
// time constant of rate trim loop
#define TRIM_TCONST 1.0f
// constructor
AP_AutoTune::AP_AutoTune(ATGains &_gains, ATType _type,
const AP_FixedWing &parms,
AC_PID &_rpid) :
current(_gains),
rpid(_rpid),
type(_type),
aparm(parms),
ff_filter(2)
{}
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
#include <stdio.h>
# define Debug(fmt, args ...) do {::printf("%s:%d: " fmt "\n", __FUNCTION__, __LINE__, ## args); } while(0)
#else
# define Debug(fmt, args ...)
#endif
/*
auto-tuning table. This table gives the starting values for key
tuning parameters based on a user chosen AUTOTUNE_LEVEL parameter
from 1 to 10. Level 1 is a very soft tune. Level 10 is a very
aggressive tune.
Level 0 means use the existing RMAX and TCONST parameters
*/
static const struct {
float tau;
float rmax;
} tuning_table[] = {
{ 1.00, 20 }, // level 1
{ 0.90, 30 }, // level 2
{ 0.80, 40 }, // level 3
{ 0.70, 50 }, // level 4
{ 0.60, 60 }, // level 5
{ 0.50, 75 }, // level 6
{ 0.30, 90 }, // level 7
{ 0.2, 120 }, // level 8
{ 0.15, 160 }, // level 9
{ 0.1, 210 }, // level 10
{ 0.1, 300 }, // (yes, it goes to 11)
};
/*
start an autotune session
*/
void AP_AutoTune::start(void)
{
running = true;
state = ATState::IDLE;
current = restore = last_save = get_gains();
// do first update of rmax and tau now
update_rmax();
dt = AP::scheduler().get_loop_period_s();
rpid.kIMAX().set(constrain_float(rpid.kIMAX(), AUTOTUNE_MIN_IMAX, AUTOTUNE_MAX_IMAX));
// use 0.75Hz filters on the actuator, rate and target to reduce impact of noise
actuator_filter.set_cutoff_frequency(AP::scheduler().get_loop_rate_hz(), 0.75);
rate_filter.set_cutoff_frequency(AP::scheduler().get_loop_rate_hz(), 0.75);
// target filter is a bit broader
target_filter.set_cutoff_frequency(AP::scheduler().get_loop_rate_hz(), 4);
ff_filter.reset();
actuator_filter.reset();
rate_filter.reset();
D_limit = 0;
P_limit = 0;
ff_count = 0;
D_set_ms = 0;
P_set_ms = 0;
done_count = 0;
if (!is_positive(rpid.slew_limit())) {
// we must have a slew limit, default to 150 deg/s
rpid.slew_limit().set_and_save(150);
}
if (current.FF < 0.01) {
// don't allow for zero FF
current.FF = 0.01;
rpid.ff().set(current.FF);
}
Debug("START FF -> %.3f\n", rpid.ff().get());
}
/*
called when we change state to see if we should change gains
*/
void AP_AutoTune::stop(void)
{
if (running) {
running = false;
if (is_positive(D_limit) && is_positive(P_limit)) {
save_gains();
} else {
restore_gains();
}
}
}
const char *AP_AutoTune::axis_string(void) const
{
switch (type) {
case AUTOTUNE_ROLL:
return "Roll";
case AUTOTUNE_PITCH:
return "Pitch";
case AUTOTUNE_YAW:
return "Yaw";
}
return "";
}
/*
one update cycle of the autotuner
*/
void AP_AutoTune::update(AP_PIDInfo &pinfo, float scaler, float angle_err_deg)
{
if (!running) {
return;
}
// see what state we are in
ATState new_state = state;
const float desired_rate = target_filter.apply(pinfo.target);
// filter actuator without I term so we can take ratios without
// accounting for trim offsets. We first need to include the I and
// clip to 45 degrees to get the right value of the real surface
const float clipped_actuator = constrain_float(pinfo.FF + pinfo.P + pinfo.D + pinfo.I, -45, 45) - pinfo.I;
const float actuator = actuator_filter.apply(clipped_actuator);
const float actual_rate = rate_filter.apply(pinfo.actual);
max_actuator = MAX(max_actuator, actuator);
min_actuator = MIN(min_actuator, actuator);
max_rate = MAX(max_rate, actual_rate);
min_rate = MIN(min_rate, actual_rate);
max_target = MAX(max_target, desired_rate);
min_target = MIN(min_target, desired_rate);
max_P = MAX(max_P, fabsf(pinfo.P));
max_D = MAX(max_D, fabsf(pinfo.D));
min_Dmod = MIN(min_Dmod, pinfo.Dmod);
max_Dmod = MAX(max_Dmod, pinfo.Dmod);
// update the P and D slew rates, using P and D values from before Dmod was applied
const float slew_limit_scale = 45.0 / degrees(1);
slew_limit_max = rpid.slew_limit();
slew_limit_tau = 1.0;
slew_limiter_P.modifier((pinfo.P/pinfo.Dmod)*slew_limit_scale, dt);
slew_limiter_D.modifier((pinfo.D/pinfo.Dmod)*slew_limit_scale, dt);
// remember maximum slew rates for this cycle
max_SRate_P = MAX(max_SRate_P, slew_limiter_P.get_slew_rate());
max_SRate_D = MAX(max_SRate_D, slew_limiter_D.get_slew_rate());
float att_limit_deg = 0;
switch (type) {
case AUTOTUNE_ROLL:
att_limit_deg = aparm.roll_limit_cd * 0.01;
break;
case AUTOTUNE_PITCH:
att_limit_deg = MIN(abs(aparm.pitch_limit_max_cd),abs(aparm.pitch_limit_min_cd))*0.01;
break;
case AUTOTUNE_YAW:
// arbitrary value for yaw angle
att_limit_deg = 20;
break;
}
// thresholds for when we consider an event to start and end
const float rate_threshold1 = 0.4 * MIN(att_limit_deg / current.tau.get(), current.rmax_pos);
const float rate_threshold2 = 0.25 * rate_threshold1;
bool in_att_demand = fabsf(angle_err_deg) >= 0.3 * att_limit_deg;
switch (state) {
case ATState::IDLE:
if (desired_rate > rate_threshold1 && in_att_demand) {
new_state = ATState::DEMAND_POS;
} else if (desired_rate < -rate_threshold1 && in_att_demand) {
new_state = ATState::DEMAND_NEG;
}
break;
case ATState::DEMAND_POS:
if (desired_rate < rate_threshold2) {
new_state = ATState::IDLE;
}
break;
case ATState::DEMAND_NEG:
if (desired_rate > -rate_threshold2) {
new_state = ATState::IDLE;
}
break;
}
const uint32_t now = AP_HAL::millis();
if (now - last_log_ms >= 40) {
// log at 25Hz
struct log_ATRP pkt = {
LOG_PACKET_HEADER_INIT(LOG_ATRP_MSG),
time_us : AP_HAL::micros64(),
type : uint8_t(type),
state: uint8_t(new_state),
actuator : actuator,
P_slew : max_SRate_P,
D_slew : max_SRate_D,
FF_single: FF_single,
FF: current.FF,
P: current.P,
I: current.I,
D: current.D,
action: uint8_t(action),
rmax: float(current.rmax_pos.get()),
tau: current.tau.get()
};
AP::logger().WriteBlock(&pkt, sizeof(pkt));
last_log_ms = now;
}
if (new_state == state) {
if (state == ATState::IDLE &&
now - state_enter_ms > 500 &&
max_Dmod < 0.9) {
// we've been oscillating while idle, reduce P or D
const float slew_sum = max_SRate_P + max_SRate_D;
const float gain_mul = 0.5;
current.P *= linear_interpolate(gain_mul, 1.0,
max_SRate_P,
slew_sum, 0);
current.D *= linear_interpolate(gain_mul, 1.0,
max_SRate_D,
slew_sum, 0);
rpid.kP().set(current.P);
rpid.kD().set(current.D);
action = Action::IDLE_LOWER_PD;
P_limit = MIN(P_limit, current.P);
D_limit = MIN(D_limit, current.D);
state_change(state);
}
return;
}
if (new_state != ATState::IDLE) {
// starting an event
min_actuator = max_actuator = min_rate = max_rate = 0;
state_enter_ms = now;
state = new_state;
return;
}
if ((state == ATState::DEMAND_POS && max_rate < 0.01 * current.rmax_pos) ||
(state == ATState::DEMAND_NEG && min_rate > -0.01 * current.rmax_neg)) {
// we didn't get enough rate
action = Action::LOW_RATE;
state_change(ATState::IDLE);
return;
}
if (now - state_enter_ms < 100) {
// not long enough sample
action = Action::SHORT;
state_change(ATState::IDLE);
return;
}
// we've finished an event. calculate the single-event FF value
if (state == ATState::DEMAND_POS) {
FF_single = max_actuator / (max_rate * scaler);
} else {
FF_single = min_actuator / (min_rate * scaler);
}
// apply median filter
float FF = ff_filter.apply(FF_single);
ff_count++;
const float old_FF = rpid.ff();
// limit size of change in FF
FF = constrain_float(FF,
old_FF*(1-AUTOTUNE_DECREASE_FF_STEP*0.01),
old_FF*(1+AUTOTUNE_INCREASE_FF_STEP*0.01));
// adjust P and D
float D = rpid.kD();
float P = rpid.kP();
if (ff_count == 1) {
// apply minimum D and P values
D = MAX(D, 0.0005);
P = MAX(P, 0.01);
} else if (ff_count == 4) {
// we got a good ff estimate, halve P ready to start raising D
P *= 0.5;
}
// see if the slew limiter kicked in
if (min_Dmod < 1.0 && !is_positive(D_limit)) {
// oscillation, without D_limit set
if (max_P > 0.5 * max_D) {
// lower P and D to get us to a non-oscillating state
P *= 0.35;
D *= 0.75;
action = Action::LOWER_PD;
} else {
// set D limit to 30% of current D, remember D limit and start to work on P
D *= 0.3;
D_limit = D;
D_set_ms = now;
action = Action::LOWER_D;
GCS_SEND_TEXT(MAV_SEVERITY_ERROR, "%sD: %.4f", axis_string(), D_limit);
}
} else if (min_Dmod < 1.0) {
// oscillation, with D_limit set
if (now - D_set_ms > 2000) {
// leave 2s for Dmod to settle after lowering D
if (max_D > 0.8 * max_P) {
// lower D limit some more
D *= 0.35;
D_limit = D;
D_set_ms = now;
action = Action::LOWER_D;
GCS_SEND_TEXT(MAV_SEVERITY_ERROR, "%sD: %.4f", axis_string(), D_limit);
done_count = 0;
} else if (now - P_set_ms > 2500) {
if (is_positive(P_limit)) {
// if we've already got a P estimate then don't
// reduce as quickly, stopping small spikes at the
// later part of the tune from giving us a very
// low P gain
P *= 0.7;
} else {
P *= 0.35;
}
P_limit = P;
P_set_ms = now;
action = Action::LOWER_P;
done_count = 0;
GCS_SEND_TEXT(MAV_SEVERITY_ERROR, "%sP: %.4f", axis_string(), P_limit);
}
}
} else if (ff_count < 4) {
// we don't have a good FF estimate yet, keep going
} else if (!is_positive(D_limit)) {
/* we haven't detected D oscillation yet, keep raising D */
D *= 1.3;
action = Action::RAISE_D;
} else if (!is_positive(P_limit)) {
/* not oscillating, increase P gain */
P *= 1.3;
action = Action::RAISE_PD;
} else {
// after getting P_limit we consider the tune done when we
// have done 3 cycles without reducing P
if (done_count < 3) {
if (++done_count == 3) {
GCS_SEND_TEXT(MAV_SEVERITY_ERROR, "%s: Finished", axis_string());
save_gains();
}
}
}
rpid.ff().set(FF);
rpid.kP().set(P);
rpid.kD().set(D);
if (type == AUTOTUNE_ROLL) { // for roll set I = smaller of FF or P
rpid.kI().set(MIN(P, (FF / TRIM_TCONST)));
} else { // for pitch/yaw naturally damped axes) set I usually = FF to get 1 sec I closure
rpid.kI().set(MAX(P*AUTOTUNE_I_RATIO, (FF / TRIM_TCONST)));
}
// setup filters to be suitable for time constant and gyro filter
// filtering T can prevent P/D oscillation being seen, so allow the
// user to switch it off
if (!has_option(DISABLE_FLTT_UPDATE)) {
rpid.filt_T_hz().set(10.0/(current.tau * 2 * M_PI));
}
rpid.filt_E_hz().set(0);
// filtering D at the same level as VTOL can allow unwanted oscillations to be seen,
// so allow the user to switch it off and select their own (usually lower) value
if (!has_option(DISABLE_FLTD_UPDATE)) {
rpid.filt_D_hz().set(AP::ins().get_gyro_filter_hz()*0.5);
}
current.FF = FF;
current.P = P;
current.I = rpid.kI().get();
current.D = D;
Debug("FPID=(%.3f, %.3f, %.3f, %.3f) Dmod=%.2f\n",
rpid.ff().get(),
rpid.kP().get(),
rpid.kI().get(),
rpid.kD().get(),
min_Dmod);
// move rmax and tau towards target
update_rmax();
state_change(new_state);
}
/*
record a state change
*/
void AP_AutoTune::state_change(ATState new_state)
{
min_Dmod = 1;
max_Dmod = 0;
max_SRate_P = 1;
max_SRate_D = 1;
max_P = max_D = 0;
state = new_state;
state_enter_ms = AP_HAL::millis();
}
/*
save a float if it has changed
*/
void AP_AutoTune::save_float_if_changed(AP_Float &v, float old_value)
{
if (!is_equal(old_value, v.get())) {
v.save();
}
}
/*
save a int16_t if it has changed
*/
void AP_AutoTune::save_int16_if_changed(AP_Int16 &v, int16_t old_value)
{
if (old_value != v.get()) {
v.save();
}
}
/*
save a set of gains
*/
void AP_AutoTune::save_gains(void)
{
const auto &v = last_save;
save_float_if_changed(current.tau, v.tau);
save_int16_if_changed(current.rmax_pos, v.rmax_pos);
save_int16_if_changed(current.rmax_neg, v.rmax_neg);
save_float_if_changed(rpid.ff(), v.FF);
save_float_if_changed(rpid.kP(), v.P);
save_float_if_changed(rpid.kI(), v.I);
save_float_if_changed(rpid.kD(), v.D);
save_float_if_changed(rpid.kIMAX(), v.IMAX);
save_float_if_changed(rpid.filt_T_hz(), v.flt_T);
save_float_if_changed(rpid.filt_E_hz(), v.flt_E);
save_float_if_changed(rpid.filt_D_hz(), v.flt_D);
last_save = get_gains();
}
/*
get gains with PID components
*/
AP_AutoTune::ATGains AP_AutoTune::get_gains(void)
{
ATGains ret = current;
ret.FF = rpid.ff();
ret.P = rpid.kP();
ret.I = rpid.kI();
ret.D = rpid.kD();
ret.IMAX = rpid.kIMAX();
ret.flt_T = rpid.filt_T_hz();
ret.flt_E = rpid.filt_E_hz();
ret.flt_D = rpid.filt_D_hz();
return ret;
}
/*
set gains with PID components
*/
void AP_AutoTune::restore_gains(void)
{
current = restore;
rpid.ff().set(restore.FF);
rpid.kP().set(restore.P);
rpid.kI().set(restore.I);
rpid.kD().set(restore.D);
rpid.kIMAX().set(restore.IMAX);
rpid.filt_T_hz().set(restore.flt_T);
rpid.filt_E_hz().set(restore.flt_E);
rpid.filt_D_hz().set(restore.flt_D);
}
/*
update RMAX and TAU parameters on each step. We move them gradually
towards the target to allow for a user going straight to a level 10
tune while starting with a poorly tuned plane
*/
void AP_AutoTune::update_rmax(void)
{
uint8_t level = constrain_int32(aparm.autotune_level, 0, ARRAY_SIZE(tuning_table));
int16_t target_rmax;
float target_tau;
if (level == 0) {
// this level means to keep current values of RMAX and TCONST
target_rmax = constrain_float(current.rmax_pos, 75, 720);
target_tau = constrain_float(current.tau, 0.1, 2);
} else {
target_rmax = tuning_table[level-1].rmax;
target_tau = tuning_table[level-1].tau;
if (type == AUTOTUNE_PITCH) {
// 50% longer time constant on pitch
target_tau *= 1.5;
}
}
if (level > 0 && is_positive(current.FF)) {
const float invtau = ((1.0f / target_tau) + (current.I / current.FF));
if (is_positive(invtau)) {
target_tau = MAX(target_tau,1.0f / invtau);
}
}
if (current.rmax_pos == 0) {
// conservative initial value
current.rmax_pos.set(75);
}
// move RMAX by 20 deg/s per step
current.rmax_pos.set(constrain_int32(target_rmax,
current.rmax_pos.get()-20,
current.rmax_pos.get()+20));
if (level != 0 || current.rmax_neg.get() == 0) {
current.rmax_neg.set(current.rmax_pos.get());
}
// move tau by max 15% per loop
current.tau.set(constrain_float(target_tau,
current.tau*0.85,
current.tau*1.15));
}
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