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/**
* @file ecl_pitch_controller.cpp
* Implementation of a simple orthogonal pitch PID controller.
*
* Authors and acknowledgements in header.
*/
#include "ecl_pitch_controller.h"
#include <math.h>
#include <stdint.h>
#include <float.h>
#include <geo/geo.h>
#include <ecl/ecl.h>
#include <mathlib/mathlib.h>
#include <systemlib/err.h>
ECL_PitchController::ECL_PitchController() :
ECL_Controller("pitch"),
_max_rate_neg(0.0f),
_roll_ff(0.0f)
{
}
ECL_PitchController::~ECL_PitchController()
{
}
float ECL_PitchController::control_attitude(const struct ECL_ControlData &ctl_data)
{
float roll = ctl_data.roll;
/* Do not calculate control signal with bad inputs */
if (!(isfinite(ctl_data.pitch_setpoint) &&
isfinite(roll) &&
isfinite(ctl_data.pitch) &&
isfinite(ctl_data.airspeed))) {
perf_count(_nonfinite_input_perf);
warnx("not controlling pitch");
return _rate_setpoint;
}
/* flying inverted (wings upside down) ? */
bool inverted = false;
/* roll is used as feedforward term and inverted flight needs to be considered */
if (fabsf(roll) < math::radians(90.0f)) {
/* not inverted, but numerically still potentially close to infinity */
roll = math::constrain(roll, math::radians(-80.0f), math::radians(80.0f));
} else {
/* inverted flight, constrain on the two extremes of -pi..+pi to avoid infinity */
/* note: the ranges are extended by 10 deg here to avoid numeric resolution effects */
if (roll > 0.0f) {
/* right hemisphere */
roll = math::constrain(roll, math::radians(100.0f), math::radians(180.0f));
} else {
/* left hemisphere */
roll = math::constrain(roll, math::radians(-100.0f), math::radians(-180.0f));
}
}
/* calculate the offset in the rate resulting from rolling */
//xxx needs explanation and conversion to body angular rates or should be removed
float turn_offset = fabsf((CONSTANTS_ONE_G / ctl_data.airspeed) *
tanf(roll) * sinf(roll)) * _roll_ff;
if (inverted)
turn_offset = -turn_offset;
/* Calculate the error */
float pitch_error = ctl_data.pitch_setpoint - ctl_data.pitch;
/* Apply P controller: rate setpoint from current error and time constant */
_rate_setpoint = pitch_error / _tc;
/* add turn offset */
_rate_setpoint += turn_offset;
/* limit the rate */ //XXX: move to body angluar rates
if (_max_rate > 0.01f && _max_rate_neg > 0.01f) {
if (_rate_setpoint > 0.0f) {
_rate_setpoint = (_rate_setpoint > _max_rate) ? _max_rate : _rate_setpoint;
} else {
_rate_setpoint = (_rate_setpoint < -_max_rate_neg) ? -_max_rate_neg : _rate_setpoint;
}
}
return _rate_setpoint;
}
float ECL_PitchController::control_bodyrate(const struct ECL_ControlData &ctl_data)
{
/* Do not calculate control signal with bad inputs */
if (!(isfinite(ctl_data.roll) &&
isfinite(ctl_data.pitch) &&
isfinite(ctl_data.pitch_rate) &&
isfinite(ctl_data.yaw_rate) &&
isfinite(ctl_data.yaw_rate_setpoint) &&
isfinite(ctl_data.airspeed_min) &&
isfinite(ctl_data.airspeed_max) &&
isfinite(ctl_data.scaler))) {
perf_count(_nonfinite_input_perf);
return math::constrain(_last_output, -1.0f, 1.0f);
}
/* get the usual dt estimate */
uint64_t dt_micros = ecl_elapsed_time(&_last_run);
_last_run = ecl_absolute_time();
float dt = (float)dt_micros * 1e-6f;
/* lock integral for long intervals */
bool lock_integrator = ctl_data.lock_integrator;
if (dt_micros > 500000)
lock_integrator = true;
/* input conditioning */
float airspeed = ctl_data.airspeed;
if (!isfinite(airspeed)) {
/* airspeed is NaN, +- INF or not available, pick center of band */
airspeed = 0.5f * (ctl_data.airspeed_min + ctl_data.airspeed_max);
} else if (airspeed < ctl_data.airspeed_min) {
airspeed = ctl_data.airspeed_min;
}
/* Transform setpoint to body angular rates (jacobian) */
_bodyrate_setpoint = cosf(ctl_data.roll) * _rate_setpoint +
cosf(ctl_data.pitch) * sinf(ctl_data.roll) * ctl_data.yaw_rate_setpoint;
/* Transform estimation to body angular rates (jacobian) */
float pitch_bodyrate = cosf(ctl_data.roll) * ctl_data.pitch_rate +
cosf(ctl_data.pitch) * sinf(ctl_data.roll) * ctl_data.yaw_rate;
_rate_error = _bodyrate_setpoint - pitch_bodyrate;
if (!lock_integrator && _k_i > 0.0f && airspeed > 0.5f * ctl_data.airspeed_min) {
float id = _rate_error * dt * ctl_data.scaler;
/*
* anti-windup: do not allow integrator to increase if actuator is at limit
*/
if (_last_output < -1.0f) {
/* only allow motion to center: increase value */
id = math::max(id, 0.0f);
} else if (_last_output > 1.0f) {
/* only allow motion to center: decrease value */
id = math::min(id, 0.0f);
}
_integrator += id;
}
/* integrator limit */
//xxx: until start detection is available: integral part in control signal is limited here
float integrator_constrained = math::constrain(_integrator * _k_i, -_integrator_max, _integrator_max);
/* Apply PI rate controller and store non-limited output */
_last_output = _bodyrate_setpoint * _k_ff * ctl_data.scaler +
_rate_error * _k_p * ctl_data.scaler * ctl_data.scaler
+ integrator_constrained; //scaler is proportional to 1/airspeed
// warnx("pitch: _integrator: %.4f, _integrator_max: %.4f, airspeed %.4f, _k_i %.4f, _k_p: %.4f", (double)_integrator, (double)_integrator_max, (double)airspeed, (double)_k_i, (double)_k_p);
// warnx("roll: _last_output %.4f", (double)_last_output);
return math::constrain(_last_output, -1.0f, 1.0f);
}