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/****************************************************************************
*
* Copyright (c) 2013 Estimation and Control Library (ECL). All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name ECL nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/**
* @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() :
_last_run(0),
_tc(0.1f),
_k_p(0.0f),
_k_i(0.0f),
_k_ff(0.0f),
_integrator_max(0.0f),
_max_rate_pos(0.0f),
_max_rate_neg(0.0f),
_roll_ff(0.0f),
_last_output(0.0f),
_integrator(0.0f),
_rate_error(0.0f),
_rate_setpoint(0.0f),
_bodyrate_setpoint(0.0f),
_nonfinite_input_perf(perf_alloc(PC_COUNT, "fw att control pitch nonfinite input"))
{
}
ECL_PitchController::~ECL_PitchController()
{
perf_free(_nonfinite_input_perf);
}
float ECL_PitchController::control_attitude(float pitch_setpoint, float roll, float pitch, float airspeed)
{
/* Do not calculate control signal with bad inputs */
if (!(isfinite(pitch_setpoint) && isfinite(roll) && isfinite(pitch) && isfinite(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 / airspeed) *
tanf(roll) * sinf(roll)) * _roll_ff;
if (inverted)
turn_offset = -turn_offset;
/* Calculate the error */
float pitch_error = pitch_setpoint - 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_pos > 0.01f && _max_rate_neg > 0.01f) {
if (_rate_setpoint > 0.0f) {
_rate_setpoint = (_rate_setpoint > _max_rate_pos) ? _max_rate_pos : _rate_setpoint;
} else {
_rate_setpoint = (_rate_setpoint < -_max_rate_neg) ? -_max_rate_neg : _rate_setpoint;
}
}
return _rate_setpoint;
}
float ECL_PitchController::control_bodyrate(float roll, float pitch,
float pitch_rate, float yaw_rate,
float yaw_rate_setpoint,
float airspeed_min, float airspeed_max, float airspeed, float scaler, bool lock_integrator)
{
/* Do not calculate control signal with bad inputs */
if (!(isfinite(roll) && isfinite(pitch) && isfinite(pitch_rate) && isfinite(yaw_rate) &&
isfinite(yaw_rate_setpoint) && isfinite(airspeed_min) &&
isfinite(airspeed_max) && isfinite(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 */
if (dt_micros > 500000)
lock_integrator = true;
/* input conditioning */
if (!isfinite(airspeed)) {
/* airspeed is NaN, +- INF or not available, pick center of band */
airspeed = 0.5f * (airspeed_min + airspeed_max);
} else if (airspeed < airspeed_min) {
airspeed = airspeed_min;
}
/* Transform setpoint to body angular rates */
_bodyrate_setpoint = cosf(roll) * _rate_setpoint + cosf(pitch) * sinf(roll) * yaw_rate_setpoint; //jacobian
/* Transform estimation to body angular rates */
float pitch_bodyrate = cosf(roll) * pitch_rate + cosf(pitch) * sinf(roll) * yaw_rate; //jacobian
_rate_error = _bodyrate_setpoint - pitch_bodyrate;
if (!lock_integrator && _k_i > 0.0f && airspeed > 0.5f * airspeed_min) {
float id = _rate_error * dt;
/*
* 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 +_rate_error * _k_p + integrator_constrained) * scaler * scaler; //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);
}
void ECL_PitchController::reset_integrator()
{
_integrator = 0.0f;
}
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