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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>
ECL_PitchController::ECL_PitchController() :
_last_run(0),
_last_output(0.0f),
_integrator(0.0f),
_rate_error(0.0f),
_rate_setpoint(0.0f),
_max_deflection_rad(math::radians(45.0f))
{
}
float ECL_PitchController::control(float pitch_setpoint, float pitch, float pitch_rate, float roll, float scaler,
bool lock_integrator, float airspeed_min, float airspeed_max, float airspeed)
{
/* 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;
float k_roll_ff = math::max((_k_p - _k_i * _tc) * _tc - _k_d, 0.0f);
float k_i_rate = _k_i * _tc;
/* 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;
}
/* 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 */
float turn_offset = fabsf((CONSTANTS_ONE_G / airspeed) *
tanf(roll) * sinf(roll)) * _roll_ff;
if (inverted)
turn_offset = -turn_offset;
float pitch_error = pitch_setpoint - pitch;
/* rate setpoint from current error and time constant */
_rate_setpoint = pitch_error / _tc;
/* add turn offset */
_rate_setpoint += turn_offset;
_rate_error = _rate_setpoint - pitch_rate;
float ilimit_scaled = _integrator_max * scaler;
if (!lock_integrator && k_i_rate > 0.0f && airspeed > 0.5f * airspeed_min) {
float id = _rate_error * k_i_rate * dt * scaler;
/*
* anti-windup: do not allow integrator to increase into the
* wrong direction if actuator is at limit
*/
if (_last_output < -_max_deflection_rad) {
/* only allow motion to center: increase value */
id = math::max(id, 0.0f);
} else if (_last_output > _max_deflection_rad) {
/* only allow motion to center: decrease value */
id = math::min(id, 0.0f);
}
_integrator += id;
}
/* integrator limit */
_integrator = math::constrain(_integrator, -ilimit_scaled, ilimit_scaled);
/* store non-limited output */
_last_output = ((_rate_error * _k_d * scaler) + _integrator + (_rate_setpoint * k_roll_ff)) * scaler;
return math::constrain(_last_output, -_max_deflection_rad, _max_deflection_rad);
}
void ECL_PitchController::reset_integrator()
{
_integrator = 0.0f;
}
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