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Lorenz Meier
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/****************************************************************************
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*
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* Copyright (c) 2013 Estimation and Control Library (ECL). All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name ECL nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/**
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* @file ecl_pitch_controller.cpp
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* Implementation of a simple orthogonal pitch PID controller.
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*
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* Authors and acknowledgements in header.
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*/
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#include "ecl_pitch_controller.h"
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#include <math.h>
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#include <stdint.h>
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#include <float.h>
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#include <geo/geo.h>
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#include <ecl/ecl.h>
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#include <mathlib/mathlib.h>
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#include <systemlib/err.h>
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ECL_PitchController::ECL_PitchController() :
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ECL_Controller("pitch"),
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_max_rate_neg(0.0f),
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_roll_ff(0.0f)
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{
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}
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ECL_PitchController::~ECL_PitchController()
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{
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}
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float ECL_PitchController::control_attitude(const struct ECL_ControlData &ctl_data)
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{
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/* Do not calculate control signal with bad inputs */
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if (!(PX4_ISFINITE(ctl_data.pitch_setpoint) &&
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PX4_ISFINITE(ctl_data.roll) &&
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PX4_ISFINITE(ctl_data.pitch) &&
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PX4_ISFINITE(ctl_data.airspeed))) {
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perf_count(_nonfinite_input_perf);
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warnx("not controlling pitch");
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return _rate_setpoint;
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}
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/* Calculate the error */
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float pitch_error = ctl_data.pitch_setpoint - ctl_data.pitch;
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/* Apply P controller: rate setpoint from current error and time constant */
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_rate_setpoint = pitch_error / _tc;
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/* limit the rate */
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if (_max_rate > 0.01f && _max_rate_neg > 0.01f) {
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if (_rate_setpoint > 0.0f) {
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_rate_setpoint = (_rate_setpoint > _max_rate) ? _max_rate : _rate_setpoint;
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} else {
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_rate_setpoint = (_rate_setpoint < -_max_rate_neg) ? -_max_rate_neg : _rate_setpoint;
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}
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}
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return _rate_setpoint;
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}
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float ECL_PitchController::control_bodyrate(const struct ECL_ControlData &ctl_data)
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{
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/* Do not calculate control signal with bad inputs */
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if (!(PX4_ISFINITE(ctl_data.roll) &&
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PX4_ISFINITE(ctl_data.pitch) &&
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PX4_ISFINITE(ctl_data.pitch_rate) &&
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PX4_ISFINITE(ctl_data.yaw_rate) &&
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PX4_ISFINITE(ctl_data.yaw_rate_setpoint) &&
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PX4_ISFINITE(ctl_data.airspeed_min) &&
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PX4_ISFINITE(ctl_data.airspeed_max) &&
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PX4_ISFINITE(ctl_data.scaler))) {
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perf_count(_nonfinite_input_perf);
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return math::constrain(_last_output, -1.0f, 1.0f);
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}
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/* get the usual dt estimate */
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uint64_t dt_micros = ecl_elapsed_time(&_last_run);
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_last_run = ecl_absolute_time();
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float dt = (float)dt_micros * 1e-6f;
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/* lock integral for long intervals */
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bool lock_integrator = ctl_data.lock_integrator;
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if (dt_micros > 500000) {
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lock_integrator = true;
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}
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/* Transform setpoint to body angular rates (jacobian) */
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_bodyrate_setpoint = cosf(ctl_data.roll) * _rate_setpoint +
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cosf(ctl_data.pitch) * sinf(ctl_data.roll) * ctl_data.yaw_rate_setpoint;
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/* apply turning offset to desired bodyrate setpoint*/
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/* flying inverted (wings upside down)*/
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bool inverted = false;
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float constrained_roll;
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/* roll is used as feedforward term and inverted flight needs to be considered */
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if (fabsf(ctl_data.roll) < math::radians(90.0f)) {
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/* not inverted, but numerically still potentially close to infinity */
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constrained_roll = math::constrain(ctl_data.roll, math::radians(-80.0f), math::radians(80.0f));
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} else {
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/* inverted flight, constrain on the two extremes of -pi..+pi to avoid infinity */
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inverted = true;
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/* note: the ranges are extended by 10 deg here to avoid numeric resolution effects */
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if (ctl_data.roll > 0.0f) {
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/* right hemisphere */
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constrained_roll = math::constrain(ctl_data.roll, math::radians(100.0f), math::radians(180.0f));
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} else {
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/* left hemisphere */
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constrained_roll = math::constrain(ctl_data.roll, math::radians(-100.0f), math::radians(-180.0f));
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}
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}
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/* input conditioning */
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float airspeed = constrain_airspeed(ctl_data.airspeed, ctl_data.airspeed_min, ctl_data.airspeed_max);
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/* Calculate desired body fixed y-axis angular rate needed to compensate for roll angle.
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For reference see Automatic Control of Aircraft and Missiles by John H. Blakelock, pg. 175
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Availible on google books 8/11/2015:
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https://books.google.com/books?id=ubcczZUDCsMC&pg=PA175#v=onepage&q&f=false*/
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float body_fixed_turn_offset = (fabsf((CONSTANTS_ONE_G / airspeed) *
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tanf(constrained_roll) * sinf(constrained_roll)));
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if (inverted) {
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body_fixed_turn_offset = -body_fixed_turn_offset;
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}
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/* Finally add the turn offset to your bodyrate setpoint*/
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_bodyrate_setpoint += body_fixed_turn_offset;
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_rate_error = _bodyrate_setpoint - ctl_data.pitch_rate;
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if (!lock_integrator && _k_i > 0.0f) {
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float id = _rate_error * dt * ctl_data.scaler;
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/*
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* anti-windup: do not allow integrator to increase if actuator is at limit
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*/
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if (_last_output < -1.0f) {
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/* only allow motion to center: increase value */
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id = math::max(id, 0.0f);
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} else if (_last_output > 1.0f) {
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/* only allow motion to center: decrease value */
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id = math::min(id, 0.0f);
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}
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_integrator += id;
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}
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/* integrator limit */
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//xxx: until start detection is available: integral part in control signal is limited here
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float integrator_constrained = math::constrain(_integrator * _k_i, -_integrator_max, _integrator_max);
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/* Apply PI rate controller and store non-limited output */
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_last_output = _bodyrate_setpoint * _k_ff * ctl_data.scaler +
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_rate_error * _k_p * ctl_data.scaler * ctl_data.scaler
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+ integrator_constrained; //scaler is proportional to 1/airspeed
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// 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);
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// warnx("roll: _last_output %.4f", (double)_last_output);
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return math::constrain(_last_output, -1.0f, 1.0f);
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}
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