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AR_AttitudeControl: throttle and steering control library

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Throttle controller has these advantages over existing controller:
based on velocity in vehicle's forward-back axis rather than ground-speed
straight-forward PID controller using speed error as input
speed control acceleration limts
stop control slows vehicle smoothly
configurable filtering

Steer controller has these advantages over existing controller:
output scaled properly for skid-steering vehicles
layered P and PID controller for angular error and rate control
configurable filtering
This commit is contained in:
Randy Mackay 2017-08-08 14:36:29 +09:00
parent a5783939ef
commit 9f876dc7a0
2 changed files with 478 additions and 0 deletions
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371
libraries/APM_Control/AR_AttitudeControl.cpp Normal file
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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/>.
*/
#include <AP_Math/AP_Math.h>
#include <AP_HAL/AP_HAL.h>
#include "AR_AttitudeControl.h"
extern const AP_HAL::HAL& hal;
const AP_Param::GroupInfo AR_AttitudeControl::var_info[] = {
// @Param: _STR_ANG_P
// @DisplayName: Steering control angle P gain
// @Description: Steering control angle P gain. Converts the error between the desired heading/yaw (in radians) and actual heading/yaw to a desired turn rate (in rad/sec)
// @Range: 1.000 10.000
// @User: Standard
AP_SUBGROUPINFO(_steer_angle_p, "_STR_ANG_", 0, AR_AttitudeControl, AC_P),
// @Param: _STR_RATE_P
// @DisplayName: Steering control rate P gain
// @Description: Steering control rate P gain. Converts the turn rate error (in radians/sec) to a steering control output (in the range -1 to +1)
// @Range: 0.100 2.000
// @User: Standard
// @Param: _STR_RATE_I
// @DisplayName: Steering control I gain
// @Description: Steering control I gain. Corrects long term error between the desired turn rate (in rad/s) and actual
// @Range: 0.000 2.000
// @User: Standard
// @Param: _STR_RATE_IMAX
// @DisplayName: Steering control I gain maximum
// @Description: Steering control I gain maximum. Constraings the steering output (range -1 to +1) that the I term will generate
// @Range: 0.000 1.000
// @User: Standard
// @Param: _STR_RATE_D
// @DisplayName: Steering control D gain
// @Description: Steering control D gain. Compensates for short-term change in desired turn rate vs actual
// @Range: 0.000 0.400
// @User: Standard
// @Param: _STR_RATE_FILT
// @DisplayName: Steering control filter frequency
// @Description: Steering control input filter. Lower values reduce noise but add delay.
// @Range: 1.000 100.000
// @Units: Hz
// @User: Standard
AP_SUBGROUPINFO(_steer_rate_pid, "_STR_RAT_", 1, AR_AttitudeControl, AC_PID),
// @Param: _SPEED_P
// @DisplayName: Speed control P gain
// @Description: Speed control P gain. Converts the error between the desired speed (in m/s) and actual speed to a motor output (in the range -1 to +1)
// @Range: 0.010 2.000
// @User: Standard
// @Param: _SPEED_I
// @DisplayName: Speed control I gain
// @Description: Speed control I gain. Corrects long term error between the desired speed (in m/s) and actual speed
// @Range: 0.000 2.000
// @User: Standard
// @Param: _SPEED_IMAX
// @DisplayName: Speed control I gain maximum
// @Description: Speed control I gain maximum. Constraings the maximum motor output (range -1 to +1) that the I term will generate
// @Range: 0.000 1.000
// @User: Standard
// @Param: _SPEED_D
// @DisplayName: Speed control D gain
// @Description: Speed control D gain. Compensates for short-term change in desired speed vs actual
// @Range: 0.000 0.400
// @User: Standard
// @Param: _SPEED_FILT
// @DisplayName: Speed control filter frequency
// @Description: Speed control input filter. Lower values reduce noise but add delay.
// @Range: 1.000 100.000
// @Units: Hz
// @User: Standard
AP_SUBGROUPINFO(_throttle_speed_pid, "_SPEED_", 2, AR_AttitudeControl, AC_PID),
// @Param: _ACCEL_MAX
// @DisplayName: Speed control acceleration (and deceleration) maximum in m/s/s
// @Description: Speed control acceleration (and deceleration) maximum in m/s/s. 0 to disable acceleration limiting
// @Range: 0 10
// @Increment: 0.1
// @Units: m/s/s
// @User: Standard
AP_GROUPINFO("_ACCEL_MAX", 3, AR_AttitudeControl, _throttle_accel_max, AR_ATTCONTROL_THR_ACCEL_MAX),
// @Param: _BRAKE
// @DisplayName: Speed control brake enable/disable
// @Description: Speed control brake enable/disable. Allows sending a reversed output to the motors to slow the vehicle.
// @Values: 0:Disable,1:Enable
// @User: Standard
AP_GROUPINFO("_BRAKE", 4, AR_AttitudeControl, _brake_enable, 0),
// @Param: _STOP_SPEED
// @DisplayName: Speed control stop speed
// @Description: Speed control stop speed. Motor outputs to zero once vehicle speed falls below this value
// @Range: 0 0.5
// @Increment: 0.01
// @Units: m/s
// @User: Standard
AP_GROUPINFO("_STOP_SPEED", 5, AR_AttitudeControl, _stop_speed, AR_ATTCONTROL_STOP_SPEED_DEFAULT),
AP_GROUPEND
};
AR_AttitudeControl::AR_AttitudeControl(AP_AHRS &ahrs) :
_ahrs(ahrs),
_steer_angle_p(AR_ATTCONTROL_STEER_ANG_P),
_steer_rate_pid(AR_ATTCONTROL_STEER_RATE_P, AR_ATTCONTROL_STEER_RATE_I, AR_ATTCONTROL_STEER_RATE_D, AR_ATTCONTROL_STEER_RATE_IMAX, AR_ATTCONTROL_STEER_RATE_FILT, AR_ATTCONTROL_DT),
_throttle_speed_pid(AR_ATTCONTROL_THR_SPEED_P, AR_ATTCONTROL_THR_SPEED_I, AR_ATTCONTROL_THR_SPEED_D, AR_ATTCONTROL_THR_SPEED_IMAX, AR_ATTCONTROL_THR_SPEED_FILT, AR_ATTCONTROL_DT)
{
AP_Param::setup_object_defaults(this, var_info);
}
// return a steering servo output from -1.0 to +1.0 given a desired lateral acceleration rate in m/s/s.
// positive lateral acceleration is to the right.
float AR_AttitudeControl::get_steering_out_lat_accel(float desired_accel, bool skid_steering, bool motor_limit_left, bool motor_limit_right)
{
// get speed forward
float speed;
if (!get_forward_speed(speed)) {
// we expect caller will not try to control heading using rate control without a valid speed estimate
// on failure to get speed we do not attempt to steer
return 0.0f;
}
// enforce minimum speed to stop oscillations when first starting to move
if (fabsf(speed) < AR_ATTCONTROL_STEER_SPEED_MIN) {
if (is_negative(speed)) {
speed = -AR_ATTCONTROL_STEER_SPEED_MIN;
} else {
speed = AR_ATTCONTROL_STEER_SPEED_MIN;
}
}
// Calculate the desired steering rate given desired_accel and speed
float desired_rate = desired_accel / speed;
return get_steering_out_rate(desired_rate, skid_steering, motor_limit_left, motor_limit_right);
}
// return a steering servo output from -1 to +1 given a yaw error in radians
float AR_AttitudeControl::get_steering_out_angle_error(float angle_err, bool skid_steering, bool motor_limit_left, bool motor_limit_right)
{
// Calculate the desired turn rate (in radians) from the angle error (also in radians)
float desired_rate = _steer_angle_p.get_p(angle_err);
return get_steering_out_rate(desired_rate, skid_steering, motor_limit_left, motor_limit_right);
}
// return a steering servo output from -1 to +1 given a
// desired yaw rate in radians/sec. Positive yaw is to the right.
float AR_AttitudeControl::get_steering_out_rate(float desired_rate, bool skid_steering, bool motor_limit_left, bool motor_limit_right)
{
// calculate dt
uint32_t now = AP_HAL::millis();
float dt = (now - _steer_turn_last_ms) / 1000.0f;
if (_steer_turn_last_ms == 0 || dt > 0.1) {
dt = 0.0f;
}
_steer_turn_last_ms = now;
_steer_rate_pid.set_dt(dt);
// get speed forward
float speed;
if (!get_forward_speed(speed)) {
// we expect caller will not try to control heading using rate control without a valid speed estimate
// on failure to get speed we do not attempt to steer
return 0.0f;
}
// enforce minimum speed to stop oscillations when first starting to move
bool low_speed = false;
if (fabsf(speed) < AR_ATTCONTROL_STEER_SPEED_MIN) {
low_speed = true;
if (is_negative(speed)) {
speed = -AR_ATTCONTROL_STEER_SPEED_MIN;
} else {
speed = AR_ATTCONTROL_STEER_SPEED_MIN;
}
}
// scaler to linearize output because turn rate increases as vehicle speed increases on non-skid steering vehicles
float scaler = 1.0f;
if (!skid_steering) {
scaler = 1.0f / fabsf(speed);
}
// Calculate the steering rate error (deg/sec) and apply gain scaler
// We do this in earth frame to allow for rover leaning over in hard corners
float yaw_rate_earth = _ahrs.get_yaw_rate_earth();
// check if reversing
if (is_negative(speed)) {
yaw_rate_earth *= -1.0f;
}
float rate_error = (desired_rate - yaw_rate_earth) * scaler;
// pass error to PID controller
_steer_rate_pid.set_input_filter_all(rate_error);
// get p
float p = _steer_rate_pid.get_p();
// get i unless moving at low speed or steering output has hit a limit
float i = 0.0f;
if (!low_speed && ((is_negative(rate_error) && !motor_limit_left) || (is_positive(rate_error) && !motor_limit_right))) {
i = _steer_rate_pid.get_i();
}
// get d
float d = _steer_rate_pid.get_d();
// constrain and return final output
return constrain_float(p + i + d, -1.0f, 1.0f);
}
// return a throttle output from -1 to +1 given a desired speed in m/s (use negative speeds to travel backwards)
// skid_steering should be true for skid-steer vehicles
// motor_limit should be true if motors have hit their upper or lower limits
// cruise speed should be in m/s, cruise throttle should be a number from -1 to +1
float AR_AttitudeControl::get_throttle_out_speed(float desired_speed, bool skid_steering, bool motor_limit_low, bool motor_limit_high, float cruise_speed, float cruise_throttle)
{
// get speed forward
float speed;
if (!get_forward_speed(speed)) {
// we expect caller will not try to control heading using rate control without a valid speed estimate
// on failure to get speed we do not attempt to steer
return 0.0f;
}
// calculate dt
uint32_t now = AP_HAL::millis();
float dt = (now - _speed_last_ms) / 1000.0f;
if (_speed_last_ms == 0 || dt > 0.1) {
dt = 0.0f;
}
_speed_last_ms = now;
// acceleration limit desired speed
if (is_positive(_throttle_accel_max)) {
// on first iteration stay at current current speed (although enforced 20ms delay may upset drag racers)
if (!is_positive(dt)) {
desired_speed = speed;
} else {
float speed_change_max = _throttle_accel_max * dt;
desired_speed = constrain_float(desired_speed, _desired_speed - speed_change_max, _desired_speed + speed_change_max);
}
}
// record desired speed for next iteration
_desired_speed = desired_speed;
// calculate speed error and pass to PID controller
float speed_error = desired_speed - speed;
_throttle_speed_pid.set_input_filter_all(speed_error);
// get p
float p = _throttle_speed_pid.get_p();
// get i unless moving at low speed or motors have hit a limit
float i = 0.0f;
if ((is_negative(speed_error) && !motor_limit_low && !_throttle_limit_low) || (is_positive(speed_error) && !motor_limit_high && !_throttle_limit_high)) {
i = _throttle_speed_pid.get_i();
}
// get d
float d = _throttle_speed_pid.get_d();
// calculate base throttle (protect against divide by zero)
float throttle_base = 0.0f;
if (is_positive(cruise_speed) && is_positive(cruise_throttle)) {
throttle_base = desired_speed * (cruise_throttle / cruise_speed);
}
// calculate final output
float throttle_out = (p+i+d+throttle_base);
// clear local limit flags used to stop i-term build-up as we stop reversed outputs going to motors
_throttle_limit_low = false;
_throttle_limit_high = false;
// protect against reverse output being sent to the motors unless braking has been enabled
if (!_brake_enable) {
// if both desired speed and actual speed are positive, do not allow negative values
if (is_positive(speed) && is_positive(desired_speed) && !is_positive(throttle_out)) {
throttle_out = 0.0f;
_throttle_limit_low = true;
}
if (is_negative(speed) && is_negative(desired_speed) && !is_negative(throttle_out)) {
throttle_out = 0.0f;
_throttle_limit_high = true;
}
}
// final output throttle in range -1 to 1
return throttle_out;
}
// return a throttle output from -1 to +1 to perform a controlled stop. returns true once the vehicle has stopped
float AR_AttitudeControl::get_throttle_out_stop(bool skid_steering, bool motor_limit_low, bool motor_limit_high, float cruise_speed, float cruise_throttle, bool &stopped)
{
// get current system time
uint32_t now = AP_HAL::millis();
// if we were stopped in the last 300ms, assume we are still stopped
bool _stopped = (_stop_last_ms != 0) && (now - _stop_last_ms) < 300;
// get speed forward
float speed;
if (!get_forward_speed(speed)) {
// could not get speed so assume stopped
_stopped = true;
} else {
// if vehicle drops below _stop_speed consider it stopped
if (fabsf(speed) <= fabsf(_stop_speed)) {
_stopped = true;
}
}
// set stopped status for caller
stopped = _stopped;
// if stopped return zero
if (stopped) {
// update last time we thought we were stopped
_stop_last_ms = now;
return 0.0f;
} else {
// clear stopped system time
_stop_last_ms = 0;
// run speed controller to bring vehicle to stop
return get_throttle_out_speed(0.0f, skid_steering, motor_limit_low, motor_limit_high, cruise_speed, cruise_throttle);
}
}
// get forward speed in m/s (earth-frame horizontal velocity but only along vehicle x-axis). returns true on success
bool AR_AttitudeControl::get_forward_speed(float &speed) const
{
Vector3f velocity;
if (!_ahrs.get_velocity_NED(velocity)) {
// use less accurate GPS, assuming entire length is along forward/back axis of vehicle
if (_ahrs.get_gps().status() >= AP_GPS::GPS_OK_FIX_3D) {
if (labs(wrap_180_cd(_ahrs.yaw_sensor - _ahrs.get_gps().ground_course_cd())) <= 9000) {
speed = _ahrs.get_gps().ground_speed();
} else {
speed = -_ahrs.get_gps().ground_speed();
}
return true;
} else {
return false;
}
}
// calculate forward speed velocity into body frame
speed = velocity.x*_ahrs.cos_yaw() + velocity.y*_ahrs.sin_yaw();
return true;
}

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#pragma once
#include <AP_AHRS/AP_AHRS.h>
#include <AP_Common/AP_Common.h>
#include <AC_PID/AC_PID.h>
#include <AC_PID/AC_P.h>
// attitude control default definition
#define AR_ATTCONTROL_STEER_ANG_P 1.00f
#define AR_ATTCONTROL_STEER_RATE_P 1.00f
#define AR_ATTCONTROL_STEER_RATE_I 0.50f
#define AR_ATTCONTROL_STEER_RATE_IMAX 1.00f
#define AR_ATTCONTROL_STEER_RATE_D 0.00f
#define AR_ATTCONTROL_STEER_RATE_FILT 5.00f
#define AR_ATTCONTROL_THR_SPEED_P 0.20f
#define AR_ATTCONTROL_THR_SPEED_I 0.20f
#define AR_ATTCONTROL_THR_SPEED_IMAX 1.00f
#define AR_ATTCONTROL_THR_SPEED_D 0.00f
#define AR_ATTCONTROL_THR_SPEED_FILT 5.00f
#define AR_ATTCONTROL_DT 0.02f
// throttle/speed control maximum acceleration/deceleration (in m/s) (_ACCEL_MAX parameter default)
#define AR_ATTCONTROL_THR_ACCEL_MAX 5.00f
// minimum speed in m/s
#define AR_ATTCONTROL_STEER_SPEED_MIN 1.0f
// speed (in m/s) at or below which vehicle is considered stopped (_STOP_SPEED parameter default)
#define AR_ATTCONTROL_STOP_SPEED_DEFAULT 0.1f
class AR_AttitudeControl {
public:
// constructor
AR_AttitudeControl(AP_AHRS &ahrs);
//
// steering controller
//
// return a steering servo output from -1.0 to +1.0 given a desired lateral acceleration rate in m/s/s.
// positive lateral acceleration is to the right.
float get_steering_out_lat_accel(float desired_accel, bool skid_steering, bool motor_limit_left, bool motor_limit_right);
// return a steering servo output from -1 to +1 given a yaw error in radians
float get_steering_out_angle_error(float angle_err, bool skid_steering, bool motor_limit_left, bool motor_limit_right);
// return a steering servo output from -1 to +1 given a
// desired yaw rate in radians/sec. Positive yaw is to the right.
float get_steering_out_rate(float desired_rate, bool skid_steering, bool motor_limit_left, bool motor_limit_right);
//
// throttle / speed controller
//
// set limits used by throttle controller
// forward/back acceleration max in m/s/s
// forward/back deceleartion max in m/s/s
void set_throttle_limits(float throttle_accel_max, float throttle_decel_max);
// return a throttle output from -1 to +1 given a desired speed in m/s (use negative speeds to travel backwards)
// skid_steering should be true for skid-steer vehicles
// motor_limit should be true if motors have hit their upper or lower limits
// cruise speed should be in m/s, cruise throttle should be a number from -1 to +1
float get_throttle_out_speed(float desired_speed, bool skid_steering, bool motor_limit_low, bool motor_limit_high, float cruise_speed, float cruise_throttle);
// return a throttle output from -1 to +1 to perform a controlled stop. stopped is set to true once stop has been completed
float get_throttle_out_stop(bool skid_steering, bool motor_limit_low, bool motor_limit_high, float cruise_speed, float cruise_throttle, bool &stopped);
// low level control accessors for reporting and logging
AC_P& get_steering_angle_p() { return _steer_angle_p; }
AC_PID& get_steering_rate_pid() { return _steer_rate_pid; }
AC_PID& get_throttle_speed_pid() { return _throttle_speed_pid; }
// get forward speed in m/s (earth-frame horizontal velocity but only along vehicle x-axis). returns true on success
bool get_forward_speed(float &speed) const;
// get throttle/speed controller maximum acceleration (also used for deceleration)
float get_accel_max() const { return MAX(_throttle_accel_max, 0.0f); }
// parameter var table
static const struct AP_Param::GroupInfo var_info[];
private:
// external references
AP_AHRS &_ahrs;
// parameters
AC_P _steer_angle_p; // steering angle controller
AC_PID _steer_rate_pid; // steering rate controller
AC_PID _throttle_speed_pid; // throttle speed controller
AP_Float _throttle_accel_max; // speed/throttle control acceleration (and deceleration) maximum in m/s/s. 0 to disable limits
AP_Int8 _brake_enable; // speed control brake enable/disable. if set to 1 a reversed output to the motors to slow the vehicle.
AP_Float _stop_speed; // speed control stop speed. Motor outputs to zero once vehicle speed falls below this value
// steering control
uint32_t _steer_turn_last_ms; // system time of last call to steering rate controller
// throttle control
uint32_t _speed_last_ms; // system time of last call to get_throttle_out_speed
float _desired_speed; // last recorded desired speed
uint32_t _stop_last_ms; // system time the vehicle was at a complete stop
bool _throttle_limit_low; // throttle output was limited from going too low (used to reduce i-term buildup)
bool _throttle_limit_high; // throttle output was limited from going too high (used to reduce i-term buildup)
};