PX4-Autopilot/src/lib/control_allocation/ControlAllocationSequentialDesaturation.cpp

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/**
 * @file ControlAllocationSequentialDesaturation.cpp
 *
 * @author Roman Bapst <bapstroman@gmail.com>
 * @author Beat Küng <beat-kueng@gmx.net>
 */

#include "ControlAllocationSequentialDesaturation.hpp"


void
ControlAllocationSequentialDesaturation::allocate()
{
	//Compute new gains if needed
	updatePseudoInverse();

	_prev_actuator_sp = _actuator_sp;

	switch (_param_mc_airmode.get()) {
	case 1:
		mixAirmodeRP();
		break;

	case 2:
		mixAirmodeRPY();
		break;

	default:
		mixAirmodeDisabled();
		break;
	}
}

void ControlAllocationSequentialDesaturation::desaturateActuators(
	ActuatorVector &actuator_sp,
	const ActuatorVector &desaturation_vector, bool increase_only)
{
	float gain = computeDesaturationGain(desaturation_vector, actuator_sp);

	if (increase_only && gain < 0.f) {
		return;
	}

	for (int i = 0; i < _num_actuators; i++) {
		actuator_sp(i) += gain * desaturation_vector(i);
	}

	gain = 0.5f * computeDesaturationGain(desaturation_vector, actuator_sp);

	for (int i = 0; i < _num_actuators; i++) {
		actuator_sp(i) += gain * desaturation_vector(i);
	}
}

float ControlAllocationSequentialDesaturation::computeDesaturationGain(const ActuatorVector &desaturation_vector,
		const ActuatorVector &actuator_sp)
{
	float k_min = 0.f;
	float k_max = 0.f;

	for (int i = 0; i < _num_actuators; i++) {
		// Do not use try to desaturate using an actuator with weak effectiveness to avoid large desaturation gains
		if (fabsf(desaturation_vector(i)) < 0.2f) {
			continue;
		}

		if (actuator_sp(i) < _actuator_min(i)) {
			float k = (_actuator_min(i) - actuator_sp(i)) / desaturation_vector(i);

			if (k < k_min) { k_min = k; }

			if (k > k_max) { k_max = k; }
		}

		if (actuator_sp(i) > _actuator_max(i)) {
			float k = (_actuator_max(i) - actuator_sp(i)) / desaturation_vector(i);

			if (k < k_min) { k_min = k; }

			if (k > k_max) { k_max = k; }
		}
	}

	// Reduce the saturation as much as possible
	return k_min + k_max;
}

void
ControlAllocationSequentialDesaturation::mixAirmodeRP()
{
	// Airmode for roll and pitch, but not yaw

	// Mix without yaw
	ActuatorVector thrust_z;

	for (int i = 0; i < _num_actuators; i++) {
		_actuator_sp(i) = _actuator_trim(i) +
				  _mix(i, ControlAxis::ROLL) * (_control_sp(ControlAxis::ROLL) - _control_trim(ControlAxis::ROLL)) +
				  _mix(i, ControlAxis::PITCH) * (_control_sp(ControlAxis::PITCH) - _control_trim(ControlAxis::PITCH)) +
				  _mix(i, ControlAxis::THRUST_X) * (_control_sp(ControlAxis::THRUST_X) - _control_trim(ControlAxis::THRUST_X)) +
				  _mix(i, ControlAxis::THRUST_Y) * (_control_sp(ControlAxis::THRUST_Y) - _control_trim(ControlAxis::THRUST_Y)) +
				  _mix(i, ControlAxis::THRUST_Z) * (_control_sp(ControlAxis::THRUST_Z) - _control_trim(ControlAxis::THRUST_Z));
		thrust_z(i) = _mix(i, ControlAxis::THRUST_Z);
	}

	desaturateActuators(_actuator_sp, thrust_z);

	// Mix yaw independently
	mixYaw();
}

void
ControlAllocationSequentialDesaturation::mixAirmodeRPY()
{
	// Airmode for roll, pitch and yaw

	// Do full mixing
	ActuatorVector thrust_z;
	ActuatorVector yaw;

	for (int i = 0; i < _num_actuators; i++) {
		_actuator_sp(i) = _actuator_trim(i) +
				  _mix(i, ControlAxis::ROLL) * (_control_sp(ControlAxis::ROLL) - _control_trim(ControlAxis::ROLL)) +
				  _mix(i, ControlAxis::PITCH) * (_control_sp(ControlAxis::PITCH) - _control_trim(ControlAxis::PITCH)) +
				  _mix(i, ControlAxis::YAW) * (_control_sp(ControlAxis::YAW) - _control_trim(ControlAxis::YAW)) +
				  _mix(i, ControlAxis::THRUST_X) * (_control_sp(ControlAxis::THRUST_X) - _control_trim(ControlAxis::THRUST_X)) +
				  _mix(i, ControlAxis::THRUST_Y) * (_control_sp(ControlAxis::THRUST_Y) - _control_trim(ControlAxis::THRUST_Y)) +
				  _mix(i, ControlAxis::THRUST_Z) * (_control_sp(ControlAxis::THRUST_Z) - _control_trim(ControlAxis::THRUST_Z));
		thrust_z(i) = _mix(i, ControlAxis::THRUST_Z);
		yaw(i) = _mix(i, ControlAxis::YAW);
	}

	desaturateActuators(_actuator_sp, thrust_z);

	// Unsaturate yaw (in case upper and lower bounds are exceeded)
	// to prioritize roll/pitch over yaw.
	desaturateActuators(_actuator_sp, yaw);
}

void
ControlAllocationSequentialDesaturation::mixAirmodeDisabled()
{
	// Airmode disabled: never allow to increase the thrust to unsaturate a motor

	// Mix without yaw
	ActuatorVector thrust_z;
	ActuatorVector roll;
	ActuatorVector pitch;

	for (int i = 0; i < _num_actuators; i++) {
		_actuator_sp(i) = _actuator_trim(i) +
				  _mix(i, ControlAxis::ROLL) * (_control_sp(ControlAxis::ROLL) - _control_trim(ControlAxis::ROLL)) +
				  _mix(i, ControlAxis::PITCH) * (_control_sp(ControlAxis::PITCH) - _control_trim(ControlAxis::PITCH)) +
				  _mix(i, ControlAxis::THRUST_X) * (_control_sp(ControlAxis::THRUST_X) - _control_trim(ControlAxis::THRUST_X)) +
				  _mix(i, ControlAxis::THRUST_Y) * (_control_sp(ControlAxis::THRUST_Y) - _control_trim(ControlAxis::THRUST_Y)) +
				  _mix(i, ControlAxis::THRUST_Z) * (_control_sp(ControlAxis::THRUST_Z) - _control_trim(ControlAxis::THRUST_Z));
		thrust_z(i) = _mix(i, ControlAxis::THRUST_Z);
		roll(i) = _mix(i, ControlAxis::ROLL);
		pitch(i) = _mix(i, ControlAxis::PITCH);
	}

	// only reduce thrust
	desaturateActuators(_actuator_sp, thrust_z, true);

	// Reduce roll/pitch acceleration if needed to unsaturate
	desaturateActuators(_actuator_sp, roll);
	desaturateActuators(_actuator_sp, pitch);

	// Mix yaw independently
	mixYaw();
}

void
ControlAllocationSequentialDesaturation::mixYaw()
{
	// Add yaw to outputs
	ActuatorVector yaw;
	ActuatorVector thrust_z;

	for (int i = 0; i < _num_actuators; i++) {
		_actuator_sp(i) += _mix(i, ControlAxis::YAW) * (_control_sp(ControlAxis::YAW) - _control_trim(ControlAxis::YAW));
		yaw(i) = _mix(i, ControlAxis::YAW);
		thrust_z(i) = _mix(i, ControlAxis::THRUST_Z);
	}

	// Change yaw acceleration to unsaturate the outputs if needed (do not change roll/pitch),
	// and allow some yaw response at maximum thrust
	ActuatorVector max_prev = _actuator_max;
	_actuator_max += (_actuator_max - _actuator_min) * MINIMUM_YAW_MARGIN;
	desaturateActuators(_actuator_sp, yaw);
	_actuator_max = max_prev;

	// reduce thrust only
	desaturateActuators(_actuator_sp, thrust_z, true);
}

void
ControlAllocationSequentialDesaturation::updateParameters()
{
	updateParams();
}