This module implements optical flow landings in which the divergence is kept constant. When using a fixed gain for control, the covariance between thrust and divergence is tracked, so that the drone knows when it has arrived close to the landing surface. Then, a final landing procedure is triggered. It can also be set to adaptive gain control, where the goal is to continuously gauge the distance to the landing surface. In this mode, the drone will oscillate all the way down to the surface. More...

#include "std.h"

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Data Structures
struct	OpticalFlowLanding

Macros
#define	GUIDANCE_H_MODE_MODULE_SETTING GUIDANCE_H_MODE_NAV

#define	GUIDANCE_V_MODE_MODULE_SETTING GUIDANCE_V_MODE_MODULE

Functions
void	guidance_v_module_init (void)

void	guidance_v_module_enter (void)
	Entering the vertical module (user switched to module) More...

void	guidance_v_module_run (bool in_flight)

Variables
struct OpticalFlowLanding	of_landing_ctrl

Detailed Description

This module implements optical flow landings in which the divergence is kept constant. When using a fixed gain for control, the covariance between thrust and divergence is tracked, so that the drone knows when it has arrived close to the landing surface. Then, a final landing procedure is triggered. It can also be set to adaptive gain control, where the goal is to continuously gauge the distance to the landing surface. In this mode, the drone will oscillate all the way down to the surface.

de Croon, G.C.H.E. (2016). Monocular distance estimation with optical flow maneuvers and efference copies: a stability-based strategy. Bioinspiration & biomimetics, 11(1), 016004. http://iopscience.iop.org/article/10.1088/1748-3190/11/1/016004

Based on the above theory, we have also developed a new strategy for landing that consists of two phases: (1) while hovering, the drone determines the optimal gain by increasing the gain until oscillation (2) the drone starts landing while exponentially decreasing the gain over time

This strategy leads to smooth, high-performance constant divergence landings, as explained in the article: H.W. Ho, G.C.H.E. de Croon, E. van Kampen, Q.P. Chu, and M. Mulder (submitted) Adaptive Control Strategy for Constant Optical Flow Divergence Landing, https://arxiv.org/abs/1609.06767

Definition in file optical_flow_landing.h.

Data Structure Documentation

◆ OpticalFlowLanding

struct OpticalFlowLanding

Definition at line 49 of file optical_flow_landing.h.

Data Fields
float	agl	agl = height from sonar (only used when using "fake" divergence)
float	agl_lp	low-pass version of agl
uint32_t	CONTROL_METHOD	type of divergence control: 0 = fixed gain, 1 = adaptive gain
float	cov_limit	for fixed gain control, what is the cov limit triggering the landing
uint32_t	COV_METHOD	method to calculate the covariance: between thrust and div (0) or div and div past (1)
float	cov_set_point	for adaptive gain control, setpoint of the covariance (oscillations)
float	d_err	difference of error for the D-gain
uint32_t	delay_steps	number of delay steps for div past
float	dgain	D-gain for constant divergence control.
float	dgain_adaptive	D-gain for adaptive gain control.
float	divergence	Divergence estimate.
float	divergence_setpoint	setpoint for constant divergence approach
bool	elc_oscillate	Whether or not to oscillate at beginning of elc to find optimum gain.
float	igain	I-gain for constant divergence control.
float	igain_adaptive	I-gain for adaptive gain control.
float	lp_const	low-pass filter constant
float	lp_cov_div_factor	low-pass factor for the covariance of divergence in order to trigger the second landing phase in the exponential strategy.
float	nominal_thrust	nominal thrust around which the PID-control operates
float	p_land_threshold	if during the exponential landing the gain reaches this value, the final landing procedure is triggered
float	pgain	P-gain for constant divergence control (from divergence error to thrust)
float	pgain_adaptive	P-gain for adaptive gain control.
float	previous_err	Previous divergence tracking error.
float	reduction_factor_elc	reduction factor - after oscillation, how much to reduce the gain...
float	sum_err	integration of the error for I-gain
float	t_transition	how many seconds the drone has to be oscillating in order to transition to the hover phase with reduced gain
float	vel	vertical velocity as determined with sonar (only used when using "fake" divergence)
uint32_t	VISION_METHOD	whether to use vision (1) or Optitrack / sonar (0)
uint32_t	window_size	number of time steps in "window" used for getting the covariance

Macro Definition Documentation

◆ GUIDANCE_H_MODE_MODULE_SETTING

#define GUIDANCE_H_MODE_MODULE_SETTING GUIDANCE_H_MODE_NAV

Definition at line 84 of file optical_flow_landing.h.

◆ GUIDANCE_V_MODE_MODULE_SETTING

#define GUIDANCE_V_MODE_MODULE_SETTING GUIDANCE_V_MODE_MODULE

Definition at line 87 of file optical_flow_landing.h.

Function Documentation

◆ guidance_v_module_enter()

void guidance_v_module_enter ( void )

Entering the vertical module (user switched to module)

Definition at line 111 of file ctrl_module_innerloop_demo.c.

◆ guidance_v_module_init()

void guidance_v_module_init ( void )

Definition at line 105 of file ctrl_module_innerloop_demo.c.

◆ guidance_v_module_run()

void guidance_v_module_run ( bool in_flight )

Definition at line 656 of file optical_flow_hover.c.

Variable Documentation

◆ of_landing_ctrl

struct OpticalFlowLanding of_landing_ctrl

Definition at line 157 of file optical_flow_landing.c.

Referenced by final_landing_procedure(), guidance_v_module_enter(), PID_divergence_control(), reset_all_vars(), send_divergence(), set_cov_div(), update_errors(), vertical_ctrl_agl_cb(), vertical_ctrl_module_init(), and vertical_ctrl_module_run().

Data Structures

Macros

Functions

Variables