🎱D.11 Regulated Pure Pursuit

Regulated Pure Pursuit Controller ဆိုတာ service နဲ့ industrial robot တွေ အတွက် အထူးထုတ် ထားတဲ့ Pure Pursuit controller တမျိုး ဖြစ်ပါတယ်။ Robot Safety ဖြစ်ရန် အလိုငှါမျက်ကွယ်ထောင့်တွေ ရောက်ရင် controller ရဲ့ linear velocity ကို လျော့ချပေးပါတယ်။

တိကျတဲ့ trajectory တွေ ၊ smoother robot motion တွေ အတွက် အခြားသော controller pkg တွေထက် path-following ကောင်းပါတယ်။ Obstacle တွေ တွေ့တဲ့ အခါ controller ကို အလိုအလျောက် အရှိန်လျော့စေပါတယ်။

ဒီလို အရှိန်လျော့စေခြင်းအားဖြင့် accident အရေအတွက်ကို လျော့ချပေးပါတယ်။ Dynamic Environments အတွက် သုံးတဲ့ robot တွေ အတွက် ဒီ Regulated Pure Pursuit controller ‌က safety ဖြစ်ပြီး path-following အတွက် Performance ကောင်းကောင်း ထုတ်ပေးနိုင်ပါတယ်။

accident အရေအတွက်ကိုလည်း လျော့ချပေးပါတယ်။ Dynamic Environments အတွက် သုံးတဲ့ robot တွေ အတွက် ဒီ Regulated Pure Pursuit controller ‌က safety ဖြစ်ပြီး path-following အတွက် Performance ကောင်းကောင်း ထုတ်ပေးနိုင်ပါတယ်။

Parameter	Description	Type	Default
desired_levelt_vel	desired max linear velocity	double	0.5
lookahead_dist	lookahead distance to find the lookahead point	double	0.6
min_lookahead_dist	minimum lookahead distance	double	0.3
max_lookahead_dist	maxmum lookahead distance	double	0.9
lookahead_time	The time to project the velocity	double	1.5
rotate_to_heading_angular_vel	If use_rotate_to_ heading is true, this's the angular velocity	double	1.8
transform_tolerance	The TF transform tolerance	double	0.1
use_velocity_scaled_lookahead_dist	Whether to use the velocity scaled lookahead distance	bool	TRUE
min_approach_linear_velovity	The minimum velocity to apply when approaching the goal (Must be >0.01)	double	0.05
approach_velocity_scaling_dist	Distance left on the path to start slowing down. (Should be less than hlaf the costmap width)	double	0.6
use_collision_detection	To enable collision detection	bool	TRUE
max_allowed_time_to_collision_up_to_carrot	time (s) to project a velocity command forward to check for collisions	double	1
use_regulated_linear_velocity_scaling	To use the regulated features for path curvature	bool	TRUE
use_cost_regulated_linear_velocity_scaling	To use the regulated features for proximity to obstacles	bool	TRUE
regulated_linear_scaling_min_radius	turning radius (m) for which the regulation features are triggered	double	0.9
regulated_linear_scaling_min_speed	minimum speed for any of the regulated heuristics can send	double	0.25
use_fixed_curvature_lookahead	To use a fixed lookahead distance to compute curvature from.	bool	FALSE
curvature_lookahead_dist	Distance to look ahead on the path to detect curvature.	double	0.6
use_rotate_to_heading	To enable rotating to rough heading and goal orientation when using holonomic planners.	bool	TRUE
allow_reversing	Enables the robot to drive in the reverse direction, when the path planned involves reversing	bool	FALSE
rotate_to_heading_min_angle	The difference in the path orientation and the starting robot orientation to trigger a rotate in place	double	0.785
max_angular_accel	Maximum allowable angular acceleration (rad/s/s) while rotating to heading	double	3.2
max_robot_pose_search_dist	Upper bound on integrated distance along the global plan to search for the closest pose to the robot pose. This should be left as the default unless there are paths with loops and intersections that do not leave the local costmap, in which case making this value smaller is necessary to prevent shortcutting.	double	Local costmap max extent (max(width, height) / 2)
use_interpolation	Enable linear interpolation between poses for lookahead point selection. Leads to smoother commanded linear and angular velocities.	bool	TRUE

The Regulated Pure Pursuit controller implements a variation on the Pure Pursuit controller that specifically t argeting service / industrial robot needs. It regulates the linear velocities by curvature of the path to help reduce overshoot at high speeds around blind corners allowing operations to be much more safe.

It also better follows paths than any other variation currently available of Pure Pursuit. It also has heuristics to slow in proximity to other obstacles so that you can slow the robot automatically when nearby potential collisions. It also implements the Adaptive lookahead point features to be scaled by velocities to enable more stable behavior in a larger range of translational speeds.

နမူနာ

controller_server:
  ros__parameters:
    use_sim_time: True
    controller_frequency: 20.0
    min_x_velocity_threshold: 0.001
    min_y_velocity_threshold: 0.5
    min_theta_velocity_threshold: 0.001
    progress_checker_plugins: ["progress_checker"] # progress_checker_plugin: "progress_checker" For Humble and older
    goal_checker_plugins: ["goal_checker"]
    controller_plugins: ["FollowPath"]

    progress_checker:
      plugin: "nav2_controller::SimpleProgressChecker"
      required_movement_radius: 0.5
      movement_time_allowance: 10.0
    goal_checker:
      plugin: "nav2_controller::SimpleGoalChecker"
      xy_goal_tolerance: 0.25
      yaw_goal_tolerance: 0.25
      stateful: True
    FollowPath:
      plugin: "nav2_regulated_pure_pursuit_controller::RegulatedPurePursuitController"
      desired_linear_vel: 0.5
      lookahead_dist: 0.6
      min_lookahead_dist: 0.3
      max_lookahead_dist: 0.9
      lookahead_time: 1.5
      rotate_to_heading_angular_vel: 1.8
      transform_tolerance: 0.1
      use_velocity_scaled_lookahead_dist: false
      min_approach_linear_velocity: 0.05
      approach_velocity_scaling_dist: 0.6
      use_collision_detection: true
      max_allowed_time_to_collision_up_to_carrot: 1.0
      use_regulated_linear_velocity_scaling: true
      use_fixed_curvature_lookahead: false
      curvature_lookahead_dist: 0.25
      use_cost_regulated_linear_velocity_scaling: false
      regulated_linear_scaling_min_radius: 0.9
      regulated_linear_scaling_min_speed: 0.25
      use_rotate_to_heading: true
      allow_reversing: false
      rotate_to_heading_min_angle: 0.785
      max_angular_accel: 3.2
      max_robot_pose_search_dist: 10.0
      use_interpolation: false