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The cob_linear_nav package provides a configurable node for simple navigation. It drives the robot on a linear path from its current position to its goal position without any obstacle avoidance. This should be carried out in another package. If the robot doesn't move anymore (e.g. due to an obstacle that stays on the robot path), the robot stops trying to reach the goal after a certain period of time (to be specified over a parameter).

ROS API

cob_linear_nav

The cob_linear_nav node takes in geometry_msgs/PoseStamped messages as a new goal, as well as nav_msgs/Odometry messages specifying the odometry of the robot. The movement commands are published as a geometry_msgs/Twist topic. It also provides the ability to send a goal using rviz on the /move_base_linear_simple/goal topic.

Subscribed Topics

/move_baser_linear_simple/goal (geometry_msgs/PoseStamped)

• new goal for the robot

odom (nav_msgs/Odometry)

• odometry of the robot

Published Topics

cmd_vel (geometry_msgs/Twist)

• movement command to robot base

Parameters

~kv (double, default: 2.5)

• Damping term for potential field like controller for translational movement.

~kp (double, default: 3.0)

• Stiffness term for potential field like controller for translational movement.

~virt_mass (double, default: 0.5)

• Virtual mass term for potential field like controller for translational movement.

~vmax (double, default: 0.3)

• Maximum allowed velocity for translational movement.

~goal_threshold (double, default: 0.03 [m])

• Distance to goal at which robot considers to have reached the goal (translational movement only).

~speed_threshold (double, default: 0.08)

• Speed at which the robot considers to have stopped (translational movement only).

~kv_rot (double, default: 2.5)

• Damping term for potential field like controller for rotational movement.

~kp_rot (double, default: 3.0)

• Stiffness term for potential field like controller for rotational movement.

~virt_mass_rot (double, default: 0.5)

• Virtual mass term for potential field like controller for rotational movement.

~vtheta_max (double, default: 0.3)

• Maximum allowed rotational velocity for movement.

~goal_threshold_rot (double, default: 0.08)

• Distance to goal at which robot considers to have reached the goal (rotational movement only).

~speed_threshold_rot (double, default: 0.08)

• Speed at which the robot considers to have stopped (rotational movement only).

~global_frame (string, default: "/map")

• Map frame.

~robot_frame (string, default: "/base_link")

• Frame of robot which is considered to be the frame that should reach the goal position.

~slow_down_distance (double, default: 0.5 [m])

• Distance to goal at which the robot starts slowing down.

~goal_abortion_time (double, default: 5.0 [s])

• Time after which the robot stops trying to reach the goal, if it does not move anymore (as indicated by the odometry). This happens when the movement is stopped by an external collision avoidance function due to e.g. obstacles on the linear path.

Usage/Examples

For the usage of cob_linear_nav, have a look at cob_navigation_global and the 2dnav_linear.launch and 2dnav_linear.xml files therein.

A sample parameter file (currently in cob_navigation_config/common/linear/ctrl_params.yaml) can look like this:

#Parameters designing the potential field controller
#Translational part
kv: 2.50 #damping 2.50
kp: 3.00 #stiffness 3.0
virt_mass: 0.50 #0.50
vmax: 0.3 #0.3
goal_threshold: 0.03 #0.03
speed_threshold: 0.08 #0.08

#Rotational part
kv_rot: 2.0 #damping 2.0
kp_rot: 2.0 #stiffness 2.0
virt_mass_rot: 0.50 #0.5
vtheta_max: 0.3 # 0.3
goal_threshold_rot: 0.08 #0.08
speed_threshold_rot: 0.08 #0.08

#tf parameters
global_frame: /map #/map
robot_frame: /base_link #/base_link

slow_down_distance: 0.5 #0.5[m] distance from robot_center to goal at which robot starts slowing down
goal_abortion_time: 5.0 #5.0[s] time until robot aborts goal due to obstacle