RefineCBF for Differential-Drive Hardware Application

ROS package for the refineCBF algorithm implementation on a Turtlebot3 as part of Nathan Cusson-Nadeau's Master's thesis at UC San Diego. RefineCBF is an algorithm from the paper Refining Control Barrier Functions using HJ Reachability by Sander Tonkens and Sylvia Herbert, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2022. It provides a constructive algorithmic approach to create valid control barrier functions (CBFs) using a unification between Hamilton-Jacobi Reachability analysis and CBF theory. Valid CBFs can be used in safety-critical controls to ensure safety during real-time operation of autonomous systems.

Requirements:

This package relies on the following:

• Ubuntu 20.04 LTS operating system. It is possible this code can run on other ROS2 compatible distributions but may require minor alterations and has not been tested.
• Python 3: sudo apt install python3.x (where x is most up-to-date python 3 distribution)
• Foxy Fitzroy ROS2 distribution with RVIZ2.
• ROS Physics Simulator Gazebo for Foxy distribution.
• hj_reachability: Toolbox for computing HJ reachability leveraging jax: pip install --upgrade hj-reachability. Requires installing jax additionally based on available accelerator support. See JAX installation instructions for details.
• cbf_opt: Toolbox for constructing CBFs and implementing them in a safety filter (using cvxpy). Run pip install "cbf_opt>=0.6.0" or install locally using the Github link and run pip install -e . in DIR to install.
• refine_cbfs: Complementary library from SASLab refineCBF research code. Contains code to define a tabular CBF (a CBF defined over a grid) and provides an interface with hj_reachability and cbf_opt to define its dynamics. Clone the repository here to some local directory: RefineCBF Repo. Install locally using: pip install <package_dir_with_setup.py> -e .
• tqdm: Provides visual feedback of for loop progression in Python. pip install tqdm
• (Optional) ros1_bridge: if needing to interface with ROS1 nodes, it may be necessary to bridge between ROS1 and ROS2 topics, this bridging package allows this. For example, if using the Vicon aerodrome arena at UCSD, the standard package publishes state information over ROS1 topics and thus a bridge must be made between them.
• (Optional) erl_quadrotor_vicon: if using the UC San Diego aerodrome arena, this package will be necessary to retrieve Vicon state information. See ERL Github. Do not let the name of the package deceive you, it can retrieve the pose of any kind of robot. This will additonally require the ROS1 distibution Noetic Ninjemys.

Documentation

See the code documentation for full description of package.

Minimal Example

To run a minimal example in Gazebo simulator:

Build the package from root of your workspace:

cd ~/<refine_cbf_ws>
source /opt/ros/<ros2_distro>/setup.bash
colcon build --symlink-install --packages-select refine_cbf

Gazebo Terminal:

source /opt/ros/<ros2_distro>/setup.bash
source ~/<refine_cbf_ws>/install/setup.bash
ros2 launch turtlebot3_gazebo refine_cbf_experiment.launch.py

RVIZ Terminal:

source /opt/ros/<ros2_distro>/setup.bash
rviz2

Apply (open) the provided rviz config file: refine_cbf.rviz

RefineCBF Terminal:

source /opt/ros/<ros2_distro>/setup.bash
cd ~/<refine_cbf_ws>/turtwig # Must be run in the root of workspace for relative folder pointers!
ros2 launch refine_cbf refine_cbf_launch.py

Time Saving Aliases for .bashrc

Adding the following aliases to your .bashrc file may save time during use. Type the desired following commands in your command line:

• Sourcing Package: echo "alias launch_rcbf='ros2 launch refine_cbf refine_cbf_launch.py'" >> ~/.bashrc
• Launching Gazebo Experiment: echo "alias rcbf_gzb='ros2 launch turtlebot3_gazebo refine_cbf_experiment_2x2.launch.py'" >> ~/.bashrc
• RefineCBF Experiment Launch: echo "alias launch_rcbf='ros2 launch refine_cbf refine_cbf_launch.py'" >> ~/.bashrc
• Running Safety Filter node: echo "alias rcbf_sf='ros2 run refine_cbf safety_filter'" >> ~/.bashrc
• Running Nominal Policy node: echo "alias rcbf_np='ros2 run refine_cbf nominal_policy'" >> ~/.bashrc
• Running Dynamic Programming node: echo "alias rcbf_dp='ros2 run refine_cbf dynamic_programming'" >> ~/.bashrc
• Running Visualization node: echo "alias rcbf_vz='ros2 run refine_cbf refine_cbf_visualization'" >> ~/.bashrc
• SSH into tb3 (add your tb3 IP address): echo "alias tb3_ssh='ssh ubuntu@<tb3_ip_address>'" >> ~/.bashrc

Package Namesake

This package is codenamed Turtwig after the turtle Pokemon!