NEXUS

A ROS 2 framework which enables configuration and orchestration of process workflows for both individual robotic cells and sets of cells (line). NEXUS facilitates the integration of hardware agnostic industrial robotics and traditional automation components, specifying each cell or line processes through re-configurable behaviour trees. Cells in a line, or hardware components in a cell, can be triggered concurrently or sequentially according to recipes, managed through the orchestrator, departing from traditional Programmable Logic Controllers.

For details on architecture and concepts see.

Requirements

• ROS 2 Iron on Ubuntu 22.04

Setup

Install system dependencies

While cargo and rustc can be installed via rosdep, the version that available is v1.66 on most target platforms. However most dependencies require newer versions of cargo and rustc. Hence for now, we will install the latest version manually. TODO: Consider adding this dep back for J turtle if Ubuntu 24.04 has the newer. cargo and rustc pkgs.

sudo apt update && sudo apt install curl
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Setup the NEXUS workspace

mkdir ~/ws_nexus/src -p
cd ~/ws_nexus/src/
git clone git@github.com:osrf/nexus
vcs import . < nexus/abb.repos
cd ~/ws_nexus
rosdep install --from-paths src --ignore-src --rosdistro iron -y -r

Build the NEXUS workspace

source /opt/ros/iron/setup.bash
colcon build --cmake-args -DCMAKE_BUILD_TYPE=Release

Configuration

The workcell and system orchestrators rely on behavior trees for orchestration. NEXUS provides several BT skills that may be reused for a variety of applications. See sample BTs for system_orchestrator and workcell_orchestrator for a pick & place application.

At present, capabilities are registered as plugins with the orchestrator at runtime. We support these capabilities out of the bo Each plugin may register one or more behavior tree nodes which can then be used to define processes as seen in the place_on_conveyor.xml. The framework to register capabilities and map them to processes that can be performed in ongoing work. See this discussion for more details.

Visualization [experimental]

At present, behavior trees can be viewed and modified using Groot. Once Groot is launched, click "Load palette from file" and select nexus_tree_nodes.xml. Then any of the configured BTs can be loaded via the "Load Tree" button. A current limitation of this approach is the need to manually update the palette file when the plugins loaded by a task capability changes. In the future, the goals is to more closely couple the generation of this file and the skill plugins the orchestrators are capable of loading.

Generating Zenoh bridge configurations

The script in nexus_network_configuration helps to simplify configuration of Zenoh bridges for multiple machines. The Zenoh bridge files are generated from NEXUS Network Configuration and nexus_endpoints.redf.yaml. After configuring the NEXUS Network Configuration, you can run ros2 run nexus_network_configuration nexus_network_configuration -n <PATH_TO_NEXUS_NETWORK_CONFIG> -r <PATH_TO_REDF_CONFIGS> -o <ZENOH_CONFIGS_OUTPUT_DIRECTORY> to generate the Zenoh bridges.

Further detailed instructions on running the Zenoh bridges with said configurations are in the package README

Demos

Follow instructions here to run pick and place demonstrations with a line comprising of two workcells that perform different types of tasks.

TODO: Add a dedicated demo package.

Generating Endpoints

The nexus_endpoints package contains ROS topics, services and actions used by NEXUS. The package is generated from nexus_endpoints.redf.yaml using redf. rust is required to generated the package, the easiest way to install rust is via rustup.

With rust installed, clone the redf repo at https://github.com/osrf/redf, then run

cargo install --path .

With redf installed, run generate_endpoints.sh to generate the package.

Contributing

All contributions are welcome! Please ensure the following guidelines are followed when submitting pull requests:

Signed commits

• Ensure all commits are signed.

Endpoints

Ensure your code does not directly import interface definitions or use hardcoded strings for ROS 2 endpoints. All endpoint properties must be retrieved from nexus_endpoints.hpp. If an endpoint is missing, first add its definition to nexus_endpoints.redf.yaml and then follow the instructions above to re-generate nexus_endpoints.hpp.

Code style

C++

The NEXUS codebase adheres to C++ style format as used in the Open-RMF project. The linter of choice is uncrustify and the configuration used may be referenced here. Instead of invoking uncrustify directly, use ament_uncrustify instead which is a wrapper around a specific version of uncrustify. You may locally run the linter as follows

sudo apt update && sudo apt install -y ros-iron-rmf-utils # This is a one-time step
source /opt/ros/iron/setup.bash
cd ~/ws_nexus/src/nexus
ament_uncrustify -c /opt/ros/iron/share/rmf_utils/rmf_code_style.cfg . --language C++ --exclude nexus_endpoints/nexus_endpoints.hpp

To automatically reformat the code, append --reformat to the ament_uncrustify line above. It is highly recommended to audit the changes by the linter before committing.

Python

The NEXUS codebase adheres to PEP8 style format for python scripts. A linter such as pycodestyle may be used for linting.