This package contains ROS2 action servers defined in the serial link interface package, using Robot Library for the underlying control algorithms.
- Real-time control of serial link robot arms,
- Joint space & Cartesian control,
- Seemless integration with the serial link action client package, and
- Classes for implementing your own custom control algorithms.
- Ubuntu 22.04, or later,
- ROS2 Humble, or later,
- RobotLibrary, and
- The serial link interfaces package.
Note
This package was built and tested using Ubuntu 22.04, and ROS2 Humble.
Your directory structure should end up looking something like this:
ros2_workspace/
├── build/
├── install/
├── log/
└── src/
├── interface_serial_link/
└── server_serial_link/
- In the
src/directory of your ROS2 workspace, clone the interfaces repository:
git clone https://github.com/Woolfrey/interface_serial_link.git
- Clone the action server repository:
git clone http://github.com/Woolfrey/server_serial_link.git
- Navigate back to the root of your ROS2 workspace and build:
colcon build
- Source the local directory (if you haven't yet altered your .bashrc file):
source ./install/setup.bash
- Check successful installation:
ros2 pkg list
If you scroll down the list, you should see both serial_link_action_server, and serial_link_interfaces.
This package contains several classes that implement action servers for the actions specified in the interface repository. The diagram below shows how the classes and nodes are organised in an executable to control a robot:
- A
RobotLibrary::Model::KinematicTreeobject is used to compute the forward kinematics & inverse dynamics of the robot. - A
ModelUpdaternode subscribes to asensor_msgs::msg::JointStatetopic and update theKinematicTreeas messages are received. - A
RobotLibrary::Control::SerialLinkBaseobject uses the model to control a branch on theKinematicTree. - The
ActionServerBaseis a templated class that provides a standardised structure & interface for all derived classes. - The derived classes, e.g.
FollowTransform,FollowJointTrajectory, use theSerialLinkBaseobject to implement the control loop in order to perform the desired action.
This package contains nodes with pre-configured actions that you can use. Of course, you can easily make your own, and mix-and-match different actions to suit your own task. Just follow the diagram above, or check how the nodes are written in the src/nodes/ directory.
Each executable requires 4 arguments:
- A path to a valid URDF file,
- The name of the endpoint link to be controlled,
- The name of the topic to publish the
serial_link_interfaces::msg::JointCommandmessage, and - The name of the
sensor_msgs::msg::JointStatetopic to subscribe to.
There is also parameters for the RobotLibrary::Control::SerialLinkBase that can be loaded via a .YAML file:
/**:
ros__parameters:
# These are for the RobotLibrary::Control class(es):
cartesian_damping: [10.0, 0.0, 0.0, 0.0, 0.0, 0.0,
0.0, 10.0, 0.0, 0.0, 0.0, 0.0,
0.0, 0.0, 10.0, 0.0, 0.0, 0.0,
0.0, 0.0, 0.0, 1.0, 0.0, 0.0,
0.0, 0.0, 0.0, 0.0, 1.0, 0.0,
0.0, 0.0, 0.0, 0.0, 0.0, 1.0]
cartesian_stiffness: [200.0, 0.0, 0.0, 0.0, 0.0, 0.0,
0.0, 200.0, 0.0, 0.0, 0.0, 0.0,
0.0, 0.0, 200.0, 0.0, 0.0, 0.0,
0.0, 0.0, 0.0, 100.0, 0.0, 0.0,
0.0, 0.0, 0.0, 0.0, 100.0, 0.0,
0.0, 0.0, 0.0, 0.0, 0.0, 100.0]
frequency: 500.0
joint_position_gain: 50.0
joint_velocity_gain: 10.0
manipulability_threshold: 0.001
max_joint_acceleration: 10.0
# These are for the underlying QPSolver class:
initial_barrier_scalar: 500.0
barrier_reduction_rate: 0.001
step_size_tolerance: 0.05
max_steps: 10
The best way to run the node is using a launch file, for example trajectory_tracking.py might look like:
import os
from launch import LaunchDescription
from launch_ros.actions import Node
def generate_launch_description():
trajectory_tracking = Node(
package = 'serial_link_action_server',
executable = 'trajectory_tracking_server',
name = 'trajectory_tracking_server',
output = 'screen',
parameters = ['config/control_parameters.yaml')],
arguments = ['urdf/robot.urdf'), # URDF location
'end_effector', # Endpoint name
'joint_commands', # Topic to publish joint commands to
'joint_state'] # Joint state topic to subscribe to
)
return LaunchDescription([trajectory_tracking])
This node contains the FollowJointTrajectory action, so you can move the robot in to different joint configurations, and the FollowTransform action. With the latter, you use a corresponding client to tell the server the frame_id of a tf2_ros::Transform that is broadcast somehow over the network. The server listens for this transform, and performs feedback control to align the robot endpoint pose with it.
This node contains the FollowJointTrajectory action, so you can move the robot in to different joint configurations, and the FollowTwist action. Using the latter's matching client, you send a goal with the topic name for a geometry_msgs::msg::TwistStamped message that is being published somehow over the ROS2 network. The action client will subscribe to this topic, and move the endpoint of the robot at the given speed.
This node contains the FollowJointTrajectory action, and the FollowCartesianTrajectory action. Using the former, you can move the robot in to different joint configurations. Using the latter, you can make the endpoint follow a trajectory defined by a series of serial_link_interfaces::msg::CartesianTrajectoryPoints. The actions erver takes these waypoints and fits a spline to them, and performs feedback control to follow it.
Contributions to this repositore are welcome! Feel free to:
- Fork the repository,
- Implement your changes / improvements, then
- Issue a pull request.
If you're looking for ideas, you can always check the Issues tab for those with 🙋 [OPEN]. These are things I'd like to implement, but don't have time for. It'd be much appreciated, and you'll be tagged as a contributor 😎
If you find this code useful, spread the word by acknowledging it. Click on Cite this repository under the About section in the top-right corner of this page
Here's a BibTeX reference:
@software{woolfrey_serial_link_action_server_2005
author = {Woolfrey, Jon},
month = apr,
title = {{S}erial {L}ink {A}ction {S}erver},
url = {https://github.com/Woolfrey/server_serial_link},
version = {1.0.0},
year = {2025}
}
Here's the automatically generated APA format:
Woolfrey, J. (2025). Serial Link Action Server (Version 1.0.0). Retrieved from https://github.com/Woolfrey/server_serial_link
This software package is licensed under the GNU General Public License v3.0 (GPL-3.0). You are free to use, modify, and distribute this package, provided that any modified versions also comply with the GPL-3.0 license. All modified versions must make the source code available and be licensed under GPL-3.0. The license also ensures that the software remains free and prohibits the use of proprietary restrictions such as Digital Rights Management (DRM) and patent claims. For more details, please refer to the full license text.