MARCH Inverse Kinematics Solver

Overiew

This package is an implementation of the pseudo-inverse Jacobian-based inverse kinematics using task priority control. In principle, it solves the inverse kinematics by converging towards the desired task configurations based on the current joint configuration.

The Inverse Kinematics Solver Node (IK Solver Node) is enacted when it receives desired feet positions from the Gait Planning Node given that the State Estimator Node updates the joint state beforehand. Using Complete Orthogonal Decomposition, it calculates the pseudo-inverse of the Jacobian which is then used to transform the weighted error between the desired and the current workspace positions into the desired joint velocity. This joint velocity is integrated over some timestep to obtain the desired position. The solving of the inverse kinematics is iterated as many times as possible within two states. The iterations is terminated once convergence, max number of iterations, or the maximum timeout are reached. The IK Solver Node then finally publishes the desired joint positions to the Hardware Interface via Joint Trajectory Controller.

The flow of the IK Solver Node integrated with the other relevant modules can be seen in the sequence diagram below.

Keywords: inverse kinematics, task priority control

License

The source is released under GNUGNU General Public License v3.0 and above

Author: Alexander James Becoy
Affiliation: Project MARCH
Maintainers:

• Alexander James Becoy, alexanderjames.becoy@projectmarch.nl

The MARCH State Estimator package has been tested under ROS2 Foxy on Ubuntu 20.04.

Installation

Building from Source

Dependencies

• Robot Operatibg System 2 (ROS2) (middleware for robotics),
• Eigen (linear algebra library)
• Boost (support for linear algebra library)

Building

To build from source, clone the latest version from this repository into MARCH’s ROS2 workspace and compile the package using

cd ~/march/ros2
rosdep install --from-paths . --ignore-src
mba
source install/local_setup.bash

Unit Tests

Run the unit tests with

colcon test --packages-select march_ik_solver && colcon test-result --verbose

or when using the MARCH aliases

mbt march_ik_solver

Usage

You can try out the inverse kinematics solver by launching the simulation.

ros2 launch march_launch march.launch.py

Then press or type the available gait modes in the newly launched Input Device GUI / Terminal.

Config files

• ik_solver.yaml: Contains the parameters for the IKSolver and Tasks. See Nodes > ik_solver_node > Parameters.

Launch files

• ik_solver.launch.py: Launch the IK Solver Node with the parameters given in the ik_solver.yaml.

Nodes

ik_solver_node

TODO: Provide description of this node

Subscribed Topics

• /state_estimation/state (march_shared_msgs/StateEstimation) Joint state, filtered IMU, feet poses, and stance leg.
• /ik_solver/buffer/input (march_shared_msgs/IKSFootPositions) header, and left foot position and right foot position in body reference frame.

Published Topic

• /joint_trajectory_controller/joint_trajectory (trajectory_msgs/JointTrajectory)

Client

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