Automatic hydrogen refuelling system
How software and hardware works together to perform highly complex task
In order to promote green mobility and to relieve the stress on public transportation, a hydrogen powered ferry with on-site hydrogen generation pier system would be introduced. By harvesting solar energy to produce hydrogen through electrolysis, a self-sustaining system would be achieved with zero carbon emission.
To achieve a fast and safe hydrogen refueling process, a fully-automated refueling system is needed. In consideration of the wobbliness of the ferry when berthed, a highly-maneuverable with high accuracy robotic arm is needed to dock with the ferry receptacle.
This study will look into the necessary hardware and software design to accomplish this challenging task
Hardware - soft capture ring
Inspired by The NASA International Space Station docking system, a similar structure with a guiding ring and soft capture mechanism was implemented in order to achieve a secure connection between the refuelling head on the pier and the receptacle on the ferry and accommodate for the sudden wobbling of the ferry.
Software - pose estimation
By using Aruco Marker together with the OpenCV library, real-time and accurate pose estimation is performed. To deal with random marker detection, a filtering algorithm is also added. To retrieve the most accurate pose information, a comprehensive camera calibration was taken to bring the reprojection error under 0.4 achieving accuracy up to 0.1 cm level.
Software - robotics arm manoeurving
Using ROS as the main operating platform enables efficient communication between different sub-systems and programs. Two different Kinova robotics arm-driving mechanisms have been tested. Due to the slow responsiveness of using cartesian position control, velocity control is implemented in the final design. The pose difference is passed to the velocity control node which converts offset in distance to velocity in cartesian space needed to reach the target location. Together with PID control, smooth tracking is achieved.
Significance of the Research
This system can also be implemented in other hydrogen-powered vehicles or normal electric vehicles in the future to minimize unnecessary manpower and acts as part of the smart city infrastructure.