Documentation updates improve ROS utilization and functionality

Lessons from UR driver updates reinforce importance of documentation

A key strength of the open-source community is the capacity to build on the knowledge of other developers who enable future advancements. Documentation plays a critical role in advancing understanding, which improves ROS utilization globally. This will be increasingly important as we move from ROS to ROS2 and document the various steps, including driver updates, necessary to execute projects.

Recent driver updates for a Universal Robots project helped demonstrate the importance of documentation to our team. In July 2019, Universal Robots updated their software for e-series and CB-series to 5.4 and 3.10. We were using the 5.4 software on UR 10e robots for a few different projects, and the ur_modern_driver [1] for ROS kinetic and melodic was no longer compatible due to this update. I updated the driver by investigating the release notes for 5.4.x.x [2] and the client_interface document [3].

UR10 E-series in the SwRI collaborative lab

To update the ROS driver for compatibility with software updates, I first identified what changes occurred and located appropriate software documentation for the hardware. The software documentation defined modules and variable types for the changes, which allowed for comparison with equivalent variables and modules in the current driver code. Without proper documentation from Universal Robots this would have been a much more difficult endeavor.

The ur_modern_driver specifically interacts with the client interface. Two variables were added to the 5.4 software client interface: a reserved byte in the Masterboard data sub package of Robot State Message to be used for internal UR use and a safety status value to the real time interface. The client interface document gave the types and sizes of these variables along with variables used in previous software versions.

The client interface for 5.3 and earlier had an internal UR int in Robot Mode Data I could compare to, and the safety status value could be compared to any of the other double variables in the previous driver’s RealTime interface. I used the search feature in QTCreator to find instances of these variables and added equivalent lines for the new ones. Then I used QTCreator’s debugger to track where new if statements and functions needed to be added to allow the driver to detect the new software version being used and access these new variables.

Working on this upgrade reinforced the necessity of good documentation. In general, the ur_modern_driver had more detailed documentation than many other ROS repos; however, it could still be improved. The README had no mention of the purpose of the use_lowbandwidth_trajectory_follower parameter in the launch files or the urXXe_bringup_joint_limited.launch file; both of these are useful when simulations are being overenthusiastic in their trajectory planning. I added documentation to the README to help others use these features to troubleshoot.

To update drivers, you will need to know what has been changed in the software, and you will ideally have access to a previous version of the driver. Because industrial hardware is intended to be reliable and accessible for multiple clients, there is often plenty of useful documentation if you can search with the correct terminology. Using the known changes and the documentation to compare with the previous driver code allowed me to update the driver fairly quickly so projects could move forward.