README

ur_robot_driver

This package contains the actual driver for UR robots. It is part of the universal_robots_driver repository and requires other packages from that repository. Also, see the main repository’s README for information on how to install and startup this driver.

Technical details

The following image shows a very coarse overview of the driver’s architecture.

Upon connection to the primary interface the robot sends version and calibration information which is consumed by the calibration_check. If the calibration reported by the robot doesn’t match the one configured (See calibration guide) an error will be printed to Roslog.

Real-time data from the robot is read through the RTDE interface. This is done automatically as soon as a connection to the robot could be established. Thus joint states and IO data will be immediately available.

To actually control the robot, a program node from the External Control URCap must be running on the robot interpreting commands sent from an external source. When this program is not running, no controllers moving the robot around will be available. Please see the initial setup guide on how to install and start this on the robot.

The URScript that will be running on the robot is requested by the External Control program node from the remote ROS PC. The robot ur_control.launch file has a parameter called urscript_file to select a different program than the default one that will be sent as a response to a program request.

Custom script snippets can be sent to the robot on a topic basis. By default, they will interrupt other programs (such as the one controlling the robot). For a certain subset of functions, it is however possible to send them as secondary programs. See UR documentation on details.
Note to e-Series users: The robot won’t accept script code from a remote source unless the robot is put into remote_control-mode. However, if put into remote_control-mode, the program containing the External Control program node can’t be started from the panel. For this purpose, please use the dashboard services to load, start and stop the main program running on the robot. See the Dashboard client documentation for details on the dashboard services.

For using the tool communication interface on e-Series robots, a socat script is prepared to forward the robot’s tool communication interface to a local device on the ROS PC. See the tool communication setup guide for details.

This driver is using ros2_control for any control statements. Therefore, it can be used with all position-based controllers available in ros2_control. However, we recommend using the controllers from the ur_controllers package. See it’s documentation for details. Note: Speed scaling support will only be available using the controllers from ur_controllers

A note about modes

The term mode is used in different meanings inside this driver. See Operation Modes for details.

controller_stopper

A small helper node that stops and restarts ROS controllers based on a boolean status topic. When the status goes to false, all running controllers except a set of predefined consistent_controllers gets stopped. If status returns to true the stopped controllers are restarted. This is done by Subscribing to a robot’s running state topic. Ideally this topic is latched and only publishes on changes. However, this node only reacts on state changes, so a state published each cycle would also be fine.