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.

ROS-API

The ROS API is documented in a standalone document.

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 ROS-API 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 ROS-Control for any control statements. Therefore, it can be used with all position-based controllers available in ROS-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.

Remote control mode

On the e-series the robot itself can operate in different command modes: It can be either in local control mode where the teach pendant is the single point of command or in remote control mode, where motions from the TP, starting & loading programs from the TP activating the freedrive mode are blocked. Note that the remote control mode has to be explicitly enabled in the robot’s settings under Settings -> System -> Remote Control. See the robot’s manual for details.

The remote control mode is needed for many aspects of this driver such as

• headless mode (see below)

• sending script code to the robot

• many dashboard functionalities such as

  • restarting the robot after protective / EM-Stop

  • powering on the robot and do brake release

  • loading and starting programs

• the set_mode action, as it uses the dashboard calls mentioned above

Headless mode

Inside this driver, there’s the headless mode, which can be either enabled or not. When the headless mode is activated, required script code for external control will be sent to the robot directly when the driver starts. As soon as other script code is sent to the robot either by sending it directly through this driver or by pressing any motion-related button on the teach pendant, the script will be overwritten by this action and has to be restarted by using the resend_robot_program service. If this is necessary, you will see the output Connection to robot dropped, waiting for new connection. from the driver. Note that pressing “play” on the TP won’t start the external control again, but whatever program is currently loaded on the controller. This mode doesn’t require the “External Control” URCap being installed on the robot as the program is sent to the robot directly. However, we recommend to use the non-headless mode and leverage the set_mode action to start program execution without the teach pendant. The headless mode might be removed in future releases.

Note for the e-Series: In order to leverage the headless mode on the e-Series the robot must be in remote_control_mode as explained above.

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.