ur_controllers

This package contains controllers and hardware interface for ros_control that are special to the UR robot family. Currently this contains

• A speed_scaling_interface to read the value of the current speed scaling into controllers.
• A scaled_joint_command_interface that provides access to joint values and commands in combination with the speed scaling value.
• A speed_scaling_state_controller that publishes the current execution speed as reported by the robot to a topic interface. Values are floating points between 0 and 1.
• A scaled_joint_trajectory_controller that is similar to the joint_trajectory_controller, but it uses the speed scaling reported by the robot to reduce progress in the trajectory.

About this package

This package contains controllers not being available in the default ros_control set. They are created to support more features offered by the UR robot family. Any of these controllers are example implementations for certain features and are intended to be generalized and merged into the default ros_control controller set at some future point.

Controller description

This packages offers a couple of specific controllers that will be explained in the following sections.

ur_controllers/SpeedScalingStateBroadcaster

This controller publishes the current actual execution speed as reported by the robot. Values are floating points between 0 and 1.

In the ur_robot_driver this is calculated by multiplying the two RTDE data fields speed_scaling (which should be equal to the value shown by the speed slider position on the teach pendant) and target_speed_fraction (Which is the fraction to which execution gets slowed down by the controller).

position_controllers/ScaledJointTrajectoryController and velocity_controllers/ScaledJointTrajectoryController

These controllers work similar to the well-known joint_trajectory_controller.

However, they are extended to handle the robot’s execution speed specifically. Because the default joint_trajectory_controller would interpolate the trajectory with the configured time constraints (ie: always assume maximum velocity and acceleration supported by the robot), this could lead to significant path deviation due to multiple reasons:

• The speed slider on the robot might not be at 100%, so motion commands sent from ROS would effectively get scaled down resulting in a slower execution.
• The robot could scale down motions based on configured safety limits resulting in a slower motion than expected and therefore not reaching the desired target in a control cycle.
• Motions might not be executed at all, e.g. because the robot is E-stopped or in a protective stop
• Motion commands sent to the robot might not be interpreted, e.g. because there is no external_control program node running on the robot controller.
• The program interpreting motion commands could be paused.

The following plot illustrates the problem:

The graph shows a trajectory with one joint being moved to a target point and back to its starting point. As the joint’s speed is limited to a very low setting on the teach pendant, speed scaling (black line) activates and limits the joint speed (green line). As a result, the target trajectory (light blue) doesn’t get executed by the robot, but instead the pink trajectory is executed. The vertical distance between the light blue line and the pink line is the path error in each control cycle. We can see that the path deviation gets above 300 degrees at some point and the target point at -6 radians never gets reached.

All of the cases mentioned above are addressed by the scaled trajectory versions. Trajectory execution can be transparently scaled down using the speed slider on the teach pendant without leading to additional path deviations. Pausing the program or hitting the E-stop effectively leads to speed_scaling being 0 meaning the trajectory will not be continued until the program is continued. This way, trajectory executions can be explicitly paused and continued.

With the scaled version of the trajectory controller the example motion shown in the previous diagram becomes:

The deviation between trajectory interpolation on the ROS side and actual robot execution stays minimal and the robot reaches the intermediate setpoint instead of returning “too early” as in the example above.

Under the hood this is implemented by proceeding the trajectory not by a full time step but only by the fraction determined by the current speed scaling. If speed scaling is currently at 50% then interpolation of the current control cycle will start half a time step after the beginning of the previous control cycle.

Changelog for package ur_controllers

2.3.12 (2024-11-14)

• [SJTC] Make scaling interface optional (#1145) (#1171)
• Contributors: Felix Exner

2.3.11 (2024-10-28)

• Allow setting the analog output domain when setting an analog output (backport of #1123)
• Service to get software version of robot (#964) (#1128)
• Contributors: mergify[bot], Jacob Larsen, Felix Exner

2.3.10 (2024-08-09)

2.3.9 (2024-07-01)

2.3.8 (2024-06-17)

• this simple fix should fix the goal time violated issue (#1000)
• Contributors: Lennart Nachtigall

2.3.7 (2024-05-16)

• Use latched publishing for robot_mode and safety_mode (#992) Co-authored-by: Felix Exner <<exner@fzi.de>>
• Contributors: Felix Exner

2.3.6 (2024-04-08)

2.3.5 (2023-12-06)

• Update read_state_from_hardware (cherry picked from commit d77db8355ce1e2c5ecacb94a9616777789d26e38)
• Renamed normalize_joint_error_ to joints_angle_wraparound_ (cherry picked from commit 6b1c5a02344c1b531ed875e4cd70b3a38355b965)
• Remove noisy controller log message (#859)
• Contributors: Felix Exner, mergify[bot]

2.3.4 (2023-09-21)

• Update sjtc to newest upstream API (#813)
• Contributors: Felix Exner

2.3.3 (2023-08-23)

• Handle api changes related to traj_external_point_ptr_ (#779)
  • Handle api changes related to traj_external_point_ptr_

  * Fix formatting ---------Co-authored-by: Robert Wilbrandt <<wilbrandt@fzi.de>> (cherry picked from commit e2b22b15ca627cfb375c3d58e585e1d3dee5f484)

• Contributors: Yadu

2.3.2 (2023-06-02)

• added missing command interfaces into gpio controller (#693)
• Fixed formatting (#685)
  • Removed empty lines from python files
  • Fixed typo in changelogs
• Adding maximum retry counter in gpio controller (Multiarm part 3) - v2 (#672)
• Ported controllers to generate_parameters library and added prefix for controllers (Multiarm part 2) (#594)
• Switched out a deprecated header to avoid buildfarm warnings.
• Introduce hand back control service (#528)
• Contributors: Felix Exner, Felix Exner (fexner), Lennart Nachtigall, livanov93

2.3.1 (2023-03-16)

• Adjust scaled jtc to new publish_state interface Until next sync we need to build against upstream ros2_controllers, as this is an API-breaking change
• Contributors: Robert Wilbrandt

2.3.0 (2023-03-02)

• Added services to set tool voltage and zero force torque sensor (#466) Added launch arguments for reverse ip and script command interface port.
• Contributors: Mads Holm Peters

2.2.4 (2022-10-07)

• Adapt jtc controller params to new param api
• Contributors: Felix Exner

2.2.3 (2022-07-27)

• Adapt ros control api (#448)
  • scaled jtc: Use get_interface_name instead of get_name

  * Migrate from stopped controllers to inactive controllers stopped controllers has been deprecated upstream

• Contributors: Felix Exner

2.2.2 (2022-07-19)

• Adapted to JTC interpolation method feature (#439)
• Made sure all past maintainers are listed as authors (#429)
• Contributors: Felix Exner

2.2.1 (2022-06-27)

2.2.0 (2022-06-20)

• Updated package maintainers
• Prepare for humble (#394)
• Update dependencies on all packages (#391)
• Update controllers' API (#351)
• Update binary dependencies (#344)
• Use upstream fts_broadcaster (#304)
• Update license to BSD-3-Clause (#277)
• Added controller stopper node (#309)
• Add missing dependency on angles and update formatting for linters. (#283)
• Payload service (#238)
• Integration tests improvement (#206)
• Add resend program service and enable headless mode (#198)
• Update controllers adding dt in to update as in ros2_control (#171)
• Update main branch with ros-controls changes (#160)
• Update CI configuration to support galactic and rolling (#142)
• Modify parameter declaration - approach equalization with ros-controls dependencies (#152)
• Moved registering publisher and service to on_active (#151)
• Correct formatting, include std::vector and update ros2_controller to master branch in repo file.
• Correct check for fixed has_trajectory_msg() See: https://github.com/ros-controls/ros2_controllers/commit/32f089b3f3b53a817412c6bbce9046028786431e
• Update for changes to ros2_control and ros2_controllers See: https://github.com/ros-controls/ros2_control/commit/156a3f6aaed319585a8a1fd445693e2e08c30ccd and: https://github.com/ros-controls/ros2_controllers/commit/612f610c24d026a41abd2dd026902c672cf778c9#diff-5d3e18800b3a217b37b91036031bdb170f5183970f54d1f951bb12f2e4847706
• Fix gpio controller (#103)
• Fixed speed slider service call (#100)
• Reintegrating missing ur_client_library dependency since the break the building process (#97)
• Setting speed slider with range of 0.0-1.0 and added warnings if range is exceeded (#88)
• Fix move to home bug (#92)
• Review CI by correcting the configurations (#71)
• Add support for gpios, update MoveIt and ros2_control launching (#66)
• Fix warning about deprecated controller_interface::return_type::SUCCESS (#68)
• Use GitHub Actions, use pre-commit formatting (#56)
• Scaled Joint Trajectory Controller (#43)
• Only load speed scaling interface
• Removed controller from config file to realign with current branch status
• Removed last remnants of joint_state_controller
• Added publisher rate
• Code formatting and cleanup
• Added publisher for speed scaling factor
• Initial version of the speed_scaling_state_controller
• Update licence.
• Fix clang tidy in multiple pkgs.
• Update force torque state controller.
• Prepare for testing.
• Update ft state controller with ros2_control changes.
• Remove lifecycle node (update with ros2_control changes).
• Claim individual resources.
• Add force torque controller.
• Claim individual resources.
• Add force torque controller.
• Add XML schema to all package.xml files Better enable ament_xmllint to check validity.
• Update package.xml files so ros2 pkg list shows all pkgs
• Clean out ur_controllers, it needs a complete rewrite
• Update CMakeLists and package.xml for:
  • ur5_moveit_config
  • ur_bringup
  • ur_description
• Change pkg versions to 0.0.0
• Contributors: AndyZe, Denis Stogl, Denis Štogl, Felix Exner, John Morris, Kenneth Bogert, Lovro, Mads Holm Peters, Marvin Große Besselmann, livanov93