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Example 5: Industrial robot with externally connected sensor

This example shows how an externally connected sensor can be accessed:

  • The communication is done using proprietary API to communicate with the robot control box.

  • Data for all joints is exchanged at once.

  • Sensor data are exchanged independently of joint data.

  • Examples: KUKA RSI and FTS connected to independent PC with ROS 2.

A 3D Force-Torque Sensor (FTS) is simulated by generating random sensor readings via a hardware interface of type hardware_interface::SensorInterface.


The commands below are given for a local installation of this repository and its dependencies as well as for running them from a docker container. For more information on the docker usage see Using Docker.

Tutorial steps

  1. To check that RRBot descriptions are working properly use following launch commands

    ros2 launch ros2_control_demo_example_5


    Getting the following output in terminal is OK: Warning: Invalid frame ID "odom" passed to canTransform argument target_frame - frame does not exist. This happens because joint_state_publisher_gui node need some time to start. The joint_state_publisher_gui provides a GUI to generate a random configuration for rrbot. It is immediately displayed in RViz.

  2. To start RRBot example open a terminal, source your ROS2-workspace and execute its launch file with

    ros2 launch ros2_control_demo_example_5

    The launch file loads and starts the robot hardware, controllers and opens RViz. In starting terminal you will see a lot of output from the hardware implementation showing its internal states. This is only of exemplary purposes and should be avoided as much as possible in a hardware interface implementation.

    If you can see two orange and one yellow rectangle in in RViz everything has started properly. Still, to be sure, let’s introspect the control system before moving RRBot.

  3. Check if the hardware interface loaded properly, by opening another terminal and executing

    ros2 control list_hardware_interfaces
    command interfaces
      joint1/position [available] [claimed]
      joint2/position [available] [claimed]
    state interfaces

    Marker [claimed] by command interfaces means that a controller has access to command RRBot.

    Now, let’s introspect the hardware components with

    ros2 control list_hardware_components

    There are two hardware components, one for the robot and one for the sensor:

    Hardware Component 1
            name: ExternalRRBotFTSensor
            type: sensor
            plugin name: ros2_control_demo_example_5/ExternalRRBotForceTorqueSensorHardware
            state: id=3 label=active
            command interfaces
    Hardware Component 2
            name: RRBotSystemPositionOnly
            type: system
            plugin name: ros2_control_demo_example_5/RRBotSystemPositionOnlyHardware
            state: id=3 label=active
            command interfaces
                    joint1/position [available] [claimed]
                    joint2/position [available] [claimed]
  4. Check if controllers are running

    ros2 control list_controllers
    forward_position_controller[forward_command_controller/ForwardCommandController] active
    fts_broadcaster[force_torque_sensor_broadcaster/ForceTorqueSensorBroadcaster] active
    joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
  5. If you get output from above you can send commands to Forward Command Controller, either:

    1. Manually using ROS 2 CLI interface.

      ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data:
      - 0.5
      - 0.5"
    2. Or you can start a demo node which sends two goals every 5 seconds in a loop

      ros2 launch ros2_control_demo_example_5

    You should now see orange and yellow blocks moving in RViz. Also, you should see changing states in the terminal where launch file is started, e.g.

    [RRBotSystemPositionOnlyHardware]: Got command 0.50000 for joint 0!
    [RRBotSystemPositionOnlyHardware]: Got command 0.50000 for joint 1!
  6. Access wrench data from 2D FTS via

    ros2 topic echo /fts_broadcaster/wrench

    shows the random generated sensor values, republished by Force Torque Sensor Broadcaster as geometry_msgs/msg/WrenchStamped message

        sec: 1676444704
        nanosec: 332221422
      frame_id: tool_link
        x: 1.2126582860946655
        y: 2.3202226161956787
        z: 3.4302282333374023
        x: 4.540233612060547
        y: 0.647800624370575
        z: 1.7602499723434448

    Wrench data are also visualized in RViz:

    Revolute-Revolute Manipulator Robot with wrench visualization

Files used for this demos

Controllers from this demo