userdoc.rst

github_url:	https://github.com/ros-controls/ros2_control_demos/blob/{REPOS_FILE_BRANCH}/example_4/doc/userdoc.rst

Example 4: Industrial robot with integrated sensor

This example shows how a sensor can be integrated in a hardware interface:

• 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 together with joint data
• Examples: KUKA RSI with sensor connected to KRC (KUKA control box) or a prototype robot (ODRI interface).

A 2D Force-Torque Sensor (FTS) is simulated by generating random sensor readings via a hardware interface of type hardware_interface::SystemInterface.

Tutorial steps

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

   ros2 launch ros2_control_demo_example_4 view_robot.launch.py

   Note

   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_4 rrbot_system_with_sensor.launch.py

   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
           joint1/position
           joint2/position
           tcp_fts_sensor/force.x
           tcp_fts_sensor/torque.z

   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 -v

   There is a single hardware component for the robot providing the command and state interfaces:

   Hardware Component 1
       name: RRBotSystemWithSensor
       type: system
       plugin name: ros2_control_demo_example_4/RRBotSystemWithSensorHardware
       state: id=3 label=active
       command interfaces
               joint1/position [available] [claimed]
               joint2/position [available] [claimed]
       state interfaces
               joint1/position [available]
               joint2/position [available]
               tcp_fts_sensor/force.x [available]
               tcp_fts_sensor/torque.z [available]

4. Check if controllers are running

   ros2 control list_controllers

   joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
   fts_broadcaster     [force_torque_sensor_broadcaster/ForceTorqueSensorBroadcaster] active
   forward_position_controller[forward_command_controller/ForwardCommandController] 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_4 test_forward_position_controller.launch.py

   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.

   [RRBotSystemWithSensorHardware]: Got command 0.50000 for joint 0!
   [RRBotSystemWithSensorHardware]: 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

   header:
     stamp:
       sec: 1676444704
       nanosec: 332221422
     frame_id: tool_link
   wrench:
     force:
       x: 2.946532964706421
       y: .nan
       z: .nan
     torque:
       x: .nan
       y: .nan
       z: 4.0540995597839355

   Warning

   Wrench messages are not displayed properly in RViz as NaN values are not handled in RViz and FTS Broadcaster may send NaN values.

Files used for this demo

• Launch file: rrbot_system_with_sensor.launch.py
• Controllers yaml: rrbot_with_sensor_controllers.yaml
• URDF: rrbot_system_with_sensor.urdf.xacro
  • Description: rrbot_description.urdf.xacro
  • ros2_control URDF tag: rrbot_system_with_sensor.ros2_control.xacro
• RViz configuration: rrbot.rviz
• Hardware interface plugin: rrbot_system_with_sensor.cpp

Controllers from this demo

• Joint State Broadcaster (ros2_controllers repository): :ref:`doc <joint_state_broadcaster_userdoc>`
• Forward Command Controller (ros2_controllers repository): :ref:`doc <forward_command_controller_userdoc>`
• Force Torque Sensor Broadcaster (ros2_controllers repository): :ref:`doc <force_torque_sensor_broadcaster_userdoc>`