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github_url:https://github.com/ros-controls/ros2_control_demos/blob/{REPOS_FILE_BRANCH}/example_10/doc/userdoc.rst

Example 10: Industrial robot with GPIO interfaces

This demo shows how to interact with GPIO interfaces.

The RRBot URDF files can be found in the description/urdf folder.

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

    ros2 launch ros2_control_demo_example_10 view_robot.launch.py

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

    ros2 launch ros2_control_demo_example_10 rrbot.launch.py

    The launch file loads and starts the robot hardware and controllers.

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

    ros2 control list_hardware_interfaces
    command interfaces
    flange_analog_IOs/analog_output1 [available] [claimed]
    flange_vacuum/vacuum [available] [claimed]
    joint1/position [available] [claimed]
    joint2/position [available] [claimed]
state interfaces
    flange_analog_IOs/analog_input1
    flange_analog_IOs/analog_input2
    flange_analog_IOs/analog_output1
    flange_vacuum/vacuum
    joint1/position
    joint2/position

    In contrast to the RRBot of example_1, you see in addition to the joints now also GPIO interfaces.

  4. Check if controllers are running by

    ros2 control list_controllers
    joint_state_broadcaster     joint_state_broadcaster/JointStateBroadcaster        active
gpio_controller             gpio_controllers/GpioCommandController               active
forward_position_controller forward_command_controller/ForwardCommandController  active

  5. If you get output from above you can subscribe to the /dynamic_joint_states topic published by the joint_state_broadcaster using ROS 2 CLI interface:

    ros2 topic echo /dynamic_joint_states --once

    This includes not only the state interfaces of the joints but also the GPIO interfaces.

    header:
  stamp:
    sec: 1730670203
    nanosec: 875008879
  frame_id: ''
joint_names:
- joint1
- joint2
- flange_vacuum
- flange_analog_IOs
interface_values:
- interface_names:
  - position
  values:
  - 0.0
- interface_names:
  - position
  values:
  - 0.0
- interface_names:
  - vacuum
  values:
  - 0.0
- interface_names:
  - analog_input2
  - analog_input1
  - analog_output1
  values:
  - 92747888.0
  - 1764536320.0
  - 0.0
---

    You can also subscribe to the /gpio_controller/gpio_states topic published by the gpio_controller using ROS 2 CLI interface:

    ros2 topic echo /gpio_controller/gpio_states

    which shows the values of the state_interfaces of the configured GPIOs

    header:
  stamp:
    sec: 1731875120
    nanosec: 2015630
  frame_id: ''
interface_groups:
- flange_analog_IOs
- flange_vacuum
interface_values:
- interface_names:
  - analog_output1
  - analog_input1
  - analog_input2
  values:
  - 0.0
  - 991951680.0
  - 1467646976.0
- interface_names:
  - vacuum
  values:
  - 0.0
---

  6. Now you can send commands to the gpio_controller using ROS 2 CLI interface. You can set a single interface or all at once in one message:

    ros2 topic pub /gpio_controller/commands control_msgs/msg/DynamicInterfaceGroupValues "{interface_groups: [flange_analog_IOs], interface_values: [{interface_names: [analog_output1], values: [0.5]}]}"

ros2 topic pub /gpio_controller/commands control_msgs/msg/DynamicInterfaceGroupValues "{interface_groups: [flange_vacuum], interface_values: [{interface_names: [vacuum], values: [0.27]}]}"

ros2 topic pub /gpio_controller/commands control_msgs/msg/DynamicInterfaceGroupValues "{interface_groups: [flange_vacuum, flange_analog_IOs], interface_values: [{interface_names: [vacuum], values: [0.27]}, {interface_names: [analog_output1], values: [0.5]} ]}"

    You should see a change in the /gpio_controller/gpio_states topic and a different output in the terminal where launch file is started, e.g.

    [ros2_control_node-1] [INFO] [1721765648.271058850] [controller_manager.resource_manager.hardware_component.system.RRBot]: Writing commands:
[ros2_control_node-1]   0.50 for GPIO output '0'
[ros2_control_node-1]   0.70 for GPIO output '1'

  7. Let's introspect the ros2_control hardware component. Calling

ros2 control list_hardware_components

should give you

Hardware Component 1
    name: RRBot
    type: system
    plugin name: ros2_control_demo_example_10/RRBotSystemWithGPIOHardware
    state: id=3 label=active
    command interfaces
            joint1/position [available] [claimed]
            joint2/position [available] [claimed]
            flange_analog_IOs/analog_output1 [available] [claimed]
            flange_vacuum/vacuum [available] [claimed]

This shows that the custom hardware interface plugin is loaded and running. If you work on a real robot and don't have a simulator running, it is often faster to use the mock_components/GenericSystem hardware component instead of writing a custom one. Stop the launch file and start it again with an additional parameter

ros2 launch ros2_control_demo_example_10 rrbot.launch.py use_mock_hardware:=True

Calling list_hardware_components with the -v option

ros2 control list_hardware_components -v

now should give you

Hardware Component 1
    name: RRBot
    type: system
    plugin name: mock_components/GenericSystem
    state: id=3 label=active
    command interfaces
            joint1/position [available] [claimed]
            joint2/position [available] [claimed]
            flange_analog_IOs/analog_output1 [available] [claimed]
            flange_vacuum/vacuum [available] [claimed]
    state interfaces
            joint1/position [available]
            joint2/position [available]
            flange_analog_IOs/analog_output1 [available]
            flange_analog_IOs/analog_input1 [available]
            flange_analog_IOs/analog_input2 [available]
            flange_vacuum/vacuum [available]

One can see that the plugin mock_components/GenericSystem was now loaded instead: It will mirror the command interfaces to state interfaces with identical name. Call

ros2 topic echo /gpio_controller/gpio_states

again and you should see that - unless commands are received - the values of the state interfaces are now nan except for the vacuum interface.

header:
  stamp:
    sec: 1731875298
    nanosec: 783713170
  frame_id: ''
interface_groups:
- flange_analog_IOs
- flange_vacuum
interface_values:
- interface_names:
  - analog_output1
  - analog_input1
  - analog_input2
  values:
  - .nan
  - .nan
  - .nan
- interface_names:
  - vacuum
  values:
  - 1.0
---

This is, because for the vacuum interface an initial value of 1.0 is set in the URDF file.

<gpio name="flange_vacuum">
  <command_interface name="vacuum"/>
  <state_interface name="vacuum">
    <param name="initial_value">1.0</param>
  </state_interface>
</gpio>

Send again topics to /gpio_controller/commands and you will see that the GPIO command interfaces will be mirrored to their respective state interfaces.

Files used for this demos

Controllers from this demo