Signal interoperability

As described in the signals page, AICA signals make it easy to exchange Cartesian and joint state variables in an internally consistent way. In components, state signals are automatically converted into smart data classes that provide useful functions for conversions, transformations and other manipulations.

Even though there is no official standard, there are a few signal types that are very commonly used in ROS. For ease of interoperability, AICA Core includes several components that translate AICA signals to common ROS messages and back. These components can be especially valuable when porting existing ROS nodes into AICA Studio using the Component SDK or when communicating with ROS nodes outside the AICA System.

AICA signals to common ROS messages

AICA state signals carrying Cartesian or joint space information can be converted into common ROS message types using the following components:

Component name	Input signal type	Output message type
Cartesian Signal to Pose Stamped Message	Cartesian state or pose	geometry_msgs::msg::PoseStamped
Cartesian Signal to Twist Stamped Message	Cartesian state or twist	geometry_msgs::msg::TwistStamped
Cartesian Signal to Wrench Stamped Message	Cartesian state or wrench	geometry_msgs::msg::WrenchStamped
Joint Signal To Joint State Message	Joint state, positions, velocities or torques	sensor_msgs::msg::JointState

Common ROS messages to AICA signals

Common ROS message types carrying Cartesian or joint space information can be converted back into AICA state signals using the following components:

Component name	Input message type	Output signal type
Pose Stamped Message to Cartesian Signal	geometry_msgs::msg::PoseStamped	Cartesian state containing pose information
Twist Stamped Message to Cartesian Signal	geometry_msgs::msg::TwistStamped	Cartesian state containing twist information
Wrench Stamped Message to Cartesian Signal	geometry_msgs::msg::WrenchStamped	Cartesian state containing wrench information
Joint State Message to Joint Signal	sensor_msgs::msg::JointState	Joint state

Behavior

All of these components are single-input single-output blocks. Each time a new message is received, it is translated and immediately published. For that reason, the rate parameter doesn't affect the behavior of these components.

AICA Signal to ROS message example

This example uses the Joint Signal To Joint State Message component to translate the joint state output from the hardware interface to a sensor_msgs::msg::JointState message and the Cartesian Signal to Pose Stamped Message component to translate the Cartesian state output to a geometry_msgs::msg::PoseStamped message.

With the application loaded and playing, the two components will publish the converted message on their output signal each time a new message is received from the hardware interface. A jsonified version of those messages can be observed in the live topic view.

With content

{
  "header": { "stamp": { "sec": 1749019367, "nanosec": 736960997 }, "frame_id": "world" },
  "pose": {
    "position": { "x": 0.37246365888399174, "y": 0.048146868357851064, "z": 0.4299999920960212 },
    "orientation": {
      "x": 0.7073880448768991,
      "y": 0.7068251811053661,
      "z": 8.971607761328708e-7,
      "w": -0.0005633114591638605
    }
  }
}

With content

{
  "header": { "stamp": { "sec": 1749019239, "nanosec": 277825301 }, "frame_id": "" },
  "name": ["joint_0", "joint_1", "joint_2", "joint_3", "joint_4", "joint_5"],
  "position": [0, 0, 0, 0, 0, 0],
  "velocity": [0, 0, 0, 0, 0, 0],
  "effort": [0, 0, 0, 0, 0, 0]
}

Application YAML

schema: 2-0-4
dependencies:
  core: v4.3.2
on_start:
  load:
    hardware: hardware
components:
  joint_signal_to_joint_state_message:
    component: aica_core_components::ros::JointSignalToJointStateMsg
    display_name: Joint Signal To Joint State Message
    inputs:
      input: /hardware/robot_state_broadcaster/joint_state
  cartesian_signal_to_pose_stamped_message:
    component: aica_core_components::ros::CartesianSignalToPoseStampedMsg
    display_name: Cartesian Signal To Pose Stamped Message
    inputs:
      input: /hardware/robot_state_broadcaster/cartesian_state
hardware:
  hardware:
    display_name: Hardware Interface
    urdf: Generic six-axis robot arm
    rate: 100
    events:
      transitions:
        on_load:
          load:
            controller: robot_state_broadcaster
            hardware: hardware
    controllers:
      robot_state_broadcaster:
        plugin: aica_core_controllers/RobotStateBroadcaster
        outputs:
          joint_state: /hardware/robot_state_broadcaster/joint_state
          cartesian_state: /hardware/robot_state_broadcaster/cartesian_state
        events:
          transitions:
            on_load:
              switch_controllers:
                hardware: hardware
                activate: robot_state_broadcaster
            on_activate:
              load:
                - component: cartesian_signal_to_pose_stamped_message
                - component: joint_signal_to_joint_state_message
graph:
  positions:
    components:
      joint_signal_to_joint_state_message:
        x: 200
        y: 880
      cartesian_signal_to_pose_stamped_message:
        x: 200
        y: 660
    hardware:
      hardware:
        x: 200
        y: -20
  edges:
    hardware_hardware_robot_state_broadcaster_on_activate_cartesian_signal_to_pose_stamped_message_cartesian_signal_to_pose_stamped_message:
      path:
        - x: 80
          y: 400
        - x: 80
          y: 720
    hardware_hardware_robot_state_broadcaster_on_activate_joint_signal_to_joint_state_message_joint_signal_to_joint_state_message:
      path:
        - x: -20
          y: 400
        - x: -20
          y: 940
    hardware_hardware_robot_state_broadcaster_joint_state_joint_signal_to_joint_state_message_input:
      path:
        - x: 120
          y: 520
        - x: 120
          y: 1060
    hardware_hardware_robot_state_broadcaster_cartesian_state_cartesian_signal_to_pose_stamped_message_input:
      path:
        - x: 140
          y: 560
        - x: 140
          y: 840

ROS message to AICA Signal example

Mirroring the first example, the following application uses the Wrench Stamped Message To Cartesian Signal component to translate a geometry_msgs::msg::WrenchStamped from some custom component to a Cartesian signal that is connected to the force controller of the hardware interface.

note

The custom component is just an example placeholder for any implementation that has a ROS standard message output, which might occur when porting existing ROS nodes into AICA Studio using the AICA SDK.

Application YAML

schema: 2-0-4
dependencies:
  core: v4.3.2
on_start:
  load:
    hardware: hardware
components:
  wrench_stamped_message_to_cartesian_signal:
    component: aica_core_components::ros::WrenchStampedMsgToCartesianSignal
    display_name: Wrench Stamped Message To Cartesian Signal
    events:
      transitions:
        on_load:
          switch_controllers:
            hardware: hardware
            activate: force_controller
    inputs:
      input: /custom_motion_generator/command
    outputs:
      output: /wrench_stamped_message_to_cartesian_signal/output
  custom_motion_generator:
    component: template_component_package::PyComponent
    display_name: Custom Motion Generator
    events:
      transitions:
        on_load:
          load:
            component: wrench_stamped_message_to_cartesian_signal
    outputs:
      command: /custom_motion_generator/command
hardware:
  hardware:
    display_name: Hardware Interface
    urdf: Generic six-axis robot arm
    rate: 100
    events:
      transitions:
        on_load:
          load:
            - controller: robot_state_broadcaster
              hardware: hardware
            - controller: force_controller
              hardware: hardware
    controllers:
      robot_state_broadcaster:
        plugin: aica_core_controllers/RobotStateBroadcaster
        events:
          transitions:
            on_load:
              switch_controllers:
                hardware: hardware
                activate: robot_state_broadcaster
            on_activate:
              load:
                component: custom_motion_generator
      force_controller:
        plugin: aica_core_controllers/effort/ForceController
        parameters:
          force_limit:
            - !!float 20.0
            - !!float 20.0
            - !!float 20.0
            - !!float 2.0
            - !!float 2.0
            - !!float 2.0
        inputs:
          command: /wrench_stamped_message_to_cartesian_signal/output
graph:
  positions:
    components:
      wrench_stamped_message_to_cartesian_signal:
        x: 100
        y: 780
      custom_motion_generator:
        x: 100
        y: 420
    hardware:
      hardware:
        x: 680
        y: -20
  edges:
    wrench_stamped_message_to_cartesian_signal_output_hardware_hardware_force_controller_command:
      path:
        - x: 660
          y: 1040
        - x: 660
          y: 820
    wrench_stamped_message_to_cartesian_signal_on_load_hardware_hardware_force_controller:
      path:
        - x: 580
          y: 920
        - x: 580
          y: 660
    hardware_hardware_robot_state_broadcaster_on_activate_custom_motion_generator_custom_motion_generator:
      path:
        - x: 40
          y: 400
        - x: 40
          y: 480
    custom_motion_generator_on_load_wrench_stamped_message_to_cartesian_signal_wrench_stamped_message_to_cartesian_signal:
      path:
        - x: 540
          y: 560
        - x: 540
          y: 740
        - x: 40
          y: 740
        - x: 40
          y: 840
    custom_motion_generator_command_wrench_stamped_message_to_cartesian_signal_input:
      path:
        - x: 500
          y: 680
        - x: 500
          y: 760
        - x: 80
          y: 760
        - x: 80
          y: 1040