joint_state_broadcaster

The broadcaster reads all state interfaces and reports them on /joint_states and /dynamic_joint_states.

Commands

Broadcasters are not real controllers, and therefore take no commands.

Hardware interface type

By default, all available joint state interfaces are used, unless configured otherwise. In the latter case, resulting interfaces is defined by a “matrix” of interfaces defined by the cross-product of the joints and interfaces parameters. If some requested interfaces are missing, the controller will print a warning about that, but work for other interfaces. If none of the requested interface are not defined, the controller returns error on activation.

Parameters

This controller uses the generate_parameter_library to handle its parameters. The parameter definition file located in the src folder contains descriptions for all the parameters used by the controller.

List of parameters

use_local_topics (bool)

Defining if joint_states and dynamic_joint_states messages should be published into local namespace, e.g., /my_state_broadcaster/joint_states.

Default: false

joints (string_array)

Parameter to support broadcasting of only specific joints and interfaces. It has to be used in combination with the interfaces parameter. If either joints or interfaces is left empty, all available state interfaces will be published. Joint state broadcaster asks for access to all defined interfaces on all defined joints.

Default: {}

extra_joints (string_array)

Names of extra joints to be added to joint_states and dynamic_joint_states with state set to 0.

Default: {}

interfaces (string_array)

Parameter to support broadcasting of only specific joints and interfaces. It has to be used in combination with the joints parameter. If either joints or interfaces is left empty, all available state interfaces will be published.

Default: {}

map_interface_to_joint_state

Optional parameter (map) providing mapping between custom interface names to standard fields in joint_states message. Usecases:

Hydraulics robots where feedback and commanded values often have an offset and reliance on open-loop control is common. Typically one would map both values in separate interfaces in the framework. To visualize those data multiple joint_state_broadcaster instances and robot_state_publishers would be used to visualize both values in RViz.

A robot provides multiple measuring techniques for its joint values which results in slightly different values. Typically one would use separate interface for providing those values in the framework. Using multiple joint_state_broadcaster instances we could publish and show both in RViz.

Format (each line is optional):

map_interface_to_joint_state:
    position: <custom_interface>
    velocity: <custom_interface>
    effort: <custom_interface>

Examples:

map_interface_to_joint_state:
    position: kf_estimated_position

map_interface_to_joint_state:
    velocity: derived_velocity
    effort: derived_effort

map_interface_to_joint_state:
    effort: torque_sensor

map_interface_to_joint_state:
    effort: current_sensor

map_interface_to_joint_state.position (string)

Default: “position”

map_interface_to_joint_state.velocity (string)

Default: “velocity”

map_interface_to_joint_state.effort (string)

Default: “effort”

use_urdf_to_filter (bool)

Uses the robot_description to filter the joint_states topic. If true, the broadcaster will publish the data of the joints present in the URDF alone. If false, the broadcaster will publish the data of any interface that has type position, velocity, or effort.

Default: true

An example parameter file

joint_state_broadcaster:
  ros__parameters:
    extra_joints: '{}'
    interfaces: '{}'
    joints: '{}'
    map_interface_to_joint_state:
      effort: effort
      position: position
      velocity: velocity
    use_local_topics: false
    use_urdf_to_filter: true

Order of the joints in the message

The order of the joints in the message can determined by 3 different parameter settings:

No defined joints parameter and use_urdf_to_filter set to false:
The order of the joints in the message is the same as the order of the joints’ state interfaces registered in the resource manager. This is typically the order in which the hardware components are loaded and configured.
No defined joints parameter and use_urdf_to_filter set to true:
The order of the joints in the message is the same as the order of the joints in the URDF file, which is inherited from the loaded URDF model and independent of the order in the ros2_control tag.
Defined joints parameter along with interfaces parameter:
The order of the joints in the message is the same as the order of the joints in the joints parameter.

If the joints parameter is a subset of the total available joints in the URDF (or) the total available state interfaces, then only the joints in the joints parameter are published in the message.

If any of the combinations of the defined joints parameter and interfaces parameter are not in the available state interfaces, the controller will fail to activate.

..note::: If the extra_joints parameter is set, the joints in the extra_joints parameter are appended to the end of the joint names in the message.