joint_state_publisher

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Description

The joint_state_publisher node publishes sensor_msgs/JointState messages for a robot described with URDF, SDF, or COLLADA formats. It reads the robot description from the robot_description topic or a file and publishes joint states for all non-fixed joints. The node can operate in several modes: publishing default/zero positions, subscribing to external joint state sources, or automatically updating joint positions with a configurable delta for animation.

Publishers

• joint_states (sensor_msgs/msg/JointState)

  • Publishes the current state of all robot joints including positions, velocities, and efforts depending on configuration

Subscribers

• robot_description (std_msgs/msg/String)

  • Receives robot description in URDF, SDF, or COLLADA format

  • QoS: Depth 1, Transient Local durability

• {source_topics} (sensor_msgs/msg/JointState)

  • Dynamically subscribes to topics specified in the source_list parameter

  • Updates joint states from external sources

Parameters

• publish_default_efforts (bool, default: false)

  • Whether to publish default effort values (0.0) for all joints

• publish_default_positions (bool, default: true)

  • Whether to publish default position values (zero position) for all joints

• publish_default_velocities (bool, default: false)

  • Whether to publish default velocity values (0.0) for all joints

• rate (int, default: 10)

  • Publishing rate in Hz for joint state messages

• source_list (string[], default: [])

  • List of topics to subscribe to for joint state updates

  • Joint states from these sources override default values

• use_mimic_tags (bool, default: true)

  • Whether to process and use mimic joint tags from the robot description

• use_smallest_joint_limits (bool, default: true)

  • Whether to use safety controller soft limits when available (reduces joint range)

• delta (double, default: 0.0)

  • Amount to increment joint positions each publish cycle

  • When > 0, joints automatically move within their limits for animation

  • Joints reverse direction at limits (continuous joints wrap around)

• zeros.{joint_name} (double)

  • Set the zero/center position for a specific joint

  • Example: zeros.joint1:=0.5 sets joint1’s zero position to 0.5 radians

• dependent_joints.{joint_name}.parent (string)

  • Specifies the parent joint for a dependent/mimic joint relationship

  • Required for each dependent joint

• dependent_joints.{joint_name}.factor (double, default: 1.0)

  • Multiplier for the dependent joint position relative to parent

• dependent_joints.{joint_name}.offset (double, default: 0.0)

  • Offset added to the dependent joint position

Example Usage

Basic usage with URDF file

ros2 run joint_state_publisher joint_state_publisher /path/to/robot.urdf

Using robot_description topic

ros2 run joint_state_publisher joint_state_publisher

With custom parameters

ros2 run joint_state_publisher joint_state_publisher \
  --ros-args \
  -p rate:=50 \
  -p publish_default_velocities:=true \
  -p use_mimic_tags:=false

With animation (auto-moving joints)

ros2 run joint_state_publisher joint_state_publisher \
  --ros-args \
  -p delta:=0.01

With custom zero positions

ros2 run joint_state_publisher joint_state_publisher \
  --ros-args \
  -p zeros.shoulder_pan_joint:=1.57 \
  -p zeros.elbow_joint:=0.785

Subscribing to external joint sources

ros2 run joint_state_publisher joint_state_publisher \
  --ros-args \
  -p source_list:=['arm_controller/joint_states','gripper_controller/joint_states']

Launch file example

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='joint_state_publisher',
            executable='joint_state_publisher',
            name='joint_state_publisher',
            parameters=[{
                'rate': 50,
                'publish_default_positions': True,
                'use_mimic_tags': True,
                'source_list': ['controller/joint_states']
            }]
        )
    ])