joint_state_topic_hardware_interface
ros2_control hardware interface for JointState topic based control
README
Joint State Topic Based System
The Joint State Topic Based System implements a ros2_control hardware_interface::SystemInterface supporting command and state interfaces through the ROS topic communication layer.
ros2_control urdf tag
The joint_state_topic_hardware_interface has a few ros2_control urdf tags to customize its behavior.
Parameters
joint_commands_topic: (default: “/robot_joint_command”). Example:
<param name="joint_commands_topic">/my_topic_joint_commands</param>.joint_states_topic: (default: “/robot_joint_states”). Example:
<param name="joint_states_topic">/my_topic_joint_states</param>.trigger_joint_command_threshold: (default: 1e-5). Used to avoid spamming the joint command topic when the difference between the current joint state and the joint command is smaller than this value, set to -1 to always send the joint command. Example:
<param name="trigger_joint_command_threshold">0.001</param>.sum_wrapped_joint_states: (default: “false”). Used to track the total rotation for joint states the values reported on the
joint_commands_topicwrap from 2pi to -2pi when rotating in the positive direction. (Isaac Sim only reports joint states from 2pi to -2pi) Example:<param name="sum_wrapped_joint_states">true</param>.
Per-joint Parameters
mimic: Defined name of the joint to mimic. This is often used concept with parallel grippers. Example:
<param name="mimic">joint1</param>.multiplier: Multiplier of values for mimicking joint defined in mimic parameter. Example:
<param name="multiplier">-2</param>.
Modifying the urdf ros2_control tag for new robots
If your robot description support mock_components you simply add an if-else statement to switch between it and <plugin>joint_state_topic_hardware_interface/JointStateTopicSystem</plugin>, make sure to add the joint_commands_topic and joint_states_topic to point to the correct topics.
<ros2_control name="name" type="system">
<hardware>
<xacro:if value="${mock_hardware}">
<plugin>mock_components/GenericSystem</plugin>
<param name="fake_sensor_commands">false</param>
<param name="state_following_offset">0.0</param>
<param name="calculate_dynamics">true</param>
</xacro:if>
<xacro:unless value="${mock_hardware}">
<plugin>joint_state_topic_hardware_interface/JointStateTopicSystem</plugin>
<param name="joint_commands_topic">/topic_based_joint_commands</param>
<param name="joint_states_topic">/topic_based_joint_states</param>
<param name="sum_wrapped_joint_states">true</param>
</xacro:if>
</hardware>
<joint name="joint_1">
<command_interface name="position"/>
<state_interface name="position">
<param name="initial_value">0.0</param>
</state_interface>
<state_interface name="velocity"/>
</joint>
...
<joint name="joint_n">
<command_interface name="position"/>
<state_interface name="position">
<param name="initial_value">0.0</param>
</state_interface>
<state_interface name="velocity"/>
</joint>
...
<joint name="mimic_joint_1">
<param name="mimic">joint_k</param>
<param name="multiplier">1</param>
<command_interface name="position" />
<state_interface name="position">
<param name="initial_value">0.0</param>
</state_interface>
<state_interface name="velocity"/>
</joint>
...
<joint name="mimic_joint_n">
<param name="mimic">joint_kn</param>
<param name="multiplier">1</param>
<command_interface name="position" />
<state_interface name="position">
<param name="initial_value">0.0</param>
</state_interface>
<state_interface name="velocity"/>
</joint>
</ros2_control>