layered_hardware

A ros2_control implementation that adopts layered scheme

The layered scheme

• every ros2_control’s component (ex. joint_limits, transmissions) is implemented as a layer plugin (base_class: layered_hardware::LayerInterface)
• plugins of non-actuator-specific layers can be reused for different actuators
• multiple layers for different vendors’ actuators can be used in the same hardware

Hardware Plugin: layered_hardware/LayeredHardware

Hardware parameters

layers (yaml, required)

• sequence of layers to be loaded by this ros2_control hardware

layers[*].name (string, required)

• arbitary name of the layer

layers[*].type (string, required)

• valid type name of the layer
• the type must be exported to the layered_hardware package
• the base class of the type must be layered_hardware::LayerInterface

Example of ros2_control tag in your robot description

<ros2_control name="LayeredHardware" type="system">
    <hardware>
        <plugin>layered_hardware/LayeredHardware</plugin>
        <param name="layers">
            - name: example_layer_1
              type: layered_hardware/ExampleLayer
            - name: example_layer_2
              ...
            ...
        </param>
        ...
    </hardware>
    ...
</ros2_control>

Layer plugin: layered_hardware/CommandClamperLayer

• loads lower and upper limits on command interfaces of joints, sensors and gpios from the ros2_control tag in the robot description
• clamps commands within the write() function (e.g. limits position command using only min and max position limits, ignoring velocity and acceleration limits)

Layer plugin: layered_hardware/JointSaturationLimiterLayer

• based on joint_limits::JointSaturationLimiter<joint_limits::JointLimits>
• applies limits to all joint command interfaces within the write() function

Hardware parameters

______ (yaml, optional)

• map of parameter names and values for this layer

___.robot_description_topic___ (string, default: '/robot_description')

• topic name for robot description, from which joint limits are loaded

Layer plugin: layered_hardware/TransmissionLayer

• based on transmittion_interface::Transmission
• converts joint commands to actuator commands based on reduction ratio of transmission within write() function
• converts actuator states to joint states within read() function

Layer plugin: layered_hardware/MockActuatorLayer

• implements mock {position, velocity, effort}-controlled actuators
• switches mock actuators’ command modes within perform_command_mode_swtich() function when controllers using associated interfaces activate
• changes actuator states based on commands within write() function
• useful to debug your command generation, state visualization nodes, or transmissions without physical actuators and dynamics simulators

Hardware parameters

______ (yaml, required)

• map of parameter names and values for this layer

___.actuators___ (map<string, map>, required)

• map of parameters for each mock actuator

___.actuators..command_mode_map___ (map<string, string>, required)

• map to actuator command mode names (position, velocity, effort) from associated interface names (typically joint interfaces)

Example of parameter description

<param name="example_mock_actuator_layer">
    actuators:
        example_actuator_1:
            command_mode_map:
                example_joint_1/position: position
                ...
        example_actuator_2:
            ...
</param>

Layer plugin: layered_hardware/MonitorLayer

• prints changes on commands and states within read() function for debug or logging purpose

Examples

• single actuator
• 3 DoF manipulator

Related packages

layered_hardware_dynamixel

• layer implementation for ROBOTIS Dynamixel actuators

layered_hardware_epos

• layer implementation for Maxon EPOS actuator drivers

layered_hardware_unitree

• layer implementation for Unitree actuators

layered_hardware_gz

• layer implementation for joints of a virtual robot in the Ignition Gazebo simulator