Add documentation for hardware interface including effort control mode

Author: urfeex

ur_robot_driver/doc/hardware_interface.rst

@@ -0,0 +1,52 @@
+:github_url: https://github.com/UniversalRobots/Universal_Robots_ROS2_Driver/blob/main/ur_robot_driver/doc/hardware_interface.rst
+
+UR Hardware interface
+=====================
+
+The UR hardware interface is the core piece of the ROS driver. It is responsible for communicating
+with the robot controller, sending commands and receiving status updates.
+
+The hardware interface is implemented using the ``ros2_control`` framework, which allows for modular
+and flexible control of the robot.
+
+.. note::
+   The hardware interface itself doesn't define how the robot's motion can be controlled through
+   ROS. For that, a **controller** is needed. There are many controllers to choose from, such as
+   the ``JointTrajectoryController`` or the ``ForceModeController``. See `ros2_controllers
+   <https://control.ros.org/rolling/doc/ros2_controllers/doc/controllers_index.html#controllers-for-manipulators-and-other-robots>`_
+   for "standard" controllers and :ref:`ur_controllers` for more information on UR-specific
+   controllers
+
+Supported control modes
+-----------------------
+
+The UR hardware interface supports the following control modes:
+
+- **Position control**: The robot's joints are controlled by specifying target positions.
+- **Velocity control**: The robot's joints are controlled by specifying target velocities.
+- **Effort control**: The robot's joints are controlled by specifying target efforts (torques).
+  (Only available when running PolyScope >= 5.23.0 / 10.10.0)
+- **Force control**: The robot's end-effector is controlled by specifying target forces
+  in Cartesian space.
+- **Freedrive mode**: The robot can be moved freely by the user without any active control.
+- **Passthrough Trajectory control**: Complete trajectory points are forwarded to the robot for
+  interpolation and execution.
+- **Tool contact mode**: The robot stops when the tool comes into contact with an object, allowing for
+  safe interaction with the environment.
+- **Speed scaling**: Speed scaling on the robot can be read and written through the hardware
+  interface.
+- **GPIO**: Digital and analog I/O pins can be read and written through the hardware interface.
+- **Payload**: Payload configuration can be changed during runtime through the hardware interface.
+- **Force torque sensor**: Force torque sensor data can be read through the hardware interface.
+  Zeroing the sensor is also supported.
+
+Interacting with the hardware interface
+---------------------------------------
+
+As stated above, motion control is done through controllers. However, the ros2_control framework
+provides a set of services to interact with the hardware interface directly. These services can be
+comfortably used through the ``ros2 control`` `command line tool
+<https://control.ros.org/rolling/doc/ros2_control/ros2controlcli/doc/userdoc.html>`_.
+
+E.g. ``ros2 control list_hardware_components`` will list all hardware components, including the UR
+hardware interface with its interfaces as listed above.

ur_robot_driver/doc/index.rst

@@ -17,6 +17,7 @@ ur_robot_driver
    usage/toc
    operation_modes
    setup_tool_communication
+   hardware_interface
    hardware_interface_parameters
    dashboard_client
    robot_state_helper