Ewellix Driver

ROS2 driver for the Ewellix TLT lifts.

Setup

Add user to dialout group to ensure the driver has permissions to access the serial device.

sudo usermod -a -G dialout UserName

Ewellix Node Usage

Run the driver:

ros2 run ewellix_driver ewellix_node

Parameters:

• port: Path to device. By default, /dev/ttyUSB0.
• baud: Baud rate, on most TLT it should be set to 38400
• timeout: Timeout in milliseconds to wait for response from SCU. By default, 1000 ms.
• joint_count: Number of actuators. By default, 2.
• conversion: Encoder ticks per meter. Varies depending on lift model. On the 500mm model, 3225 encoder ticks per meter.
• rated_effort: Rated force of lift. On the 500mm model, 2000 N.
• tolerance: Distance from commanded position to consider within bounds. By default 0.005 meters.
• frequency: Publishing loop rate. By default, 10 Hz.

Running the driver with parameters:

ros2 run ewellix_driver ewellix_node --ros-args -p port:=/dev/ttyUSB0

Moving the lift:

ros2 topic pub /command ewellix_interfaces/msg/Command "ticks: 0
meters: 0.0"

ticks range from 0 to 865.

meters range from 0.0 to max height defined by the model. If both are defined, ticks takes priority over meters.

Ewellix Hardware Interface Usage

If the generate_ros2_control_tag is enabled in the ewllix_lift macro defined in ewellix_macro.xacro, the hardware interface will be loaded by the controller manager.

Using the position_controllers/JointGroupPositionController send a position command to the lift's actuators.

Moving the lift:

ros2 topic pub /lift_position_controller/commands std_msgs/msg/Float64MultiArray "layout:
  dim: []
  data_offset: 0
data: [0.0]"

data list specifies the desired position of the lower and upper joint.

Note, the command sent is applied to both actuators. Therefore, on the TLT500, send a 0.25 command to extend the lift to 500mm.

Example: Visualization

To visualize a model of the lifts in RViz, use the example rviz.launch.py.

ros2 launch ewellix_examples rviz.launch.py

By default, the TLT x25 (2000N, 500mm) model is selected.

To change the model, select a different parameter file. The parameter files can be found in the config directory of the description package.

For example, to visualize the TLT x13 model, navigate to the ewellix_lift directory and run the following command:

ros2 launch ewellix_examples rviz.launch.py lift_parameters:=$PWD/ewellix_description/config/tlt_x13.yaml

Example: Simulation without MoveIt!

To simulate the lift with a simple controller, use the defaults on the simulation.launch.py.

ros2 launch ewellix_examples simulation.launch.py rviz:=true

To change the model, the same parameter is available as in the visualization example:

ros2 launch ewellix_examples simulation.launch.py lift_parameters:=$PWD/ewellix_description/config/tlt_x13.yaml rviz:=true

By default, the controller loaded to the ROS 2 control plugin is the JointGroupPositionController using the jpc.yaml.

Example: Simulation with MoveIt!

To simulate the lift with the JointTrajectoryController compatible with MoveIt!, use the following parameters:

ros2 launch ewellix_examples simulation.launch.py controller_file:=jtc.yaml moveit:=true rviz:=true

References

1. Ewellix serial control unit (SCU) installation, operation, and maintenance manual.
2. Ewellix RS232 interface for serial control unit.
3. Ewellix TLT lifting columns