A general purpose controller which can be used to trigger command interfaces.

This controller is a derivative of the ros2_control GpioCommandController.

Features

The key differences between this controller and the GpioCommandController is two-fold:

Use Joint interfaces

Besides GPIO interfaces, this controller allows Joint interfaces to be used, enabling the user to utilize the controller in broader applications and simplifying the URDF description.

Single write to command interfaces

The GpioCommandController writes the latest received command to the configured state interfaces on every update cycle. On the contrary, the SingleTriggerController only writes to the command interfaces once in the subscription callback when a new command has been received. The user can for example leverage this by clearing the command interface (writing NaN or 0.0 to it) in the hardware interface once the latest trigger has been handled.

Interfaces

Subscribers

• /<controller_name>/commands [control_msgs/msg/DynamicJointState]: A subscriber for configured command interfaces.

Publishers

• /<controller_name>/states [control_msgs/msg/DynamicJointState]: A subscriber for configured command interfaces.

Parameters

The parameter configuration is slightly adapted to accomodate for gpios and joints. Take a look at parameters.md for reference.

Note

Contrary to the GpioCommandController, if no state interfaces are configured no states will be published.

Example

A single trigger controller to trigger the homing of a joint.

controllers.yaml

The relevant part of the controllers.yaml file could look like this:

...
homing_controller:
  ros__parameters:
    type: single_trigger_controller/SingleTriggerController
    joints:
      - j1
      - j2
      - j3
      - j4
    command_interfaces:
      joints:
        j1:
          - interfaces:
            - home
        j2:
          - interfaces:
            - home
        j3:
          - interfaces:
            - home
        j4:
          - interfaces:
            - home

    state_interfaces:
      joints:
        j1:
          - interfaces:
            - home
        j2:
          - interfaces:
            - home
        j3:
          - interfaces:
            - home
        j4:
          - interfaces:
            - home

ros2_control URDF

The relevant part of the ros2_control tag in the robots URDF description file could look like this:

...
    <joint name="${prefix}j1">
        ...
        <command_interface name="home">
            <param name="<a-parameter>">0.0</param>
        </command_interface>
        <state_interface name="home"/>
        ...
    </joint>
...

Trigger the homing

One can for example manually trigger homing via the ROS2 control CLI like this:

ros2 topic pub -1 /homing_controller/commands control_msgs/msg/DynamicInterfaceGroupValues "{interface_groups: [j1], interface_values: [{interface_names: [home], values: [1.0]}]}"

Handling the Trigger

Inside the harware interfaces write() method one can handle a trigger like described in the following pseudo-code:

std::string interface_name = "j1/home";
float command = get_command(interface_name);
if(command){
    // Call triggered function
    call_to_some_function();
    set_command(interface_name, 0.0);
}

Dependencies

This controller has been tested with ROS2 Jazzy and ROS2_control Jazzy.

Install

Clone the repository into the ros2 workspace and build.