Components architecture and examples. by destogl · Pull Request #22 · ros-controls/roadmap

destogl · 2020-08-04T16:22:03Z

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design_drafts/components_architecture_and_urdf_examples.md

Co-authored-by: Bence Magyar <bence.magyar.robotics@gmail.com>

Karsten1987

In principle this looks good to me. I think we need more flesh to this though to describe things in more detail.

I think use-cases can be shifted around, maybe even combined - thinking about 1 & 4 as well as 6 & 7 & 8. Within these blocks, only the difference could be then highlighted.

Karsten1987 · 2020-08-11T22:36:52Z

design_drafts/components_architecture_and_urdf_examples.md

+
+![ros2_control Components Achitecture][ros2_control_arch_resource_manager]
+
+[ros2_control_arch_resource_manager]: images/components_architecture.png "ROS2 Control - Components Architecture"


Not sure how to comment on the image, so I'll do it here:
I think it's an implementation detail to mention "ActuatorHardwareInterface" and would remove that row of boxes with "template to implement ..."

As for wording, I know it's a constant bike shedding, but I don't see the point to add "Hardware" to "ActuatorHardware". Same for sensors and systems.

However, what this document lacks in my opinion is a general introduction/motivation and explanation of wording. Basically saying what's meant with "actuator", what's a system etc. Basically explaining the vision. Saying that a robot hardware with a basic main loop had to be written for ROS1, the goal here with ROS2 is to create an architecture to dynamically compose a robot.

Not sure how to comment on the image, so I'll do it here:
I think it's an implementation detail to mention "ActuatorHardwareInterface" and would remove that row of boxes with "template to implement ..."

I wanted to have this implementation detail in it. The image is something between implementation UML and architecture and I hope for a user would be clear where to starts its implementation.

As for wording, I know it's a constant bike shedding, but I don't see the point to add "Hardware" to "ActuatorHardware". Same for sensors and systems.

I did it mainly to make a difference between "Joint" and "Sensor" on the right side, and those implementations of interfacing the hardware directly. This wording is in line with ROS1 ros_control with RobotHardware and RobotHardwareInterface.

However, what this document lacks in my opinion is a general introduction/motivation and explanation of wording. Basically saying what's meant with "actuator", what's a system etc.

I agree with you. My intention of current state of PR is to clarify the URDF structures, so we can start implement this in the main repository.

Karsten1987 · 2020-08-11T22:42:17Z

design_drafts/components_architecture_and_urdf_examples.md

+
+## URDF Examples
+
+ros2_control implementation examples are presented for the following robot/robot-cell architectures:


what's a robot cell?

What is the proper English term for a fenced area where robot is, usually with other machines like feeders, doing his thing? image

In German is called "RoboterZellle". Therefore, I thought "cell" is a good term.

Caged robots is the common term in English I believe

Karsten1987 · 2020-08-11T22:48:59Z

design_drafts/components_architecture_and_urdf_examples.md

+
+Note:
+  * Everything within the `<classType>` tag is implemented as a plugin.
+  * The examples below have some `<param>` tags defined for each plugin which are primarily for demonstration, not part of a pre-defined xml schema. Components can define their own parameters.


I don't understand this. The param tag should be part of the xml schema - otherwise this tag wouldn't be allowed. I think what you want to mention is that the attributes and values are free to be chosen per plugin, is that right?
But we have to maybe clarify how these parameters are being used. Saying how each plugin is supposed to obtain these parameters.

I reword this. Is it better now?

But we have to maybe clarify how these parameters are being used.

This would be done in the example implementation.

Karsten1987 · 2020-08-11T22:53:10Z

design_drafts/components_architecture_and_urdf_examples.md

+      <param name="example_param_write_for_sec">2</param>
+      <param name="example_param_read_for_sec">2</param>
+    </hardware>
+    <joint name="joint1">


I know we've talked about this and you don't like it, but I think it is clearer here to replace "joint" with "joint_handle" or something similar to emphasize that this joint is purely virtual and abstract to any hardware specific implementation.

this joint is purely virtual and abstract to any hardware specific implementation

I do not agree. On this level, in the RessourceManager all joints are actually the real joints of the hardware. First when we go into ControllerManager virtual joints are used. (This is also shown, not in full detail, in the image)

Then I still don't understand what's happening with joints. In my understanding, the term joint here described something abstract which encapsulates common pattern like joint limits etc before these values are then finally passed to the system implementation.

There's the forward facing XML format we are trying to set up and the code that this will eventually tie into. I would 100% consider joint_handle an implementation detail nobody should care about when defining/reading a URDF. No matter how this is implemented, the URDF should never refer to handles, let's keep it at the abstract terms level.

Karsten1987 · 2020-08-11T22:56:34Z

design_drafts/components_architecture_and_urdf_examples.md

+Note:
+  * `ros2_control_components/PositionJoint`type has implicitly:
+    ```xml
+      <commandInterfaceType>position</commandInterfaceType>
+      <stateInterfaceType>position</stateInterfaceType>
+    ```


I wonder if this note should come later in the document as we've never mentioned "commandInterface" up to this point.

We should add some general description at the beginning.

design_drafts/components_architecture_and_urdf_examples.md

Karsten1987 · 2020-08-11T23:17:26Z

design_drafts/components_architecture_and_urdf_examples.md

+      <param name="max_values">1</param>
+    </joint>
+  </ros2_control>
+  <ros2_control name="2DOF_System_Robot_ForceTorqueSensor" type="sensor">


I think it deserves a bit more context or description that we have two separate ros2_control tags in here and thus treat the two components individually.

design_drafts/components_architecture_and_urdf_examples.md

Co-authored-by: Karsten Knese <Karsten1987@users.noreply.github.com>

after testing them with parser in ros-controls/ros2_control#127

bmagyar · 2020-08-21T07:07:31Z

follow-up: #23

bmagyar

This is now ready to merge, please open follow-up issues/PRs with changes you wish.

Components archtiecture and examples.

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destogl requested review from Karsten1987 and bmagyar August 4, 2020 16:22

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Karsten1987 reviewed Aug 11, 2020

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Correct XML snippets

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after testing them with parser in ros-controls/ros2_control#127

destogl mentioned this pull request Aug 17, 2020

Add component parser ros-controls/ros2_control#122

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bmagyar merged commit 6002b60 into ros-controls:master Aug 21, 2020

destogl deleted the control_components_design branch September 8, 2020 11:13

destogl mentioned this pull request Sep 11, 2020

Make Robot class as main Container used from controller_manager ros-controls/ros2_control#106

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		![ros2_control Components Achitecture][ros2_control_arch_resource_manager]

		[ros2_control_arch_resource_manager]: images/components_architecture.png "ROS2 Control - Components Architecture"


		## URDF Examples

		ros2_control implementation examples are presented for the following robot/robot-cell architectures:

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destogl commented Aug 4, 2020

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bmagyar commented Aug 21, 2020

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