Handle registry writing from Srv and reading from Topic

[pucciland95]

Hi all!

I would like to propose a new feature that I think may be rather useful to alternate streaming motion and custom URSCRIPT.

In particular, I would like to investigate whether, in your opinion, it is feasible to expand the set_io to set input_registry.
At the same time, stream in a topic the output_registry or in io_states or in a different topic.

As of now I do not think it is possible to do this easily since dashboard allow to load immutable urscripts and returning to external_control takes some time.
Urscriptinterface instead requires the robot to be in external_control which I would like to avoid and it requires particular care in a correct script encoding.

What do you think about this?

[urfeex]

To be fair, a PoC could be done by building a new node ontop of the client library. I think, I don't fully understand what you want to achieve and why.

If you want to integrate things into the current driver structure, you would have to add the registers to the hardware interface's command interfaces and add a new controller reading the topics that you want forwarding the data to the register buffers.

[pucciland95]

Hi Felix, and thanks for replying,

the idea is exactly to provide the user with a new controller that allows him/her to read the registries through topics and write them through ROS2 services.

The reason for this is to be able to change URSCRIPT variables from ROS2 applications. Consider the following use-case:

You have the robot commanded through the external control urscript node getting commands from a ROS2 application. The user then wants to execute a custom URSCRIPT with some parameters (i.e. robot pose), both known at runtime. As of now, there is no way to communicate to the robot such information other than loading a custom script through the Urscriptinterface, which is pretty susceptible to encoding errors.
On the other hand, if writing to the registry were possible, you would call:

1. set a registry X to the URSCRIPT routine to run and registries Y, Z, ..., to all other required data (i.e. robot pose)
2. call /hand_back_control to exit from External Control
3. read from registry X and use a switch statement to execute a particular URSCRIPT routine
4. read from registries Y, Z,... runtime data (i.e. robot pose)
5. execute requested URSCRIPT routine
6. Routine finished and main URSCRIPT restarts, returning to External Control and then be controlled from the ROS2 application

In a few words, a kind of state machine to alternate the control between an external ROS2 application and URSCRIPT.

Do you think there is an easier way to do so?

[urfeex]

Using our ScriptCommandInterface would allow similar patterns. However, at the moment one needs to modify the client library in order to add custom functionality. We'd like to refactor that (see UniversalRobots/Universal_Robots_Client_Library#364).

As written above, creating a new node that contains an RTDE client to set the registers should be enough and less work than piping everything through ros2_control in that case. Since the routine should be executed independently of ros2_control, that also seems to be a fair approach to the problem.