Does the rsi_hw_interface driver modify the target joint positions?

[tllatzal]

Hello everyone,

we want to use the kuka_experimental package to control a KR16 R1610 using ROS. I have a question regarding the functionality of the rsi_hw_interface.
Please correct me if I am wrong: The RSI interface is quite a low level interface to the robot so the Kuka controller does not do any trajectroy planning while RSI is active and simply moves the joints to the target joint positions received every 4 ms. So the trajactory (and velocity and acceleration) planning has to be done on the ROS side. Are the trajectories planned by ROS (e.g. Moveit) parsed and streamed directly via the RSI interface to the robot or are they modified by the rsi_hw_interface driver to account for joint movements too big for the 4 ms timeframe?

Thanks a lot

[gavanderhoorn]

Are the trajectories planned by ROS (e.g. Moveit) parsed and streamed directly via the RSI interface to the robot

No.

or are they modified by the rsi_hw_interface driver to account for joint movements too big for the 4 ms timeframe?

Neither.

This may sound pedantic, but it's important to be as precise as possible when talking about this.

The hardware_interface (ie: KukaHardwareInterface) does nothing more than periodically forward to the controller (over RSI) whatever gets written into joint_position_command_ (here). It doesn't do any interpolation, checking or parsing.

Which "entity" writes into joint_position_command_ would depend on how the ros_control stack is configured. Typically, one of the ros_control controllers is used.

Which controller that would be is up to you.

If you configure it to be a joint_trajectory_controller, that controller will be responsible for making sure that robot joint limits are not violated.

[gavanderhoorn]

Closing this as it's a question and not an actionable issue or defect.

[gavanderhoorn]

See #126 and #89 for some related issues.

[gavanderhoorn]

Note:

received every 4 ms

there is no assumption about the period in the hardware_interface. As RSI supports multiple, this would not work.

[tllatzal]

Thanks a lot for the extremely fast and helpful answers. That helps me a lot understanding how it all works