How to use force control with ros.

[josefinemonnet]

I am currently controlling the robot with the moveit api using position control. How is it possible to overlay a certain force value in z-direction?

[mhubii]

hi @josefinemonnet, this currently requires enhancements, also refers to #115 (comment). Apologies.

You can run the wrench command controller stand-alone:

https://lbr-stack.readthedocs.io/en/latest/lbr_fri_ros2_stack/lbr_demos/lbr_demos_cpp/doc/lbr_demos_cpp.html#lbr-wrench-command-controller-hardware-only

However, load data calibration is undocumented #235. I wish we had more resources for quicker improvements.

[jomon250]

Thank you @mhubii for the quick_response. Just for my understanding, without adapting the currently available controllers (joint poisition and wrench), I can only control either the wrench or the joint positions, right? So what I have to do is to write a controller which takes wrench as well as joint position commands and sends them to the interface? Here it says that with the LBRWrenchCommand.msg I may command wrench as well as joints, right?

[jomon250]

Another opportunity would be to simply use the Cartesian Impedance Controller, wouldn't it? I could tune the stiffness-value in z accordingly, and the other stiffness values relatively high, so that it follows the commanded trajectory. I am just wondering why it says here, that I have to choose between the position and the joint impedance controller but not the cartesian impedance controller?

[mhubii]

sorry bit occupied atm. Yes,

Another opportunity would be to simply use the Cartesian Impedance Controller, wouldn't it?

Yes, you can select the Control Mode: Cartesian Impedance Controller and Command Mode: Position (on the KUKA smartPAD). You can set a desired stiffness in the Java application. When in contact with something, you can command a delta x, and this should create your target force a la F=kdx.

have to choose between the position and the joint impedance controller but not the cartesian impedance controller?

At the time the Cartesian Impedance Controller wasn't properly tested, so left undocumented.