There are several ways to connect to Visual Components to KUKA, Fanuc, ABB and other robot controllers. For OPC UA, a robot manufacturer will probably adhere to the VDMA companion specification, so expect to find and use same variable names in the OPC UA server.
Latest update for KUKA is the KRC 5 controller is shipped with the KUKA.DeviceConnector (KDC) package which supports OPC UA and MQTT. The KDC requires a license. OPC UA supports pub/sub and MQTT is just for monitoring. I have tested it with KUKA.Sim Pro, KUKA.Sim 4.0.1 and Visual COmponents 4.3. Another option is the open-source UDP server which you can find on GitHub and it is more or less approach of read/write config/system variables of the controller. Other option packages like Ethernet can be used for socket connection, which is easy to do in component script.
I have not noticed any updates done by ABB to its OPC UA server, so this article is still up-to-date. There are several ways to connect to ABB robot controller, so it is matter of choice in a way depending on the project and its requirements.
For Fanuc, the controller needs “HMI Device” option, and if you are using RoboGuide use the latest version if possible. I have not tested this nor do I know the cost of the option, but I will surely follow up on this at the beginning of August. From Fanuc documentation, the OPC UA server seems to only support publishing, so mainly for monitoring and the setup for testing in different networks seems tedious, but that is common when dealing with certs, etc. I will follow up to see if it is like the KDC in which you can use method calls. Someone testing with UA Expert can comment on this now. Note that Visual Component OPC UA connection plugin does not support method calls, but others have worked around this by implementing their own OPC UA client in component script.
I don’t know the plans of other players, but Hyundai’s Hi6 should have OPC UA server.