Revert "Remove tf_prefix from ur_control.launch.py (UniversalRobots#1020

)"

tf_prefix is used as a substitution argument inside the controllers.yaml

Therefore, it needs to be specified as an argument for the ur_conttrol.launch.py file

ur_robot_driver/launch/ur_control.launch.py

@@ -68,6 +68,8 @@ def launch_setup():
         parameters=[
             LaunchConfiguration("update_rate_config_file"),
             ParameterFile(controllers_file, allow_substs=True),
+            # We use the tf_prefix as substitution in there, so that's why we keep it as an
+            # argument for this launchfile
         ],
         output="screen",
     )
@@ -280,6 +282,15 @@ def generate_launch_description():
             "publishes the description topic.",
         )
     )
+    declared_arguments.append(
+        DeclareLaunchArgument(
+            "tf_prefix",
+            default_value="",
+            description="tf_prefix of the joint names, useful for "
+            "multi-robot setup. If changed, also joint names in the controllers' configuration "
+            "have to be updated.",
+        )
+    )
     declared_arguments.append(
         DeclareLaunchArgument(
             "use_mock_hardware",