Why Wrist 3 Accumulates Multiple Revolutions
Repeatedly rotating a pipe with the Wrist 3 joint can make its reported joint value grow beyond the desired [-2π, 2π] range. This creates a compatibility problem when ROS MoveIt expects joint values within that interval, even though the robot remains at an equivalent physical orientation.
Reset the Revolution Counter from URScript
Call the controller-provided revolution-counter reset command after the rotational operation:
reset_revolution_counter()This provides the URScript behavior needed to reset the accumulated revolution count. The available evidence does not identify firmware prerequisites, arguments, return values, or whether the command can target an individual joint; verify those details on the installed controller before integrating it into production logic.
Use Cartesian Targets for Minimum Joint Travel
When the program supplies a Cartesian target, the controller can select a joint solution that avoids moving Wrist 3 through the long rotational path. This addresses motion selection, while reset_revolution_counter() addresses the accumulated joint representation. Treat these as separate operations when deciding whether the requirement is shorter motion, bounded reported angles, or both.
Implementation and Verification
- Complete the pipe-rotation operation.
- Invoke
reset_revolution_counter()at a controlled point before handing the joint state to ROS MoveIt. - Read the resulting joint state and confirm that Wrist 3 is represented within the required
[-2π, 2π]interval. - Run the subsequent planned move at controlled conditions and verify that Wrist 3 does not take the long rotational path.
Do not infer the physical motion produced by the reset from the command name alone. Validate both the reported joint value and actual robot motion on the installed UR3e controller, especially before coordinating the two-robot configuration.
FAQ
How do I reset the Wrist 3 revolution count in URScript?
Execute reset_revolution_counter() after the multi-revolution operation, then read the joint state to confirm the resulting Wrist 3 value.
Can URScript keep Wrist 3 between -2π and 2π?
The revolution-counter reset is the supported action identified for this requirement. Verify after each reset that the reported value is inside [-2π, 2π] before passing it to ROS MoveIt.
How can I stop Wrist 3 from taking the long path?
Supply a Cartesian target so the controller can find a joint solution that avoids the long Wrist 3 rotation. Test the selected path under controlled conditions before production use.
