External force moved gripper fingers? Any suggestions

I am testing grasping of a Fetch robot using Isaac Sim. I saw the following behavior when the robot lifting the object. The two fingers are moved during this motion. Do you have any suggestions on how to fix this? I assume the fingers should not move during this lifting motion.

Hi Yu, the first things I would try is cranking up the solver iteration on the articulation root, and maybe also increase the stiffness of those two joints. I’ll try to replicate this on our side and see what else can help.

Hi! I have tried to increase the stiffness of the finger joints and increase the solver position iteration count/solver velocity iteration count. But I got the same scenario of the finger movement.

For more information, the Fetch USD file is converted from the official Fetch URDF using the URDF importer. The code of this experiment can be found here: GitHub - IRVLUTD/SceneReplica: Code release for SceneReplica paper.