How can I get the fingertip position of Robotiq 2F 140 gripper?

[junshi356rl]

Hi everyone,

I am working on a reinforcement learning grasping task in Isaac Lab (running on Isaac Sim 5.1.0). The setup involves a UR10 arm equipped with a Robotiq 2F-140 gripper, using the default USD assets provided with Isaac Lab.

The Issue: I need the precise position of the gripper fingertips to design a reward function that encourages the fingers to approach the cube. However, I am encountering the following problems:

1. The fingertip prim does not have a corresponding entry in the robot's body_names (or body indices).
2. When querying the position of the inner_finger (the parent of the fingertip), the returned transform seems to correspond to the wrist or palm base rather than the actual finger link.
3. Consequently, when using left_inner_finger and right_inner_finger positions in the reward function, the policy learns to push the cube with the palm base instead of performing a proper reach-and-grasp motion.

My Question: Could anyone suggest the correct method to query or calculate the center/tip position of the gripper fingertips for use in RL observations or rewards? Should I be computing the transform relative to a specific parent link, or is there a specific API call I am missing?

Thanks in advance for your help!