Gripper stuck when grasping object

[JonathanYang0127]

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Description

When using the gripper goto function (regardless of blocking), the franka hand gripper gets stuck when asked to fully close when there is an object between its fingers. As a result, it does not respond to all future commands because it continuously attempts to reach the fully closed position.

Expected Behavior

With blocking off, the gripper should respond to a new command regardless of whether the old one was achieved.

[AlexanderKhazatsky]

I'm experiencing this issue as well. Specifically, I'm experiencing two issues:

1. The gripper pauses unnecessarily when going to a new width (ex from fully open to fully closed). Some extra details: I'm controlling the gripper with a delta (ie. close 10 more mm, 10 more mm, etc). So the pauses may be due to gripper delay on commands (see point 3). However, this control framework works totally fine with the robotiq gripper.
2. When the gripper tries to grasp an object, if it isn't able to fully able to go to the desired location, it gets stuck - even after I update the desired state to be fully open. It only starts to move after I remove the object blocking the gripper fingers from closing.
3. Generally, the default franka gripper is significantly slower at responding to commands than the robotiq gripper.

I'm not sure how much of these issues is Polymetis though, and how much is the robotiq gripper. However, based on what I've heard from other people, it sounds like some of these shouldn't be happening? Specifically the getting stuck.

[AlexanderKhazatsky]

Here’s some videos of the issues discussed:

FullSizeRender.MOV

[AlexanderKhazatsky]

IMG_6232.mov

[AlexanderKhazatsky]

Wanted to bump this issue :)

[exhaustin]

Hello sorry for the slow response. I cannot change the behavior of goto for the Franka Hand as we are simply wrapping around franka::Gripper::move.
What I can do is to expose franka::Gripper::grasp, which is designed to avoid this issue when grasping. I've done that in the PR mentioned above and will close the issue since there is nothing I can do more than that.

So basically, the thing with the Franka Hand is that you can either move to a specific width (and get blocked until it errors out if the gripper is unable to reach the width), or close the gripper all the way until the fingers hit something.

Thanks as always for the detailed description of the issue, I hope your fingers are fine :)