[Polymetis] exposing new gripper api to completely fix gripper stuck issue

[buoyancy99]

Description

A while ago, this issue found an issue when using polymetis to control franka gripper. This is a very critical problem as one cannot control gripper to grasp one object and release it.

This PR offers a partial fix to the issue, but on real robots this doesn't solve the problem.

Instead, one should follow the official C++ example from franka to achieve the desired behavior of getting gripper unstuck from previous commands. This example essentially calls gripper.stop() to terminate a previous command that cannot be achieved, whenever a new command is about to be sent.

This PR exposes the GripperInterface.stop API, so one can call GripperInterface.stop() before GripperInterface.goto or GripperInterface.grasp to get gripper unstuck.

I've tested on hardware.

Type of change

Please check the options that are relevant.

• Bug fix (non-breaking change that fixes an issue)
• Proposes a change (non-breaking change that isn't necessarily a bug)
• Refactor
• New feature (non-breaking change that adds a new functionality)
• Breaking change (fix or feature that would break some existing functionality downstream)
• This is a unit test
• Documentation only change
• Datasets Release
• Models Release

Type of requested review

• I want a thorough review of the implementation.
• I want a high level review.
• I want a deep design review.

Before and After

If this PR introduces a change or fixes a bug, please add before and after screenshots (if this is causes a UX change) or before and after examples(this could be plain text, videos etc ) to demonstrate the change.

If this PR introduces a new feature, please also add examples or screenshots demonstrating the feature.

Testing

Please describe the tests that you ran to verify your changes and how we can reproduce.

Checklist:

• I have performed manual end-to-end testing of the feature in my environment.
• I have added Docstrings and comments to the code.
• I have made changes to existing documentation where needed.
• I have added tests that show that the PR is functional.
• New and existing unit tests pass locally with my changes.
• I have added relevant collaborators to review the PR before merge.
• [Polymetis only] I ran on hardware (1) all scripts in tests/scripts, (2) asv benchmarks.

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[Harimus]

Will this PR be merged anytime soon? I have similar issues.

although unlike #1418 for me it does not get stuck when using grasp(), but it does with goto() call is used and it doesn't get sufficiently close to the width specified. Which is same behavior to the FrankaAPI call on C++ (or their python wrapper on ROS)

[IlkwonHong]

Hello thanks for sharing your work.
I copy and pasted your modification of 3 files, but my gripper is still stucked after closing finger with goto function. I definitely called GripperInterface.stop before opening it
Is there anything I missed?