The franka_gazebo gripperAction action Service implementation should be improved

[rickstaa]

The simulated gripper is implemented suboptimal in franka_ros (see frankaemika/franka_ros#172):

1. Gripper PID gains need improvement for the /franka_gripper/gripper_action/goal action to set the gripper width accurately when the gripper is vertical (see this and this comment).
2. Additionally, there is a need to enhance the functionality of the /franka_gripper/gripper_action/goal action. The gripperAction currently has a limitation—it can only grasp objects when the gripper width is explicitly specified. On the other hand, the grasp action can grasp things but cannot set a desired gripper width. In reinforcement learning, it would be advantageous for the robot to autonomously learn and set the gripper width while grasping objects, even without prior knowledge of the object size.

EDIT: I worked around issue two by setting the /franka_gripper/gripper_action/width_tolerance parameter to a value more significant than the max gripper width (see https://frankaemika.github.io/docs/franka_ros.html#frankagrippersim).

TODOs

• Provide a way to grasp objects.
• Tune the gripper PID gains.

[rickstaa]

Fixed when frankaemika/franka_ros#172 is fixed.

[hamsadatta]

Hi @rickstaa ,
I am trying to manually grasp the object using moveit. But I see the below behavior (check the animation). The gripper's finger moves back once it detects an object. How to disable that feedback behavior. I also tried to set the "brute_force_grasping" argument to true but did it not bring any change. My "control_type" is set to "trajectory".

panda_grasp.mp4

[rickstaa]

Hi @rickstaa , I am trying to manually grasp the object using moveit. But I see the below behavior (check the animation). The gripper's finger moves back once it detects an object. How to disable that feedback behavior. I also tried to set the "brute_force_grasping" argument to true but did it not bring any change. My "control_type" is set to "trajectory".

panda_grasp.mp4

@hamsadatta thanks for your bug report. I also need to fix this for my own research so I will take a look this week 👍🏻. I got it to work earlier.

[rickstaa]

@hamsadatta, I've dedicated some time to delve into this issue (see frankaemika/franka_ros#172 (comment)). It appears that Franka has made specific enhancements to the simulated gripper actions. While the /franka_gripper/grasp/goal can now effectively grasp objects, it falls short when setting a specific gripper width. Conversely, the /franka_gripper/gripper_action/goal can manipulate the gripper's position but cannot grasp objects. I'll explore potential workarounds briefly, but a resolution from @frankaemika upstream must address this issue comprehensively.

[rickstaa]

@hamsadatta I just merged #199, which makes brute_force_grasping the default and depricates the launchfile argument. Grasping should now work in the simulation.