Gripper controller not working properly in Ignition Fortress

[andreamaimone]

Hello,
I am trying to run a simulation with ROS2 Humble and Ignition Fortress, using gz_ros2_control plugin. I am using the 2f-140 gripper and I am facing issues when trying to control it with ros controllers position_controllers/GripperActionController and forward_command_controller/ForwardCommandController. In particular, I am using the position command interface on the joint "finger_joint". The controls do not work if the initial position of the joint is 0, otherwise they work only when closing the gripper. In fact, when trying to open it, its structure breaks as shown in the picture below. Has anyone faced the same issue? Do you know what could be the reason of this malfunction, or how to solve it?
Thank you all in advance.

[username1024zy]

解决了吗？

[andreamaimone]

I think the problem was that Ignition physics engine was breaking for some reason because the collisions of inner knuckles and inner fingers were interpenetrating each other. I solved the problem by adding a damping value and a friction value to the mimic joints. In fact, these are set by default to 0 if not specified in the xacro. I added them as follow:
<joint ...>
<dynamics damping="5.0" friction="2.0"/>
</joint>
in robotiq_2f_140.xacro file.
By doing this I have no other problem in simulating and controlling the gripper.
I do not know the exact reason behind this problem and if the correction I applied is totally correct, so I'll leave this issue open so that maybe someone can clarify it to me.