gearbox joint does not work correctly

edit

Hello everyone. I am a user of Gazebo & ROS.

I am using mimic_joint_pluginto open/close a robot gripper. This works correctly (An example motion is here https://youtu.be/SqPNVJqgZns).

My xacro file is here link. Please see lines 125 to 131.

<gazebo>
  <plugin name="crane_x7_gripper_mimic_joint" filename="libroboticsgroup_gazebo_mimic_joint_plugin.so">
    <joint>${name}_finger_a_joint</joint>
    <mimicJoint>${name}_finger_b_joint</mimicJoint>
    <multiplier>1</multiplier>
  </plugin>
</gazebo>

So mimic_joint_plugin is not official plugin of Gazebo, I am trying to use gearbox joint instead of the plugin. This works notcorrectly (An example motion is here https://youtu.be/-G1jMrhYzSc).

I think the finger_b_link couldn't follow the motion of finger_base_link.

I add a gearbox joint and comment out the plugin in the xacro file.

<gazebo>
  <joint name="${name}_finger_gearbox" type="gearbox">
    <parent>${name}_finger_a_link</parent>
    <child>${name}_finger_b_link</child>
    <gearbox_reference_body>${name}_base_link</gearbox_reference_body>
    <gearbox_ratio>1</gearbox_ratio>
    <axis>
      <xyz>0 1 0</xyz>
    </axis>

    <axis2>
      <xyz>0 1 0</xyz>
    </axis2>
  </joint>
</gazebo>

<!--
<gazebo>
  <plugin name="crane_x7_gripper_mimic_joint" filename="libroboticsgroup_gazebo_mimic_joint_plugin.so">
    <joint>${name}_finger_a_joint</joint>
    <mimicJoint>${name}_finger_b_joint</mimicJoint>
    <multiplier>1</multiplier>
  </plugin>
</gazebo>
-->

Where should I fix in the xacro file?

Thanks.