gazebo里机械臂受到外力后，仍然保持不动

[一条很有用的咸鱼saltedfish]

如图，kuka的机械臂，可以在gazebo中正常打开，但移动下方的方块砸机械臂，它一点而都不动，也尝试过直接给机械臂施加力和力矩，机械臂也不动，下面粘贴urdf部分urdf文件，

<link name="base_link">
    <inertial>
        <origin xyz="-0.027804 0.00039112 0.14035" rpy="0.0 0.0 0.0" />
        <mass value="1572.9"/>
        
        <inertia ixx="89.282" ixy="-0.47721" ixz="0.85562" iyy="107.51" iyz="0.0067576" izz="172.02"/>
    </inertial>
    <visual>
        <origin xyz="0.0 0.0 0.0" rpy="-1.57 0.0 0.0"/>
        <geometry>
            <mesh filename="file://$(find mybot1_description)/meshes/visual/base_link.dae" scale="1.0 1.0 1.0"/>
        </geometry>
        <material name="">
            <color rgba="0.75294 0.75294 0.75294 1"/>
        </material>
    </visual>
    <collision>
        <origin xyz="0.0 0.0 0.0" rpy="-1.57 0.0 0.0"/>
        <geometry>
            <mesh filename="file://$(find mybot1_description)/meshes/collision/base_link.stl" scale="1.0 1.0 1.0"/>
        </geometry>
    </collision>
</link>

<link name="link_1">
    <inertial>
        <origin xyz="-0.036811 -0.024697 0.56577" rpy="0.0 0.0 0.0"/>
        <mass value="1385.5"/>
        <inertia ixx="90.873" ixy="33.809" ixz="17.159" iyy="147.03" iyz="0.063634" izz="168.19"/>
    </inertial>
    <visual>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
        <geometry>
            <mesh filename="file://$(find mybot1_description)/meshes/visual/link_1.dae" scale="1.0 1.0 1.0"/>
        </geometry>
        <material name="">
            <color rgba="0.75294 0.75294 0.75294 1"/>
        </material>
    </visual>
    <collision>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
        <geometry>
            <mesh filename="file://$(find mybot1_description)/meshes/collision/link_1.stl" scale="1.0 1.0 1.0"/>
        </geometry>
    </collision>         
</link>

<joint name="joint_1" type="revolute">
    <origin xyz="-0.00262 0.00097586 0.33099" rpy="0.0 0.0 0.0"/>
    <parent link="base_link"/>
    <child link="link_1"/>
    <axis xyz="0.0 0.0 1.0"/>
    <dynamics damping="0.1" friction="0.1"/>
    <limit lower="-3.228859205" upper="3.228859205" effort="1000.0" velocity="2.146755039"/>
</joint>

还有部分xacro文件内容
```
<gazebo reference="link_1">
<material>Gazebo/Orange</material>
<self_collide>false</self_collide>
<gravity>true</gravity>
</gazebo>
<gazebo>
<is_static>false</is_static>
<self_collide>true</self_collide>
</gazebo>
<ros2_control name="GazeboSystem" type="system">
<hardware>
<plugin>gazebo_ros2_control/GazeboSystem</plugin>
</hardware>
<joint name="joint_1">
<command_interface name="position"/>
<command_interface name="effort"/>
<!-- <command_interface name="velocity"/> -->
<state_interface name="position">
<param name="initial_value">0</param>
</state_interface>
<state_interface name="velocity"/>
<state_interface name="effort"/>
</joint>