robot arm is broken link by link in gazebo

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Hi all,

I have succeeded loading my designed robot arm in rviz and finished planning and executing. Right now I want to use load kinect to get some simulated data for robot arm. Hence I am trying to load urdf file in gazebo. The problem is my robot arm is broken link by link. It seems joint element in urdf doesn't work. I followed the tutorial of urdf in gazebo and added friction and damping in the urdf. I am not sure where I got wrong. Thanks in advance for any suggestions.

Here is the pic that robot arm in the rviz

Here is the view that joint in gazebo:

Here is the pic of using simulation pause:

The pic of fixing exploding problem:

Here is the sample of urdf for the robot arm:

<link
name="base_link">
<inertial>
  <origin
    xyz="0.0321026763828113 2.50206915787532E-06 0.0657435992941309"
    rpy="0 0 0" />
  <mass
    value="1.10920648420033" />
  <inertia
    ixx="0.00147297997205269"
    ixy="5.79000298722719E-08"
    ixz="0.000465603614160418"
    iyy="0.00175551330106354"
    iyz="8.33670869119005E-08"
    izz="0.000282540363613262" />
</inertial>
<visual>
  <origin
    xyz="0 0 0"
    rpy="0 0 0" />
  <geometry>
    <mesh
      filename="package://finalarm_dualmotor/meshes/base_link.STL" />
  </geometry>
  <material
    name="">
    <color
      rgba="0.752941176470588 0.752941176470588 0.752941176470588 1" />
  </material>
</visual>
<collision>
  <origin
    xyz="0 0 0"
    rpy="0 0 0" />
  <geometry>
    <mesh
      filename="package://finalarm_dualmotor/meshes/base_link.STL" />
  </geometry>
</collision>
</link>
 <link
name="link_2">
<inertial>
  <origin
    xyz="-0.109631651147839 0.00554931888805481 -0.00279543211641581"
    rpy="0 0 0" />
  <mass
    value="0.471538287399184" />
  <inertia
    ixx="0.000342180694725082"
    ixy="0.000123860746353015"
    ixz="-6.21619859185448E-05"
    iyy="0.000321444130264041"
    iyz="0.000137295563003535"
    izz="0.000525597338936957" />
</inertial>
<visual>
  <origin
    xyz="0 0 0"
    rpy="0 0 0" />
  <geometry>
    <mesh
      filename="package://finalarm_dualmotor/meshes/link_2.STL" />
  </geometry>
  <material
    name="">
    <color
      rgba="0.752941176470588 0.752941176470588 0.752941176470588 1" />
  </material>
</visual>
<collision>
  <origin
    xyz="0 0 0"
    rpy="0 0 0" />
  <geometry>
    <mesh
      filename="package://finalarm_dualmotor/meshes/link_2.STL" />
  </geometry>
</collision>
</link>

 <joint
name="joint_1"
type="revolute">
<origin
  xyz="0.0672 0 0.058"
  rpy="0.46565 1.5708 0" />
<parent
  link="base_link" />
<child
  link="link_2" />
<axis
  xyz="-1 0 0" />
<limit
  lower="-3.14"
  upper="3.14"
  effort="6"
  velocity="2.0" />
<dynamics damping="0.7"/>
</joint>