In Gazebo, my robot can't see AR tag

edit

OS : Ubuntu 16.04 ROS : Kinetic Simulator : Gazebo

I made an AR tag model using Blender. (.dae) And make a SDF file for Gazebo. I can see the AR tag in Gazebo.

<?xml version='1.0'?>
<sdf version='1.6'>
    <model name='ar_tag_00'>
        <pose>4 0 0  0 0 0</pose>
        <static>true</static>
        <link name="ar_00">
            <visual name="visual">
                <pose>2 0 0 0 0 0</pose>
                <geometry>
                    <mesh><uri>model://ar_tags_for_turtlebot3_exp_house/meshes/ar_tag_00.dae</uri></mesh>
                </geometry>
            </visual>
        </link>
    </model>
</sdf>

But, my robot can't see the AR tag. It just see the box !!! In Rviz, it is same. Robot can't sense any obstacle(LIDAR). But, In camera, robot can see the box..

I don't know why. Please help me.