In Gazebo, my robot can't see AR tag

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. ---------- 4 0 0 0 0 0true2 0 0 0 0 0model://ar_tags_for_turtlebot3_exp_house/meshes/ar_tag_00.dae ---------- 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.