导入kuka iiwa R820 进 ROS 和 gazebo， 失败，一直报错

我先用了roslaunch iiwa_gazebo iiwa_gazebo.launch。 然后报错
RLException: [iiwa_gazebo.launch] is neither a launch file in package [iiwa_gazebo] nor is [iiwa_gazebo] a launch file name
The traceback for the exception was written to the log file

然后看网上攻略，输了这行代码
source /home/fan/catkin_ws/devel/setup.bash

结果还是报错。

原来是忘了 导入相应的urdf 文件，已经解决