Adding a camera to my urdf

Hello, I am trying to add a camera to the end of an arm using xacros. The camera link URDF is: 30.01.3962634R8G8B88008000.01100arm_sensors/cameratrue0.0image_rawcamera_infocamera When I run the launch file it reports an error saying that the parent param is missing: samper@samper:~$ roslaunch cern_tim_arm_simulator arm_tim_simulator.launch spawn_arm:=true robotic_arm:=schunk_lwa4p world:=tunnel spawn_collimator:=true camera_on_arm:=true ... logging to /home/samper/.ros/log/2c17a290-4b39-11e5-b79f-605718079cbb/roslaunch-samper-16690.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB. Traceback (most recent call last): File "/opt/ros/indigo/share/xacro/xacro.py", line 60, in xacro.main() File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 696, in main eval_self_contained(doc) File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 626, in eval_self_contained eval_all(doc.documentElement, macros, symbols) File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/__init__.py", line 552, in eval_all (",".join(params), str(node.tagName))) xacro.XacroException: Parameters [parent] were not set for macro camera while processing /home/samper/ROS_Workspaces/ROS_Cern/src/ros_cern/tim_gazebo/load_world.launch: while processing /home/samper/ROS_Workspaces/ROS_Cern/src/ros_cern/robotic_arm/launch/schunk_lwa4p_and_tim.launch: Invalid tag: Cannot load command parameter [robot_description]: command [/opt/ros/indigo/share/xacro/xacro.py '/home/samper/ROS_Workspaces/ROS_Cern/src/ros_cern/robotic_arm/arm_description/robots/schunk_lwa4p/schunk_lwa4p_arm_and_tim_camera.urdf.xacro'] returned with code [1]. Param xml is The traceback for the exception was written to the log file I would really appreciate if someone could give me any clue. Thank you in advance. JLuis Samper PS: it only works if i delete the tag and its content