roslaunch error , rplidar

edit

From this part, I have several error.

When I input this,

 $ roslaunch rplidar_ros rplidar.launch

it shows

[rplidar.launch] is neither a launch file in package [rplidar_ros] nor is [rplidar_ros] a launch file name
The traceback for the exception was written to the log file

However, if I input

ubuntu@ubuntu:~/catkin_ws$ source /home/ubuntu/catkin_ws/devel/setup.bash
ubuntu@ubuntu:~/catkin_ws$ roslaunch rplidar_ros rplidar.launch
... logging to /home/ubuntu/.ros/log/687ff54e-e312-11e6-a5f7-0022cffa2d4b/roslaunch-ubuntu-7014.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.

started roslaunch server http://ubuntu:54487/

SUMMARY
========

PARAMETERS
 * /rosdistro: indigo
 * /rosversion: 1.11.20
 * /rplidarNode/angle_compensate: True
 * /rplidarNode/frame_id: laser
 * /rplidarNode/inverted: False
 * /rplidarNode/serial_baudrate: 115200
 * /rplidarNode/serial_port: /dev/ttyUSB0

NODES
  /
    rplidarNode (rplidar_ros/rplidarNode)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
process[rplidarNode-1]: started with pid [7032]
RPLIDAR running on ROS package rplidar_ros
SDK Version: 1.5.7
Error, cannot bind to the specified serial port /dev/ttyUSB0.
[rplidarNode-1] process has died [pid 7032, exit code 255, cmd /home/ubuntu/catkin_ws/devel/lib/rplidar_ros/rplidarNode __name:=rplidarNode __log:=/home/ubuntu/.ros/log/687ff54e-e312-11e6-a5f7-0022cffa2d4b/rplidarNode-1.log].
log file: /home/ubuntu/.ros/log/687ff54e-e312-11e6-a5f7-0022cffa2d4b/rplidarNode-1*.log
all processes on machine have died, roslaunch will exit
shutting down processing monitor...
... shutting down processing monitor complete
done