robot_pose_ekf is not active

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hello ı need to use robot_pose_ekf to publish odom for gmapping. ı see my imu data but still robot_pose_ekf not active. I use static transform publisher imu to base_footprint. what ı should to do for that ?

this is my result of $ rosservice call /robot_pose_ekf/get_status:

http://i.imgur.com/Fp4mQNM.png

status: Input:
 * Odometry sensor
   - is NOT active
   - received 0 messages
   - listens to topic /odom
 * IMU sensor
   - is active
   - received 5907 messages
   - listens to topic /imu_data
 * Visual Odometry sensor
   - is NOT active
   - received 0 messages
   - listens to topic 
Output:
 * Robot pose ekf filter
   - is NOT active
   - sent 0 messages
   - pulishes on topics /robot_pose_ekf/odom_combined and /tf

mine robot_pose_ekf launch file :

   <launch>
<node pkg="robot_pose_ekf" type="robot_pose_ekf" name="robot_pose_ekf">
  <param name="output_frame" value="odom"/>
  <param name="base_footprint_frame" value="base_footprint"/>
  <param name="freq" value="30.0"/>
  <param name="sensor_timeout" value="1.0"/>  
  <param name="odom_used" value="false"/>
  <param name="imu_used" value="true"/>
  <param name="vo_used" value="false"/>
</node>
</launch>