robot_pose_ekf does not publish anything

edit

I am trying to use robot_pose_ekf with imu data but it does not produce any output .

output of :rostopic hz /robot_pose_ekf/odom

subscribed to [/robot_pose_ekf/odom]

launch file :

< launch> < node pkg="robot_pose_ekf" type="robot_pose_ekf" name="robot_pose_ekf" output="screen">
<param name="output_frame" value="odom"/>
< param name="freq" value="30.0"/>
<param name="sensor_timeout" value="1.0"/>
<param name="publish_tf" value="true"/>
< param name="odom_used" value="false"/>

< param name="imu_used" value="true"/>
< param name="vo_used" value="false"/>
</node>
</launch>

output of : rostopic hz /imu_data

subscribed to [/imu_data]
average rate: 8.382
min: 0.115s max: 0.126s std dev: 0.00357s window: 8
average rate: 8.350
min: 0.115s max: 0.126s std dev: 0.00306s window: 16
average rate: 8.333
min: 0.115s max: 0.126s std dev: 0.00301s window: 24

output of : rostopic echo /imu_data

header:
seq: 780
stamp:
secs: 1385929326
nsecs: 189629077
frame_id: base_link
orientation:
x: 0.103565725066
y: 0.10414370554
z: 0.000989699922996
w: 0.989154815831
orientation_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
angular_velocity:
x: 0.0
y: 0.0
z: 0.0
angular_velocity_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
linear_acceleration:
x: 40.0
y: -39.0
z: -1004.0
linear_acceleration_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---

Please help