Hokuyo Laser Scanner not updating fastly

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In Hokuyo Laser the scan values are getting dealyed from gazebo

  <gazebo reference="hokuyo_link">
<sensor type="ray" name="head_hokuyo_sensor">
  <pose>0.0 0 0.0 0 -0 0</pose>
  <ray>
    <scan>
      <horizontal>
        <samples>720</samples>
        <resolution>1</resolution>
        <min_angle>-1.58079</min_angle>
        <max_angle>1.58079</max_angle>
      </horizontal>
    </scan>
    <range>
      <min>0.08</min>
      <max>5</max>
      <resolution>0.01</resolution>
    </range>
    <noise>
      <type>gaussian</type>
      <mean>0.0</mean>
      <stddev>0.01</stddev>
    </noise>
  </ray>
  <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_laser.so">
    <always_on>1</always_on>
    <topicName>/sk/laser/scan</topicName>
    <frameName>hokuyo_link</frameName>
    <visualize>true</visualize>
  </plugin>
  <always_on>1</always_on>
  <update_rate>30</update_rate>
  <visualize>true</visualize>
</sensor>

</gazebo>