Solved some misspellings in the node parameters.

launch/hokuyo_laser2d.launch

@@ -8,10 +8,10 @@
 
   <node pkg="urg_node"
         type="urg_node"
-        name="${node_name}"
+        name="$(arg node_name)"
         output="$(arg output)"
         launch-prefix="$(arg launch_prefix)">
-    <rosparam file="$(arg device_file)" command="load" />
+    <rosparam file="$(arg config_file)" command="load" />
   </node>
 
 </launch>