Cron_config.xml

<?xml version="1.0"?>
<config>
  <modules>
     <MyCompanyName_HelloWorld>
     <version>0.1.0 </version>
     </MyCompanyName_HelloWorld>
  </modules>
  <global>
    <models>
        <helloworld>
             <class>MyCompanyName_HelloWorld_Model</class>
        </helloworld>
    </models>
  </global>
  <crontab>
        <jobs>
            <mycompanyname_helloworld>
                <schedule>
                    <cron_expr>*/10 * * * *</cron_expr>
                </schedule>
                <run>
                    <model>MyCompanyName_HelloWorld_Model_Cron::job</model>
                </run>
            </mycompanyname_helloworld>
        </jobs>
    </crontab>
</config>