public function keepaliveAction()
 {
     $id = $this->_getParam('id', 0);
     $this->_helper->viewRenderer->setNoRender();
     $this->_helper->getHelper('layout')->disableLayout();
     $creditnoteDb = new Sales_Model_DbTable_Creditnote();
     $creditnoteDb->lock($id, $this->_user['id'], $this->_date);
 }