A preliminary ejection sensor of an ink jet recording apparatus includes a vibration plate adapted to vibrate on receipt of an ink droplet ejected from an ejection port on a recording head in order to detect the vibration of the vibration plate depending on variation of a gap between a core and the...http://www.google.de/patents/US5731826?utm_source=gb-gplus-sharePatent US5731826 - Ink jet recording apparatus, ink jet recording head therefor and method for determining the ejection state thereof 
