A door is mounted within a doorway to be pivotal about a pivot axis disposed close to and along one of side surfaces of the doorway to selectively open and close the doorway. A guide roller protrudes toward the upper surface of the doorway from the upper edge of the door at a location...http://www.google.es/patents/US5762123?utm_source=gb-gplus-sharePatente US5762123 - Door system
