A system includes a docking station, for location on a surface to be worked, and a self-propelled working tool. The station has a primary transmission part. The tool has a body, a surface-engaging wheel, and a secondary transmission part. The station and the tool can establish contact with each other...http://www.google.com/patents/US6586908?utm_source=gb-gplus-sharePatent US6586908 - Docking system for a self-propelled working tool
