US Patent 7503091 Automatic window cleaning apparatus

A window cleaning apparatus includes a cleaning mechanism that is mounted for movement relative to a window. The cleaning mechanism includes one or more cleaning tools, such as a brush and a wiper blade, and an onboard hydro-mechanical motor that provides the motive force for moving the cleaning mechanism. The cleaning mechanism has first and second drive wheels that engage first and second upright tracks, respectively, mounted on opposite sides of the window. The motor receives pressurized water from a water source (e.g., a water line of the building) and derives output mechanical power for rotating the drive wheels, which move along the tracks.