US Patent RE42155 Light-weight self-propelled vacuum cleaner

A vacuum cleaner power head (40) for vacuum cleaning and having two counter rotating agitators 52 and 54. Motor (60) rotates agitators (52) and (54) through transmission (70), and also rotates suction fan (65) to provide suction air to the rotary brush agitators. Exterior housing 48 and inner housing (49) provide air suction passageways to direct suction air through fan (65) and out of the housing to a dirt collection bag (34). Self-propelled function is provided by using user force on handle (32) to create differential contact friction between the two counter-rotating rotary brush agitators so that a net traction force is generated that propels power head (40) in the direction the user is pushing.