Non-circular gear
Non-circular_gear.gif
A non-circular gear (NCG) is a special gear design with special characteristics and purpose. While a regular gear is optimized to transmit torque to another engaged member with minimum noise and wear and with maximum efficiency, a non-circular gear's main objective might be ratio variations, axle displacement oscillations and more. The number of possible uses is limited only by the inventor's imagination and includes textile machines, potentiometers and CVTs (continuously variable transmissions).
A regular gear pair can be represented as two circles rolling together without slip. In the case of non-circular gears, those circles are replaced with anything different from a circle, which is how NCG got its name. This is also the reason NCG in most cases is not round, however round NCGs looking like regular gears are possible too (small ratio variations result from meshing area modifications).
Generally NCG should meet all the requirements of regular gearing, but in some cases, for example variable axle distance, could prove impossible to support and such gears require very tight manufacturing tolerances and assembling problems arise. Because of complicated geometry, NCGs are most likely spur gears and molding or electrical discharge machining technology is used instead of generation.