The Geneva mechanism translates continuous rotational motion into intermittent rotary motion. Originating from clock-work design, it has been used in many different applications from old movie projectors to space-grade telescopes.

History and Applications

The device is believed to have been created initially by a Swiss watch maker. He wanted to find a way to keep his watch from overwinding. Adding an additional wheel with a stop allowed for the watch to count the number of turns that the dial was wound. The Geneva mechanism was born here, and it continued into many different fields.

Film Projector

The next place where these mechanisms are commonly found are old film cameras and movie projectors. Film makers were having issues with projecting frames rapidly on the projection surface. The film running by the bulb too fast caused extremely blurry movies. The Geneva mechanism solved this by allowing the film to take a short pause at each frame so the viewer’s brain could comprehend the still image. Once it was flicked through fast enough, the illusion of motion was achieved.

Dawn Framing Camera

Another fascinating application was in the Dawn mission to photograph telescopic images of the asteroid 4 Vesta in 2011. The Geneva mechanism was used to swap filters for the telescope lens, and if there was a failure, it would ensure that at least on filter would be usable.

Other Uses Some other notable uses for this mechanism are pen changing mechanisms for large plotters, automated sampling devices, banknote counting machines, and other indexable equipment commonly used in manufacturing processes (like tool changers in CNC machines.)

When Should I Use This Mechanism?

Whenever you have a constantly spinning component that wants to be translated into a rotational-stepping output, this is the mechanism to use. It is reliable and relatively sturdy at lower to medium speeds.

It’s also very useful as a counter. Each rotation indexes the Geneva wheel by one step, you can link each step to a new number on a dial.