Saturday, April 26, 2008

Geneva Mechanism, Maltese Cross or Geneva Stop

The Geneva Drive is also called the Maltese Cross or the Geneva Stop.
Animated Geneva mechanismThe Geneva mechanism was originally invented by a watch maker from Geneva to prevent the spring of a watch from being over-wound.

The most common use of the mechanism is to convert a continuous rotary motion into an intermittent rotary motion. In operation, a drive wheel with a pin enters into one of several slots on the driven wheel and thus advances it by one step (or "station"). The drive wheel also has a raised circular disc that serves to lock the driven wheel in a fixed position between steps.
Steps in motion of a Geneva mechanismHistorically, this mechanism is was often used in movie film cameras and projectors to increment the film one frame at a time. Many automata use the Geneva mechanism for various purposes. In my own piece, The Birthing Engine, I used a 4-station Geneva wheel to control the appearance of the four babies that emerge from the mother.

Here is an 3-D animation of a shifter system that uses a Geneva mechanism:The mechanism in the animation above is patented by Barloworld CVT Technologies and is used in their positive drive CVT as a ratio shifting mechanism.

Here are some books that show various forms of Geneva mechanisms:

Five Hundred and Seven Mechanical Movements
Mechanisms and Mechanical Devices Sourcebook
1800 Mechanical Movements, Devices and Appliances
Pictorial Handbook of Technical Devices
Machine Devices and Components Illustrated Sourcebook
Cam Design and Manufacturing Handbook

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