The 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.
Historically, 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