Mechanical Library: Geneva Movement

#005 Geneva Movement

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Definition

A Geneva movement (also called a Maltese cross mechanism) is a precision mechanical system that transforms continuous rotational motion into intermittent rotational motion, making it essential in devices requiring periodic movement like film projectors, mechanical watches, and automated assembly machines.

The mechanism consists of a driving wheel with a pin that engages with slots in a driven wheel (the Maltese cross), creating precise, jerky rotational intervals where the driven wheel remains stationary for periods before making quick, controlled movements when engaged by the driving wheel's pin. periodic movement like film projectors, mechanical watches, and automated assembly machines.

Key Facts

They provide excellent positional accuracy with minimal backlash, making them ideal for precise indexing operations.
The system is self-locking when not being driven, preventing unwanted movement and providing stability during rest periods
Engineers can adjust the ratio of motion-to-dwell time by modifying the number of slots in the driven wheel, with more slots creating shorter movements and longer rest periods.
The mechanism can withstand a surprising amount of strain, and can be made extremely small, as seen in watches. However, it is often contained in oil to guard against friction.

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This model demonstrates a central white driving wheel with a metal pin that moves a 4 slot geneva mechanism, typically known as a Maltese cross and an 8 slot geneva mechanism on the left. The 4 slot turns 90 degrees at every rotation, the 8 slot turns 45 degrees.