The Geneva drive or Maltese cross is a mechanism that translates a continuous rotation into an intermittent rotary motion. It is an intermittent gear where the drive wheel has a pin that reaches into a slot of the driven wheel and thereby advances it by one step. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps.
Besides the external Geneva drive shown in the diagram above, there is also an internal Geneva drive. The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses. The axis of the drive wheel of the internal Geneva drive can have a bearing only on one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always smaller than 180° in an external Geneva drive and always greater than 180° in an internal one, where the switch time is therefore greater than the time the driven wheel stands still.
Source: http://en.wikipedia.org/wiki/Category:Free_animated_images
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