Geneva drive

The Geneva drive is also called a "Maltese cross mechanism" due to the visual resemblance when the rotating wheel has four spokes.

This intermittent motion is implemented by a Geneva drive, which in turn actuates a claw that engages sprocket holes in the film.

The Geneva drive also provides a precisely repeatable stopped position, which is critical to minimizing jitter in the successive images.

A Geneva drive was used to change filters in the Dawn mission framing camera used to image the asteroid 4 Vesta in 2011.

The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses.

[3]: 128 The figure shows the motion curves for an external four-slot Geneva drive, in arbitrary units.

A discontinuity appears in the acceleration when the drive pin enters and leaves the slot, occurring at the instant the rigid bearing surfaces make contact or separate.

Animation showing a six-position external Geneva drive in operation.
An illustration that shows the four stages (motion stop at 90 degrees angle) of one full cycle of a Geneva drive.
Movie projector with hand crank and Geneva drive
Geneva stop with five spokes, allowing four rotations of the driving wheel
Motion curves for one turn of the drive wheel, from top to bottom: angular position θ, angular velocity ω, angular acceleration α and angular jerk j a .