Geneva Stop
The Geneva stop is named after the city of its invention where it was used in the construction of clocks.
The Geneva stop is used to provide intermittent motion, the orange wheel turns continuously, the dark blue pin then turns the blue cross quarter of a turn for each revolution of the drive wheel.
The crescent shaped cut out in dark orange section lets the points of the cross past, then locks the wheel in place when it is stationary.
The Geneva stop mechanism is used commonly in film projectors to move the film on one frame at a time.
Comments
nessabug12345
WHAT KIND OF MOTION DOES IT
MAKE IF ANY?
robives
Intermittent. The blue wheel turns quarter of a turn for each turn of the orange wheel. Notice that the blue wheel is stationary for much of the rotation of the orange wheel.
Is this mechanism similar to that in the Jack in the Box?
Scott
Hi Rob,
I'm trying to utilize a similar mechanism but want it to do a 180 degree rotation between steps. Any ideas on how to accomplish that? On an automaton, I'm trying to make a vertical sign rotate from "for sale" to "sold" every once in a while (a 180 degree rotation).
Scott
Scott, check out the various Flip Face posts, I think they'll cover what you are after. - RI
KeithMc
I'm not a member. I just ran across this, while searching for other things, and thought I'd chime in, to help...
A 180 degree index can easily be accomplished by combining the output of the above Geneva Wheel (the Maltese Cross component) with a pair of spur gears, to create a 2:1 speed increase ratio.
For example, a 40 tooth gear and a 20 tooth gear make a 2:1 ratio. (The 40T gear is your 2x gear, and your 20T gear is your 1x gear.) Choose sufficiently large tooth count spur gears, to allow the 2x gear to extend beyond the tines of the Cross part of the Geneva Wheel. As long as the tooth ratio is 2:1, between the two spur gears, you're golden.
Couple the larger (2x) gear to the driven cross, on the cross' shaft, but spaced sufficiently to prevent interference with the Geneva mechanism's operation.
On an adjacent, separate shaft (mounted such that the gears will mesh), attach the 1x gear. Couple the 1x gear to the sign (IOW, mount it on the same shaft as the 1x gear).
Now, the sign shaft with the smaller gear will travel twice as fast as the cross' shaft with the larger gear.Therefore, whenever the Cross makes an index step of 90 degrees, due to the 2:1 ratio, the sign will index 180 degrees.
Good luck.
- Keith Mc., from MMTD (The Mechanism and Machine Tool Design list, on Yahoo)
Kristo
Hi Scott,
Why don't you add a second pin 90 deg apart from the first one, replicating the cutout in the yellow wheel as well for the second pin. this way as soon as the first pin leaves the cross plate the second one will engage it for another 90 deg rotation
Kristo
Could you give an example of when this would be used?
Geneva stops are used for intermittent motion, the classic example is in film projectos where the film needs to be moved forwards one frame then held still as the projection light shines through it. - RI