Mechanisms

Is it me? Or are you just e-gear-to see me? I guess wheel have to see...

Today we are reviewing a mechanism from the Schröder Collection (Foundation of Science and Technology in Florence, Italy). More specifically, the FST1356 Maltese Cross Intermittent Mechanism (also known as the Geneva Drive). This mechanism translate continuous rotational motion into intermittent motion.

As the drive wheel (red) spins, the pin slides into the driven wheel (blue). While the pin is in contact with the driven wheel, both pieces turn. Conversely, any time when the pin is not in contact with the driven wheel, the driven wheel does not turn -- thus the intermittent motion. The inner semi-circular shape holds the driven wheel in place whilst the drive wheel turns.

The Geneva Drive modifications:

• Internal Geneva Drive: the driven wheel sits on top of the drive wheel
• Spherical Geneva Drive: the driven wheel is composed of a notched demi-sphere

I think one of the most interesting motions you can get out of simple mechanisms like this are the ones that go between continuous and discontinuous motion. For example, how might this mechanism have to be adjusted if we wanted to to use an ovular/elliptical shape rather than a symmetric circular one? How might one go about adjusting the drive wheel for a driven wheel with more than four notches? (see cheat solution here)

This mechanism could be used as a wind-ing tool, such as in clocks or other such tools. Another possible application could be in assembly-line type machinery: for example, in machines that are filling bags of candy, the motion needs to be intermittent in order for the machines to have the time to fill the bags before moving on. A much simpler example would be the rotation of frames on a film real rotating intermittently (but at a very fast rate).