https://en.wikipedia.org/wiki/File:Geneva_mechanism_6spoke_animation.gif
http://benbrandt22.github.io/genevaGen/
3. Geneva mechanism
Fig. 4.5.3 Geneva mechanism
The Geneva drive is also commonly called a Maltese cross mechanism. The Geneva mechanism translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps (Fig. 4.5.3). There are three basic types of Geneva motion mechanisms namely external, internal and spherical. The spherical Geneva mechanism is very rarely used. In the simplest form, the driven wheel has four slots and hence for each rotation of the drive wheel it advances by one step of 90°. If the driven wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.
In an internal Geneva drive the axis of the drive wheel of the internal drive is supported on only one side (Fig. 4.5.4). 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 is always greater than 180° in an internal one. The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses.
Fig. 4.5.4 Internal Geneva mechanism
Because the driven wheel always under full control of the driver, impact is a problem. It can be reduced by designing the pin in such a way that the pin picks up the driven member as slowly as possible. Both the Geneva mechanisms can be used for light and heavy duty applications. Generally, they are used in assembly machines.
Intermittent linear motion from rotary motion can also be obtained using Geneva mechanism (Fig. 4.5.5). This type of movement is basically required in packaging, assembly operations, stamping, embossing operations in manufacturing automation.
Fig. 4.5.5 Linear intermittent motion using Geneva mechanism
