Report on Geneva Mechanism | Mini Project

The Geneva wheel or Maltese cross is a cam like mechanism that provides intermittent rotary motion and is widely used in both low and high speed applications. Geneva mechanism is extensively used in automatic machinery where turret, spindle or worktable must be indexed. Geneva mechanism is popular from longer times by means of producing positive incremental motion.

Construction :

The basic structure of 4 slot geneva mechanism is shown in figure below.

The system consist of constantly rotating disk coupled with a slotted disk, which gives rise to the desire discrete motion. 
A rotation of 2p radians of the former cause 2p/N radians of rotation of the latter, where N is the number of slots available on the slotted disk.
Thus, one complete rotation of the slotted wheel requires N complete rotations of the other disk, thereby also increasing the time period.

Working :

Refer the figure above. Pinwheel W rotates constantly about axis A and has a pin 'a' attached to it. This pin 'a' engages into the slots 's' of the geneva  wheel 'G' and rotates it as long as it is engaged with the slot. While the wheel rotates continuously, the Geneva wheel has a discrete rotation about axis 'b'. 
Wheel 'G' has a rotation time period of 'tr' when it is moving with disk 'W' and an idling time period of 'ti', when the pin 'a' is not inside one of the slots 's' and is moving freely. 
The three quarter wheel 'L' is placed in order to prevent any unintentional rotation of wheel 'G' while it is idling. 
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Sujit Kadus

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