Geneva wheel mechanism

Geneva wheel mechanism, illustrated in Fig. 1, is an example
of intermittent gearing that converts continuous rotary motion
into intermittent rotary motion. Geneva wheel C makes a quarter
turn for every turn of lever AB attached to driving wheel A.
When pin B on lever AB turns clockwise, it enters one of the
four slots of geneva wheel C; the pin moves downward in the
slot, applying enough torque to the geneva wheel to turn it counterclockwise
1/4 revolution before it leaves the slot. As wheel A
continues to rotate clockwise, it engages the next three slots in a
sequence to complete one geneva wheel rotation. If one of the
slots is obstructed, the pin can only move through part of the
revolution, in either direction, before it strikes the closed slot,
stopping the rotation of the geneva wheel. This mechanism has
been used in mechanical windup watches, clocks, and music
boxes to prevent overwinding.