Geneva mechanism is commonly used indexing mechanism where an intermittent motion is required.
The Inverse Geneva mechanism, which is a variation of the Geneva mechanism, is used where the wheel has to rotate in the same Direction as crank. It requires less radial space and the locking device can be a circular segment attached to the crank that locks by wiping against a built up rim on the periphery of the wheel.
The design and fabricating of a conventional Geneva mechanism is generally simple and inexpensive because there is no specially curved profile on any of the components except straight lines and circular arcs. However, due to the discontinuity of the acceleration at the beginning and ending positions, the shortcoming of using conventional Geneva mechanism is the large impact when the driving crank engages and disengages with the wheel slot.
CLASSIFICATION OF GENEVA MECHANISM
- EXTERNAL GENEVA MECHANISM:
- INTERNAL GENEVA MECHANISM:
- SPHERICAL GENEVA MECHANISM:
How Geneva Mechanism Works?
|Animation Of External Geneva Mechanism|
|Animation Of Internal Geneva Mechanism|
ADVANTAGES OF GENEVA MECHANISM
i. Geneva mechanism may be the simplest and least Expensive of all intermittent motion mechanisms.
ii. They come in a wide variety of sizes, ranging from those used in instruments, to those used in machine tools to index spindle carriers weighing several tons.
iii. They have good motion curves characteristics compared to ratchets, but exhibit more “jerk” or instantaneous change in acceleration, than better cam systems
iv. Geneva maintains good control of its load at all Times, since it is provided with locking ring surfaces.
DISADVANTAGES OF GENEVA MECHANISM
i. The Geneva is not a versatile mechanism.
ii. The ratio of dwell period to motion is also established Once the no of dwells per revolution has been selected.
iii. All Geneva acceleration curves start and end With finite ac-celeration & deceleration.
iv. This means they produce jerk.
APPLICATIONS & USES
- MECHANICAL WATCHES
- CNC MACHINE
- IRON RING CLOCK
- Modern film projectors may also use an electronically controlled indexing mechanism or stepper motor, which allows for fast-forwarding the film.
- Geneva wheels having the form of the driven wheel were also used in mechanical watches, but not in a drive, rather to limit the tension of the spring, such that it would operate only in the range where its elastic force is nearly linear.
- Geneva drive include the pen change mechanism in plotters, automated sampling devices
- Indexing tables in assembly lines, tool changers for CNC machines, and so on.
- The Iron Ring Clock uses a Geneva mechanism to provide intermittent motion to one of its rings.
See Also : Project related to Geneva Mechanism