MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM
INTRODUCTION:-
The geneva drive is a gear mechanism that translates a continuous rotation movement into interiment rotary motion. The rotating wheel is usually equipped with a pin that reaches into slot located in the other wheel(driven wheel) that advances it by one step at time. The main wheel also has an elevated circular blocking disc that locks the rotating driven wheel in position between steps.
One application of the geneva mechanism is in film movie projectors and cameras, where the film is pulled through an exposure gate with periodic starts and stops. The film advances frame by frame, each frame standing still in front of the lens for portion of the frame cycle, and rapidly accelerating, advancing, and decelerating during the rest of the cycle.
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. In watches, the drive wheel is the one that winds up the spring, and the geneva wheel with four or five spokes and one closed slot prevents the overwinding of the spring.
An internal Geneva drive is a variant on the design. The axis of the drive wheel of the internal drive can have a bearing only on one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always smaller than 180 degrees in an external geneva drive and always greater than 180 degrees in an internal one. The external form is the more common, as itcan be built smaller and can withstand high mechanical stresses.
MODELING AND ASSEMBLY:-
The modeling of the both the wheels and assembly is carried out in solidwoks.
DRIVEN WHEEL:-
DRIVING WHEEL:-
ASSEMBLY:-
RESULTS:-
The material selected for both the wheels before running the motion analysis is dry steel.
At 60fps with constant velocity of 10 rmp
CONTACT FORCE:-
with pecision contact
without precision contact
ANGULAR DISPLACEMENT:-
with pecision contact
without precision contact
ANGULAR VELOCITY:-
with pecision contact
without precision contact
AT 120fps WITH CONSTANT VELOCITY OF 20RPM
CONTACT FORCE:-
with pecision contact
without precision contact
ANGULAR DISPLACEMENT:-
with pecision contact
without precision contact
ANGULAR VELOCITY:-
with pecision contact
without precision contact
CONCLUSIONS:-
- The precise contact gives a more accurate result as the curves become less fluctuating and smooth
- When the driver tries to enter in the slot of the driven wheel it faces a jerk as the entry is not smooth. Therefore the plot at the entry to the slot suddenly increases in the contact force which decreases as the driver enters into the slot.
- For Contact force of the 20 RPM as we increase the rotation of the driver the contact force at the entry also increases and it then drastically decrease.
- The angular velocity of the driven wheel also increases if we increase the rotation of the driver which is seen from the plot.
- The angular displacement plot shows that the displacement occurs between -180 to 180 degree and it repeats the pattern in each revolution starting from 0.