Motion analysis of Internal Geneva mechanism using Solidworks motion study

MULTIBODY DYNAMICS:

A multibody dynamics (MBD) system is one that consists of solid bodies, or links, that are connected to each other by joints that restrict their relative motion. The study of MBD is the analysis of how mechanism systems move under the influence of forces, also known as forward dynamics.

GENEVA MECHANISM:

The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion. The rotating drive wheel is usually equipped with a pin that reaches into a slot located in the other driven wheel that advances it by one step at a time. Because the mechanism needs to be well lubricated, it is often enclosed in an oil capsule.

Contact force is any force that requires contact to occur. This is the force which makes the driving and driven wheels to contact.

Angular displacement of a body is the angle in radians(or degrees or revolutions) through which a point revolves around a centre or line has been rotated in a specified sense about a specified axis.

INTERNAL GENEVA DRIVE:

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 switch time is greater than the time the driven wheel stands still. This is also a main difference between them.

APPLICATIONS:

1. Switzerland is known for its mechanical watches- Rolex, Omega, Rado. The name derives from the device’s earliest application in mechanical watches.
2. Also one of the application of Geneva drive is the movie projectors. These were used earlier as the film doesn’t run continuously, instead the film was advanced frame by frame, each frame standing still in front of the lens for a very short period of time. In modern projectors, stepper motors are used.
3. Other applications of this mechanism include automated sampling devices, banknote counting machines, CNC machines, turret lathes & turret drills.

The external form is the more common, as it can be built smaller and can withstand higher mechanical stresses.

Explanation:

1. Models are developed based on given drawings.
2. The parts are assembled based on the dimensions determined using the drawings.
3. The motion of the wheels is to be constrained about their axes.
4. Motor is fitted to the driver.
5. Suitable speed of the motor is chosen.
6. After running the simulation, required plots are obtained.
7. Precise contact is used to get accurate values.

Results:

Angular Displacement of the driven wheel with time:

Contact force (between driving and the driven wheel) as a function of time:

CONCLUSIONS:

1. It is observed that contact force increases with increase in speed.
2. There is a sudden increase in the contact force between driver and driven wheel when it starts to enter the slot of the drien wheel.
3. Once the driver wheel enters the slot the magnitude of contact force reduces drastically.
4. Precise contact gives more accurate results by using the equations that represent the solid bodies
5. The angular displacement plot shows that the pattern is repeated in each revolution of the driver wheel. There isnot much difference in the angular displacement with and without presice contact.