Challenge

DESIGN AND MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM

MMohd Azhar Merchant18 Jun 2020

MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM

AIM:

To create 3D model and to perform motion analysis of the Internal Geneva mechanism by plotting Contact forces, angular displacement, and angular velocity of the driver and driven wheel on SOLIDWORKS MOTION

WHAT IS MULTIBODY DYNAMICS:

Multibody dynamics is the study of the motion/behavior of different components/mechanisms in its operating conditions.

It is the study of the dynamic response of a mechanism/assembly under loading conditions.

GENEVA MECHANISM:

The name, Geneva drive, is derived from the device's earliest application in mechanical watches, which were popularized in Geneva, being the classical origin of the watchmaking industry.

The Geneva drive 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 wheel (driven wheel) that advances it by one step at a time. The drive wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps.

Driver Wheel: It is the prime mover of the mechanism, it rotates continuously.

Pin: This is the small projection in the driver wheel that helps to transmit power from the driver wheel to the driven wheel.

Driven wheel: It is also known as the Geneva wheel which will have the slots, in which the pin moves and rotates the Geneva wheel.

Types of Geneva mechanism:

External Geneva mechanism.
Internal Geneva mechanism.
Spherical Geneva mechanism.

External Geneva mechanism Internal Geneva mechanism

Uses and applications:

It is applicable in the production and automobile industries for mass production.

Indexing tables in assembly lines, tool changes for CNC machines, and so on.

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.

One application of the Geneva drive is in film movie projectors and movie cameras, where the film is pulled through an exposure gate with periodic starts and stops.

Objective:

To create 3D models for driver and driven wheels.
To perform motion analysis of the driver wheel and driven wheel.
To plot the Contact forces (b/w driving and driven wheel) as a function of time, Angular velocity of the driving and driven wheel and angular displacement of the driven wheel with and without Precise contact for

60 fps for 10 rpm driving wheel speed.
120 fps for 20 rpm driving wheel speed.

3D CAD MODEL:

1) DRIVER WHEEL 2) DRIVEN WHEEL

ASSEMBLY:

PLOTS AND RESULTS:

Without precise contact 60 Frames per second for 10 rpm :

1) Angular displacement of driven wheel V/s Time:

2) Angular velocity of driven Wheel V/s Time:

3)Contact forces V/s Time:

4) Angular velocity of driver wheel V/s Time:

With precise contact 60 Frames per second for 10 rpm :

1) Angular displacement of driven wheel V/s Time:

2) Angular velocity of driven Wheel V/s Time:

3) Contact forces V/s Time:

4) Angular velocity of driver wheel V/s Time:

Without precise contact 120 Frames per second for 20 rpm :

1) Angular displacement of driven wheel V/s Time:

2) Angular velocity of driven Wheel V/s Time:

3) Contact forces V/s Time:

4) Angular velocity of driver wheel V/s Time:

With precise contact 120 Frames per second for 20 rpm :

1) Angular displacement of driven wheel V/s Time:

2) Angular velocity of driven Wheel V/s Time:

3) Contact forces V/s Time:

4) Angular velocity of driver wheel V/s Time:

CONCLUSIONS FROM PLOTS:

Points observed from all the 4 cases,

2 cases of with and without precise contact at 60fps and 10rpm of driver wheel and also

2 cases of with and without precise contact at 120 fps and 20 rpm of driver wheel

1) As seen in the angular displacement plot the driven wheel completely rotates 360 degrees it starts from -180 degrees and reaches 0 degrees and then to 180 degrees and back to +180 degrees (as it continuously makes a whole 360-degree rotation). And the graph is almost the same for both the precise and without precise contact.

2) From the angular velocity plot of the driven wheel, we can see that as the pin enters into the slot there is a large amount of fluctuation of angular velocity for a very short duration of time because there is the sudden application of motion on the body which causes sudden jerk at the entrance of the pin and as seen in case of precise contact these fluctuations gets magnified further.

After the pin enters into the slot of the driven wheel there is a gradual increase in the angular velocity of the driven wheel and reaches the maximum limit of 25 deg/sec in the case when the driver wheel is rotating at 10rpm and reaches 50 deg/sec when the driver wheel is rotating at 20rpm when the pin reaches the furthest point in the slot and then the angular velocity starts gradually reducing and becomes almost zero as the riven wheel becomes stationary and again increases and the cycle continues.

there are small wiggles in the plot when precise contact is not considered which are eliminated when the precise contacts are considered

3) The angular velocity plot for the driver wheel remains the same for both with and without precise contact which is it remains constant at 60 deg/sec as the constant angular velocity input is given to the driver wheel.

4) From the contact forces plot, we can see that the magnitude of contact forces remains negligibly very small for most of the rotation except at the point when the pin enters into the slot of the driven wheel where there is a sudden increase in the contact forces due to sudden contact which leads to jerk, as seen in case of precise contact the magnitude of the contact forces are magnified due to consideration of precise contacts between the surfaces when compared to the case without precise contact.

GOOGLE DRIVE LINKS FOR THE CAD FILES:

https://drive.google.com/drive/folders/1-pR0QRLXLoBR0Y7zv95hHyV1SOgHzVpS?usp=sharing

YOUTUBE LINKS FOR RESULT ANIMATIONS AND PLOTS:

1) Motion analysis of Internal Geneva mechanism on Solidworks Motion @10 rpm w/o precise contact: