Internal Geneva Mechanism

AIM: To carry out the motion analysis of internal Geneva mechanism.

INTRODUCTION: A Geneva mechanism is a gear mechanism used to convert a rotary motion into intermittent motion or periodic motion. Generally, this mechanism consists of assembly of driving wheel and driven wheel. The driving wheel is powered by use of motor and the geneva wheel gets driven by the driving wheel.

THEORY: Basically, in this project of internal geneva mechanism a continuous rotary motion of driving wheel is converted into a periodic motion of geneva wheel.This is achieved by a geometry shown below:-

The pin which is located near to the circumference of driver enters tangentially into the slots of driven wheel causing the driven wheel to rotate by an angle of 45 degree.Hence, the intermittent motion is obtained at outlet.

EXPLANATION:-

Steps to carry out motion analysis

Components used in the analysis are driver wheel and the geneva wheel which is the driven wheel. We have the 2D drwaings of the components. For motion analysis we require 3D cad models.

So we will be using solidworks software to create 3D models and to carry out the mption study.

Firstly we will be creating the 2D design with the help of given drawing and dimentions. To create a 2D drawing in solidworks click on part-then select the front plane and start drawing the 2D drawing.

After completion of drawing following 2D drawing is obtained:-

GENEVA WHEEL

DRIVING WHEEL

After extruding the above drawings we get the following 3D models

GENEVA WHEEL

DRIVING WHEEL

Once the 3D models are obtained the next thing to assemble them with repect to eachother. The final assembly will look like shown below:-

MOTION STUDY AND ANALYSIS

To carry out motion study, click on motion study and select motion analysis.

Then we attach a motor to the driving wheel. Click on motor icon, select rotary motor, clockwise direction of rotation and select the rpm as 10.

Now click on motion study properties, select 60 frames per second and use the precise contact.

In the motion tray, drag the time span upto 20 seconds.

Next click on contacts, select solid contact and select the steel dry material for both the wheels.

RESULTS

1) To obtain the plot of contact forces between driver wheel and driven wheel.

For contact force plot, click on results and plots, select forces then select contact forces and select the surfaces of driver pin and driven wheel surface. The following plot is obtained:-

From this plot we observe that the contact forces are maximum i.e 495N during the 7th sec.

2) To find angular displacement of driven wheel.

Click on results and plots, then select displacement, then select angular displacement and select the driven wheel. The following plot is obtained:-

From the plot we see that the angular velocity is maximum approximately at the 9^th second and then gradually decreases.

3) Comparison of contact forces with and without precise contact

As we have already obtained the plot for contact forces between driving and driven wheel we will now modify the setting by unselecting the precise contact and adding these results to the previous obtained plot. The comparison plot so obtained is as below:-

4) To obtain the plot of driver wheels angular velocity at 120 frames per second and at 20 rpm.

Click on motion study properties. Then select 120 frames per second and select the motor speed as 20 rpm from the motor properties. The plot obtained is as below:-

From the plot it is seen that the angular velocity of driving wheel remains constant during the simulation.

CONCLUSION:-

• The precise contact curve is more smooth than the non-precise one. Therefore the results of the precise one will be more accurate and true.
• The angular velocity of the driving wheel remains constant during the simulation.