Internal Geneva Mechanism
Internal Geneva Mechanism
In this mechanism, the driver is connected to the driven wheel internally. The axis of the driver wheel of the internal mechanism 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° in an external. The driver wheel rotates the driven wheel by 90° in each step.
Tasks of the project
- Create 3D models for driver and driven wheels.
- Perform motion analysis by rotating the driver wheel at 10rpm.
- Obtain the following plots Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- Compare the contact forces with and without "Precise contact".
- Show image for precise contact selection.
- Export the results that you get to Excel and make the plots over there.
- Use 60 Frames per second for 10 rpm and then 120 Frames per second for 20 Rpm.
- Make a plot of the driver wheel's angular velocity and discuss the results.
3 D model
The 3D models are created using the following dimensions
Driver wheel dimension
Driven wheel dimension
Created 3D model
Driver wheel
Driven wheel
Then the models were assembled using assembly constraints.
Assembled model
Motion analysis
Motion analysis is performed at
- The torque of the driver wheel 10 rpm with 60 frames per sec without precise contact.
- The torque of the driver wheel 10 rpm with 60 frames per sec with precise contact.
- The torque of the driver wheel 20 rpm with 120 frames per sec without precise contact.
- The torque of the driver wheel 20 rpm with 120 frames per sec with precise contact.
The following results were obtained.
For 10rpm
Contact force without precise contact
The plots are done in Excel
Angular displacement without precise contact
Precise contact selection
precise contact is selected as shown in the below image.
Contact force with precise contact
Angular displacement with precise contact
For 20 rpm
Contact force without precise contact
Angular displacement without precise contact
Contact force with precise contact
Angular displacement with precise contact
Angular velocity of the driver wheel(10rpm)
Angular velocity of the driver wheel(20rpm)
Observations
- It is observed that contact force increases with an increase in rpm. There is a sudden increase in the contact force between driver and driven wheel as it just starts to enter the slot. This is because initially the driver wheel will try to enter the slot smoothly but due to some movement of driven wheel, it will first have a slight impact on the driven wheel. Once the driver wheel enters the slot the magnitude of contact forces reduces drastically.
- Precise contact gives more accurate results by using the equations that represent the solid bodies.
- We can also see from the contact force plots of the 2 RPM's that as we increase the rotation of the driver the contact force at the entry also increases and then it drastically decreases.
- The angular velocity plot reveals that at first, there is a jerk felt by the driven wheel and we see a peak in the angular velocity plot and then when it enters the slot there is an acceleration in the driven wheel but as the motion progresses there is a reduction in the velocity and hence retardation occurs.
- The maximum velocity is at the point where the pin of the driver reaches the bottom point of the driven wheel.
- The 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 pattern is repeated in each revolution of the driver wheel. There is not much difference in the angular displacement with and without precise contact.
The animation link for the motion analysis