INTERNAL GENEVA MECHANISM
AIM: Design and motion analysis of Internal Geneva Mechanism
INTRODUCTION:
Geneva Mechanism
The Geneva Mechanism 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 wheel (driven wheel) that advances it by one step at a time. The main wheel also has an elevated circular blocking disc that locks the rotating driven wheel in position between steps.
OBJECTIVE:
- Create 3D model for driver and driven wheels.
- Performing motion analysis at different RPMs.
- Obtain the following plots-
- Contact force (b/w driver and driven wheel) vs Time
- Angular Displacement (driven wheel) vs Time
- Angular velocity (driver wheel) vs Time
PROCEDURE:
Initially, a 2D drawing is generated with defined dimensions from the reference provided. The 2D CAD drawings are as follows:
To create a 3D model, extrude the sketches made in the previous step using the ‘extrude boss/ base’ command in SolidWorks.
Now, both the parts are assembled in the assembly file. While inserting the 1st component, the solidworks automatically make the 1st component stable so, we have to make it float for the free movement. The position of the driver wheel has to be judged accordingly in order to have hinder free movement.
The Multi-body-dynamics are calculated using ‘Motion Study’ in SolidWorks. The motor with the desired RPM is assigned to the Driver Wheel. The contacts are also specified to have appropriate force transmission.
PLOTS:
Angular velocity = 10 RPM
Contact force vs Time (No precise contact)
The figure signifies that contact force varies significantly at points when th driver wheel makes contact with the driven wheel. This is due to sudden jerk produced while making contact.
Angular Displacement vs Time (No precise contact)
The plot intends to project the gradual decrement in displacement after a sudden increment at 2.5s.
Angular Velocity vs Time (No precise contact)
We can conclude from the plot that the angular velocity remains somewhat constant throughout the motion with the exception of some time steps.
Contact force vs Time (Precise contact)
In the plot, the use of precise contact is clearly visible due to sharp and accurate results obtained.
Angular Displacement vs Time (Precise contact)
The plots show smoother curves as a result of precision contact b/w the driver wheel and the driven wheel.
Angular Velocity vs Time (Precise contact)
Angular velocity = 20 RPM
Contact force vs Time (No precise contact)
Consistency in the plot is visible after changing the RPM of the driver wheel. Also the jerk felt during contact is more proportionate due to higher RPM.
Angular Displacement vs Time (No precise contact)
The trend observed in plot is followed throughout with consistency.
Angular Velocity vs Time (No precise contact)
The angular velocity remains constant in the entire cycle of movement.
Contact force vs Time (Precise contact)
Sharper plot obtained due to precise contact between plot obtained due to the driver wheel and the driven wheel.
Angular Displacement vs Time (Precise contact)
The plot depicts smoothness and accuracy when compared to its unprecise contact twin.
Angular Velocity vs Time (Precise contact)
The transition is smoother, although some variation exist. The higher RPM makes the mechanical motion of the mechanism much more reliable.
CONCLUSION: The motion study helps us to simulate the real time performance of the internal Geneva mechanism and thereby give an outline to develop our model for better output.