DESIGN AND MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM (using SOLIDWORKS)
AIM:
To design and simulate the Multi-Body Dynamics of an Internal Geneva Gear Mechanism using SOLIDWORKS
OBJECTIVES:
- To understand the mechanism of internal Geneva gear
- To perform the motion analysis of the mechanism using SOLIDWORKS
INTRODUCTION:
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 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.
Uses:
This mechanism has been used in movie projectors and movie cameras, mechanical watches, pen change mechanism in plotters and so on.
Internal Geneva gear:
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 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 Geneva drive and always greater than 180° in an internal one, where the switch time is therefore greater than the time the driven wheel stands still.
DESIGNING THE INTERNAL GENEVA GEAR:
The driven wheel component is as follows:
After designing the driven wheel, the sketch is extruded upto 40mm.
The driving wheel /driver component is as follows:
The base of the driver is extruded upto 20mm. Then, the connecting pin is extruded upto 40mm.
The assembly of both the components is as follows:
MOTION ANALYSIS:
- A rotary motor was used to rotate the gear at 10 RPM in first case and in second case at 20 RPM. The axis of the rotary motor is coincident to that of the driver.
- Then, the contact was made between the driver wheel and the driven wheel.
- Then, in the fps was changed to 60 in first case and to 120 in second case for better visualization of the mechanism.
- Also, mechanism was run for two cases, namely, with precise contact and without. That means, in the first case, calculations will be made taking considerations into all the equations of the solid body and contact of the body accurately. In the second case, for motion only, contacts will not be considered so accurately.
- Then, following plots were plotted:
- At 10 RPM,
Angular displacement of the driven wheel:
Contact forces between the driver and the driven wheel (with precise contact):
Contact forces without precision:
Angular velocity of the driver wheel:
- At 20 RPM,
Angular displacement of the driven wheel:
Contact forces with precision:
Contact forces without precision:
Angular velocity of the driver wheel:
CONCLUSION:
- We can conclude that, contact forces in both the cases (namely with and without precision), the graph differs as the analyzer analyses it with the above conditions mentioned (in Motion Analysis point 4).
- We could also observe that the angular velocity is at its peak when it enters the slot and subsequently decreases.
- The displacement is intermitent in nature hence the angular displacement plot repeats itself at regular intervals.
- Contact force is proportional to speed of driver it increases with increase in the speed.
- Contact force between driver and driven wheel is highest at the initial stage, when it enters the slot due to the movement of the driven wheel.
ORIGINALITY CHECK FOR PRECISION CONTACT:
For 60 fps,
For 120 fps,
ATTACHMENTS:
The CAD models are converted to .zip format and shared via the following Google Drive link:
https://drive.google.com/drive/folders/1ytDipZ_do6s1MUXZhBU0VrDiYsQE-5Ya?usp=sharing
The motion of the mechanism can be seen through the following link: