Internal Geneva Mechanism
Aim: To create the 3D model of the internal Geneva mechanism.
OBJECTIVES:
- Create 3D models for driver and driven wheels.
- Perform motion analysis by rotating the driver wheel at 10rpm with 60 frames per second, 20 rpm with 120 frames per second.
- To make plots for contact force (between driving and the driven wheel) as a function of time with and without precision, angular displacement of driven wheel, angular velocity of driver wheel.
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.
The Geneva mechanism are further classified as:
- EXTERNAL GENEVA MECHANISM: In this type of mechanism, the Geneva cross is connected with cam drive externally which is the most popular and can withstand higher mechanical stresses. The driver grooves lock the driven wheel pins during dwell. During movement, the driver pin mates with the driven-wheel slot.
- INTERNAL GENEVA MECHANISM: In this type of mechanism, the Geneva cross and cam drive are connected internally in the closed box. The driver and driven wheel rotate in same direction. The duration of dwell is more than 180º of driver rotation.
Applications and uses:
- It is applicable in the production industries and in automobile industries for mass production.
- Modern film projectors may also use an electronically controlled indexing mechanism or stepper motor, which allows for fast-forwarding the film.
- 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.
- Indexing tables in assembly lines, tool changers for CNC machines, and so on.
3D MODELS:
- DRIVER WHEEL:
a. 2d drawing:
b. Based on above given 2D diagram the 3D model is designed :
- DRIVEN WHEEL:
a. 2d drawing:
b. Based on above given 2D diagram the 3D model is designed :
- ASSEMBLY OF THE DRIVER AND DRIVEN WHEEEL:
GRAPHS PLOTTED:
- Study1 : 10 rpm motor speed and 60 frames per second.
a. Contact force between driving and driven wheel without precision 10 rpm:
- Solidworks plot:
so from the above graph we may see that when there is contact of the driver spindle with driven slot there is a spike shown in the graph.so when the time increases and when there is contact between the driver slot and spindle then there is increase in the height of the wave .
- Excel plot:
b. Contact force between driving and driven wheel with precision 10 rpm:
- Solidworks plot:
so from the above graph we may see that when there is proper contact of the driver spindle with driven slot there is a spike shown in the graph.so when the time increases and when there is contact between the driver slot and spindle then there is increase in the height of the wave .
- Excel plot:
c. Angular displacement for driven wheel 10rpm:
- Solidworks plot:
The angular displacement is calculated in the 180 cycle. so here we can see that the starting angle is between 90 to 180 and then since it is clockwise rotation the plot drops from 180 to -180 and then moves till 0 and the same continues for the next rotation.
- Excel plot:
d. Angular velocity for driver wheel 10rpm:
- Solidworks plot:
Here we can see that with increase in time the angular velocity remains constant.
- Excel plot:
- Study2 : 20 rpm motor speed and 120 frames per second.
a. Contact force between driving and driven wheel without precision 20 rpm:
- Solidworks plot:
so from the above graph we may see that when there is contact of the driver spindle with driven slot there is a spike shown in the graph.so when the time increases and when there is contact between the driver slot and spindle then there is increase in the height of the wave .
- Excel plot:
b. Contact force between driving and driven wheel with precision 20 rpm:
- Solidworks plot:
so from the above graph we may see that when there is proper contact of the driver spindle with driven slot there is a spike shown in the graph.so when the time increases and when there is contact between the driver slot and spindle then there is increase in the height of the wave .
- Excel plot:
c. Angular displacement for driven wheel 20rpm:
- Solidworks plot:
The angular displacement is calculated in the 180 cycle. so here we can see that the starting angle is between 90 to 180 and then since it is clockwise rotation the plot drops from 180 to -180 and then moves till 0 and the same continues for the next rotation.
- Excel plot:
d. Angular velocity for driver wheel 10rpm:
- Solidworks plot:
Here we can see that with increase in time the angular velocity remains constant.
- Excel plot:
CONCLUSION:
So here we were able to make the 3D models for driver and driven wheel and make its assembly.
Further using the motion analysis we were able to make different plots which gave an idea how the driver and driven wheels were rotating.
ANIMATION: