Internal Geneva Mechanism
MOTION STUDY AND ANALYSIS OF INTERNAL GENEVA MECHANISM
AIM – Create 3D models of driver, driven wheels and perform motion analysis using Solidworks.
OBJECTIVES-
- Create 3D models for driver and driven wheels.
- Perform motion analysis by rotating the driver wheel at 10rpm and 20rpm.
- 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
- Make a plot of the driver wheel's angular velocity and discuss the results.
INTRODUCTION- The Geneva mechanism translates a continuous rotation into an intermittent rotary motion.
Types of Geneva motion mechanisms –
- External
- Internal
- Spherical
External Geneva Mechanism - The rotating drive wheel is usually equipped with a pin that reaches into a slot located in the 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.
Internal Geneva Mechanism - The axis of the drive wheel is supported on only 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 is always greater than 180° in an internal one.
Applications: Geneva drive is used in film movie projectors and movie cameras. Geneva wheels were also used in mechanical watches. Other applications of the Geneva drive include the pen change mechanism in plotters, automated sampling devices, banknote counting machines.
PROCEDURE-
1) Make 2d sketches based on drawing provided in question and using Line, Circle, Offset, Circular sketch pattern and Power trim tool.
2) Using Extrude Boss/Base tool in features toolbar create 3D models. Thickness of Driving wheel is 20mm and for pin above its top surface is 40mm. For driven wheel thickness is 40 mm.
3) Provide proper mates with Front, Top and bottom planes to get perfect assembly for motion study.
GENEVA DRIVEN WHEEL
GENEVA DRIVING WHEEL
INTERNAL GENEVA MECHANISM
4) Enable Solidworks Motion from Tools > Add in. Click on Motion Study palette. Select Motion Analysis from Drop Down Menu.
5) Click on motor icon. By default, selection is Rotary Motor. Select Driver wheel in component. In Motion select Constant Speed with 10 RPM.
6) Click on Contact and select Geneva Driving Wheel and Geneva Driven Wheel.
7) Click on Motion property manager and set Frame per seconds to 60. Now click on Calculate.
8) Click on Plot option and create plot for Contact force (between driving and the driven wheel) as a function of time, angular Displacement of the driven wheel and angular velocity of driving wheel.
9) Now again click on Motion property manager and select Use precise contact option. Obtain the required plots.
10) Now set Motor at 20RPM and Frames per second to 120. Now, perform motion study again both with and without precise contact to obtain the plots.
PRECISION CONTACT SELECTION
RESULTS & EXPLANATION-
- Rotary motor speed 10 RPM
- Contact Force without precision contact
- Contact force with Precision Contact
- Angular displacement of driven wheel without precision contact
- Angular displacement of driven wheel with precision contact
- Angular velocity of driving wheel.
- Rotary Motor Speed 20 RPM
- Contact Force without precision contact
- Contact force with Precision Contact
- Angular displacement of driven wheel without precision contact
- Angular displacement of driven wheel with precision contact
- Angular velocity of driving wheel
CONCLUSIONS:
- Using 'Precise Contact' generates a more accurate result. Curves in the plots with precise contact fluctuate less. Moreover, the values obtained from the precise contact plot are more flexible and true.
- When the driver tries to enter in the slot of the driven wheel it faces a jerk as the entry is not smooth. Also, in case the driven wheel is in motion the jerk increases. Therefore, we can see also from the plot that at the entry to the slot gives rise to a sudden increase in the contact force which decreases as the driver enters into the slot.
- . Contact force plots of both 10 RPM and 20RPM reveals that as we increase the rotation of the driver the contact force at the entry also increases and then it decreases significantly and rises again when pin enters next slot.
- The angular displacement plot shows that the displacement occurs between -180° to 180° degree repeats the pattern for each revolution starting from 0°.
- It is observed that at the higher RPM we get the higher angular displacement. In the 20 RPM graph, we have lines nearer to each other than the 10 RPM graph.
- We get peak points in the angular displacement graph of the driven member due to jerk motion experienced when pin of the driver sudden come into the contact with slot of driven wheel.
Google drive Link: