Internal Geneva Mechanism

                                                       Internal Geneva mechanism

AIM

To create the 3D model of the internal Geneva mechanism using the 2D CAD drawings and simulating it using SOLIDWORKS motion.

 

INTRODUCTION

The Geneva mechanism is a gear mechanism that translates a continuous rotation movement of driver into intermittent rotary motion of driven. The rotating wheel device is usually provided 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. This mechanism is provided where there is requirement of intermittent processes of operations.

The major applications where the internal Geneva mechanism is used are as follows

1. Movie projectors and Movie cameras
2. Mechanical watches
3. Pen change mechanism in plotters

OBJECTIVE

• 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
• To navigate to the "Precise Contact" follow the steps given below

APPROACH

To perform the motion analysis of internal Geneva mechanism by initially designing 3D parts of CAD drawings shown. Designing individual parts in SolidWorks.                                     

                                                            2D DRIVEN

                                                       2D DRIVER

3D CAD Drawings

1.Driving wheel

• Designing the first part which is Driving wheel based on 2D drawing.
• Selecting front plane and choose the option for sketching
• Draw a circle with center at origin of diameter 420 mm diameter, similarly draw a small circle with diameter 40 mm and at of distance of 160 mm from the centre.
• Extrude the sketch with thickness of 20 mm
  

2.Driven wheel

• Select front plane and draw a circle with diameter 1120mm. 
• Make slot in the driven wheel using offset option
  
• Draw Internal circle with radius 120 mm
  
• Draw Fillet of the 50-millimetre radius as shown in figure
• Extruding with 40 millimetres. 

ASSEMBLY DESIGN

Initially importing the components and assembling it by constraining the degree of freedoms as per requirement.

Simulation and Analysis:

• To perform simulation and analysis by choosing the Solidworks motion option from Solidworks Add-Ins. 
• To provide rotation to the Driving wheel by assigning motor.
• Giving solid body contact by selecting contact option and selecting both partsn and we can assign different materials for both.
• To analyse multiple parameters, plotting different graphs, the plot results as follows.

ANALYSIS @10RPM

1.Contact Force vs Time

There is sudden increase in force value at the start of contact

2.Angular Velocity vs Time

The angular velocity of the driven wheel is initially decreased due to contact, then sudden increment takes place .

3. Contact force with precise contact 120FPS

The contact force is continuously changing in a given time interval and we can calculate each and every point of a jerk as shown in the plot The Precise Contact gives a more accurate result than the previous result

Proof of precise contact selection

ANALYSIS @20RPM

1.Contact Force vs Time

Since there is increase in rpm so the variation happens as shoen in above figure where there is increase in magnitude of force

2.Angular Velocity vs Time

3. Contact force with precise contact

The contact force is continuously changing in a given time interval and we can calculate each and every point of a jerk as shown in the plot The Precise Contact gives a more accurate result than the previous result

Moreover there is increase in fps so tht the simulation runs smooth

Comparing the contact forces with and without Precise contact:

By comparing the contact forces with and without 'Precise Contact', we can conclude that the Precise Contact gives a more accurate results. We can also see the small variation in the plot with the help of Precise Contact.

Conclusions

From the above plots we can easily get to know the different parametes that are changing with respect to time and hence we can choose the sutiable material, condition for working of the operations.

LINK to view 3D diagrams AND PLOTs

https://drive.google.com/drive/folders/12O94Aat3-hqyHZyksLfKVPdLWja6Jsha?usp=sharing