Multi Body Dynamics of Internal Geneva Mechanism using SolidWorks

Aim:-

• To Use the following 2D CAD drawings to create the 3D model of the internal Geneva mechanism and

• To create 3D models for driver and driven wheels.
• To perform motion analysis by rotating the driver wheel at 10rpm.
• To Obtain the following plots
• Contact force (between driving and the driven wheel) as a function of time.
  • Angular Displacement of the driven wheel.
• To Compare the contact forces with and without "Precise contact"
  • To Show image for precise contact selection
  • To Export the results that you get to Excel and make the plots over there.

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. And it is commonly used indexing mechanism where an intermittent motion is required.

Theory:-

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.

The Inverse Geneva mechanism, which is a variation of the Geneva mechanism, is used where the wheel has to rotate in the same Direction as crank. It requires less radial space and the locking device can be a circular segment attached to the crank that locks by wiping against a built up rim on the periphery of the wheel.

The design and fabricating of a conventional Geneva mechanism is generally simple and inexpensive because there is no specially curved profile on any of the components except straight lines and circular arcs. However, due to the discontinuity of the acceleration at the beginning and ending positions, the shortcoming of using conventional Geneva mechanism is the large impact when the driving crank engages and disengages with the wheel slot.

Classification of Geneva Mechanism:-

• Internal Geneva Mechanism.
• External Geneva Mechanism.
• Spherical Geneva Mechanism.

Advantages:-

• Geneva mechanism may be the simplest and least Expensive of all intermittent motion mechanisms.
• Geneva maintains good control of its load at all Times, since it is provided with locking ring surfaces.

Disadvantages:-

• The Geneva is not a versatile mechanism.
• This means they produce jerk.

Applications:-

• Stepper.
• Mechanical Watches.
• Plotters.
• CNC Machines, etc.

The Entire Motion study setup:-

• By the use of given 2D CAD drawings with dimensions, we will create the 3D model of the Internal Geneva Mechanism i.e., the Driver and Driven wheels.
• Then we will perform motion analysis by rotating the driver wheel at 10rpm.
• Then we will obtain the required plots i.e.,
• The Contact force and
• Angular displacement.
• And then we compare the contact forces with and without precise contact.
• Then we will show the precise contact selection
• And we will use 60 Frames per second for 10rpm and
• After completing the previous study then 120 Frames per second for 20rpm.
• We will change the rpm to 20.
• And finally we export or produce the required results or plots.

Results:-

3D sketch:-

Performing motion analysis by rotating the driver wheel at 10rpm:-

https://youtu.be/oQaCP88Hhuw

Material used:- Steel(Dry)

Plots:-

Comparision of contact forces with and without precise contact:-

fig.1. Contact force between driver and driven wheel with precision

fig.2. Contact force between driver and driven wheel without precision

Angular displacement of the driven wheel with and without precision:-

fig.1. Angular displacement of the driven wheel with precision

fig.2. Angular displacement of the driven wheel without precision

Precise contact selection:-

A plot of the driver wheel's angular velocity with 120 Frames per second for 20 Rpm:-

Procedure for designing:-

First we'll design the driven component with the given dimensions in the part design.

The commands used are:-

• Circle
• Smart dimension
• Offset
• Circular Pattern
• Trim
• Extrusion

Then we will design the driver component with specified dimensions in the part design

The commands used are:-

• Circle
• Smart dimension
• Extrusion

Then we will design the smaller pin in the driver component.

And then we will import these two driver components into the assembly and mate it

Then we will create an another assembly and import these all drawings and we will consrain it by mating each other.

Then we will perform the required tasks and we will get the output.

Conclusion:-

So, we have successfully designed the Internal Geneva Mechanism and observed the plots varying with different conditions.