Motion Analysis of an Internal Geneva Mechanism

Aim: To conduct a motion study for an internal gearing Geneva Mechanism.

Background:

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 that advances it by one step at a time.

The setup under consideration here is an internal geneva mechanism. Here the driver wheel is located on the inside and the pinion of the driver meshes with slots on the inside of the driven gear as shown below:

The driver is the smaller gear on the inside. This is fixed and rotation is the only allowed degree of freedom.

Procedure:

1. Construct the model as per the dimensions in the question-
   
2. Turn on "Solidworks Motion" in the "Solidworks Add-ons" ribbon.
3. Now in the bottom "Motion Study 1" should have been created.
4. Apply motor torque to the axis of the drive wheel. Select RPM here as either 10 or 20.
5. Add solid body contact between the small pinion and the slot surface of the driven. These are the two contact bodies.
6. We will be running the simulation for 2 RPMs and 2 cases for each RPM.
   1. For 10 RPM,
      1. the first case is where we run it at 60 fps and no precise contact
      2. the second case, we run it with precise contact:
         
   2. For 20 RPM,
      1. the first case is where we run it at 120 fps and no precise contact
      2. the second case, we run it with precise contact:
         
7. Run the simulation for each case and extract the graphs.

Results:

1. 10 RPM [No Precise Contact]:
   1. Force vs Time:
      
   2. Angular Displacement of Driver Wheel:
      
   3. Angular Displacement of Driven Wheel:
      
      
      
2. 10 RPM [Precise Contact]:
   1. Force vs Time:
      
   2. Angular Displacement of Driver Wheel:
      
   3. Angular Displacement of Driven Wheel:
      
3. 20 RPM [No Precise Contact]:
   
   1. Force vs Time:
      
   2. Angular Displacement of Driver Wheel:
      
   3. Angular Displacement of Driven Wheel:
      
4. 20 RPM [Precise Contact]:
   
   1. Force vs Time:
      
   2. Angular Displacement of Driver Wheel:
      
   3. Angular Displacement of Driven Wheel:
      
5. Angular Velocity of Driver Comparison:
   
   1. 10 RPM:
      
   2. 20 RPM:
      

Results Summary:

1. Increasing RPM increases the number of peaks in the graph. 20 RPM shows more number of peaks than 10.
2. Adding precise contact deceased the force by 300 N from for the 10 RPM case but added an extra peak at 1.5 seconds interval.
3. However, adding precise contact for 20 RPM increased the force by 3 times from 1744 N to 6839 N.
4. Angular Velocity of both RPMs of the driver is fairly constant around the value of zero, showing that it is a very small value.

Animation:

Animation on YouTube