Internal Geneva Mechanism

Objective:

1. Build the driver and driven wheel and assemble them partially.
2. Analyze the assembly under different rotational speeds and forces.
3. Analyze the difference in the contact forces with and without 'Precise contact'.
4. Observe the variation of angular velocity with time.

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 main wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps.

Theory

The Geneva wheel is also commonly called as the Maltese cross mechanism due to the visual resemblance. In the most common arrangement, the driven wheel has 4 slots and thus advances for each rotation of the driver wheel by 1 step of 90 degrees. If the driven wheel has 'n' slots, it advances by 360/n degrees per full rotation of the driven wheel. Since the mechanism needs to be well lubricated, it is often enclosed in an oil capsule.

Assembly of the Internal Geneva Wheel Mechanism

Results of the Simulation

10 rpm, 60 fps Contact force v/s time

20 rpm, 120 fps Contact force v/s time with precise contact

20 rpm, 120 fps Contact force v/s time without precise contact

10 rpm, 60 fps Angular displacement v/s time

20 rpm, 60 fps Contact force v/s time

10 rpm, 60 fps Angular velocity v/s time

20 rpm, 120 fps Angular velocity v/s time

20 rpm, 120 fps Angular velocity v/s time with precise contact

Conclusions

• The second and third image tells us that the average force in increased when precise contact is enabled.
• The angular velocity reduces with time.