Internal Geneva Mechanism

MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM using SOLIDWORKS

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.

Below Figures Shows the Basic Layout of a Geneva Drive.(First figure represents External Geneva Mechanism, while second figure represents Internal Geneva Mechanism ) ref[1]

An internal Geneva drive is a variant on the design. The axis of the drive wheel of the internal drive can have a bearing only on 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 always greater than 180° in an internal one, where the switch time is therefore greater than the time the driven wheel stands still.

Aim: Create a motion Study of an internal Geneva mechanism in SolidWorks using the given design specifications and find the following results:

1. Contact Forces with the function of time
2. Angular displacement of driver wheel
3. Angular velocity of driven wheel
4. Comparing the results with precise contacts

Design Specifications

Creating a 3d CAD Model

Internal Geneva Mechanism- Parts with Assembly

Creating Motion Study

Study 1:

Important defined Parameters:

1. Motor: Constant Speed - 10 RPM
2. Solid Body Contacts with both materials type – Dry Steel
3. Results:

• Contact Forces

• Angular Displacement of Driven Wheel

• Angular Velocity od Driven wheel

Motion Animation: Refer

https://youtu.be/_PFzqN82BX0

Study 2:

Important defined Parameters:

1. Motor: Constant Speed - 20 RPM
2. Solid Body Contacts with both materials type – Dry Steel
3. Results:

• Contact Forces

• Angular Displacement of Driven Wheel

• Angular Velocity of Driven wheel

Motion Animation: Refer

https://youtu.be/85hhe_XGZRM

Comparison of above motion study with Precise Contact

The above results were compared with precise control options which were set in motion analysis settings with 10 rpm at 60 fps and 20 rpm at 120 fps.

Motor Speed 10 RPM

Contact Forces: (top to bottom: Normal Plot,Precise Plot)

• Angular Displacement of Driver wheel: (top to bottom: Normal Plot,Precise Plot)

• Angular Velocity of Driven Wheel: (top to bottom: Normal Plot,Precise Plot)

Motor Speed 20 RPM

Contact Forces: (top to bottom: Normal Plot, Precise Plot)

• Angular Displacement of Driver wheel: (top to bottom: Normal Plot,Precise Plot)

• Angular Velocity of Driven Wheel: (top to bottom: Normal Plot,Precise Plot)

Exporting Graphs from Excel

As the graphs are similar to those shown above, only precise Contact forces at 10 rpm were exported in Excel and are displayed as follows:

Conclusion

Following conclusions can be extracted from the abve motion analysis

1. Contact forces increases with increase in the speed of the driving wheel.
2. Using precise contacts settings, there is a little change in the values which may be significant in many enginnering applications.
3. From the angular velocity graph of driven wheel (Both at 10 or 20 rpm case) it is depicted that we get intermittent output at driven wheel for a constant angular velocity of driving wheel, which is the basic principle of a Geneva Mechanism.
4. Using Precise Contact settings, we are able to get jerk free intermittent angular velocity at the output of driven wheel.
5. Exporting the data to Excel helps us in better visualisation of the results along with all the motion study values.

References

1. https://en.wikipedia.org/wiki/Geneva_drive
2. Internal Geneva Mechanism Animation (figure 2)