Internal Geneva Mechanism

Hello Everyone,

I'm Abhishek Dhardwivedi, and here is my Project on Internal Geneva Mechanism.

AIM: To do Motion analysis of Internal Geneva Mechanism.

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.

Uses & Applications:

• One application of the Geneva drive is in film movie projectors and movie cameras, where the film is pulled through an exposure gate with periodic starts and stops.
• Geneva wheels having the form of the driven wheel were also used in mechanical watches.
• A Geneva drive was used to change filters in the Dawn mission framing camera used to image the asteroid 4 Vesta in 2011.
• Geneva Mechanism also used in banknote counting machines.
• Other applications of the Geneva drive include the pen change mechanism in plotters, automated sampling devices, and many forms of indexable equipment used in manufacturing (such as the tool changers in CNC machines; the turrets of turret lathes, screw machine, and turret drills; some kinds of Indexing head and rotary table; and so on).

Classification of Geneva Mechanism:

- Geneva Mechanism classified into three categories;

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

Advantages:

• Geneva Mechanism is the simplest & least expensive intermittent Mechanism.
• They come in a wide variety of sizes, ranging from those used in instruments, to those used in machine tools to index spindle carriers weighing several tons.
• They have good motion curves characteristics compared to ratchets, but exhibit more “jerk” or instantaneous change in acceleration, than better cam systems.

Dis-advantages:

• The Geneva is not a versatile mechanism and produce jerk.
• The ratio of dwell period to motion is also established once the no of dwells per revolution has been selected.
• All Geneva acceleration curves start and end with finite acceleration & deceleration.

Experiment:

Here, Internal Geneva Mechanism is analysed at 10 RPM & at 20 RPM both with precise contact & without precise contact respectively.

Material Used: Steel (Dry) for both Driving & driven Wheel.

Here, Red coloured model is the Driving Wheel of the Internal Geneva Mechanism.

While Blue coloured model is the Driven Wheel of the Internal Geneva Mechanism & Pin is shown with Green Colour.

Models:

The Model is designed as per the dimensions provided by the skill-lync project.

Link for the models & assembly:

Internal Geneva Mechanism (Models)

Analysis at 10 RPM:

The Internal Geneva Mechanism is analysed at 10 RPM with 60 frames per second wihout Precise Contact & with Precise contact respectively.

Both of the analysis is described below:

Result of 10 RPM:

• The Contact Force decrease when the setting changes from without Precise Contact to Precise Contact.
• The Angular Acceleration of Driving Wheel also decrease when the setting changes from without Precise Contact to Precise Contact.

Analysis at 20 RPM:

The Internal Geneva Mechanism is analysed at 20 RPM with 120 frames per second wihout Precise Contact & with Precise contact respectively.

Both of the analysis is described below:

Result of 10 RPM:

• The Contact Force increases when the setting changes from without Precise Contact to Precise Contact.
• The Angular Acceleration of Driving Wheel also increase when the setting changes from without Precise Contact to Precise Contact.

Conclusions:

• There is a large increase in Contact Force while increasing the speed from 10 RPM to 20 RPM.
• Also, The angular accelaration of Driving Wheel increases in a large amount when the speed changes from 10 RPM to 20 RPM.(i.e. 90 to 1152 deg/s2)
• But there is unusual decrease in contact force & angular accelaration of driving wheel when the setting changes from without Precise Contact to Precise Contact at 10 RPM.
• While there is unusual increase in contact force & angular accelaration of driving wheel when the setting changes from without Precise Contact to Precise Contact at 20 RPM.
• All Geneva acceleration curves start and end with finite acceleration & deceleration.
• Also, from the Visual anslysis, it is found that there is backward thrust(to or fro motion) at the driving wheel when the Driven wheel starts rotating.
• This creates an imbalance of the mechanism.
• And, this thrust increases with the increase in speed.
• So, it perform a smooth rotation only at small speeds.
• Thus, Mechanism has a limited applications.
• Thus,The Geneva is not a versatile mechanism and produce jerk.