Motion Analysis of an Internal Geneva Mechanism

OBJECTIVE

To perform motion analysis of an internal geneva mechanism.

INTRODUCTION

The Geneva drive is a gear mechanism that translates a continuous rota 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.

Geneva drive is used indexing equipment. The tool changers in C.N.C machines, the turrets of the turret lathes, screw machines, turret drills, indexing heads and rotary tables are some of the examples used in the manufacturing industry.

In the project, motion analysis of an internal geneva mechanism is performed to determine the contact force and its effect on the angular velocity of the driver is studied.

THEORY

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.

METHODOLOGY

Modelling: Driver and driven wheel are modelled in SolidWorks and assembled.

Material: Steel

RESULT

Case 1: Speed=10 rpm

Figure: Angular Velocity(driver) in degrees/sec i. Without Precision Contact ii. With Precision Contact

Figure: Contact Force in Newtons i. Without Precision Contact ii. With Precision Contact

Figure: Angular Displacement(driven wheel) in degrees i. Without Precision Contact ii. With Precision Contact

Case 2: Speed=20 rpm

Figure: Angular Velocity(driver) in degrees/sec i. Without Precision Contact ii. With Precision Contact

Figure: Contact Force in Newtons i. Without Precision Contact ii. With Precision Contact

Figure: Angular Displacement(driven wheel) in degrees i. Without Precision Contact ii. With Precision Contact

CONCLUSION

• When precision contact is used, solid elements are used in meshing the body. Thus the solution is accurate compared to the solution obtained without precision contact, where planar elements are used.
• As the angular velocity increases, the force exerted by the driver pin on the driven wheel when it comes in contact increases.