MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM USING SOLIDWORKS MBD

AIM:

1. To create 3D models of the driver and driven wheels in the internal geneva mechanism using SolidWorks.
2. To assemble both the parts to create the working mechanism.
3. To run the basic motion analysis, by adding a motor to the driving wheel at varying speeds 10 and 20 rpm with 60 and 120 frames per second respectively.
4. to plot Contact force (between driving and the driven wheel) as a function of time and Compare the contact forces with and without "Precise contact"
5. To plot the angular velocity and angular displacement of the wheels at 10 and 20 rpm.

INTRODUCTION:

The Geneva drive is also commonly called a Maltese cross mechanism. The Geneva mechanism translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps.

In an internal Geneva drive, the axis of the drive wheel of the internal drive is supported on only one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always greater than 180° in an internal one.

MOTION ANALYSIS PROCEDURE:

For Contact force and Angular displacement,

1] rpm of motor = 10 and without precise contact (60 Frames )

2] rpm of motor = 10 and with precise contact (60 Frames )

3] rpm of motor = 20 and without precise contact (120 Frames )

4] rpm of motor = 20 and with precise contact (120 Frames )

For Angular displacement, I have considered both precise and no precise contacts in both 10 and 20 rpm.

For Angular velocity, I have considered only the non-precision contact for both 10 and 20 rpm.

MODELING AND ASSEMBLY:

3D model using a 2D drawing file:

DRIVEN WHEEL:

DRIVER WHEEL:

OBSERVATIONS:

Plots for 10 RPM:

Contact force without precision contact @ 10 RPM:

Contact force with 60fps and precision contact @ 10 RPM:

Angular Displacement without precision contact @ 10 RPM:

Angular Displacement with 60fps and precision contact @ 10 RPM:

Plots for 20 RPM:

Contact force without precision contact @ 20 RPM:

Contact force with 120fps and precision contact @ 20 RPM:

Angular Displacement without precision contact @ 20 RPM:

Angular Displacement with 120fps and precision contact @ 20 RPM:

ANGULAR VELOCITY COMPARISON:

Angular velocity for 10 RPM without precision:

Angular velocity for 20 RPM without precision:

ANIMATION:

Internal geneva mechanism

RESULTS:

1. Contact forces between driver and driven wheel increase with an increase in the rpm.
2. Precise contact gives analytically correct results.
3. The angular velocity of the driven wheel increase with an increase in rpm.
4. Angular velocity starts increasing from the engagement point due to acceleration and reaches maximum and retardation occurs thus, decreases till the disengagement point.
5. Whenever the pin enters a slot, it experiences a jerk which increases in the contact force at first, and then it becomes steady.