Internal Geneva Mechanism (Multibody Dynamics using Solidworks)

AIM: 1. To create 3D models of the driver and driven wheels of the internal geneva mechanism

using SolidWorks.

2. To assemble both the parts to create the full mechanism.

3. To run the basic motion analysis, by rotating the driving wheel by 10 and 20 rpm respectively.

4. To enable the precision contact option and study its effects on the plots.

5. To plot the contact force between both the wheels(with and without precision).

6. To plot the angular velocity and angular displacement of the wheels.

THEORY:

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.

There are three basic types of Geneva motion mechanisms namely external, internal, and spherical. The spherical Geneva mechanism is very rarely used. In the simplest form, the driven wheel has four slots, and hence for each rotation of the drive wheel, it advances by one step of 90°. If the driven wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.

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 smaller than 180° in an external Geneva drive and is always greater than 180° in an internal one. The external forM is the more common, as it can be built smaller and can withstand higher mechanical stresses.

Because the driven wheel always under full control of the driver, the impact is a problem. It can be reduced by designing the pin in such a way that the pin picks up the driven member as slowly as possible. Both the Geneva mechanisms can be used for light and heavy-duty applications. Generally, they are used in assembly machines.

Modeling and Assembly:

The emodeling of both the wheels as well as the assembly is being carried using SolidWorks.

RESULTS:

The material selected for both the wheels, before running the motion analysis, is dry steel.

FOR 10 RPM:

Contact Force between the wheels @ 10 rpm:

Contact Force with the precision of 60 frames per second@ 10 rpm:

Angular velocity of the driven wheel@ 10 rpm:

Angular velocity with precision of 60 fpm @10 rpm:

Angular Displacement of the driven wheel @10 rpm:

Angular Displacement of the driven wheel @10 rpm with same precision:

FOR 20 RPM:

Contact Force between the wheels @20rpm:

Contact Force between the wheels @20rpm with the precision of 120 fpm:

Angular velocity of the driven wheel @20rpm:

Angular velocity of the driven wheel @20rpm with the precision of 120 fpm:

Angular displacement of the driven wheel @20 rpm:

Angular displacement of the driven wheel @20 rpm with same precision:

CONCLUSIONS:

1. The 'Precise Contact' gives a more accurate result as we can see that the curves in the plots with precise contact become less fluctuating and smooth. Moreover, the values obtained from the precise contact plot are more flexible and true.

2. When the driver tries to enter in the slot of the driven wheel it faces a jerk as the entry is not smooth therefore, we can see also from the plot that at the entry to the slot gives rise to a sudden increase in the contact force which decreases as the driver enters into the slot.

3. We can also see from the contact force plots of the 2 RPM's that as we increase the rotation of the driver the jerk force/contact force at the entry also increases and then it drastically decreases.

4. The angular velocity plot reveals that at first, there is a jerk felt by the driven wheel and we see a peak in the angular velocity plot and then when it enters the slot there is an acceleration in the driven wheel but as the motion progresses there is a reduction in the velocity and hence retardation occurs. The maximum velocity is at the point where the pin of the driver reaches the bottom point of the driven wheel.

5. The angular velocity of the driven wheel also increases if we increase the rotation of the driver which is seen from the plot.

6. The angular displacement plot shows that the displacement occurs between -180 to 180 degrees and it repeats the pattern in each revolution starting from 0.