Internal Geneva Mechanism using Solidworks

AIM:

1. To create 3D models of 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 & 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.

PROCEDURE:

1. Create driving part first
2. Create an circle for the given dimesion and extrude it for 20mm.
3. Now select a face on the extruded the object and draw a circle and extrude it for 40mm.
4. The geneva wheel is created according to the given dimension with help of extrude, fillet , mirror and offset option with the dimension given below in 2D CAD drawing for both driving wheel and driven geneva wheel.
5. Both of the part is assembled using various mating condition as in image.
6. The assembled image is follow and center distance between the driving and driven wheel was given as 226.27mm aprox which gave neccesary distance for driving wheel shaft and driven wheel slot to mate properly and execute the mechanism as shown in figure 6.
7. Now we simulate the mechanism for various condition and plot the graph.

Modeling and Assembly:

3D Model of Internal Geneva mechanism Driver Wheel

3D Model of Internal Geneva mechanism Driven

Assembly of Internal Geneva mechanism

Motion study of Assembly of Internal Geneva mechanism with/without precise contact

PLOTS: Assumed the material as Dry Steel for both the wheels.

• CONDITION 1

1. Speed 10RPM Constant speed motor
2. Frames per Second 60
3. Without Precise contact

• CONDITION 2

1. Speed 10RPM Constant speed motor
2. Frames per Second 60
3. With Precise contact considered

• CONDITION 3

1. Speed 20RPM Constant speed motor
2. Frames per Second 60
3. Without Precise contact

• CONDITION 4

1. Speed 20RPM Constant speed motor
2. Frames per Second 60
3. With Precise contact considered

• CONDITION 5

1. Speed 20RPM Constant speed motor
2. Frames per Second 120
3. Without Precise contact

• CONDITION 6

1. Speed 20RPM Constant speed motor
2. Frames per Second 120
3. With Precise contact considered

Plots of Angular Velocity of driver wheel

Conclusion

• If the rpm of the driver wheel increases then the angular displacement of the driven wheel increases according to the time.
• In this geneva mechanism model if the driver wheel rotate 4 times then driven wheel rotate only 1 times. Its speed ratio is 4:1.
• By showing the angular displacement graph of the driven wheel it observe that for a few second driven wheel will at the rest position and again revolve upto 90 degree and this process will continued.