Internal Geneva Mechanism

AIM

Simulate motion characteristics of an Internal Geneva Mechanism using constraints in MOTIONVIEW with an specified angular velocity of the driver.

OBJECTIVE

1. Create 3D models for driver and driven wheels of Internal Geneva Mechanism.
2. Creating Assembly of Internal Geneva Mechanism.
3. Motion Study of the whole Internal geneva mechanism assembly (using precision and without precision).
4. Plot a graph of Contact force (between driving and the driven wheel) as a function of time.
5. Plot a graph of angular Displacement of the driven wheel.

THEORY

GENEVA MECHANISM

A Geneva Mechanism is a commonly used mechanism for producing an intermittent rotary motion from a uniform input speed. The driven member, or star wheel, contains evenly spaced slots into which the roller of the driving crank slides into. The number of slots determines the ratio between the dwell (stationary) and motion periods of the driven shaft. The mechanism requires a minimum of three slots to function and additional slots can be added. If the driven wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.

APPLICATIONS OF GENEVA MECHANISM

• Both the Geneva mechanisms can be used for light and heavy duty applications. Generally, they are used in assembly machines.
• The Geneva mechanism is a timing device. It is used in many counting instruments and in other applications where an intermittent rotary motion is required. The Geneva mechanism was originally invented by a watch maker.
• The watch maker only put a limited number of slots in one of the rotating disks so that the system could only go through so many rotations. This prevented the spring on the watch from being wound too tight, thus giving the mechanism its other name, the Geneva Stop. The Geneva Stop was incorporated into many of the first film projectors used in theaters.
• Another area where the Geneva Mechanism has been explored is the automotive industry where the internal combustion engine would revolve around the mechanism. The pins and slots of the mechanism form the combustion chambers which are utilized to drive the Geneva wheels to convert linear motion into rotary motion which can power automobiles or even be used in small engine applications.

CAD MODEL

A cad model of internal Geneva mechanism is created consisting of a driven and driving wheel. The two components are then assembled using assembly mates.

RESULTS

1.FOR 10 RPM

• Contact Force with Precision

• Contact Force without Precision

• Angular Displacement of a driven wheel with precision

• Angular Displacement of a driven wheel without precision

• Angular Velocity of the driver wheel

2. FOR 20 RPM

• Contact Force with Precision

• Contact Force without Precision

• Angular Displacement of a driven wheel with precision

• Angular Displacement of a driven wheel without precision

CONCLUSION

• Contact force is proportional to speed of driver it increases with increase in the speed.
• Contact force between driver and driven wheel is highest at the initial stage, when it enters the slot due to the movement of the driven wheel.
• Precise contact gives more accurate results as seen from the above plots.
• In angular velocity plot we see peak when it enters the slot and as the motion progresses there is reduction in the velocity.
• The displacement is intermitent in nature hence the angular displacement plot repeats itself at regular intervals.
• Here for one rotation of the driver wheel the driven wheel rotates by 90 degree.
• Hence for one complete rotation of driven wheel , 4 rotations of the driver wheel is required.

YOUTUBE LINK

https://youtu.be/WJb2okhXh18