Internal Geneva Mechanism

NAME :- PRAJWAL SUTE

AIM:- To design Internal Geneva Mechanism, perform the motion study on it and interpret the plots obtain by motion study.

INTRODUCTION

Geneva mechanism is used to convert continuous rotary motion into intermittent rotary motion. This is one of the most commonly used in both high and low rotating machines. Generally, Geneva Mechanism consists of two important members: the crank with a pin or roller (driver member) and the follower or slotted plate or wheel (driven member). The crank member provides an intermittent rotation to the follower member and keeps it from spinning between the stages of meeting. The two members should be designed so that the driving pin enters or leaves the slots tangentially. This allows meeting with a lowest amount of impact or shock.

There are three different standard type Geneva mechanisms known as External, Internal and Spherical Geneva mechanisms. Among the three types, the external Geneva mechanisms are the most widely used, mainly because of their simplicity. Spherical Geneva mechanisms enjoy superior dynamic performance characteristics when compared to the other members of the Geneva family. This type of Geneva mechanism is capable of delivering superbly smooth and "shock free" output.

Whereas Internal Geneva is particular type of Geneva is the most compact one among the three. The driver member is contained in the same space occupied by the driven member making this mechanism suitable for situations in which space is a critical factor. When compared to the external Geneva’s, in internal Geneva’s, the function of the locking plate is delivered by the geometry of the driven member.

MOTION STUDY

Motion studies are graphical simulations of motion for assembly models. Motion Analysis is most advanced motion simulation and it can be used for accurately simulating and analyzing the effects of motion elements (including forces, springs, dampers, and friction) on an assembly. Motion Analysis uses computationally strong kinematic solvers, and accounts for material properties as well as mass and inertia in the computations. You can also use Motion Analysis to plot simulation results for further analysis. You can incorporate visual properties such as lighting and camera perspective into a motion study.

Motion studies do not change an assembly model or its properties. They simulate and animate the motion you prescribe for a model. You can use mates to restrict the motion of components in an assembly when you model motion.

PROCEDURE

1. Referring to the drawings given draw the parts separately in the Solidworks as driver and driven member.

2. Create new assembly in the solidworks as “Internal Geneva Mechanism”. Add the created parts into it.

3. Make both as float.

4. Add the mate as coincident to the driven part front plane with the assembly front plane.

5. Add the mate as coincident between center axis of driven part and top plane.

6. Do the same mate with right plane.

7 Add the distance mate between front plane of the driver part and assembly front plane as thickness of the driven part.

8. Add the mate as coincident between center axis of driver part and top plane.

9. Add the distance mate between center axis of driver part and right plane.

10. Now go to motion study select motion analysis.

11. Add the motor to the driver with 10 rpm.

12. Go to the contact and select the parts and add steel dry to both.

13. Click on the calculate and see the simulation.

14. Plot the graph between contact force vs time.

15. Plot second graph between angular displacement of driven part vs time.

16. Plot the third graph between angular velocity of driver part vs time.

17. Now change the frames to 60 and plot all the above graphs.

18. Now change the rpm to 20 and perform the motion study.

OBSERVATIONS

1. At 60rpmThe contact force is maximum at the entry of the driver pin into the driven slot and decreases as it rotates. The same force follows the mirror pattern during the reverse travel through the slot.

• The contact is maximum (higher than in non-precise contact, almost 10 times higher) at the entry of the pin into the slot. The pin leaves with the minimum force.

• Angular displacement of the driven part is rapidly increased for fraction of time. Then it linearly reduces as time passes and becomes constant. Follows the same pattern.
• Angular velocity of driver wheel is constant over the time.

2. At 120rpm

• The contact force is maximum at the entry of the driver pin into the driven slot and decreases as it rotates. The same force follows the mirror pattern during the reverse travel through the slot.

• The contact is maximum (higher than in non-precise contact, almost 20 times higher) at the entry of the pin into the slot. The pin leaves with the minimum force.

• Angular displacement of the driven part is rapidly increased for fraction of time. Then it linearly reduces as time passes and becomes constant. Follows the same pattern.

• Angular velocity of driver wheel is constant over the time.

CONCLUSION

1. The contact force is increases with the rpm. But the nature of the curve is independent of the rpm. The contact force is maximum at the entry of the driver pin into the driven slot and decreases as it rotates. The same force follows the mirror pattern during the reverse travel through the slot.
2. The contact force is dependent on the precise contact. As the contact becomes precise contact is maximum (higher than in non-precise contact, almost 10 times higher) at the entry of the pin into the slot. The pin leaves with the minimum force. The nature is independent of the rpm.
3. Angular displacement of the driven part is rapidly increased for fraction of time. Then it linearly reduces as time passes and becomes constant. Follows the same pattern for all rpm.
4. Angular velocity of driver wheel is constant over the time and neither dependent on the precise contact nor on rpm of the wheel.