Internal Geneva Mechanism

1. AIM :- To analyse the multi body dynamics for Internal Geneva Mechanism using SolidWorks.

2.OBJECTIVES:

• To create 3D models for driver and driven wheels
• To perform motion analysis by rotating the driver wheel at 10rpm.
• To obtain the following plots: Contact force (between driving and the driven wheel) as a function of time; Angular Displacement of the driven wheel
• To compare Angular Velocity of the driver wheel for 10RPM and 20RPM
• To compare the contact forces with and without PRECISE CONTACT

3.INTRODUCTION-

The Geneva mechanism is type of mechanism which convert rotary motion into intermittent rotational motion. The rotating drive wheel is usually equipped with a pin that reaches into a slot-shaped groove located in the outer wheel (driven wheel) that advances it by one step at a time. The main wheel also has an elevated circular blocking disc that “locks” the rotating driven wheel in position between steps.

Internal geneva mechanism :

An internal Geneva drive is a variant of the design. The axis of the drive wheel of the internal drive can have a bearing only on 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 always greater than 180° in an internal one, where the switch time is therefore greater than the time the driven wheel stands still.

PROCEEDURE :

Driven wheel

1. Open soildworks then click new and select new part. First, we make driven wheel so select from tree manager front plane.Now select circle and draw three circles of respected diameter , select centreline we choose offset entities and then click ok.

2.Trim the edges using trim entities and the 2d draaing looks like this

:

3.After extruding the surface we get the required driven wheel as shown . The following image is the 3D moddel of the driven wheel which is made according to the required dimensions suitably .

Driving wheel :

1.Exit the sketch after drawing and create a new sketch.Hide the part 1 and draw the driving wheel according to suitable dimensions .

The 2D image is made using the solidworks software as shown in figure .

2.The extusion is done in order to make a 3D model of the sasme using solidworks as follows . The model is depicted below :

ASSEMBLY :

1.First click on new and then select assembly and then click ok.Then insert driving and driven part of Geneva mechanism.Then choose driven wheel and select mate with front plane with uppper sitance 20 mm

2. And same mate with also driving wheel.Then apply constraint to axis of driven wheel with top and right plane while doing mate.

3.Then apply distance mate between both the axis of driven and driving wheel.Then assemble components and final assembly is look like this

MOTION ANALYSIS :

1.First we have to add soildworks motion to perform motion analysis in motion study. To perform motion study click on motion analysis and click on motion analysis then click on motor option select driver wheel axis and direction to be clockwise and motor rpm set as 10 rpm .

CASE 1: Driver Wheel at 10 RPM with PRECISE Contacts(60FPS)

PLOT 1 :

Contact force (between driving and the driven wheel) as a function of time

PLOT EXPLANATION : -On observing the reaction force plot, we can see that a common pattern from 0 seconds to 6 seconds is repeating.

-After this,the cycle repeats and continues.

ANGULAR DISPLACEMENT OF THE DRIVEN WHEEL:

PLOT EXPLANATION :In angular displacement plot, we can see that a common pattern(from 0 seconds to 6 seconds) is repeating.

-After this, the cycle repeats and continues.

Angular Velocity of the driver wheel:

*On analysing the angular velocity graph, we can see that a common pattern(from 0 seconds to 6 seconds) is repeating.

*After this, the cycle repeats and continues.

NOW ,

CASE 2- Driver Wheel at 10 RPM with NOT PRECISE Contacts(60FPS):

Contact force (between driving and the driven wheel) as a function of time:

It is noted that there is a cycle of pattern in between 0 to 6 seconds.After that the same cycle repeats again

Angular Displacement of the driven wheel:

-In angular displacement plot, we can see that a common pattern(from 0 seconds to 6 seconds) is repeating.

Angular Velocity of the driver wheel:

On analysing the angular velocity graph, we can see that a common pattern(from 0 seconds to 6 seconds) is repeating.

CASE 3- Driver Wheel at 20 RPM with Precise Contacts(120FPS):

Contact force (between driving and the driven wheel) as a function of time

On observing the reaction force plot, we can see that a common pattern from 0 seconds to 3 seconds is repeating.

Angular Displacement of the driven wheel :

-In the angular displacement plot, we can see that a common pattern(from 0 seconds to 10 seconds) repeats twice.

Angular Velocity of the driver wheel:

On analyzing the angular velocity graph, we can see that a common pattern(from 0 seconds to 3 seconds) is repeating.

CONCLUSION

-The plots are depicted for vaious cases and analysed .On comparing graphs for 10 RPM with precise contacts(study1) and without precise contacts(study2), the values for precise contacts in much greater than not precise contacts. Therefore, using precise contacts the results are quite accurate or precise.

-On increasing the number of revolutions per minute for the motor, the number of cycles increases which can be seen in comparing the graphs of 10 RPM and 20 RPM.

-After comparing contact forces for precise and not precise contacts in spreadsheets, we observed that maximum forces for "precise contacts" are greater than "not precise contacts". In a precise contacts graph, the maximum force is 1.7232E+03 newton at 6.033 seconds whereas for not precise contacts is 1.6356+03 newton at 6.00 seconds.

GOOGLE DRIVE LINK :

For motion analysis simulation of internal geneva mechanism .

https://drive.google.com/file/d/1be5cj6cdxzeb-5omI7miWNxxl10A9GJ3/view?usp=sharing