MBD on Internal Geneva Mechanism

Introduction

In this project, we’re going to design an internal Geneva mechanism and do multi-body dynamics of it using Solid works. Moreover analyzing some dependent parameters with respect to time on which are playing a role in the motion. These parameters are here contact force between driver and driven wheel and angular displacement with respect to time. After that, we will generate the plots of the same thing for two conditions

1. Without precision
2. With precision

And discuss the effect of it here.

Theory: Before discussing let’s first get to know about what exactly a Geneva mechanism is?

Components used: Driver wheel and driven wheel.

Material Used for the driver and driven wheel is Steel (dry).

Geneva Mechanism or also referred to as the Maltese cross mechanism is a mechanical system which is used to convert continuous rotatory motion into the intermittent rotary motion. In simpler terms it is used to convert continuous rotary motion into stepped rotary motion with fixed time of interval i.e. after a particular time interval driven wheel will rotate by a fixed amount.

This mechanism can be used where we need both the conditions simultaneously.

1. Specified rotation of the shaft
2. These rotations are in a particular interval of time.

EXTERNAL GENEVA MECHANISM

Geneva mechanism can be of 2 types:

1. External type
2. Internal type

Working of Internal Geneva Mechanism

Initializing as motor starts and driver wheel starts rotation as soon as the pin comes in contact with the slot the driven wheel starts rotating wheel and it will do a to and fro motion respective to the slots along with rotation. Now as soon as the pin leaves the contact with the slot the motion stops (not considering inertia as a lighter body is there.) and after a particular time interval, the same cycle repeats and keeps ongoing.

Moreover, the driver wheel has to rotate more than 180 degrees to complete one step of the driven wheel while in the case of external type angle is always less than 180 degree. One more thing is there that is the driver wheelbase plane and driven wheelbase plane are parallel and at a distance i.e. equal to the thickness of the driver wheel.

INTERNAL GENEVA MECHANISM

Modeling

Points to consider while modeling, assembling and motion analysis

1. Check the unit system is in meters as it will help to complete the process with ease.
2. Make sure your sketch is fully defined when the final sketch is ready.
3. While extruding, make sure to extruding the sketch from the selected surface wherever required.
4. Restrict the additional movements of components properly.
5. Axis distance should be fixed so that the condition which is rotating about their axis (stationary axis) will be satisfied.
6. Change the frame rate as per requirements.
7. Define contacts between bodies as per requirement.
8. Make sure to define materials as well.

Applications:

1. It is used in theatres movie projectors where intermittent rotation is required and the time value helps to determine the no. of frames every second but in this case, rest time is very less.
2. It can be used in turret lathe where no. of tools are added and after each operation i.e. after a certain time gap next tool will get functional.
3. Widely used in analog watches.
4. It can also be used for indexing.
5. Moreover, it is also used in the production of the automobile sector.

RESULTS

1. Contact force at rpm 10 w.r.t time.

For the above graph, it was the reaction force generated while pin and slot came in contact. As soon as the driver wheel starts rotating and come in contact with the slot in the driven wheel, the graph starts rising, and force keeps on increasing, as friction is also considered and reached to a maximum value after that it keeps on decreasing and tend to zero in idle time.

2. The angular velocity at rpm 10 of driven wheel w.r.t time.

This graph shows the angular velocity of the driven wheel w.r.t time and we can see that it’s parabolic nature due to the kind of relative motion between the driver wheel and driven wheel. And in idle time this graph remains constant for that period of time.

3. The angular displacement at 10 rpm of driven wheel w.r.t time.

In this graph, we start with 135 degrees and the angular displacement reaches the minimum value of -180 during no. of rotation i.e. this graph is for repetitive cycles.

With precision case:

1. Contact Force at 10rpm w.r.t time.

Here everything will remain the same, except the FPS is 60 here and the precision contact is enabled which leads to more accurate results.

2. Angular velocity of Driven wheel at 10rpm w.r.t time.

A similar thing happened here, the graph is more accurate as the frame is increased to 60 and precise contact between bodies is enabled.

3. The angular displacement of Driven wheel at 10 rpm w.r.t time.

These are the similar results obtained for a different value of the angular velocity of the driver wheel.

With precision contact

1. Contact Force of Driven wheel at 20rpm w.r.t time.

2. Angular velocity of Driven wheel at 20rpm w.r.t time.

3. The angular displacement of Driven wheel at 20 rpm w.r.t time.

Without precision at 20 rpm

1. Contact Force of Driven wheel at 20rpm w.r.t time.

2. The angular velocity of Driven wheel at 20rpm w.r.t time.

3. The angular displacement of Driven wheel at 20 rpm w.r.t time.

All Animation and Assembly File Links: https://drive.google.com/drive/folders/1d8av9T0b0O0GhcAEUxIDeBUDgNlNg3iL?usp=sharing

Conclusion: Hence we studied the behavior of the Internal Geneva mechanism and perform motion analysis such that we were able to predict the behavior and pattern of the driven wheel with respect to time.