MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM Using SOLIDWORKS
Geneva mechanism, also called Geneva Stop, one of the most commonly used devices for producing intermittent rotary motion, characterized by alternate periods of motion and rest with no reversal in direction. It is also used for indexing (i.e., rotating a shaft through a prescribed angle).
The name, Geneva drive, is derived from the device's earliest application in mechanical watches, which were popularized in Geneva, being the classical origin of the watchmaking industry.
The Geneva drive is also called a "Maltese cross mechanism" due to the visual resemblance when the rotating wheel has four spokes, since they can be made small, and are able to withstand substantial mechanical stress. These mechanisms are frequently used in mechanical watches.
There are three types of Geneva mechanism
Internal Geneva mechanism
External Geneva mechanism
Spherical Geneva mechanism
Here in this project, we will analyze the MBD of an internal Geneva mechanism
An internal Geneva mechanism 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.
To study the motion of an internal geneva mechanism we will first create the 3D model of the driving and driven wheel
Now as of now we have drawn the CAD model of the driver and the driven wheel now using the Extrude boss base option we will create the 3D models of the driver and driven wheel. Once we are ready with the 3D models we will assemble them and restrain them as per the requirements as shown below.
Now we are done with assembly now we will study the motion in order to do that we will go for a SOLIDWORKS add-in called Solidworks Motion.
Now we will add a motor to the driver wheel;
Now we will perform two case studies,
1. Constant speed motor @ 10 RPM speed
We are considering solid body contact and both the wheels are made up of Steel.
We will change the motion analysis properties for 10 RPM
we will keep the precise contact option unticked and set the frame rate to 60 fps.
We will run the analysis and the plots for
- Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- The driver wheel's angular velocity is obtained.
The results are as follows
Fig:- Contact force (between driving and the driven wheel) as a function of time without precise contact for 10 rpm @ 60 fps
Fig:- Angular Displacement of the driven wheel without precise contact for 10 rpm @ 60 fps
Fig:- Angular velocity of the driver wheel without precise contact for 10 rpm @ 60 fps
Now again we will change the motion analysis properties
This time we will keep the precise contact option ticked and set the frame rate to 60 fps.
We will run the analysis and the plots for
- Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- The driver wheel's angular velocity is obtained.
The results are as follows
Fig:- Contact force (between driving and the driven wheel) as a function of time with precise contact for 10 rpm @ 60 fps
Fig:- Angular Displacement of the driven wheel with precise contact for 10 rpm @ 60 fps
Fig:- Angular velocity of the driver wheel with precise contact for 10 rpm @ 60 fps
Now I have rendered the animation for 10 RPM @ 60 fps and setting the playback speed to 5X to make the animation smooth.
Now our second case
1. Constant speed motor @ 20 RPM speed
We are considering solid body contact and both the wheels are made up of Steel.
We will change the motion analysis properties for 20 RPM
we will keep the precise contact option unticked and set the frame rate to 120 fps.
We will run the analysis and the plots for
- Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- The driver wheel's angular velocity is obtained.
The results are as follows
Fig:- Contact force (between driving and the driven wheel) as a function of time without precise contact for 20 rpm @ 120 fps
Fig:- Angular Displacement of the driven wheel without precise contact for 20 rpm @ 120 fps
Fig:- Angular velocity of the driver wheel without precise contact for 20 rpm @ 120 fps
Now again we will change the motion analysis properties
This time we will keep the precise contact option ticked and set the frame rate to 120 fps.
We will run the analysis and the plots for
- Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- The driver wheel's angular velocity is obtained.
The results are as follows
Fig:- Contact force (between driving and the driven wheel) as a function of time with precise contact for 20 rpm @ 120 fps
Fig:- Angular Displacement of the driven wheel with precise contact for 20 rpm @ 120 fps
Fig:- Angular velocity of the driver wheel without precise contact for 20 rpm @ 120 fps
Now I have rendered the animation for 10 RPM @ 60 fps and setting the playback speed to 5X to make the animation smooth.
Conclusion:-
The motion analysis of the internal geneva mechanism was performed and various plots were plotted for the post-processing.
The increase in RPM increases contact forces. Through precise contact, the computed contact is analytically more correct
By using precise contact, SolidWorks calculate contact approximately using the geometry of many-sided polygons. Through precise contact, the computed contact is analytically more correct. Increasing the frames per second makes the simulation very smooth & reduces the incremental steps. For angular displacement & velocity plot, there is no such difference to mention in the case of with and without precise contact.
The CAD and CSV files are attached for reference.