Internal Geneva Mechanism
Aim :- Using the following 2D CAD drawings to create the 3D model of the internal Geneva mechanism.
Objective :-
- Create 3D models for driver and driven wheels.
- Perform motion analysis by rotating the driver wheel at 10rpm.& 20 rpm
- Obtain the following plots for Contact force (between driving and the driven wheel) as a function of time. & Angular Displacement of the driven wheel.
- Compare the contact forces with and without "Precise contact"
- Export the results that you get to Excel and make the plots over there
- Make a plot of the driver wheel's angular velocity and discuss the results
Theory :-
The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion.
The rotating drive wheel is usually equipped with a pin that reaches into a slot located in the other wheel (driven wheel) that advances it by one step at a time. The drive wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps
An internal Geneva drive is a variant on 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.
Procedure :-
SolidWorks Parts & Assembly figures :-
Explanation :-
- Software used solidworks-2016
- To draw the 3D part from the given 2D drawing we start from the selecting the part design providing the proper dimension and using proper drawing tools to create the 3d model of the driven wheel of the Geneva mechanism.
- Now we have the dimensions or the details provided for the driver & driven wheel by using that we can create new part by applying the proper drawing tools and dimension. we obtain the 3d driver wheel of Geneva mechanism also using the command Extrude boss base to convert the 2D drawing to 3D
- The fallowing parts are shown in the above snap for the driver & driven wheel of the Geneva mechanism
- The next step is to assemble the all parts to obtain a motion between them
- Now to start with the assembly drawing, selecting the parts created for the driver & driven wheel and to assemble it using the mating/Mate command
- Assemble the parts one over other using proper mate command using the help of the three planes, thus the driven wheel is placed over the driver using the mate function
- Now it’s time for the motion study, as asked in the challenge using the motor to rotate the driver with 10 rpm & 20 rpm for 60 & 120 FPS respectively
- Providing the timeline for the motion study and calculate the motion study. For say 10 , 15 , 20 seconds thus this will create motion analysis of the Geneva mechanism and desired simulation/animation of the motion is created
- Lastly use the plot/figure function to obtain graphs for the contact forces, angular displacement & angular velocity w.r.p to time .
Graphs / Plots :-
Contact Forces Graph for driver & driven wheel is shown below
graph 1 for - 10 rpm , 60 fps
graph 2 for - 20 rpm , 120 fps
Angular displacement graph shown below
graph 1 for - 10 rpm , 60 fps
graph 2 for - 20 rpm , 120 fps
Contact forces graph with precise contact for driver & driven wheel as shown below
graph 1 for - 10 rpm , 60 fps
graph 2 for - 20 rpm , 120 fps
Angular Velocity graph for the driver wheel shown below :-
- when the pin on the driver wheel moves into the slots on the geneva driven wheel there is a small jerk, the jerk is seen during the entry and also in the further motion of the pin in the slot
- so to obtain the contact forces i choosed the pin surface and the slot face where there is a contact betn them to obtain the contact force graph
- the graph is showing the variation betn the contact force at motor speed of 10 rpm & at 20 rpm the graph is significantly diffrent , when there is contact betn the face and the pin suface the graph status shows the variation in the line
- similarly for the angular displacement the graph is obtained shows a drastic fall at 5 sec the angular velocity graph is also obtained for the driver wheel it shows a smooth SHM motion.
Result / Conclusion :-
- Thus using the solidworks we have created a 3d model of the internal geneva mechanism by using the provided 2d drawing details
- assembled the 3d parts created for the driver & driven wheel and obtained the motion study for the internal geneva mechanism
- also created the graph / plots for the contact forces with and without precise contact , for the angular displacement & for the angular velocity of the driven & driver wheel respectively . at the motor running at 10 & 20 rpm for 60 & 120 fps respectively.
- The google drive link is provided below ( all the graphs as well as the file for the parts & assembly is provided )
https://drive.google.com/drive/folders/15KbFoYnYg13BKmSzCz2g1sVmTOCRw-dn?usp=sharing
- The youtube video link for the motion analysis video is provided below for the internal geneva mechanism.