Internal Geneva Mechanism
Motion analysis of internal geneva mechanism
Objective :
To Create 3D models for driver and driven wheels and compare motion analysis with and without Precise contact for rotation of driver wheel at 10 rpm at 60fps and 20 rpm at 120 fps for the plots of Contact force (between driving and the driven wheel) as a function of time and Angular Displacement of the driven wheel.
About geneva mechanism :
The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion. the difference between Geneva Drive mechanisms and other gears is that Geneva Drive mechanisms have unusual teeth. Unlike in typical gears, the interaction between the part being driven and the part doing the driving is not continuous and the resultant motion is intermittent. Geneva Drives work by having the driving part, or wheel, interlocking with the driven part intermittently. The number of spokes that the driven part has and the speed with which the driving part rotates determines the frequency and distance of travel. There is an elevated segment on the driving wheel which keeps the driven part in position till the next revolution is complete. The external Geneva Drive is by far the most common type, although there are other variations possible in the design. The external drive can be built to withstand higher levels of stress and are generally more robust and sturdy than other variants.
fig.1 External Geneva drive fig.2 Internal Geneva drive
The Internal Geneva Drive has the driving part below the driven wheel, with the driving part often being much smaller than the driven wheel. 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.
Modeling of the driver and driven wheel :
We have given the 2D drawing of the driver and driven wheel which will be extruded to form the 3D model of driver and driven wheel
Assembling of the driver and driven wheel :
To assemble the driver and driven wheel firstly we float the driver wheel then we are constraining the driver part to rotate about its central axis which is done by constraining the central axis with the top and right plane with it we have also given the constraint of the front plane of the assembly to the driver component front plane
now to constrain the driven wheel and we give the distance between the center axis of driver wheel and the center axis of the driven wheel and constraining right plane to assemblies right plane which satisfy the condition to revolve the driven wheel
Motion study :
To do motion analysis we are going to choose the Solidworks motion option from Solidworks Add-Ins To Rotate the Driving wheel we are going to assign motor for driving wheel to do that select motor option in motion analysis and select driving wheels ax after that, we are going to assign solid body contact by selecting contact option and selecting driver and driven wheel now from Menu we can assign a material to the parts.
Finding results :
For the plotting of contact force contact pair is used as follows :
Results
At 10 rpm 60fps :
without precise contact:
the contact force between driver and driven wheel
The angular displacement of driver wheel
With precise contact
the contact force between driver and driven wheel
The angular displacement of driver wheel
At 20 rpm 120 fps
Without precise contact
the contact force between driver and driven wheel
The angular displacement of driver wheel
With precise contact
the contact force between driver and driven wheel
The angular displacement of driver wheel
Explanation of the results :
From the study, we can say that with precise contact the maximum force is observed greater and minimum difference in angular displacement As we change the values of rpm from 10 to 20 we can say that contact force increases also When the driver tries to enter in the slot of the driven wheel it faces a jerk. as the entry is not smooth. therefore, we can see from the plot, a sudden increase in the contact force at the entry to the slot. As we increase the rpm the angular displacement is also increased
Animation video: https://youtu.be/NVobrOIXL-4
Reference: https://en.wikipedia.org/wiki/Geneva_drive
Files: https://drive.google.com/drive/folders/1Lrc3jaKyW8ygo42HN_A2DKKBGyVGhANy?usp=sharing