Internal Geneva Mechanism
AIM:
To model parts for the internal geneva mechanism, provide assembly for them, generate plots for contact forces and angular velocity in case of driver motor at 10RPM and 20RPM and then compare the results after enabling 'contact precision'.
INTRODUCTION:
In this motion study, we have to simulate the internal geneva gear mechanism and study its behaviour at different. For the modelling of the parts, the follwing data was taken as reference:
THEORY:
Geneva gear is a type of gear arrangement that enables us to transfer continuous rotation to intermediate rotation ie, the driven gear keeps stopping in a fixed interval of time. It consists of two gears, the driver gears rotates at a continous motion while the driven gear shows discontnuity. They have a very limited use since this type of motion conversion is not really helpful in many fields.
SIMULATION:
To carry out the simulation, we first have to model the gear parts with reference to the mentioned data. They can be modelled with simple extrusion from the sketch itself. And then, perform the motion study by giving the relevant information after performing the assembly.
DRIVER GEAR:
It can be simply modelled by extruding the reference sketch with appropriate dimentions.
DRIVEN GEAR:
It can be modelled in the same way, by simply extruding the base reference sketch.
ASSEMBLY:
The assembly of the parts was possible by creating a reference sketch in the top plan of the assembly and then alligning the gear parts with reference to that sketch with the help of concentric and coincident mates and then allign the gears in such a way that they dont mesh into each other.
After completing the modelling and assembly of the gear parts, we have to begin the motion study by applying appropriate input data.
RESULTS:
CASE-1(10 RPM):
plots without precise contact:
contact force variation with time between the driver and driven gear:
angular displacement variation of the driven gear with time:
after precise contact:
contact force variation with precise contact enabled:
angular displacement variation with precise contact:
YOUTUBE LINK FOR THE STUDY ANIMATION AT 60FPS:
https://www.youtube.com/watch?v=2Bn7CI4LtOM&feature=youtu.be
CASE-2(20 RPM):
plots without precise contact:
contact force variation with time between the driver and driven gear:
angular displacement variation of the driven gear with time:
after precise contact:
contact force variation with precise contact enabled:
angular displacement variation with precise contact:
YOUTUBE LINK FOR THE STUDY ANIMATION AT 120FPS:
https://www.youtube.com/watch?v=2_WjQuC0kC8
CONCLUSiON:
In the contact force plot, we see sudden peaks in the magnitude in certain intervals of time. This occurs as the driver gear shows a nonn continous motion and it shows stopped movements in certain intervals of time. The peaks occur only when the driver gear pushes the driven gear and represents the motion of the driven gear during its entire simulation.
In the angular displacement plot of the driven gear, we see the that its revolves and repeats its motion. We can also notice that it happens so with small amount of "steps". This tells that the driven gear shows a rotastionsal motion with continous and repetitive intervals in between.
By comparing the plots with and without precise contact, we get to observe that precise contact option results in a much accurate plots. Here, the computed contact is analytically correct, but the computation can take longer than an approximate solution.