Internal Geneva Mechanism
AIM
The aim of this challenge to model the parts of the internal geneva mechanism ie; (the driver part and the driven part) and to assemble them in the right way to do the motion analysis and fetch the required results in form of plots and also as simulations.
INTRODUCTION
Firstly the models of both the parts are created according to the sketch provided and then they are made to be assembled in the correct way so that they are only able to rotate and not translate, and followed by the motion analysis study and from where the results are being collected, the results vary according to the challenge.
MODELING PROCESS:
The first part(Driven wheel);
The front plane is chosen for the modeling of this part where firstly the outer circle is drawn and the inner circle of lesser dimension is also drawn and a smaller circle is drawn and a cross of construction line is provided such a way that it is at the origin and two lines are drawn from the construction line away from them at given dimension and these lines are patterned circularly and the unwanted lines are trimmed off, then the fillet is provided as shown in the sketch. Now the sketch is extruded to a distance specified in the diagram where only the needed contour is selected.
https://drive.google.com/file/d/1Zxo8FBoxJfhJ2lSOwehvmlQfuvVer9q1/view?usp=sharing
The above mentioned is the link for the Driven part file.
The second part(Driver wheel);
The front plane is selected for sketching and the outer circle is drawn and the cross is created with the construction line and a very small circle is drawn inside the larger circle of given dimension and the center distance is provided with respect to the origin and the make vertical constrain is given to the origin of the circle. Now the extrusion part comes where we have to extrude two times firstly the full part extrusion of the large circle and secondly the smaller extrusion of other circles with given dimensions.
https://drive.google.com/open?id=1RmwY7Htl_YZ2Ag5A5fEm2KaFOBI2ggB1
The above mentioned is the link for the driver part file.
ASSEMBLY PROCESS:
Firstly the driven wheel is placed in the assembly screen and made it float, and the driver wheel is placed which is automatically made float. Then the coincident mates of the driver and the driven with respect to the planes of the assembly are given in the mate command by making the temporary axis visible and so the mates are added, now the parts can only rotate and cannot move, now a distance mate is given by trail and error way so that it doesn't affect the motion study ie between the plane of assembly and the face of the driven wheel, then to make the driver wheel in position another distance mate is provided by calculating center axis distance, and now all the mates are provided accordingly and the assembly is ready for motion analysis.
https://drive.google.com/open?id=1ZyG4IreQha3_f63sr-9K8uLx5FmNndtt
The above mentioned is the link for the assembly part file.
MOTION STUDY SETUP:
The term motion study is referred to as the study of the behavioral aspects of any mechanism or machinery with respect to the inputs given the inputs can vary with respect to project or part, and also the analysis of the output is done at the same time it can be got as a plot from the entities we provide or from the outputs generated.
Here we are going to perform this motion study on the internal geneva mechanism for which firstly the motion addon is selected from Solidworks add-in's and the in the bottom bar we go to new motion study and select the motion analysis from the dropdown, then we proceed on, now we'll have to provide the rotational motion by giving motor with required RPM and also the needed axis in our case its driver wheel axis, then we'll need to set up contact that id between the drive wheel and the driven wheel. That's all the setup is completed, now clicking on the calculate button will show us the motion simulation.
And moving on for the results we click on the plot graph icon and select the required one from drop-down ie displacement or force etc, and select the part for which we require a plot. That's how a result is generated and this result is exported to the spreadsheet for further researches and works.
PLOTS:
The below mentioned are the plots from the results of motion study;
- Contact force (between driving and the driven wheel)
The above plot is obtained from the motion study of internal geneva mechanism where after the simulation of the working the results are made to be a plot with given specifications ie
-Forces
-contact force
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Reaction force in Newton), X-axis(Time in sec)
OBSERVATION AND RESULT
The above graph is the one which is obtained from exporting the plot from Solidworks to the spreadsheet, according to the graph at the beginning there's a contact between the spindle and the slot in the driven wheel, and the graph goes down since the contact between them becomes stable and rises a little when the spindle comes out of the slot and there's a peak on the graph that is because of the higher contact or the oscillation of contact at the entry point of the slot after which the graph is repeated for the number of revolutions based on the time of motion study.
- Angular Displacement of the driven wheel
The above plot is obtained from the motion study of internal geneva mechanism where after the simulation of the working the results are made to be a plot with given specifications ie
-Displacement/velocity/acceleration
-Angular Displacement
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Angular Displacement in Deg), X-axis(Time in sec)
OBSERVATION AND RESULT
The above graph is the one which is obtained from exporting the plot from Solidworks to the spreadsheet, according to the graph the angular displacement of the driven wheel changes from positive 180 degrees to negative 180 degrees since in the driven wheel one slot is being chosen for the study the motion of that is possibly from 0 degrees to 180 degrees as a form of a semicircle and the same at its negative side. And there's only one positive and one negative for the above graph since it depends on the cycles ie time provided for the analysis.
- Comparison of contact forces with and without "Precise contact"
The above image shows that the precise contact option is checked, it's been highlighted.
The main advantage of this precise contact option is that the computed contact is analytically correct rather than being approximately correct but still this makes the simulation time to increase and also provides graphs with no distortion in its line or plots.
The plots obtained from the motion study results are quite similar to the one without precise contact, but still, we are able to figure out the difference between or even compare those two plots.
OBSERVATION AND RESULT
The difference is, firstly the forces are a bit lower than the non-precise one which may be due to the starting force or so, and then the curve is really smoother than the older one where the spindle is coming out of the slots and also the horizontal line ie the point where there no contact between the driver and the driven is really smooth straight line when compared to the no-precise contact one.
- driver wheel's angular velocity
The above plot is obtained from the motion study of internal geneva mechanism where after the simulation of the working the results are made to be a plot with given specifications ie
-Displacement/velocity/acceleration
-Angular Velocity
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Angular Velocity in Deg), X-axis(Time in sec)
OBSERVATION AND RESULT
The above graph is the one which is obtained from exporting the plot from Solidworks to the spreadsheet, according to the graph the angular Velocity is constant ie 120 degrees per sec which is due to the motor RPM we have given to the driver part 20RPM, and from the graph, we can see that the plot is sinusoidal but within the range or constant at 120degrees per sec which can be due to the distortion from the contact created between the driver and the driven at the critical contact such as starting of the slot and leaving the slot.