Internal Geneva Mechanism
AIM - TO SIMULATE AND ANALYSE THE WORKING OF AN INTERNAL GENEVA MECHANISM
INTRODUCTION AND THEORY - A Geneva Mechanism also known as the Geneva Actuator is a mechanism that converts the uniform rotary motion into an intermittent rotary motion. Basically the Geneva mechanism consist of two main component, the first one is the prime mover or the driving wheel and the second one is the geneva wheel or the driven wheel .The Geneva Wheel is basically a slotted wheel.
WORKING PRINCIPLE - As it is very clear from the image, when the driving wheel or the prime mover is given some angular displacement, the extruded material on the top of the prime mover(the knob) which is fitted in the slot of the driven wheel tends to push the driven wheel. Since the driven wheel is pivoted about its centre thus it undergoes a circular motion. Now when the knob comes out of the slot of the driven wheel the driven wheel stops for a while, as soon as the knob enters the second slot of the driven wheel the whole mechanism is repeated once again. In this way we get the continuous intermittent rotary motion one of the other and the process continuous until the prime mover stops rotating. There are lots of industial applications of geneva mechanism.
SETUP - At first we have to make the cad model of the driven and the driving wheel of the mechansim for that skill lync has already provided the drawing view so at first we will model the driving wheel
DRIVING WHEEL CAD MODEL
Step 1 - Open the Solidworks software and choose unit system as MMGS (Millimeter, Gram, Seconds).
Step 2 - Go to feature tree and choose front plane and choose sketch, now u will notice that the command bar shows all the sketch tools (eg- line, rectangle, circle, polygon, etc.).
Step 3 - Now choose the circle command and choose the origin as the center of the the circle and draw a circle by dragging the mouse.
Step 4 - Go to top left corner on the sketch tool bars and choose smart dimensions. Assign 420 mm diameter to the circle.
Step 5 - Exit the sketch and go to features and choose extruded boss/base and assign a thickness of 20mm in one direction only. After all these 5 steps your model should look like this.
Step 6 - Now choose any one of the circular faces and right click and choose sketch.
Step 7 - Go to sketch tool bar and choose constrcution line and draw a vertical line starting from the the centre of thr circle with length of 160 mm.
Step 8 - Now choose circle command and draw a circle of diameter 40 mm having centre at the end of the construction line.
Step 9 - Exit the sketch, go to features and choose extruded boss/ base and extrude upto 40 mm in one direction and don't forget to check the merge results option.
Step10- Save the part file and name it as DRIVING WHEEL. This is what the cad model of the driving wheel looks like.
DRIVEN WHEEL CAD MODEL
Step 1 - Now create a new part file
Step 2 - Similar to that what we have did earlier, we will choose the unit system as MMGS.
Step 3 - Now choose front plane and choose sketch. Simply draw the sketch of the driven wheel that has been provided by the skill lync. Make sure that the sketch is fully defined (i.e, it is black in color). Exit the sketch.
Step 4 - Now go to features choose extruded boss/base and extrude upto 40 mm.
Step 5 - Save the part file as DRIVEN WHEEL. This is what the part file looks like.
ASSEMBLY OF GENEVA MECHANISM
Step 1 - Go to new file and select assembly.
Step 2 - Since it is not very clear how to assemble the two mating components so what we will do is we will first draw the sketch on the top plane and then constrain both the components with respect to that particular sketch. This is what the sketch looks like.
Step 3 - Now exit the sketch and call the part in the assembly domain. For that, go to assembly and choose insert component and browse for the part files and drop into the workspace.
Step 4 - Now go to assembly choose mate and then choose the base of the driving wheel and the top plane and apply coincident constrain.
Step 5 - Now choose one of the circular edges of the driving wheel and the small circle of the sketch that we have drawn before and apply concentric mate. Uncheck the lock rotation option.
Step 6 - Select the outer circular edge of the driven wheel and the bigger circle in the sketch and apply concentric mate. Uncheck the lock rotation option.
Step 7 - Again choose the lower face of the driven wheel and the upper face the driving wheel and apply coincident mate.
Step 8 - Now align the knob of the driving wheel into the slot of the driven wheel. The assembly is complete.
MOTION ANALYSIS
Step 1 - Go to command ribbon and choose SOLIDWORKS Add Ins and select SOLIWORKS Motion.
Step 2 - You will see that the motion analysis control manager will be opened, if not then go to right side corner and click on the arrow facing upward.
Step 3 - Now go to left side hit the dropdown and choose Motion Analysis, see the image below for reference.
Step 4 - Go to Motion Study Properties, drop down to Motion Analysis, and fill the various parameters such as
Frames per second = 60
Animate during simulation
Use precise contact
Accuracy high
Step 5 - Now go to contact, choose solid bodies and select both the components and apply contact between them.
Step 6 - Now choose motor from the motion analysis tool bar and fill various parameters
Motor location = choose axis if the driving wheel or u can also select the circular edge of the driving wheel
Motor direction = ACW
constant speed at 10 RPM.
Step 7 - Go to result and plot and choose, forces>> contact forces>> magnitude, and then select both the component and then drop down to plot results and choose time.
Step 8 - Choose calculate and then run the motion study.
Step 9 - Similarly perform the motion study at 20 RPM and 120fps.
OBSERVATIONS AND RESULTS
From the plot 1 at 10 RPM and 60fps it was found that at regular intervals there was increase in the contact forces
and this increase in contact forces was more abrupt when the motion was analysed at 20 RPM and 120fps (i.e, plot 2)
the following results were obtained.
SIMULATION OF THE MECHANISM