Motion Analysis of Internal Geneva Mechanism using SOLIDWORKS

Aim: Perform MBD on Geneva Mechanism in SOLIDWORKS

Objective:

• Create 3D models for driver and driven wheels.
• Perform motion analysis by rotating the driver wheel at 10rpm.
• Obtain the following plots

1. Contact force (between driving and the driven wheel) as a function of time.
2. Angular Displacement of the driven wheel.

• Compare the contact forces with and without "Precise contact"
• Show image for precise contact selection
• Use 60 Frames per second for 10 rpm and then 120 Frames per second for 20 Rpm
• Once we have completed the previous study, change the rpm to 20
• Make a plot of the driver wheel's angular velocity and discuss the results

Procedure:

• Geneva Driving Wheel

First, we select top plane and select sketch option. Then we draw a circular and give it diameter 420mm. Then we again select circle option to draw a circle, move our cursor over centre of the first sketched circle and move the cursor in upward direction when we start to see dotted orange lines. Then we created a circle of diameter 40mm. We give dimension to both the circles using smart dimension option. We select centre of both the circles and giver dimension 160mm.

Then we extruded boss the larger circle by 20 mm, while selecting the contour we need to be carefully select both the circles. Then we extruded boss the smaller circle (to see the sketch we need to right-click on sketch in design tree and press the eye icon), this time we select surface/face/plane option, select the face of larger circle and give value of 40mm to boss. Atlas we right click on the sketch in design tree and press on the eye icon to hide the sketch. After successfully modelling the Geneva driving wheel, we save the file.

• Geneva Driven Wheel

First, we select top plane and sketch then we select circle and draw three circles. We smart dimension them 1120mm diameter, 520mm radius, 120mm radius. Then we select the 520mm radius circle, right click on it and then select for construction option. Then we draw two perpendicular from centre to the circumference of 520mm radius circle, select these two lines and click on offset entity option. We provide 20mm value and check on both sides and caps end and confirm it. Then we select power-trim option and remove required parts of the sketch. We then extruded boss the sketch by 40mm. After that we select filler tool and select edges of inner circle and gave them fillet of 50mm radius. After successfully modelling the Geneva driven wheel, we save the file.

• Assembly

In Solidworks we select new assembly, load both the previous parts. Right click on the first part and select float option. We then perform following mates using mate option,

• Driving wheel top plane to assemble top plane
• Axis of driving wheel to assembly right plane
• Axis of driving wheel to assembly front plane
• Axis of driven wheel to assembly front plane
• Top plane driven wheel to assembly top plane
• Distance between axis of both driving and driven wheels is 226.27417mm

• Motion Analysis

First, we enable SOLIDWORKS Add-Ins by right clicking the ribbon title bar and select SOLIDWORKS Motions. From drop down menu at left hand we select motion analysis. The we add motor to the driving wheel with 10 rpm, establish contact between two wheels and click on calculation to start motion analysis. In preferences we can change the frames per seconds 60 and enable precision contact.

To obtain plots, we select result and plot option and select the desired option to obtain the plots.

For Contact force (between driving and the driven wheel) as a function of time.

Forces -> Contact Forces -> Magnitude -> Select both wheels

Angular Displacement of the driven wheel.

Displacement/Velocity/Acceleration -> Angular Displacement -> Magnitude -> Select driven wheel

Two Different result can be obtained viz. with precision contact and without precision contact.

To enable precision contact, click on gear icon

Then select use precision contact

Result:

Motion Analysis at 10 RPM and 60fps. Link.

Contact force (between driving and the driven wheel) as a function of time. (With Precision Contact)

Contact force (between driving and the driven wheel) as a function of time without precision contact

As we compare plot of contact forces with precision (Reaction Force 1) with contact force without precision (Reaction Force 2) we can observe that there’s a lot of fluctuation in the values of force in without precision case. This is because when precision contact is on the program tries to establish perfect contact between the bodies by slightly changing the value; this gives us a smooth motion between the bodies and thus a plot with less fluctuating value is obtained.

Angular Displacement of the driven wheel.

This plot shows the angular displacement of the driven wheel of the internal Geneva mechanism.

Angular Velocity at 10RPM at 60fps

Angular Velocity at 20RPM at 120fps

As we compare the plots of angular velocity at 10 rpm and 60 fps and angular velocity 20 rpm and 120 fps, we observe that the values of velocity surges significantly in case of 20rpm-120fps while the plot seems fair for angular velocity at 10rpm-60fps. This happens because in case of 20rpm the pin of driven wheel experiences more inertial force compared to 10rpm case, thus due to this increased inertial force the values for angular velocity also increases for 20rpm case.

Errors: The mechanism was not positioned properly. This problem was solved by positioning them properly.

Previously I input random value for distance between two bodies therefore the contact between two bodies was not perfect. After some research I found a formula for distance between two bodies, so I calculated the distance between two bodies according to that formula and solved the issue.

References:

https://www.engineersedge.com/mechanics_machines/geneva_internal_mechanism_14920.htm

Google Drive Link: https://drive.google.com/drive/folders/14X1-wXduQV3TqXFs9xGmOtPSDCzYWZ80?usp=sharing