Internal Geneva Mechanism

Aim:

• To Create 3D models for driver and driven wheels from the given layout.
• To Perform motion analysis by rotating the driver wheel at 10rpm.
• To plot graph for

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

• To Compare the contact forces with and without "Precise contact"

Introduction:

A Geneva Mechanism is a type of gear mechanism where the rotation from one wheel is used to rotate the driven wheel part into segregated rotation or intermittent rotation. In general, the driving wheel has a pin located near to its periphery that rotates and translates along the slots of the driven wheel. The driven wheel has slot in the form of a cross-shaped. The basic idea behind working of this mechanism is that once the pin from the driving wheel enters into the narrow region slot, the driving wheel will rotate the driven wheel. Whereas, once the pin comes out of the slot the driving wheel will rotate but the driven wheel won’t. Hence, the driven wheel is rotating at specific interval. Twoa types of Geneva Mechanism are being used: External and Internal.

Basic Understanding of Motion Study:

In SolidWorks, after creating individual part models and then assembling the same into a final design, a motion study is made to understand the behavior of that particular design. To perform a motion study following steps are made:

1. Go to “SolidWorks Add-ins” on the top and then go to “SolidWorks motion”. After clicking, go to bottom and click on motion study.
2. Change animation setting to study motion.
3. Make sure temporal axes of the components are made visible.
4. Select “Motor” and place wherever is needed. Go to motor setting to adjust RPM, type of motor and time delay etc.
5. Precision can also be adjusted by clicking onto setting symbol of motion study.
6. On contact type, the contact areas are specified and then material is selected. Also, quantity such as force, displacement and other parameters can be calculated and plotted.
7. Select “Calculate” button. After this, go to result and plot icon to plot graphs.

Procedure:

1. Individual components of Geneva mechanism are created.
2. In SolidWorks, the scale is adjusted to MMGS.
3. Driven wheel component was made by using simple commands such as circle, extrude feature, and then a circle for pin was made on one face of the base and then dimensions are defined as per given blueprint. After completing the modelling, it was then saved.
4. For driving wheel component, outer circle was made with specified dimension. It was then extruded by required dimension.
5. One face was selected and then sketched. The slot was sketched as per dimensions specified on the blueprint. Appropriately fillet was used and then saved.
6. For assembly, the components were imported by “Browse” icon. All component imported in the SolidWorks were right-clicked and then “float” was selected.
7. Mating was done with respective to assembly’s right plane and front plane. Mating was done between the components by giving and offset distance as required.
8. Additionally, all the individual parts and the final assembly were save as JPEG format from the “File option”.

Observations:

CAD Models:

Driver Component:

Driven Component:

Final Assembly:

Motor speed adjusted @ 10 RPM (Contact Forces)

Angular Velocity@10 RPM

Motor Speed adjusted @20 RPM (Contact Forces)

Angular Velocity@ 20 RPM

Contact Forces @120fps @20 RPM

Angular Velocity @120fps @20 RPM

Contact Forces @60fps @10RPM

Angular Velocity@10RPM@60fps

Inferences:

• In normal condition without precision, it is observed for contact force @10 RPM had an initial peak at fraction of seconds followed by no peaks. Whereas for 20 RPM setting, peaks were observed between 0.5 to 1 seconds.
• Angular Velocity for both the cases showed initial peak.
• No changes were observed when adjustment changed to 60fps and 120 fps.
• On running the motion study simulation, it was observed that both driver and the driven wheel rotated as a single unit. No, intermittent was observed in the driven wheel.

Possible cause for not getting result as expected:

Clearly, there has been some mistakes in the mating of assembly as the pin pf the driver wheel did not rotated at intended path.