Internal Geneva Mechanism - SolidWorks

Internal Geneva Mechanism - SolidWorks

1. AIM:

To create a 3d model and study the motion and parameter graphs of Internal Geneva Mechanism.

2. INTRODUCTION:

- Motion studies are graphical simulations of motion for assembly models.

- Motion studies do not change an assembly model or its properties. They simulate and animate the motion you prescribe for a model.

- Motion study has 3 components out of which 2 are enabled by default. They are -

1. Animation - Basic animation and also can add motors and define the assembly positions at different points in time.
2. Basic Motion - Animation but with mass consideration. Effect of gravity, spring, dampers can also be turned on.
3. Motion Analysis - Proper analysis using all physics options including force, pressures. It includes powerful solvers which calculate answers accurately and also provide plot options.

- Geneva Mechanism:

• The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion.

• The rotating drive wheel is usually equipped with a pin that reaches into a slot located in the other wheel (driven wheel) that advances it by one step at a time. The drive wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps.

• There are 2 types of Geneva mechanisms : Internal and External.

External Geneva Mechanism Internal Geneva Mechanism

Where Geneva Mechanisms are used?

- In film movie projectors and movie cameras, where the film is pulled through an exposure gate with periodic starts and stops. The film advances frame by frame, each frame standing still in front of the lens for a portion of the frame cycle (typically at a rate of 24 cycles per second), and rapidly accelerating, advancing, and decelerating during the rest of the cycle.

- In the pen change mechanism in plotters, automated sampling devices, banknote counting machines, and many forms of indexable equipment used in manufacturing (such as the tool changers in CNC machines; the turrets of turret lathes, screw machines, and turret drills etc.)

3. OBECTIVES:

- Create 3D models for driver and driven wheels.

- Perform motion analysis by rotating the driver wheel at 10rpm and 20rpm

- Obtain the plots of Contact force (with and without precision), Anglular displacement of driven wheel, Angular velocity of driver wheel.

4. FLOW OF PROJECT:

1. Create 3D CAD models on the basis of 2D drawings provided.
2. Assemble the CAD models using proper constraints.
3. Use the assembly in motion analysis and set-up the motion parameters like rpm, material etc.
4. Run the calculation.
5. Save the animation,
6. Plot graphs and export to Excel.

5. MOTION STUDY SETUP:

1. Initially, the 2D drawings were used as a reference to make 3D CAD models of the geneva mechanism parts namely, driving wheel and driven wheel.
2. Those parts were imported to a new assembly and assembly was made. Both the parts were constrained to a certain degree so as to allow required degree of freedom for circular motion.
3. A new motion study having type as Motion Analysis was selected.
4. Driving wheel was given a rotation of 10RPM and contact between driving and driven wheel was established assuming steel material(dry) for both of them.
5. In motion settings, Frames per Second was set to 60.
6. Finally, the solver of SolidWorks calculated the study and simulation video and results were out.
7. The same process was repeated for 20RPM and 120FPS. For plotting graph, specifically for contact forces, in Motion study settings under motion analysis, the precise contact option was ticked accordingly.

6. OBSERVATION, RESULTS AND CONCLUSION:

60 FPS validation for 10RPM

120 FPS validation for 20RPM

Plots:

1. Contact Forces with and without precision and 10 and 20RPM

From this graph, we can point out a few things -

• For 10 RPM, Contact force without precision between driving and driven wheel is higher than that with precision contact.
• For 20 RPM, Contact force withour precision between driving and driven wheel is lower than that with precision contact.
• From force values and RPM, we can say that as RPM increases, the Contact force also increases.

2. Angular Displacement of Driven wheel:

From this graph, we can point out a few things -

• The flat lines in both the graphs indicate that the driver wheel stub is not in engagement with driven wheel.
• As and when the driver wheel mates with driven wheel, the angular displacement occurs and stops after it reaches 90 degree.
• Thus we can say that if in 1 rotation, angular displacement is 90 degrees, then we need 4 rotations to completely rotate the driven wheel i.e. by 360
• The small spikes in middle shows the engagement interaction i.e. collision while engaging.

3. Angular Velocities:

They are constant over time, as set in SolidWorks.

Thus, above conclusions can be drawn from plots obtained.

To view the animation of Internal Geneva Mechanism at 10RPM and 60FPS, click here

To view the animation of Internal Geneva Mechanism at 20RPM and 120FPS, click here

7. REFERENCES:

- https://en.wikipedia.org/wiki/Geneva_drive

- http://help.solidworks.com/2020/English/SolidWorks/motionstudies/c_introduction_to_motion_studies.htm