Internal Geneva Mechanism using SOLIDWORKS
Aim:
To create the 3D model of the internal Geneva mechanism and run motion analysis.
Theory:
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.
- Internal Geneva Mechanism: An internal Geneva drive is a variant on the design. The axis of the drive wheel of the internal drive can have a bearing only on one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always smaller than 180° in an external Geneva drive and always greater than 180° in an internal one, where the switch time is, therefore, greater than the time the driven wheel stands still.
Objectives:
- Create 3D models for driver and driven wheels.
- Perform motion analysis by rotating the driver wheel at 10rpm.
- Obtain the following plots
- Contact force (between driving and the driven wheel) as a function of time.
- Angular Displacement of the driven wheel.
- Compare the contact forces with and without "Precise contact"
- Show image for precise contact selection
- Export the results that you get to Excel and make the plots over excel.
- Use 60 Frames per second for 10 rpm and then 120 Frames per second for 20 Rpm
- Once you have completed the previous study, change the rpm to 20
- Make a plot of the driver wheel's angular velocity and discuss the results.
3D models for driver and driven:
- Geneve Driven:
- Geneva Driver:
- Assembly:
Motion Study:
Motion studies are graphical simulations of motion for assembly models. You can incorporate visual properties such as lighting and camera perspective into a motion study.
Motion studies do not change an assembly model or its properties. They simulate and animate the motion you prescribe for a model.
- Motion study of assembly:
- 10 RPM constant speed and motor contacted to the geneva driver and solid contact is selected between the geneva driver and geneva driven and motion study run for 20sec. For this setup objective plot are as follows.
- The contact force between driven wheel and driver wheel.
- Excel plot
- Angular Displacement of the driven wheel
- Excel plot
- Contact force with Precise Contact (60 frame/sec and 10 rpm)
- Excel plot
- Contact force without Precise Contact (60 frame/sec and 10 rpm)
- Excel Plot
2. 20 rpm and 120 frame/sec are setup for motion study now
- Contact force without Precise Contact (120 frame/sec and 20 rpm)
- Excel plot
- Contact force with Precise Contact (120 frame/sec and 20 rpm)
- Excel Plot
- Angular velocity of driver wheel(20rpm )
- Excel Plot
- Precise settings:
Conclusion:
As we can see in why comparing contact plots at both 10rpm and 20rpm contact force is independent of angular velocity and precise contact.
Angular velocity varies linearly while both wheels in contact due to contact motion get transferred between wheels hence friction also takes place because the material of wheels is taken as steel(dry) so surface roughness caused friction.
The angular displacement of the driven wheel varies rapidly as pin comes in contact with the driven wheel slot.
YouTube link: