MBD of Internal Geneva Mechanism
Objective
To create a 3d model of internal Geneva mechanism and perform analysis by rotating it at 10 rpm,20rpm with 60 and 120 fps and obtain plots of Contact Forces, Angular displacement and Angular velocity also compare the plots of contact forces with precision on and precision off.
Let’s start right from the basics
What is a Mechanism?
Mechanism is a process through which a device that consist of moving components transforms input forces and movement into a desired set of output forces and movement.
What is a Geneva drive?
The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation into fragmentary motion
What is an Internal Geneva mechanism?
An internal Geneva drive is a variant of the Geneva mechanism. The prime difference between an internal Geneva mechanism and the external Geneva mechanism is the angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel. In an external Geneva drive the angle of rotation is always smaller than 180° and always greater than 180° in an internal one so the switch time is therefore greater than the time the driven wheel stands still.
Parts
Driver Gear:
Driver gear is one which is connected to the power source or the gear where the motion is applied and this gear often has the 1st contact with motion.
Driven Gear:
Driven Gear is one which is meshed with the driver gear. This rotates as an effect of the motion created by the power source in the driver gear.
Working procedure and application.
The driver wheel is usually equipped with a pin that stretches into a slot located in the driven wheel that advances it by one step at a time. Based on the number of slots, speed of driver wheel the position is calculated.
Applications include Mechanical watches, Tool changer in plotters and CNC Machines, Currency Note counting machine.
Methodology
- First create the 3d parts with the specifications given.
- Make a sketch on driven gear add a fillet of 160 deg. This is for mating the driver pin along the driven gear.
- Mate the gears using coincidence and distance mates.
- Add solid contacts and apply motion with the required rpm.
Mates,Motor and Solidcontacts
Mates
Motor
Solid contacts
Motion study and Plots
Motor with 10 rpm
10rpm 60fps without precise contact
Contact forces
19062 N
Angular displacement
Angular Velocity
10rpm 60fps with precise contact
Contact forces
15768 N
Angular Displacement
Angular Velocity
Motor with 20 rpm
20rpm 120fps without precise contact
Contact forces
45335N
Angular Displacement
Angular Velocity
20rpm 120fps with precise contact
Contact forces
42467N
Angular Displacement
Angular Velocity
Comparsion of contact forces with and without precise contacts
With 10rpm and 60 fps
With 20rpm and 120 fps
Results
- As clearly seen in the above graphs when the analysis is run without precise contact the contact forces are higher. Higher the rpm higher are the contact forces.
- With respect to angular displacement there is a slight jerk when the pin enters the slot which can be clearly seen in the graph
- Solidworks uses precise contact to give the exact results.
Conclusion
In the end the required graphs are plotted and the necessary observations are made.
Motion Study animation