Internal Geneva Mechanism
Aim:To,
1. Create 3D models for driver and driven wheels.
2. Perform motion analysis by rotating the driver wheel at 10rpm.
3. Obtain the following plots
a.Contact force (between driving and the driven wheel) as a function of time.
b. Angular Displacement of the driven wheel.
4. 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 there
Introduction:
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.
The Geneva drive is also called a "Maltese cross mechanism" due to the visual resemblance when the rotating wheel has four spokes, since they can be made small, and are able to withstand substantial mechanical stress. These mechanisms are frequently used in mechanical watches.
Application of Geneva Wheel Mechanism:
Geneva drive is 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.
Geneva wheels having the form of the driven wheel were also used in mechanical watches, but not in a drive, rather to limit the tension of the spring, such that it would operate only in the range where its elastic force is nearly linear
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. (source:Wiki)
CLASSIFICATION OF GENEVA MECHANISM:
EXTERNAL GENEVA MECHANISM
In this type of mechanism, the Geneva cross is connected with cam drive
externally which is the most popular and can withstand higher mechanical
stresses. The driver grooves lock the driven wheel pins during dwell.
During movement, the driver pin mates with the driven-wheel slot.
INTERNAL GENEVA MECHANISM
In this type of mechanism, the Geneva cross and cam drive are connected
internally in the closed box. The driver and driven wheel rotate in same
direction. The duration of dwell is more than 180º of driver rotation
SPHERICAL GENEVA MECHANISM
In this type of mechanism, the Geneva cross is in spherical shape and cam
drive are connected in externally, which is extremely rare . The driver and
driven wheel are on perpendicular shafts. The duration of dwell is exactly
180° of driver rotation.
Models of Parts and assembly:
https://drive.google.com/drive/folders/17fHteErDCSdP28eUjRr9zZF4dAnQfgT0?usp=sharing
Procedure:
1) 3D models of Driven and Driving wheel is developedfrom given drawings.
2) The parts are assembled based on the dimensions determined using the drawings.
3) constraines to rotation about the axes.
- A motor is to be defined at the axis of driving wheel at required rpm.
- Contact has to be established between the wheels and the simulation is ready to be run.
- After running the simulation required plots are to be extracted.
Link for the motin study animation:
For 10 RPM Non Precise Contacts:
Plots of 10 RPM Non Precise Contacts:
a) 10 RPM Angular Displacement of Non Precise Contact For Driver Wheel:
b) 10 RPM Angular Displacement of Non Precise Contact For Driven Wheel:
c) 10 RPM Force Contact Driver and Driven Wheel:
d) 10 RPM Angular Velocity of Non Precise Contact For Driver Wheel:
e) 10 RPM Angular Velocity of Non Precise Contact For Driven Wheel:
For 10 RPM Precise Contacts:
Plots of 10 RPM Precise Contacts:
a) 10 RPM Angular Displacement of Precise Contact For Driver Wheel:
b) 10 RPM Angular Displacement of Precise Contact For Driven Wheel:
c) 10 RPM Force Contact Driver and Driven Wheel:
d) 10 RPM Angular Velocity of Precise Contact For Driver Wheel:
e) 10 RPM Angular Velocity of Precise Contact For Driven Wheel:
Comparison of Precise and Non Precise Values:
Comparison of Precise Angular Displacement and Non Precise Angular Displacement Values of Driver Wheel for 10 RPM:
Comparison of Precise Angular Displacement and Non Precise Angular Displacement Values of Driven Wheel for 10 RPM:
Comparison of Precise Angular Velocity and Non Precise Angular Velocity of Driver Wheel for 10 RPM:
Comparison of Precise Angular Velocity and Non Precise Angular Velocity of Driven Wheel for 10 RPM::
Comparison of Precise Reaction Force and Non Precise Reaction Force for 10 RPM:
Comparison of Precise Angular Displacement & Non Precise Angular Displacement Values of Driver Wheel for 20RPM:
Comparison of Precise Angular Displacement & Non Precise Angular Displacement Values of Driven Wheel for 20RPM:
Comparison of Precise Angular Velocity and Non Precise Angular Velocity of Driver Wheel for 20 RPM:
Comparison of Precise Angular Velocity and Non Precise Angular Velocity of Driven Wheel for 20 RPM:
Comparison of Precise Reaction Force and Non Precise Reaction Force for 20 RPM:
Conclusion drawn from the obtained plots:
1.In order to increase the contact force we need to increase the speed of rotation.
2.Higher the Frames we capture better and accurate are the results we obtain.
3.After attaininig a certain value the angular displacement remains constant even with increase in speed