Internal Geneva Mechanism
Internal Geneva Mechanism
Aim: - Create 3D models for driver and driven wheels of Internal Geneva Mechanism and obtain the following result.
- Creating Assembly of Internal Geneva Mechanism
- Internal Geneva Mechanism motion analysis
- 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"
- Make a plot of the driver wheel's angular velocity and discuss the results
Abstract
In this Project, creating a 3D part of Driver and Driven mechanism and its assembly, to setting the motion analysis for an Internal Geneva Mechanism at 10rpm and 20rpm with 60 frames and 120 frames respectively. Then obtaining the plots of Contact force (between driving and the driven wheel) as a function of time, Angular Displacement of the driven wheel, and plot of the driver wheel's angular velocity.
Multibody Dynamics (MBD)
MBD system is one that consists of solid bodies, or links, that are connected to each other by joints that restrict their relative motion. The study of MBD is the analysis of how mechanical systems move under the influence of forces, also known as forwarding dynamics.
Motion study
Motion study is a business efficiency technique. It is the part of method study and is one of the oldest branches of work-study. Every work consists of some motion. These motions are productively used in workplace to organize a better method of performing a job.
SOLIDWORKS Motion studies are graphical simulations of motion for assembly models. Motion simulation assumes all parts to be rigid during the simulation, meaning that during contacts, no deformations will take place.
Internal 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.
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.
In the most common arrangement of the Geneva drive, the client wheel has four slots and thus advances the drive by one step at a time (each step being 90 degrees) for each full rotation of the master wheel. If the steered wheel has n slots, it advances by 360°/n per full rotation of the propeller wheel. Because the mechanism needs to be well lubricated, it is often enclosed in an oil capsule.
Angular Displacement
The angular displacement is defined as the angle through which an object moves on a circular path. It is the angle, in radians, between the initial and final positions.
(θfinal - θinitial) = angular displacement
θ = s/r
θ = angular displacement through which movement has occurred
s = distance travelled
r = radius of the circle
Angular Velocity
In physics, angular velocity refers to how fast an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital angular velocity refers to how fast a point object revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. Spin angular velocity is independent of the choice of origin, in contrast to orbital angular velocity which depends on the choice of origin.
Cad Geometry
Geneva Driver Wheel
Driving wheel is the wheel that transmits force or torque into the driven wheel and causing the rotation. A motor is connected to driver wheel and motor delivers enough torque to the driving wheel to rotate the driven wheel.
Geneva Driven Wheel
Driven wheel is the wheel from which output rotation is extracted. The driven wheel is rotated by driving wheel.
Geneva Mechanism Model Assembly
PROCEDURE TO CREATE ASSEMBLY
- Creating 3D model of driver and driven wheel.
- Assembling the 3D model of driver and driven wheel by use the following constraints.
- Using Multibody Dynamics to find the Motion Analysis driver and driven wheel.
- In driver wheel motor is fixed to rotate at the constant speed of 10rpm and then increased to 20rpm and also change frame 60f and 120f.
- Fixing the contact type as Solid bodies of driver and driven wheel and assigning material like a steel.
Following observation of result: -
- Comparing the Contact Forces with and without Precise contact and Using 60 Frames per second for 10 rpm and then 120 Frames per second for 20 Rpm
- Angular Displacement of the driver and driven wheel.
Contact force at 10rpm at 60f without Precise contact
Contact force at 10rpm at 60f with Precise contact
Contact force at 10rpm at 120 frame Precise contact
From the comparison of the cases we can see that the contact force with "precise contact" option on is quiet high than the forces without precise contact. Which can see from the graph that is made in excel file which is attached to this challenge.
Angular Displacement driven wheel at 10 RPM
Angular Displacement driven wheel at 20 RPM
The angular velocity of the driver at 10RPM
The angular velocity of the driver at 20RPM
Conclusion:
As observed from the above graphs of the contact forces with and without precise contact, we can conclude that with precise contact the mechanism is smoother with minimal forces, and without precise contact has the greater contact forces as seen in the graphs the following information given in below,
- Precise Contact gives has higher contact force and accurate results comparing as compare to non-precise contact force.
- Increase the motor rpm of the driver wheel contact force also get increased.
- When the parts come closer and mate each other for fulfilment of mechanism the suddenly rise in contact force.
- Improve design of driven part to avoid backlash.
- Improve material strength to avoid pitting of both part (for same type of result may occur in manufactured product).
VIDEO LINK: -
https://www.youtube.com/watch?v=rbtV0rBE0vY