Motion Analysis of Internal Geneva Mechanism

Aim: To Perform Motion Analysis Of Internal Geneva Mechanism

Objective:

1. To create 3D model of driver and driven wheel
2. To assemble the driver and driven wheel with proper constraint
3. To perform motion study
4. To do analysis of result

Theoretical background:

• Multi-Body Dyanamics:

A multibody dynamic (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 mechanism systems move under the influence of forces, also known as forward dynamics. A study of the inverse problem, i.e. what forces are necessary to make the mechanical system move in a specific manner is known as inverse dynamics.

Motion analysis is important because product design frequently requires an understanding of how multiple moving parts interact with each other and their environment. From automobiles and aircraft to washing machines and assembly lines - moving parts generate loads that are often difficult to predict. Complex mechanical assemblies present design challenges that require a dynamic system-level analysis to be met.

• 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 two types of Geneva mechanism:

1] External Geneva Mechanism:

2] 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.

Applications:

1. It is use in Movie projectors and Movie Camera.
2. It is use in Mechanical watches.
3. It is also used in plotters, automated sampling devices.
4. It is also Used in banknote counting machines.

Parameter:

1. Contact force:

A contact force is any force that requires contact to occur. Contact forces are ubiquitous and are responsible for most visible interactions between macroscopic collections of matter. Moving a couch across a floor, pushing a car up a hill, kicking a ball or pushing a desk across a room are some of the everyday examples where contact forces are at work.

2. Angular displacement:

Angular displacement is defined as “the angle in radians (degrees, revolutions) through which a point or line has been rotated in a specified sense about a specified axis”. It is the angle of the movement of a body in a circular path.

3. Angular velocity:

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.

3-D Model:

1] Driver of internal Geneva mechanism:

https://drive.google.com/file/d/1FaF3jpH_-03sj-IjcLS234QeNw4MfOM_/view?usp=sharing

2] Driven wheel of Internal Geneva Mechanism:

https://drive.google.com/file/d/1FaF3jpH_-03sj-IjcLS234QeNw4MfOM_/view?usp=sharing

3] Assembly of Internal Geneva Mechanism:

https://drive.google.com/file/d/1xpE8DJILs15ltzEI5FqhrY76Rb7FIMQd/view?usp=sharing

Procedure Followed:

1] 3-D model is made with the help of given drawing.

2] Parts are assembled by giving proper constraint with plane and parts.

3] with the help of Motion Analysis Add-on , we have perform Motion study.

4] In motion study we have given 10 rpm and 20 rpm as input to driver wheel.

5] we have performed motion study for 60 and 120 frame per second.

6] we have extracted useful data from Motion study like contact force, angular displacement, angular velocity.

Problem Encountered:

while doing assembly give the mates with respect to parts or planes but not with respect to sketches it will create problem while doing motion study.

plots :

1] Contact force with precise contact for 10 rpm :

2] Contact force without precise contact for 10 rpm :

3] Angular velocity of Driven wheel for 10 rpm:

4] Angular displacement of Driven wheel for 10 rpm :

5] Angular velocity of Driven wheel for 20 rpm :

Conclusion:

1. If we increase rpm of driven wheel then contact force also increases.
2. Angular velocity of driven wheel first increases then decreases and remain constant for some time and then large increase in angular velocity and this cycle repeats and each time there is increase in angular velocity of driven wheel.
3. With the precise contact we get accurate results.

Result : We performed the motion study of Internal Geneva mechanism successfully.