Important Short Questions and Answers: Basics of Mechanisms

1.  Define Kinematic link.

It is a resistive body which go to make a part of a machine having relative motion between them.

2.  Define Kinematic pair.

When two links are in contact with each other it is known as a pair. If the pair makes

constrain motion it is known as kinematic pair.

3.  Define Kinematic chain.

When a number of links connected in space make relative motion of any point on a link with respect to any other point on the other link follow a definite law it is known as kinematic chain.

4.  Write the Grubler’s criterion for determining the degrees of freedom of a mechanism having plane motion.

n=3(l-1)-2j h-Higher pair joint l-Number of links

j-Lower pair joint

5.  Define degree of freedom, what is meant by mobility.

The mobility of a mechanism is defined as the number of input parameters which must be independently controlled in order to bring the device into a particular position.

6.  Write the Kutzbach’s relation.

Kutzbach’s criterion for determining the number of degrees of freedom or movability

(n) of a plane mechanism is n=3(l-1)-2j-h n-Degree of freedom. l-Number of

links. h-Higher pair joint j-Lower pair joint.

7.  Define Grashoff’s law and state its significance.

It states that in a planar four bar mechanism, the sum of shortest link length and longest link length is not greater than the sum of remaining two links length, if there is to be continuous relative motion between two members.

Significance:

Grashoff’s law specifies the order in which the links are connected in a kinematic chain. Grashoff’s law specifies which link of the four-bar chain is fixed.(s+1)=(p+q) should be satisfied, if not, no link will make a complete revolution relative to another. s= length of the shorter length

l= length of the longest link

p & q are the lengths of the other two links.

8.  Define Inversion of mechanism.

The method of obtaining different mechanism by fixing different links in a kinematic chain

is known as inversion of mechanism.

9.  What is meant by Mechanical advantage of mechanism?

It is defined as the ratio of output torque to the input torque also defined as the ratio of

load to effort.

M.A ideal = TB / TA TB =driven (resisting torque) TA =driving torque

10. Define Transmission angle.

The acute angle between follower and coupler is known as transmission angle.

11. Define Toggle position.

If the driver and coupler lie in the same straight line at this point mechanical advantage is maximum. Under this condition the mechanism is known as toggle position.

12.            List out few types of rocking mechanism.

Pendulum motion is called rocking mechanism.

1. Quick return motion mechanism.

2. Crank and rocker mechanism.

3. Cam and follower mechanism.

13.            Define pantograph.

It is device which is used to reproduce a displacement exactly in a enlarged scale. It is used in drawing offices, for duplicating the drawing maps, plans, etc. It works on the principle of 4 bar chain mechanism.

Eg. Oscillating-Oscillating converter mechanism

14.            Name the application of crank and slotted lever quick return motion mechanism.

1. Shaping machines.

2. Slotting mechanism.

3. Rotary internal combustion engine.

15.            Define structure.

It is an assemblage of a number of resistant bodies having no relative motion between

them and meant for carrying loads having straining action.

16. What is simple mechanism?

A mechanism with four links is known as simple mechanism.

17. Define mechanism.

When one of the links of a kinematic chain is fixed, the chain is known as a mechanism.

18. Define equivalent mechanism; and spatial mechanism.

Equivalent mechanism: The mechanism, that obtained has the same number of the degree

of freedom, as the original mechanism called equivalent mechanism.

Spatial mechanism: Spatial mechanism have special geometric characteristics in that all revolute axes are parallel and perpendicular to the plane of motion and all prism axes lie in the plane of motion.

19. Define double slider crank chain mechanism.

A kinematic chain which consists of two turning pair and two sliding pair is known as double slider crank mechanism.

20. Define single slider crank chain mechanism.

A single slider crank chain is a modification of the basic four bar chain. It consists of one sliding pair and three turning pair.

Applications:

Rotary or Gnome engines       Crank and slotted lever mechanism

Oscillating cylinder engine      Ball engine

Hand pump

21. Define Sliding pair.

In a sliding pair minimum number of degree of freedom is only one.

22. Define Turning pair.

In a turning pair also degree of freedom is one. When two links are connected such that one link revolves around another link it forms a turning pair.

23. Define cylindrical pair.

In a cylindrical pair degree of freedom is two. If one link turns and slides along another

link it forms a cylindrical pair.

24. Define Rolling pair.

In a rolling pair degree of freedom is two. The object moves both linearly and angularly.

25. Define Spherical pair.

In a spherical pair degree of freedom is three. It can both move left and right,up and down, and rotate along the same point.

26. Define Lower pair.

If contact between two links is surface contact also having degree of freedom one, then the pair is known as lower pair. Example: Sliding pair.

27. Define higher pair.

If contact between two links is either point contact or line contact then the pair is known as higher pair.

Example: Point contact-Rolling pair. Line contact-Cylindrical pair.