me 6401 kom 2 marks q & a

2 MARKS Q & A

ME6401 – KINEMATICS OF MACHINERY

N.SITHIVINAYAGAM, AP/MECH

II YEAR ‘A’ BATCH

DEPARTMENT OF MECHANICAL ENGINEERING

MRK INSTITUTE OF TECHNOLOGY

KATTUMNANNARKOIL – 608301

1

ME 6401 – KINEMATICS OF MACHINES

2 MARKS QUESTION AND ANSWERUNIT-I

1. Differentiate between a machine and a structure.(Nov/Dec 2002)

SI. No Machine Structure

1 Relative motion exists between its parts.No relative motion exists between its members.

2 It transforms available energy into useful work.

It does not convert the available energy into work.

3 Links are meant to transmit motion and forces.

Members are meant for carrying loads having straining action.

2. State and sketch any two inversions of a double slider mechanism.

(Nov/Dec 2002)

3. How many inversions are possible from a four-bar kinematic chain? Name them

based on their input-output motions.(Apr/May 2003)

Three in versions are possible from a four-bar kinematic chain. They are:

Crank-rocker mechanism or Rotary – oscillating converter.

Double crank mechanism or Rotary – rotary converter.

Double rocker mechanism or Oscillating – oscillating converter.

2

4. What are the three conditions to obtain a four-bar crank – rocker mechanism?

(APR/MAY 2003)

The linkage should be class I four bar linkage. That is, if the sum of the lengths of

the largest and the shortest links is less than the sum of the lengths of the other two

links, the linkage is known as a class I, four bar linkage.

The shortest link should be made a crank (which can revolve) and any of the

adjacent links is fixed.

The link opposite to the crank i.e., rocker should oscillate.

5. State at least one similarity and one difference between a helical pair and a cylindric

pair. (Nov/Dec 2003)

Similarity : Both are lower pairs.

Difference : Helical pair has a incompletely constrained motion whereas

cylindric pair has completely constrained motion.

6. Define transmission angle of a four- bar mechanism. What are the worst values

of transmission angle? (Nov/Dec 2003)

Definition : The angle between the coupler and the follower in a four-bar

mechanism is called the transmission angle.

Worst value of transmission angle is less than 45◦.

7. State any four types of kinematic pairs according to the types of relative motion

between them. (Nov/Dec 2004)

i) Sliding pair; (ii) Turning pair ;(iii) Rolling pair; and (iv) Screw pair

8. Explain with a neat sketch, the space centrode and body centrode. (Nov/Dec 2004) The locus of the instantaneous centre in space during a definite motion of the body

is called the space centrode.

3

The locus of the instantaneous centre relative to the body itself is called the body

centrode.

The space and body centrodes are illustrated in Fig.l.

9. What is a machine? Give two examples. Also differentiate between a machine and a

structure. (April/May 2005)

A machine is a device which receives energy and transforms it into some useful work.

Examples : Machine tools such as lathe, shaper, planer.

Difference : For machine, relative motion exists between its parts. But structure is an

assemblage of number of resistant bodies having no relative motion between them.

10.Explain Grubler’s criterion for determining degree of freedom for mechanism.(April/May 2005)

The grubler’s criterion for plane mechanism is given by

3 l −2 j −4 = 0

Where

l = Number of links in the mechanism, and

j = Number of binary joints.

The Grubler’s criterion applies to mechanisms with only single degree of freedom

joints and the overall mobility of the mechanism is unity.

11.Define kinematic chain(Nov/Dec 2005)

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A kinematic chain may be defined as a combination of kinematic pairs, joined in such a

way that the relative motion between the links or elements is completely of successfully

constrained.

12.Define lower pair and higher pair, give two examples for each pairs. (Nov/Dec 2005)

Lower pair : If a pair in motion has a surface contact between the two elements, it is

called a lower pair.

Examples: Nut and bolt; Bolt and socket joint.

Higher pair : If a pair in motion has a line or point contact between the two elements,

it is called a higher pair.

Examples: Belt, rope and chain drives; Gear, cam and follower.

13.Draw a four bar mechanism and show that it has one degree of freedom as per

Kutzbach criterion. (May / June 2006)

The four bar mechanism is shown in Fig.1. it has four links and four binary joints,

ie., l = 4 and j =4.

Kutzbach criterion, n = 3 (l−1) −2 j −h

= 3 ( 4−1 )−2 (4 )− 0 = 1

Thus the four bar mechanism has one degree of freedom.

14.Define inversion of mechanism. (May / June 2006)

The method of obtaining different mechanisms by fixing different links in a kinematic

chain is known as inversion of the mechanism.

15.Identify the possible motion (s) and name of the kinematic pairs of the following

combinations: (a) Members of a scissor. (b) A two pin plug inserted in a two pin socket.

(May / June 2006)

(a) Incompletely constrained motion and closed pair (also known as self – closed pair) or

lower pair.

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(b)Completely constrained motion and unclosed pair (also known as open pair or force –

closed pair) or lower pair.

16.State the differences between a crank – rocker mechanism and a drag –link

mechanism. (May / June 2006)

In a crank – rocker mechanism, one link oscillates while the other link rotates

about the fixed link, as shown in Fig.1.

If the shortest link, i.e., link 1 (crank) is fixed, the adjacent links 2 and 4 would

complete revolutions, as shown if Fig.2. The mechanism thus obtained is known as

drag-link mechanism or double-crank mechanism.

17.Define kinematic pair and illustrate any two types of constrained pair.

(May / June 2006)

When any two links or elements are connected in such a way that their relative motion is

completely or successfully constrained, they form a kinematic pair.

Examples :

(i) Square bar moving in a square hole (Refer Fig.1) and

(ii) A shaft with collars at its ends moving in a round hole (Refer Fig. 2).

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18.What is Kutzbach criterion for planar mechanism? (Nov/ Dec 2006)

A kinematic chain having ‘l’ links and ‘j’ binary joints then the mobility according to

Kutzbach criterion, is n = 3(l-1) -2j.

19.Sketch an exact straight line mechanism, with link proportions. (Nov/ Dec 2006)

20.Write expression governing Kutzbach criterion for mobility of a planer mechanism.

(Nov/ Dec 2006)



21.Name any four common mechanisms with specific application. (Nov/ Dec 2006)

SI .No. Mechanism Application1. Crank and lever mechanism Beam engine

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2.

3.

4.

Double crank mechanism

Double rocker mechanism

Whitworth quick-return mechanism

Coupling rod of a locomotive

Pantograph; Ackerman Steering

Shaping and slotting machines

22.Enumerate the difference between a machine and a structure. (May / June 2007)







23.List out the inversions of a double slider crank chain. (May / June 2007)

1) Elliptical trammel. 2) Scotch yoke mechanism. 3) Oldham’s Coupling.

24.Define Degree of Freedom and give the DOF for a shaft in a circular hole. (Nov / Dec

2007)

The ‘Mobility of a mechanism’ or ‘Degree of freedom’ is defined as the number of

input parameters (usually pair variables) which must be controlled independently

in order to bring the device into a particular position.

Two DOF for a shaft in a circular hole.

25.State Grashoff’s laws for a four bar linkage. (May / June 2007)

Grashoff’s law state that the sum of the shortest and longest links cannot be greater

than the sum of the remaining two links lengths, if there is to be continuous relative

motion between two members.

26.Define Degree of Freedom. (April / May 2008)


input parameters (usually pair variables) which must be controlled independently in order

to bring the device into a particular position.

27.Define Grashoff’s law. (April / May 2008)8




28.Define Degree of Freedom. (Nov / Dec 2008)

The ‘Mobility of a mechanism’ or ‘Degree of freedom’ is defined as the number of input

parameters (usually pair variables) which must be controlled independently in order to bring

the device into a particular position.

29.State Grubbler’s criterion for planar mechanisms. (Nov / Dec 2008)

(i) According to Kutzback criterian,

Mobility, n = 6 ( l−1) −5 p1 − 4 p2 − 3 p3 − 2 p4 − 1 p5

where l = Number of links in the mechanism,

p1 = Number of pairs having one degree of freedom, and

p2 = Number of pairs having 2 degree of freedom and so on.

30.Give any two inversions of a single slider chain. (May/June 2009)

Whitworth quick return mechanism

Crank and slotted lever mechanism.

Oscillating cylinder engine.

Gnome engine.

31.Write Grashoff’s law for 4- bar mechanism. (May/June 2009)

According to Grashoff’s law,

S + l ≤ p+q

where S and l be the shortest and longest links respectively, and

p and q be the length of the other two lines.

32.State Gruebler’s criterion for spatial mechanism. (Nov/ Dec 2009)

Gruebler’s criterion states that the overall mobility of the mechanism is unity. The

Gruebler’s equation for spatial mechanisms is given by

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6 l − 5 p1 − 7 = 0

where l = Total number of links, and

p1 = Number of pairs having single degree of freedom.

33.Define ‘Mechanical Advantage’. (Nov/ Dec 2009)

Mechanical advantage is defined as the ratio of the load to the effort.

34.Explain the term kinematic link. Give the classification of kinematic link (Nov/ Dec

2011)

A link or an element is defined as that part of machine which has motion relative to

some other part.

There are three types of links as classified below:

35.Explain the terms: (a) Lower pair, (b) higher pair. (Nov/ Dec 2011)




Higher pair : If a pair in motion has a line or point contact between the two elements, it

is called a higher pair.


36.What is the significance of Grashof’s law for a four bar mechanism? (Nov/ Dec 2011)

Grashof’s law specifies the order in which the links are connected in a kinematic

chain.

Grashof’s law specifies which link of the four-bar chain is fided.

s + l ≤ p + q

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If this inequality is not satisfied, no link will make a complete revolution relative to

another.

37.State the application of an offset slider-crank mechanism. (Nov/ Dec 2011)

The offset slider crank mechanism is used to get reciprocating motion of the slider

and is also used as a quick return mechanism.

38.Write Grashoff’s law for 4-bar mechanism(Nov/ Dec 2012)




39.What is meant by indexing mechanism? Where do we use it’? (Nov/ Dec 2012)

Indexing mechanism is used when intermittent rotary motion is required generally

in machine tools where turret or work table is required to be indexed.

40.Define sliding connectors. (Nov/ Dec 2013)

Sliding connectors are used when one slider (the input) is to drive another slider

(the output). Usually the two slider operate in the same plane but in different directions.

41.Differentiate rotation and translation. (Nov/ Dec 2013)

Translation is defined as a stat of motion of body for which the displacement

difference between any two points is zero.

Rotation is a state of motion of the body for which different points of the body are

equal.

42.Differentiate between the machine and structure.( May / June 2014)







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43.Classify the constrained motion. ( May / June 2014)

There are three types.

Completely constrained motion (eg. Square bar moving in a square hole)

In completely constrained motion ( eg. Circular shaft in a hole)

Successfully constrained motion (eg. Piston and cylinder)

44.Define ‘Degree of freedom’ (or) what is meant by mobility?


parameters which must be controlled independently in order to bring the device into a

particular position.

The degrees of freedom of a mechanism (n) is given by

n = 3(L-1)-2j-h

L = Number of links

j = Number of joints

h = Number of higher pairs.

45.What is meant by 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.

46.Classify the constrained motion.


1) Completely constrained motion (eg. Square bar moving in a square hole)

2) In completely constrained motion ( eg. Circular shaft in a hole)

3) Successfully constrained motion (eg. Piston and cylinder)

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47.How to determine the given assemblage of links forms the kinematic chain or not?

If the given assemblage satisfies the following two equations (for lower pair) then it is

called as kinematic chain.

l = 2 p − 4

j = 32

l − 2

where l = Number of links,

p = Number of pairs, and

j = Number of joints.

48.What is meant by number synthesis?

Expressing mobility or degree of freedom of a mechanism in terms of the number of links

and the number of pair connections of a given type is known as number synthesis.

49.What are the some important inversions of four bar chain mechanism?

1. Crank-rocker mechanism (or) Crank-lever mechanism (or) Rotary-oscillating

converter.

2. Crank – crank mechanism (or) Double crank mechanism (or) Rotary –rotary

converter.

3. Rocker-rocker mechanism (or) Double – rocker mechanism (or) Double –lever

mechanism (or) an Oscillating – oscillating converter.

50.What is toggle position?

It is the position of a mechanism at which the mechanical advantage is infinite and the

sine of angle between the coupler and driving link is zero.

51. What is pantograph?

Pantograph is a device which is used to reproduce a displacement exactly in an enlarged

or reduced scale. It is used in drawing offices, for duplicating the drawings, maps, plans,

etc. It works on the principle of 4 bar chain mechanism.

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52.What are the important applications of single slider crank mechanism?

1) Rotary or Grome engines.

2) Crank and slotted lever mechanism.

3) Oscillating cylinder engine.

4) Bull engine

5) Hand pump.

53.Compare machine and structure.


1Relative motion exists between its

parts.

No relative motion exists between

its members.

2It transforms available energy into

useful work.

It does not convert the available

energy into work.

3Links are meant to transmit motion

and forces.

Members are meant for carrying

loads having straining action.

4 Examples : Scooter, Car, Bus Examples: Roof trusses, bridges.

54. Give some examples for kinematic pairs.

1) Crank and connecting rod

2) Connecting and piston rod

3) Piston and engine cylinder.

55.Discuss Elliptical trammel

Elliptical trammel is an instrument used for drawing ellipses. It is the best example for

first inversion of double slider crank chain.

56. Compare Movablility and Mobility.

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Movablility includes the 6 degree of freedom of the device as a whole, as though the

ground links were not fixed, and this applies to a kinematic chain.

Mobility neglects these and considers only the internal relative motions, thus applying a

mechanism.

57.What is meant by transmission angle?

In a four bar chain mechanism the angle between the coupler and the follower link

is called as the transmission angle.

58. What is meant by Ackermann steering?

Ackermann steering is the one of the mechanism used in vehicles. It is obtained by

inversion of four bar chain.

59. Write down the Grashof’s Law for a four bar mechanism?

Grashof’s law states that the sum of the shortest and longest links cannot be greater

than the sum of the remaining two links lengths if there is to be continuous relative


60. Explain the working principle of bicycle bells.

Bicycle bells are working on the principle of snap action mechanism or toggle

mechanism or flip flop mechanism.

61. What is meant by motion adjustment mechanism?

The mechanism used to adjust or modify the motion of the link is known as motion

adjustment mechanism. Motion adjustment is obtained by wedges, levers and rack and

pinion.

62. Whether a cycle chain is kinematic chain or not?

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A cycle chain is a combination of several links with turning pair. Hence it is not a

kinematic chain.

63. Define instantaneous centre.

Instantaneous centre of a moving body may be defined as that centre which goes

on changing from one instant to another.

64. What is instantaneous axis?

Instantaneous axis is a line drawn through an instantaneous centre and

perpendicular to the plane of motion.

65. What is resistant body?

A body is said to be resistant if it is capable of transmitting the required force with

negligible deformation. A link need not necessarily be a rigid body, but it must be a

resistant body.

66. What is link?

A link or an element is defined as that part of a machine which has motion relative

to some other part. A link need not to be a single unit, but it may consist of several parts

which are manufactured as separate units.

67. What are the different types of links?

1) Rigid link.

2) Flexible link.

3) Fluid link.

68.What is meant by 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.

69.What is the use of oldham’s coupling?

It is used for transmitting motion between two shafts which are parallel but not

coaxial.

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CHAPTER -2 : KINEMATICS OF MOTION

1. Define rubbing velocity. What will be the rubbing velocity at a pin joint when the two

links move in and opposite directions? (Oct/ Nov 2002)

Definition: The rubbing velocity is defined as the algebraic sum between the angular

velocities of the two links which are connected by pin joints, multiplied by the radius of

the pin.

Rubbing velocity at a pin joint when the two links move in the opposite directions

= (ω1+ω2)×r

Where ω1and ω2 = Angular velocities of the link 1 and link 2 respectively, and

r = Radius of the pin.

2. Define Instantaneous centre. How many instantaneous centres are in a single crank

mechanism? (Oct/ Nov 2002)

Definition: Instantaneous centre of a moving body is defined as the centre which goes


In a single slider crank mechanism, there are four links.

∴Number of instantaneous centres, N=

n (n−1 )2

=4 (4−1)

2=6

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3. Sketch the Geneva wheel indexing mechanism and state its application. (April /

May 2003)

Geneva mechanism is used in rotary tables and indexing turrets in machine tools

and in automatic machines. The sketch is shown in Fig.1.

4. Distinguish normal component of acceleration and tangential component of

acceleration. (April / May 2003)

Normal (or Radial or centripetal) component is perpendicular to the velocity of

the particle at the given instant. In other words, the normal component acts parallel

to the link.

a linkr = ω2 × Length of the link =

vlink2

Length of the link

Tangential component is parallel to the velocity of the particle at the given instant.

In other words, it acts perpendicular to the link.

a linkt = α × Length of the link

5. Define instantaneous centre of rotation and write the equation to determine the nuber

of instantaneous centres of a mechanism. (Nov / Dec 2003)

Definition: Instantaneous centre of a moving body is defined as the centre which

goes on changing from one instant to another.

Number of instantaneous centres, N=

n (n−1 )2

= , where n = Number of links

6. In a revolving stage with a speed of 3rpm, a person is walking with a speed of 0.5m/sec

along a radial path. Determine the magnitude of the coriolis component of acceleration

in this motion. (Nov / Dec 2003)

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Given Data: N = 3rpm; ω =

2 π (3)60

= 0 .314 rad /s ; v=0 . 5 m /s .

Solution: Coriolis acceleration, ac = 2 .v .ω

= 2×0 . 5×0 . 314 = 0 . 314 m /s2

7. Define rubbing velocity at a pin joint. What will be the rubbing velocity at pin joint

when the two links move in the opposite direction? (Nov / Dec 2004)

Definition: The rubbing velocity is defined as the algebraic sum between the

angular velocities of the two links which are connected by pin joints, multiplied by

the radius of the pin.

Rubbing velocity at pin joint when = (ω1 + ω2 ) r

the two links move in opposite direction

where ω1 and ω2 = Angular velocities of two links, and


8. When coriolis component of acceleration occur? (Nov / Dec 2004)

Coriolis component of acceleration occurs when a point on one link is sliding

along another rotating link, such as in quick return mechanism.

9. Briefly explain the types of instantaneous centres. (April / May 2005)

Three types of instantaneous centres are (refer Fig.1) :

Fixed instantaneous centres: From the Fig.1, I12 and I14 are called the fixed

instantaneous centres as they remain in the same place for all configurations of the

mechanism.

Permanent instantaneous centres: I23 and I34 are called the permanent

instantaneous centres as they move when the mechanism moves, but the joints are

of permanent nature.

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Neither fixed nor permanent centres: I13 and I23 are neither fixed nor permanent

instantaneous centres as they vary with the configuration of the mechanism.

10.What type of link will have only centripetal component of acceleration and what types

of link will have only linear acceleration? (April / May 2005)

The link which rotates at a constant velocity will have only centripetal i.e., radial

component of acceleration.

The link which moves in a linear direction will have only linear i.e., tangential


11.Explain Grubbler’s criterion for determining degree of freedom for mechanism. (Nov /

Dec 2005)

The grubbler’s criterion for plane mechanism is given by

3 l −2 j −4 = 0

Where



The Grubler’s criterion applies to mechanisms with only single degree of freedom joints and the overall mobility of the mechanism is unity.

12.Define rubbing velocity. What will be the rubbing velocity at a pin joint when the two

links move in and opposite directions? (Nov / Dec 2005)

20



the pin.


= (ω1+ω2)×r



13.A four-bar mechanism has coupler pin centres at A and B, and fixed pivot centres at

A0 and B0 Write the two vector equations involving the output velocity vector of B.

(May / June 2006)

vBA

→= ωBA . BA

vBA

→= ωBA . BA

vBB0

→= v A

→+ v BA

→

14.How will you determine the total acceleration of a point on a link, when the normal

component of acceleration and the tangential component of acceleration are known?

(May / June 2006)

The total acceleration of a point on a link is the vector sum of their components of the

radial acceleration and tangential acceleration.

15.Illustrate the instantaneous centres of a typical four bar. (May / June 2006)




mechanism.

21






16.State the condition for a link to experience coriolis acceleration.`(May / June 2006)

Coriolis acceleration occurs when a point on one link is sliding along another

rotating link, such as in quick return mechanism.

17.Illustrate the space centrode and body centrode. (Nov / Dec 2006)

The locus of the instantaneous centre in space during a definite motion of the body



centrode.


18.Write the condition for coriolis component of acceleration. (Nov / Dec 2006)

22



19.Explain normal component of acceleration. (Nov / Dec 2006)

Normal or radial component of acceleration is perpendicular to the velocity of the

particle at the given instant. The magnitude is given by aBA

r = ω2 . AB = v2 BAAB .

20.State corioli’s law (Nov / Dec 2006)

Whenever a point on one link is sliding along another rotating link, then the total

acceleration will have one additional acceleration component known as Coriolis

component.

21.What is the speciality of a planar four bar linkage with regard to coupler curve?

(May / June 2007)

The connecting rod of a four –bar linkage is also

known as the ‘coupler’ and the points belonging to it are

called ‘coupler points’ the following figure shows part of

a coupler curve S, traced by the coupler point C.

The shape and state of the coupler curves changes

with the changing positions of the coupler point C. some

of the important characteristics of these curves are known as double points, cusps and

symmetry.

22.Define instantaneous centre of velocity? (May / June 2007)

Instantaneous centre of a moving body is defined as the centre which goes on

changing from one instant to another.

23.Define rubbing velocity. (May / June 2007)


3 l −2 j −4 = 0

Where


j = Number of binary joints.23

The Grubler’s criterion applies to mechanisms with only single degree of freedom joints

and the overall mobility of the mechanism is unity.

24.Define Corioli’s component of acceleration. (May / June 2007)

Corioli’s component of acceleration occur when a point on one link is sliding

along another rotation link, such as in quick return mechanism.

25.What is Corioli’s component of acceleration? (Nov / Dec 2007)

Corioli’s component of acceleration occurs when a point on one link is sliding


26.State the Freudenstein’s equation for a four-bar mechanism. (Nov / Dec 2007)

The Freudenstein equation that gives length ratios (design parameter) of a four –

bar mechanism is as below:

k 1 =l1

l2

; k2 =l1

l4

; k 3 =l12 + l2

2 − l32 + l4

2

2 l2 l4

Where l1 l3 and l4 represent the length of the four links of four – bar mechanism

respectively. k1 , k2 and k3 are the three length ratios.

27.Explain the Coriolis component of acceleration. (April / May 2008)

aBCC = 2 v ω

where = Angular velocity of ‘oA’ and

V = Linear velocity of ‘B’.

28.What is higher pair? (April / May 2008)

If a pair in motion has a line or point contact between the two elements, it is called

a higher pair.

29.Define “Actual Mechanical Advantage” (Nov / Dec 2008)

The mechanical advantage is defined as the ratio of output torque to the input

torque. It is also defined as the ratio of the load to the effort.

24

ar

at

a

M . A .(ideal ) =T B

T A

where TB = Driven (resisting torque), and

TA = Driving torque

30.How the direction of coriolis component of acceleration is determined? (Nov / Dec

2008)

The direction of Coriolis component is the direction of relative velocity vector for

the two coincident points rotated at 90◦ in the direction of angular velocity of rotation of

link.

31.Draw an acceleration polygon for a crank rotating at an angular speed of ‘’ rad/sec

and angular acceleration of ‘α’ rad/ sec2. (May / June 2009)

Refer Fig.1. ar ω2 . r

a t α . r

Fig.1

32.Explain how the direction of Coriolis acceleration is obtained. (May / June 2009)



link.

33.What is Coriolis acceleration? (Nov / Dec 2009)



34.What is meant by virtual centre? (Nov / Dec 2009)

25

The combined motion of rotation and translation of the link may be assumed to be

a motion of pure rotation about some centre known as virtual centre or instantaneous

centre.

35.Define transmission angle of the four-bar mechanism. What is the worst value of

transmission angle? (Nov / Dec 2011)

Definition: The angle between the coupler and the follower is a four-bar


Worst value of transmission on angle is less than 45◦.

36.What is coriolis component of acceleration? (Nov / Dec 2011)



component.

37.For what kind of relative motion, the Coriolis component of acceleration occurs?

Sketch the links to illustrate. (Nov / Dec 2011)

When a point on one link is sliding along another rotating link, then the point is

known as coincident point. At the coincident point the Coriolis component of

acceleration occurs Refer Fig.1.

26

38.State the relationship between crank angle ‘θ’ and connecting rod angle ‘’ of a single

slider crank mechanism. (Nov / Dec 2011)

sin φ = rl

sin θ = sin θn

39.What is a configuration diagram? What is its use? (Nov / Dec 2012)

Configuration diagram is a line sketch of a given mechanism drawn to a suitable scale.

The configuration diagram forms the basis for the construction of both velocity and

acceleration diagrams.

40.Define rubbing velocity. What will be the expression for rubbing velocity at a pin joint

when the two links rotate in opposite direction? (Nov / Dec 2012)


angular velocities of the two links which are connected by pin joints, multiplied

by the radius of the pin.


= (ω1+ω2)×r



41.Define number of instantaneous centre. (Nov / Dec 2013)


n (n−1 )2

where n = Number of links

42.What is low degree of complexity? (Nov / Dec 2013)

In a complex mechanism if only one radius of path curvature of one motion

transfer point is not known such a mechanism is called a mechanism with low degree of

complexity.

27

43.Define instantaneous centre (May / June 2014)



44.What is the expression for Coriolis component of acceleration? (May / June 2014)

aBCC = 2 v ω



45.Define instantaneous centre and instantaneous axis.

Instantaneous centre: Instantaneous centre of a moving body is defined as the centre

which goes on changing from one instant to another.

Instantaneous axis: Instantaneous axis is a line drawn through an instantaneous centre

and perpendicular to the plane of motion.

46.A pin joins two links A and B, A rotates with ω A angular velocity and B rotates with

ωB

angular velocity in opposite direction. What is the rubbing velocity of that pin?

Rubbing velocity of pin = (ω1 + ω2 ) × r

Where r is the radius of the pin.

47.What is meant by the efficiency of a mechanism?

Efficiency of a mechanism is defined as the ratio of product of force and velocity in

driven link to the product of force and velocity in driving link.

η =F B vB

FA v A

28

orη =

T B ωB

T A ωA

where A = Driving link B = Driven link,

T = Torque F = Force

V = Velocity, and ω = Angular velocity.

48.How to represent the direction of linear velocity of any point on a link with respect to

another point on the same link?

The direction of linear velocity of any point on a link with respect to another point on the

same link is perpendicular to the line joining the points.

49.What is the magnitude of linear velocity of a point B on a link AB relative to A?

The magnitude of linear velocity of a point B on a link AB, which rotates with ‘’

angular velocity with respect to A is:

vBA = ωBA × AB

50.What is the expression for Coriolis component of acceleration?

aBCC = 2 v ω

Where = Angular velocity of ‘OA’, and


51.What are the properties of instantaneous centre?

A rigid link rotates instantaneously relative to another link at the instantaneous centre

for the configuration of the mechanism.

29

The two rigid links have no linear velocity relative to each other at the instantaneous

centre. At this point the two rigid links have the same linear velocity relative to the

rigid link. In other words, the velocity of the instantaneous centre relative to any third

rigid link will be same whether the instantaneous centre is regarded as a point on the

first rigid link or on the second rigid link.

52.How many instantaneous centres are possible in a four bar chain mechanism?


n (n−1 )2


in four bar chain mechanism, n = 4

∴ N =4 (4 −1 )

2 = 6 centres are possible.

53.What are the two components of acceleration?

Radial component of acceleration,

aOBr = ωOB

2 × OB

Tangential component of acceleration,

aOBt = αOB × OB

where ωOB = Angular velocity of link OB,

αOB = Angular acceleration of link OB, and

OB = Length of link OB.

54.Define kennedy’s theorem.

The Kennedy’s theorem states that if three bodies move relatively to each other,

they have three instantaneous centres and lie on a straight line.

55. In a four bar chain mechanism crank AB = 0.3 metre rotates with 100 r.p.m and lever

CD oscillates with a linear velocity of 5 m/s and what is the mechanical advantage of

the system.30

Mechanical advantage=

v AB

v DC

v AB = ϖ AB × AB

=2 π N AB

60× AB

= 2 π × 10060

× 0 .3 = 3 .14 m /s .

vDC = 5 m/ s

Mechanical advantage = 3. 14

5= 0 . 628

56. In the four bar chain, considering mechanical advantage of 0.7, FB = 50 N, what is

the force acting on pin C.

Given Data : M.A = 0.7

FB = 50 N

FC = ?

Solution : M.A =

FC

FB

0.7 = FC

50

FC = 35N

CHAPTER -3: KINEMATICS OF CAM

31

1. Sketch any four types of follower used in cam. (Oct / Nov 2002)

2. Sketch the velocity and acceleration profile of a follower which moves with simple

harmonic motion. (Oct / Nov 2002)

Fig.3. Displacement, velocity and acceleration diagrams when the follower moves with SHM

3. State the advantages of cam mechanisms over linkage mechanisms. (April / May 2003)

Cam mechanisms are simple and inexpensive. They have few moving parts and

occupy a very small space. The versatility and flexibility of the cam design are more than

that of the linkage mechanisms.

4. Briefly write about undercutting in cam mechanisms. (April / May 2003)

32

The cam profile must be continuous curve without any loop. If the curvature of the

pitch curve is too sharp, then the part of the cam shape would be lost and thereafter the

intended cam motion would not be achieved. Such a cam is said to be undercut.

5. Define pressure angle of a cam mechanism and state the best value of the pressure

angle. ( Nov / Dec 2003)

Definition: It is the angle between the direction of the follower motion and a

normal to the pitch curve.

Best value of the pressure angle is 30°.

6. State the advantages of tangent cam ( Nov / Dec 2003)

Tangent cams are symmetrical and easy to manufacture.

They are less costly to manufacture.

They are used for operating the inlet and exhaust valves of I.C. engine.

7. State law of gearing( Nov / Dec 2004)

The law of gearing states that the common normal at the point of contact between a

pair of teeth must always pass through the pitch point.

8. Explain the term interference as applied to gears. ( Nov / Dec 2004)

The phenomenon when the tip of tooth undercuts the root on its mating gear is

known as interference.

9. Sketch a cylindrical cam, the follower reciprocates in a direction parallel to the cam

axis and also a cylindrical cam with oscillation follower. (April / May 2005)

A cylindrical cam with a follower reciprocates in a direction parallel to the cam

axis is shown in Fig.2(a).

A cylindrical cam with oscillating follower is shown in Fig.2 (b).

33

10.Derive the equation to determine the maximum velocity and the maximum acceleration

when the follower has simple harmonic motion. (April / May 2005)

(v0)max= π Sω

2 θ0

; (vR )max= π ω S

2 θR

;

(α0 )max= π2 ω2 S

2 θ02

; (αR )max= π2 ω2 S

2 θR2

;

11.Sketch displacement, velocity and acceleration diagram for simple harmonic motion

and indicate the maximum velocity and maximum acceleration position.

(Nov/ Dec 2005)


34

12.Sketch any four types of follower with cam arrangement. (Nov/ Dec 2005)

13.Enumerate any four different types of follower motions of a cam. (May / June 2006)

14.State the expressions to determine the maximum velocity and acceleration when the

follower moves with simple harmonic motion. (May / June 2006)

Maximum velocity:

(v0)max= π Sω

2 θ0

;

(vR )max= π ω S

2 θR

;

Maximum acceleration:


2 θ02


2 θR2

;

Where S = Stroke of the follower,

ω = Angular velocity of the cam in rad/s, and

θ0 and θR = Angle of ascent and angle of descent.

35

15.State, atleast, one disadvantage of flat faced follower over roller follower in a cam

mechanism. (May / June 2006)

Advantage: Limited space and reduced failure at pin points.

Disadvantage : Comparatively more surface stress and wear rate.

16.What are undercutting and its effect on a cam-roller follower system?

(May / June 2006)




17.What are the advantages of roller follower than knife-edge follower? (Nov / Dec 2006)

The rate of wear at the contacting end of the roller follower is comparatively lesser

than that of the knife-edge follower.

18.Sketch the displacement, velocity and acceleration diagram when a follower moves

with uniform velocity. (Nov / Dec 2006)

36

19.What are the classifications of cams based on contact surfaces? (Nov / Dec 2006)

Cylindrical cam and Radial or Disc cam.

20.State the basic requirements for high speed cams. (Nov / Dec 2006)

For any high speed cam application it is extremely important that not only the

displacement and velocity curves but also the acceleration curve be made continuous for

the entire motion cycle. No discontinuities should be allowed at the boundaries of

different sections of the cam.

21.What are high speed cams? Give examples. (May / June 2007)

……………..

22.Construct the displacement diagram for the follower motion to be cycloidal. (May /

June 2007)

23.State the expressions for maximum velocity and acceleration of a follower moves with

cycloidal motion. (May / June 2007)

(vC )max= 2 ω S

θ0

; (vR )max= 2 ω S

θR

; (αO )max= 2π ω2 S

(θ0)2

; (αR )max= 2π ω2 S

(θR)2

37

24.What is prime circle of a cam? What is the radial distance between the prime circle and

base circle for a cam with knife edge follower? (May / June 2007)

The smallest circle drawn tangent to the pitch curve is known as the prime circle.

The radial distance between the prime circle and base circle for a cam with knife edge

follower is zero.

25.What is a circular arc cam? (Nov / Dec 2007)

When the flanks of the cam connecting the base circle and nose are of convex circular

arcs, then the cam is known as circular arc cam.


cycloidal motion. (Nov / Dec 2007)

(vC )max= 2 ω S

θ0

; (vR )max= 2 ω S

θR


(θ0)2


(θR)2

27.Define pitch curve of the cam. (April / May 2008)

The locus or path of the tracing point is known as the pitch curve.

28.Define undercutting in gears. (April / May 2008)

Fig.1 shows a pinion and a gear wheel in mesh. If the addendum of the mating gear

is more than the limiting value, it interferes with the dedendum of the pinion and the two

gears are locked. (Refer Fig.1(a))

38

Now, instead of the gear mating with the pinion, a cutting rack is used to cut the

teeth in the pinion. Then the portion of the pinion tooth will be removed as shown in

Fig.1(b).

29.Draw at least any four types of cam with followers. (Nov / Dec 2008)

30.What are the different types of motion with which a follower can move? (Nov / Dec

2008)

Uniform velocity or uniform motion

simple harmonic motion SHM

Uniform acceleration and retardation, and

Cycloidal motion

31.What is the significance of pressure angle in cam? (May / June 2009)

As the pressure angle increases, the force required to lift the follower increases.

32.What is the follower motion used for high speed cams? Why? (May / June 2009)

Cycloidal motion because it results in lower jerks.

33.Why is roller follower preferred to knife edge follower? (Nov / Dec 2009)

Because rate of wear is greatly reduced in roller follower. Also side thrust exists

between the follower and guide is less in roller follower.

34.Define ‘under cutting in cam’. (Nov / Dec 2009)39




35.Define pressure angle of a cam mechanism and stat the best value of the pressure

angle. (Nov / Dec 2011)



Best value of the pressure angle is below 30◦.

36.State the advantages of tangent cams. (Nov / Dec 2011)




37.Sketch the shapes of displacement, velocity and acceleration diagrams for ‘uniform

acceleration and retardation’ motion of a follower. (Nov / Dec 2011)

40

38.Why sometimes the axes of translating roller followers in cam follower mechanisms

are offset from the axis of rotation of cam? (Nov / Dec 2011)

The offset causes a reduction of the side thrust present in the follower

39.Define rubbing velocity. What will be the expression for rubbing velocity at a pin joint

when the two links rotate in opposite direction? (Nov / Dec 2012)

amax = 2 π S

θ2ω2

Where, S = Follower lift,

= Angular velocity of cam, and

θ = Angle of ascent / descent.

41

40.Why sometimes the axes of translating roller followers in cam follower mechanisms

are offset from the axis of rotation of cam? (Nov / Dec 2012)

An offset is usually provided to decrease pressure angle and thereby the side thrust

in guides of follower.

41.Define pressure angle in gears. (Nov / Dec 2013)

Pressure angle is the angle between the common normal to two gear teeth at the

point of contact and the common tangent at the pitch point.

42.Write the procedure to draw the cam profile. (Nov / Dec 2013)

43.Define tangent cam. (May / June 2014)

When the flanks of the cam are straight and tangential to the base circle and nose

circle, the cam is known as tangent cam.

44.What are the different motions of the follower? (May / June 2014)


Simple harmonic motion SHM


Cycloidal motion

45.What is a cam?

42

A cam is a rotating machine element which gives reciprocating or oscillating

motion to another element known as follower.

46.Give some examples of cam.

1) Radial or disc cams.

2) Cylindrical or barrel cams.

3) End or face cams.

4) Wedge cams.

47.Define tangent cam.

When the flanks of the cam are straight and tangential to the base circle and

nose circle the cam is known as tangent cam.

48.What ate the different motions of the follower?

1) Uniform motion.

2) Simple harmonic motion.

3) Uniform acceleration and retardation.

4) Cycloidal motion.

49.How can high surface stress in flat faced follower be minimized?

High surface stress in the follower is minimized by machining the flat end of

the follower to a spherical shape.

50.Where are the roller follower extensively used?

Roller followers are extensively used where more space is available such as

in stationary gas oil engines, and aircraft engines.

51.Define dwell period?

The period during which the follower remains at rest is called dwell period.

52.Explain offset follower.

When the motion of the follower is along an axis away from the axis of the

cam centre, it is called offset follower.

43

53.Define trace point.

It is a reference point on the follower and is used to generate the pitch curve.

In case of knife edge follower the knife edge represents the trace point and the pitch

curve corresponds to the cam profile.

54.Define pressure angle with respect to cams.

It is the angle between the direction of the follower motion and a normal to

the pitch curve. This angle is very important in designing a cam profile. If the pressure

angle is too large, a reciprocating follower will jam in its bearings.

55.Define lift or stroke in cam.

It is the maximum travel of the follower from its lowest position to the topmost position.

56.Define undercutting in cam. How it occurs?

The cam profile must be continuous curve without any loop. If the curvature

of the pitch curve is too sharp, then the part of the cam shape would be lost and thereafter

the intended cam motion would not be achieved. Such a cam is said to be undercut.

Undercutting occurs in the cam because of attempting to achieve too great a

follower lift with very small cam rotation with a smaller cam.

57.What do you know about nomogram?

In nomogram, by knowing the values of total lift of the follower and the cam

rotation angle for each segment of the displacement diagram, we can read directly the

maximum pressure angle occurring in the segment for a particular choice of prime curcle

radius.

58.How can you prevent undercutting in cam?

1) By decreasing the follower lift.

2) By increasing cam rotation angle.

3) By increasing the cam size.

44

59.What do you know about gravity cam?

In this type, the rise of the cam is achieved by the rising surface of the cam

and the return by the force of gravity or due to the weight of the cam.

60.Write the different types of follower.

1) Knife edge follower

2) Roller follower

3) Mushroom or flat faced follower

4) Spherical faced or curved shoe follower.

61.What is cam profile?

The surface of cam which comes into contact with follower, is known as

cam profile.

62.What is base circle?

It is the smallest circle that can be drawn to the cam profile. The radius of

the base circle is called the least radius of the cam.

63.What is trace point?

It is a reference point on the follower to trace the cam profile. In case of a

knife edge follower, the knife edge itself is a tracing point and in roller follower, the

centre of the roller is the tracing point.

64.What is pitch curve?

The locus or path of the tracing point is known as the pitch curve. For the

purpose of laying out the cam profiles, it is assumed that the cam is fixed and the

follower rotates around it.

65.What is prime circle?

The smallest circle drawn tangent to the pitch curve is known as prime circle.

66.What is pressure angle?

45

It is the angle between the direction of the follower motion and a normal to

the pitch curve. This angle is very important in cam design as it represents steepness of

the cam profile.

67.What is pitch point?

It is the point on the pitch curve at which the pressure angle is maximum.

68.What is pitch circle?

It is the circle passing through the pitch point and concentric with the base circle.

69.What is cam angle?

It is the angle of rotation of the cam for a definite displacement of the follower.

CHAPTER -4: TOOTHED GEARING

1. Explain any two methods of reducing or eliminating interference in gears.

(Oct / Nov 2002)

i. The height of the teeth may be reduced.

ii. The pressure angle may be increased.

iii. The face of the gear tooth may be relieved.

2. State the law of gearing. (Oct / Nov 2002)

The law of gearing states that for obtaining a constant velocity ratio, at any instant

of teeth the common normal at each point of contact should always pass through a pitch 46

point (fixed point), situated on the line joining the centres of rotation of the pair of mating

gears.

3. State the relationship between circular pitch and the module. (April / May 2003)

Circular pitch(Pc ) = π × mod ule (m ).

4. Briefly write about reverted gear train with suitable sketch. (April / May 2003)

When the axes of the first gear (i.e., first driver) and the last gear (i.e., last driven

or follower) are co-axial, then the gear train is known as reverted gear train. Refer Fig.2.

5. Prove or disprove that in a spur gear pair, pure rolling occurs only at one point along

the path of contact. (Nov / Dec 2003)

We know that in a spur gear pair, at the pitch point there is no sliding. The action

is pure rolling. We also know that the path of contact should always pass through the

pitch point. Thus the pure rolling occurs only at one point along the path of contact.

47

6. What is meant by an epicyclic gear train? Give a practical example. (Nov / Dec 2003)

When the gears are arranged in such a manner that one or more gears move upon

and around another gear, then the gear train is known as epicyclic gear train.

Examples : Differential gears of automobile, back gear of lathe, wrist watches, etc.

7. Define : (a) normal pitch and (b) axial pitch relating to helical gears. (Nov / Dec 2004)

Normal pitch: It is the distance between similar faces of adjacent teeth, along a het on

the pitch cylinder normal to the teeth.

Axial pitch: It is the distance measured parallel to the axis, between similar faces of

adjacent teeth.

8. List any four types of cam followers. (Nov / Dec 2004)

(i) Knife edge follower ; (ii) Roller follower ;

(iii) Mushroom or flad faced follower ; and (iv) Spherical faced follower

9. What is meant by contact ratio in gear? And write the equation to determine this value.

(April / May 2005)

Contact ratio in gear refers to the number of teeth in contact.

Contact ratio =

Length of are of contactCircular pitch

10.How to change the direction of rotation of the output gear in simple gear train without

changing the direction of rotation of input gear? (April / May 2005)

By using intermediate idle gears.

48

11. What is the effect of centrifugal tension in belt drives.

Centrifugal tension will increase the tension on both tight and slack sides.

Centrifugal tension has no effect on the power transmitted by the belt drive.

12.What is the condition to be satisfied for self-locking of screw jack?

For a screw to be self-locking, friction angle must be greater than helix angle α.

The efficiency of self-locking screws should be less than 50%.

49

ANNA UNIVERSITYB.E. Degree Examinations, April / May 2003


2 MARKS QUESTION AND ANSWER

13.How many inversions are possible from a four-bar kinematic chain? Name them based

on their input-output motions.

Three in versions are possible from a four-bar kinematic chain. They are:

Crank-rocker mechanism or Rotary – oscillating converter.

Double crank mechanism or Rotary – rotary converter.

Double rocker mechanism or Oscillating – oscillating converter.

14. What are the three conditions to obtain a four-bar crank – rocker

mechanism?

The linkage should be class I four bar linkage. That is, if the sum of the lengths of

the largest and the shortest links is less than the sum of the lengths of the other two

links, the linkage is known as a class I, four bar linkage.

The shortest link should be made a crank (which can revolve) and any of the

adjacent links is fixed.

The link opposite to the crank i.e., rocker should oscillate.

15. Sketch the Geneva wheel indexing mechanism and state its application.

Geneva mechanism is used in rotary tables and indexing turrets in machine tools

and in automatic machines. The sketch is shown in Fig.1.

50

16. Distinguish normal component of acceleration and tangential component

of acceleration.

Normal (or Radial or centripetal) component is perpendicular to the velocity of

the particle at the given instant. In other words, the normal component acts parallel

to the link.

a linkr = ω2 × Length of the link =

vlink2

Length of the link

Tangential component is parallel to the velocity of the particle at the given instant.

In other words, it acts perpendicular to the link.

a linkt = α × Length of the link

17.State the advantages of cam mechanisms over linkage mechanisms.

Cam mechanisms are simple and inexpensive. They have few moving parts and

occupy a very small space. The versatility and flexibility of the cam design are more than

that of the linkage mechanisms.

18.Briefly write about undercutting in cam mechanisms.




19.State the relationship between circular pitch and the module.

Circular pitch(Pc ) = π × mod ule (m ).

20.Briefly write about reverted gear train with suitable sketch.

51

When the axes of the first gear (i.e., first driver) and the last gear (i.e., last driven or

follower) are co-axial, then the gear train is known as reverted gear train. Refer Fig.2.

21.State the laws of dry friction.

The force of friction directly proportional to the normal load between the surfaces.

The force of friction is independent of the area of the contact surface for a given

normal load.

The force of friction depends upon material which the contact surfaces or made.

The force of friction is independent of the velocity of sliding of one body relative

to other body.

22. The coefficient of friction between the belt and the pulley in a belt and the pulley in a

belt drive is 0.3. The angle of lap is 165◦. If the tension on the tight side is 3000 N,

determine the tension on the slack side.

Given Data :

μ = 0 .3 ; θ = 165∘ × π180∘ = 2.879 rad ; T1 = 3000 N .

Solution : We know that,

T1

T2

= e μθ .

or

3000T 2

= e0 .3×2.879

or T 2 = 1264 . 49 N

52

ANNA UNIVERSITYB.E. Degree Examinations, November/December 2003


2 MARKS QUESTION AND ANSWER

23.State at least one similarity and one difference between a helical pair and a cylindric

pair.

Similarity : Both are lower pairs.

Difference : Helical pair has a incompletely constrained motion whereas

cylindric pair has completely constrained motion.

24. Define transmission angle of a four- bar mechanism. What are the worst

values of transmission angle?

Definition : The angle between the coupler and the follower in a four-bar


Worst value of transmission angle is less than 45◦.

25.Define instantaneous centre of rotation and write the equation to determine the nuber

of instantaneous centres of a mechanism.

Definition: Instantaneous centre of a moving body is defined as the centre which

goes on changing from one instant to another.


n (n−1 )2

= , where n = Number of links

26.In a revolving stage with a speed of 3rpm, a person is walking with a speed of 0.5m/sec

along a radial path. Determine the magnitude of the coriolis component of acceleration

in this motion.

Given Data: N = 3rpm; ω =

2 π (3)60

= 0 .314 rad /s ; v=0 . 5 m /s .

Solution: Coriolis acceleration, ac = 2 .v .ω

= 2×0 . 5×0 . 314 = 0 . 314 m /s2

54

27.Define pressure angle of a cam mechanism and state the best value of the pressure

angle.



Best value of the pressure angle is 30°.

28. State the advantages of tangent cam and




29.Prove or disprove that in a spur gear pair, pure rolling occurs only at one point along

the path of contact.

We know that in a spur gear pair, at the pitch point there is no sliding. The action

is pure rolling. We also know that the path of contact should always pass through the

pitch point. Thus the pure rolling occurs only at one point along the path of contact.

30.What is meant by an epicyclic gear train? Give a practical example.



Examples : Differential gears of automobile, back gear of lathe, wrist watches, etc.

55

31.Prove or disprove that the efficiency of a screw jack is independent of load raised.

ηscrew jack = Ideal effortActual effort

=P0

P= W tan α

W tan (α +φ )= tan α

tan (α +φ )

Thus the efficiency of a screw jack is independent of the load raised.

32. State the condition and the equation for the velocity of the belt for the transmission of

maximum power in a flat belt drive.

Condition: The power transmitted shall be maximum when the centrifugal tension

(T c) is one third of the maximum belt tension (T).

Equation: Maximum velocity, vmax = √ T

3 m

56

ANNA UNIVERSITYB.E. Degree Examinations, November / December 2004

ME 232 – KINEMATICS OF MACHINES2 MARKS QUESTION AND ANSWER

33. State any four types of kinematic pairs according to the types of relative motion

between them.

i) Sliding pair; (ii) Turning pair ;(iii) Rolling pair; and (iv) Screw pair

34.Explain with a neat sketch, the space centrode and body centrode. The locus of the instantaneous centre in space during a definite motion of the body



centrode.


35.Define rubbing velocity at a pin joint. What will be the rubbing velocity at pin joint

when the two links move in the opposite direction?


angular velocities of the two links which are connected by pin joints, multiplied by

the radius of the pin.

Rubbing velocity at pin joint when = (ω1 + ω2 ) r

the two links move in opposite direction

where ω1 and ω2 = Angular velocities of two links, and


57

36.When coriolis component of acceleration occur ?



37.State law of gearing



38.Explain the term interference as applied to gears.

The phenomenon when the tip of tooth undercuts the root on its mating gear is

known as interference.

39.Define : (a) normal pitch and (b) axial pitch relating to helical gears.

Normal pitch: It is the distance between similar faces of adjacent teeth, along a het on

the pitch cylinder normal to the teeth.

Axial pitch: It is the distance measured parallel to the axis, between similar faces of

adjacent teeth.

40.List any four types of cam followers.

(i) Knife edge follower ; (ii) Roller follower ;

(iii) Mushroom or flad faced follower ; and (iv) Spherical faced follower

41.Obtain an expression for length of an open belt drive

Lopen = ( π2 ) (d1 + d2) + 2 x +

(d1 d2 )2

4 x

Where d1 and d2 = Diameters of the larger and smaller pulleys, and

x = Distance between the centres of two pulleys

42.What is the minimum force required to slide a body on a rough horizontal plane ?

Refer Fig.2. The minimum force required to slide a body on a rough horizontal

plane is P =

W sin ( α − φ )sin [θ −( α φ )]

Fig.2.

58



43. What is a machine? Give two examples. Also differentiate between a machine and a

structure.

A machine is a device which receives energy and transforms it into some useful work.

Examples : Machine tools such as lathe, shaper, planer.

Difference : For machine, relative motion exists between its parts. But structure is an

assemblage of number of resistant bodies having no relative motion between them.

44.Explain Grubler’s criterion for determining degree of freedom for mechanism.


3 l −2 j −4 = 0

Where





45.Briefly explain the types of instantaneous centres.




mechanism.




59



46.What type of link will have only centripetal component of acceleration and what types

of link will have only linear acceleration?

The link which rotates at a constant velocity will have only centripetal i.e., radial


The link which moves in a linear direction will have only linear i.e., tangential


47.Sketch a cylindrical cam, the follower reciprocates in a direction parallel to the cam

axis and also a cylindrical cam with oscillation follower.

A cylindrical cam with a follower reciprocates in a direction parallel to the cam

axis is shown in Fig.2(a).

A cylindrical cam with oscillating follower is shown in Fig.2 (b).

60

48.Derive the equation to determine the maximum velocity and the maximum acceleration

when the follower has simple harmonic motion.

(v0)max= π Sω

2 θ0

; (vR )max= π ω S

2 θR

;


2 θ02


2 θR2

;

49.What is meant by contact ratio in gear? And write the equation to determine this value.

Contact ratio in gear refers to the number of teeth in contact.

Contact ratio =

Length of are of contactCircular pitch

50.How to change the direction of rotation of the output gear in simple gear train without

changing the direction of rotation of input gear?

By using intermediate idle gears.

51.What is the condition for self locking in screws?

A screw will be self – locking if the friction angle () is greater than helix angle (α)

or coefficient of friction (µ) is greater than tangent of helix angle (tan α).

52. Find the power transmitted by a flat belt over a pulley of 600 mm in diameter at 200

revolutions per minute. The maximum and minimum tensions in the belt are 2500 N

and 124 N.

Given Data : D = 600 mm; N = 200 rpm; T1 = 2500N; T2 = 124 N.

Solution: v = π D N

60=

π (0. 6 ) 20060

= 6 . 28 m /s

Power transmitted, P =(T 1 − T 2) v = (2500 − 124 ) 6 . 28 = 14 . 92 kW

61



53. Define kinematic chain

A kinematic chain may be defined as a combination of kinematic pairs, joined in such a

way that the relative motion between the links or elements is completely of successfully

constrained.

54.Define lower pair and higher pair, give two examples for each pairs.




Higher pair : If a pair in motion has a line or point contact between the two elements,

it is called a higher pair.


55.Explain Grubbler’s criterion for determining degree of freedom for mechanism.

The grubbler’s criterion for plane mechanism is given by

3 l −2 j −4 = 0

Where





62

56. Define rubbing velocity. What will be the rubbing velocity at a pin joint

when the two links move in and opposite directions?



the pin.


= (ω1+ω2)×r



57.Sketch displacement, velocity and acceleration diagram for simple harmonic motion

and indicate the maximum velocity and maximum acceleration position.


58.Sketch any four types of follower with cam arrangement.

63

59.State law of gearing The law of gearing states that for obtaining a constant velocity ratio, at any instant

of teeth the common normal at each point of contact should always pass through a pitch


gears.



60.State any two advantages of in volute gears. In volute tooth gears, variation in centre distance does not affect the velocity ratio. In volute tooth gears are easier to manufacture when compared to cycloidal tooth

gears.61.Distinguish between simple gear train and epicyclical gear train.

When there is only one gear on each shaft, it is known as simple gear train. When the gears are arranged in such a manner that one or more gears move upon


62. What is the condition for self –locking in screws? For a screw to be self-locking, friction angle must be greater than helix angle α.

The efficiency of self-locking screws should be less than 50%.

A screw will be self – locking if the friction angle () is greater than helix angle (α)

or coefficient of friction (µ) is greater than tangent of helix angle (tan α).

64

ANNA UNIVERSITYB.E. Degree Examinations, May / June 2006


63. Draw a four bar mechanism and show that it has one degree of freedom as per

Kutzbach criterion.

The four bar mechanism is shown in Fig.1. it has four links and four binary joints,

ie., l = 4 and j =4.

Kutzbach criterion, n = 3 (l−1) −2 j −h

= 3 ( 4−1 )−2 (4 )− 0 = 1

Thus the four bar mechanism has one degree of freedom.

64.Define inversion of mechanism.

The method of obtaining different mechanisms by fixing different links in a kinematic

chain is known as inversion of the mechanism.

65.Illustrate the instantaneous centres of a typical four bar.Three types of instantaneous centres are (refer Fig.1) :



mechanism.






65

66.State the condition for a link to experience coriolis acceleration.



67.Enumerate any four different types of follower motions of a cam.

68.State the expressions to determine the maximum velocity and acceleration when the

follower moves with simple harmonic motion.

Maximum velocity :

(v0)max= π Sω

2 θ0

;

(vR )max= π ω S

2 θR

;

Maximum acceleration :


2 θ02


2 θR2

;

Where S = Stroke of the follower,

ω = Angular velocity of the cam in rad/s, and

θ0 and θR = Angle of ascent and angle of descent.

69.Define the following terms used in gears : (a) Pitch circle, (b) Circular pitch, (c)

Diametral pitch and (d) Module.

(a)Pitch circle : It is an imaginary circle which by pure rolling action, would give the

same motion as the actual gear.

66

(b)Circular pitch : It is the distance measured along the circumference of the pitch circle

from a point on one tooth to the corresponding point on the adjacent tooth.

(c) Diameteral pitch : It is the ratio of number of teeth to the pitch circle diameter.

(d)Module : It is the ratio of the pitch circle diameter to the number of teeth.

70.Define the terms “velocity ratio” and “sliding velocity” in a spur gear pair.

Velocity ratio : It is the ratio of speed of driving gear to the speed of the driven gear.

Sliding velocity : It is the velocity of one tooth relative to its mating tooth along the

common tangent at the point of contact.

71.With a neat sketch show that angle of repose α is equal to the limiting angle of

friction.

W sin α = F = µ. RN

= µW cos α

or tan α = µ = tan

Thus, α = .

Hence the angle of repose α is equal to the limiting angle of friction .

72. Define mechanical efficiency of screw and nut assembly.

The mechanical efficiency of screw and nut assembly may be defined as the ratio

between the ideal effort (P0) (i.e., the effort required to move the load, neglecting friction)

to the actual effort (P) (i.e., the effort required to move the load taking friction into

account).

67



73. Identify the possible motion (s) and name of the kinematic pairs of the following

combinations: (a) Members of a scissor. (b) A two pin plug inserted in a two pin socket.

(c) Incompletely constrained motion and closed pair (also known as self – closed pair) or

lower pair.

(d)Completely constrained motion and unclosed pair (also known as open pair or force –

closed pair) or lower pair.

74.State the differences between a crank – rocker mechanism and a drag –link

mechanism.

In a crank – rocker mechanism, one link oscillates while the other link rotates

about the fixed link, as shown in Fig.1.

If the shortest link, i.e., link 1 (crank) is fixed, the adjacent links 2 and 4 would

complete revolutions, as shown if Fig.2. The mechanism thus obtained is known as

drag-link mechanism or double-crank mechanism.

75.A four-bar mechanism has coupler pin centres at A and B, and fixed pivot centres at

A0 and B0 Write the two vector equations involving the output velocity vector of B.

vBA

→= ωBA . BA

vBA

→= ωBA . BA

vBB0

→= v A

→+ v BA

→

68

76.How will you determine the total acceleration of a point on a link, when the normal

component of acceleration and the tangential component of acceleration are known?

The total acceleration of a point on a link is the vector sum of their components of the

radial acceleration and tangential acceleration.

77.State, atleast, one disadvantage of flat faced follower over roller follower in a cam

mechanism.

Advantage: Limited space and reduced failure at pin points.

Disadvantage : Comparatively more surface stress and wear rate.

78.What are undercutting and its effect on a cam-roller follower system?




79.Prove or disprove that pure rolling is possible at one point only, on the line of action,

between two meshing gear teeth profiles.

This statement is known as law of gearing or conditions of correct gearing. For its

proof, …………..

80.Distinguish, with suitable free hand sketches, a non-reverted gear train and a reverted

gear train.

Reverted gear train : If the axes of the first and the last wheels of a compound gear

coincide, it is called a reverted gear train. Refer Fig.4.

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Non -reverted gear train : If the axes of the first and the last wheels of a compound gear

do not coincide, it is called a non- reverted gear train. Refer Fig.5.

81.In a screw jack, the coefficient of friction between screw and nut is 0.1 and the helix

angle of the screw thread is 3.5◦. Find the efficiency of the screw jack.

Given Data : µ = 0.1; α = 3.5◦

Solution : µ = tan = 0.1 or = tan -1 (0.1) = 5.71◦

∴ η = tan α

tan (α +φ )= tan 3 .5 °

tan (3 . 5° + 5 .71 ° )= 37 .72 %

82.A force of 80 N is applied to the brake of a bicycle rear wheel and the distance covered

by the bicycle before coming to rest is 12.5 metres. If the coefficient of friction is 0.6,

find the work done against the friction.

Given Data : F = 80 N; S = 12.5m; µ = 0.6.

Solution : F = µ RN or RN = 80/0.6 = 133.33 N

Workdone = RN x S = 133.33 x 12.5

= 1666.6 N.M

70



83. Define kinematic pair and illustrate any two types of constrained pair.

When any two links or elements are connected in such a way that their relative motion is

completely or successfully constrained, they form a kinematic pair.

Examples :

(iii) Square bar moving in a square hole (Refer Fig.1) and

(iv) A shaft with collars at its ends moving in a round hole (Refer Fig. 2).

84.Explain Kutzbach criterion for the movability of a mechanism having plane notion.

A kinematic chain having ‘l’ links and ‘j’ binary joints then the mobility according

to Kutzbach criterion, is n = 3(l-1) -2j.

85.Illustrate the space centrode and body centrode.

The locus of the instantaneous centre in space during a definite motion of the body



centrode.


71

86.Write the condition for coriolis component of acceleration.



87.What are the advantages of roller follower than knife-edge follower?

The rate of wear at the contacting end of the roller follower is comparatively lesser

than that of the knife-edge follower.

88.Sketch the displacement, velocity and acceleration diagram when a follower moves

with uniform velocity.

89.State the condition for constant velocity ratio of toothed wheels.




gears.



90.Explain the construction of involute teeth and its advantages. 72

………………………………

91.Derive the minimum force required to slide a body on a rough horizontal surface.

……………………….

92. Write the equation to determine the efficiency of a screw jack.

η screw jack = tan αtan (α + φ )

Where α = Helix angle, and

= Friction angle.

73



70.What is Kutzbach criterion for planar mechanism?



71.Sketch an exact straight line mechanism, with link proportions.

72.Explain normal component of acceleration.

Normal or radial component of acceleration is perpendicular to the velocity of the

particle at the given instant. The magnitude is given by aBA

r = ω2 . AB = v2 BAAB .

73.State corioli’s law



component.

74.What are the classifications of cams based on contact surfaces?

Cylindrical cam and Radial or Disc cam.

75.State the basic requirements for high speed cams.

For any high speed cam application it is extremely important that not only the

displacement and velocity curves but also the acceleration curve be made continuous for

the entire motion cycle. No discontinuities should be allowed at the boundaries of

different sections of the cam.74

76.Define module of gears and its relation to circular pitch.

Module is the ratio of the pitch circle diameter to the number of teeth.

Pitch circle, Pc = x Module

77.Explain briefly the use of differential in an automobile.

The function of a differential gear in an automobile is to :

(i) Transmit motion from engine to rear wheels, and

(ii)Rotate the rear wheels at different speeds while the automobile is taking a turn.

78.What are timing belts?

Timing belts provide a precise speed ratio. They have teeth that mesh with grooves

in the sheaves in such a way that no slippage occurs.

79. Explain briefly significance of friction in braking.

……………………………

75



80.Write expression governing Kutzbach criterion for mobility of a planer mechanism.



81.Name any four common mechanism with specific application.

SI .No. Mechanism Application1.

2.

3.

4.

Crank and lever mechanism

Double crank mechanism

Double rocker mechanism

Whitworth quick-return mechanism

Beam engine

Coupling rod of a locomotive

Pantograph; Ackerman Steering

Shaping and slotting machines

82.What is the speciality of a planar four bar linkage with regard to coupler curve?

The connecting rod of a four –bar linkage is also

known as the ‘coupler’ and the points belonging to it are

called ‘coupler points’ the following figure shows part of

a coupler curve S, traced by the coupler point C.

The shape and state of the coupler curves changes

with the changing positions of the coupler point C. some

of the important characteristics of these curves are known as double points, cusps and

symmetry.

83.Define instantaneous centre of velocity?

Instantaneous centre of a moving body is defined as the centre which goes on

changing from one instant to another.

84.What are high speed cams? Give examples.

……………..

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85.Construct the displacement diagram for the follower motion to be cycloidal.

86.Define the law of gearing with the equation.




gears.

87.What are the principal reasons for the use of non-standard gears?

Non- standard gears are used for obtaining improved performance and for more

economic production.

88.What do you mean by friction angle?

The friction angle () is the angle at which the resultant reaction R makes with the

normal reaction RN. tan = µ.

89. What are the significance of fiction with regard to power transmission devices like

clutches and bearings?

The power transmission devices like clutches and bearings work on the principle of

friction. When two friction surfaces are brought in contact with each other and pressed,

they are united due to the friction between them.

77



90.Enumerate the difference between a machine and a structure.







91.List out the inversions of a double slider crank chain.

1) Elliptical trammel. 2) Scotch yoke mechanism. 3) Oldham’s Coupling.

92. Define rubbing velocity. The grubler’s criterion for plane mechanism is given by

3 l −2 j −4 = 0

Where



The Grubler’s criterion applies to mechanisms with only single degree of freedom joints

and the overall mobility of the mechanism is unity.

93.Define Corioli’s component of acceleration.

Corioli’s component of acceleration occur when a point on one link is sliding

along another rotation link, such as in quick return mechanism.


cycloidal motion.

(vC )max= 2 ω S

θ0

; (vR )max= 2 ω S

θR


(θ0)2


(θR)2

78

95.What is prime circle of a cam? What is the radial distance between the prime circle and

base circle for a cam with knife edge follower?

The smallest circle drawn tangent to the pitch curve is known as the prime circle.

The radial distance between the prime circle and base circle for a cam with knife edge

follower is zero.

96.What is axial pitch of a helical gear?

It is the distance measure parallel to the axis, between similar faces of adjacent

teeth.

97.List out the applications of epicyclic gear train.

Differential gears of automobile, back gear of lathe, wrist watches, etc.

98.What is the condition of maximum efficiency of a screw jack?

For efficiency to tbe maximum sin (2α+) = 0,

or 2 α + φ = 90∘ or α = 45∘ − φ

2; ηmax = 1 − sin φ

1 + sin φ

99.What are the advantages of wire ropes over fabric ropes?

High strength to weight ratio.

More reliable in operation.

Silent operation even at high working speeds.

79



100. Define Degree of Freedom and give the DOF for a shaft in a circular hole.


input parameters (usually pair variables) which must be controlled independently

in order to bring the device into a particular position.

Two DOF for a shaft in a circular hole.

101. State Grashoff’s laws for a four bar linkage.




102. What is Corioli’s component of acceleration?

Corioli’s component of acceleration occurs when a point on one link is sliding


103. State the Freudenstein’s equation for a four-bar mechanism.

The Freudenstein equation that gives length ratios (design parameter) of a four –

bar mechanism is as below:

k 1 =l1

l2

; k2 =l1

l4

; k 3 =l12 + l2

2 − l32 + l4

2

2 l2 l4

Where l1 l3 and l4 represent the length of the four links of four – bar mechanism

respectively. k1 , k2 and k3 are the three length ratios.

104. What is a circular arc cam?

When the flanks of the cam connecting the base circle and nose are of convex circular

arcs, then the cam is known as circular arc cam.

80


cycloidal motion.

(vC )max= 2 ω S

θ0

; (vR )max= 2 ω S

θR


(θ0)2


(θR)2

106. Differentiate diametral pitch and circular pitch of a friction wheel.

Pitch circle : It is an imaginary circle which by pure rolling action, would give the same

motion as the actual gear.

Circular pitch : It is the distance measured along the circumference of the pitch circle

from a point on one tooth to the corresponding point on the adjacent tooth.

107. What is reverted gear train?

When the axes of the first gear and the last gear are co-axial, then the gear train is

known as reverted gear train.

108. Diagrammatically represent the forces acting on a body when it slides either up

or down on an inclined plane without considering the effect of friction.

109. List out any four desirable characteristics of brake lining material.

A high and uniform coefficient of friction.

Ability to withstand high temperatures, together with high heat dissipation

capacity.

Adequate mechanical and thermal strengths.

High resistance to wear.

81



110. Define Degree of Freedom.


input parameters (usually pair variables) which must be controlled independently in order

to bring the device into a particular position.

111. Define Grashoff’s law.




112. Explain the Coriolis component of acceleration.

aBCC = 2 v ω



113. What is higher pair?

If a pair in motion has a line or point contact between the two elements, it is called

a higher pair.

114. Define pitch curve of the cam.

The locus or path of the tracing point is known as the pitch curve.

115. Define undercutting in gears.

Fig.1 shows a pinion and a gear wheel in mesh. If the addendum of the mating gear

is more than the limiting value, it interferes with the dedendum of the pinion and the two

gears are locked. (Refer Fig.1(a))

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Now, instead of the gear mating with the pinion, a cutting rack is used to cut the

teeth in the pinion. Then the portion of the pinion tooth will be removed as shown in

Fig.1(b).

A gear having its material removed in this manner is said to be undercut and the

process is known as undercutting.

Undercutting will not take place if the teeth are designed to avoid interference.

However, when the actual gear meshes with the undercut pinion, no interference occurs.

116. Define interference in gears.

The phenomenon when the tip of tooth undercuts the roots on its mating gear is known as

interference.

117. Define pressure angle and explain the effect of different pressure angle.

It is the angle between the direction of the follower motion and a normal to the

pitch curve. This angle is very important in designing a cam profile. If the pressure angle

is too large, a reciprocating follower will jam in its bearings.

118. What is creep in the case of belt?

When the belt passes from the slack side to the tight side, a certain portion of the

belt extends. And it contracts again when the belt passes from the tight side to slack side.

Due to these changes of length, there is a relative motion between the belt and the pulley

surfaces. This relative motion is termed as creep.

119. Which type of screw thread is preferable in power transmission?

Square thread. Example: Lead screw in lathe.

83



120. Define Degree of Freedom.


parameters (usually pair variables) which must be controlled independently in order to bring

the device into a particular position.

121. State Grubbler’s criterion for planar mechanisms.

(ii) According to Kutzback criterian,

Mobility, n = 6 ( l−1) −5 p1 − 4 p2 − 3 p3 − 2 p4 − 1 p5

where l = Number of links in the mechanism,

p1 = Number of pairs having one degree of freedom, and

p2 = Number of pairs having 2 degree of freedom and so on.

122. Define “Actual Mechanical Advantage”

The mechanical advantage is defined as the ratio of output torque to the input

torque. It is also defined as the ratio of the load to the effort.

M . A .(ideal ) =T B

T A

where TB = Driven (resisting torque), and

TA = Driving torque

123. How the direction of coriolis component of acceleration is determined?



link.

84

124. Draw at least any four types of cam with followers.

125. What are the different types of motion with which a follower can move?


simple harmonic motion SHM


Cycloidal motion

126. State the law of gearing.




gears.

127. What are various types of torques in an epicyclic gear train?

Input torque on the driving member.

Output torque or load torque on the driven member.

Braking torque on the fixed member.

128. How centrifugal tension affects the power transmission in belt drive?

During operation, as the belt passes over a pulley the centrifugal effect due to its

self weight tends to lift the belt from the pulley surface. This reduces the normal reaction

and hence the frictional resistance. The centrifugal force produce additional tension in the

belt.

129. Define the term “Limiting friction”.

The limiting angle of friction () is defined as the angle at which the resultant

reaction ‘R’ makes with the normal reaction ‘RN’.

85

ar

at

a



1. Give any two inversions of a single slider chain.

Whitworth quick return mechanism

Crank and slotted lever mechanism.

Oscillating cylinder engine.

Gnome engine.

2. Write Grashoff’s law for 4- bar mechanism.

According to Grashoff’s law,

S + l ≤ p+q

where S and l be the shortest and longest links respectively, and

p and q be the length of the other two lines.

3. Draw an acceleration polygon for a crank rotating at an angular speed of ‘’ rad/sec

and angular acceleration of ‘α’ rad/ sec2.

Refer Fig.1. ar ω2 . r

a t α . r

Fig.1

4. Explain how the direction of Coriolis acceleration is obtained.



link.

5. What is the significance of pressure angle in cam?

As the pressure angle increases, the force required to lift the follower increases.

86

6. What is the follower motion used for high speed cams? Why?

Cycloidal motion because it results in lower jerks.

7. What are the advantages and disadvantages of involute gear tooth profile?

Advantages : Variable centre distance; Constant pressure angle; Easy manufacturing.

Disadvantages: Interference occurs; Weaker teeth; More wear and tear.

8. What are the applications of reverted gear trains?

The reverted gear trains are used in automobile gear boxes, lathe back gears,

industrial speed reducers, etc.

9. What is the apparent coefficient of friction in belt drives?

‘µ cosec β’ in the tension ratio equation is known as the apparent coefficient of friction.

10. Distinguish between sliding and rolling friction.

Sliding friction occurs in between two sliding surfaces whereas rolling friction

occurs in between two rolling surfaces.

87



1. State Gruebler’s criterion for spatial mechanism.

Gruebler’s criterion states that the overall mobility of the mechanism is unity. The

Gruebler’s equation for spatial mechanisms is given by

6 l − 5 p1 − 7 = 0

where l = Total number of links, and

p1 = Number of pairs having single degree of freedom.

2. Define ‘Mechanical Advantage’.

Mechanical advantage is defined as the ratio of the load to the effort.

3. What is Coriolis acceleration?



4. What is meant by virtual centre?

The combined motion of rotation and translation of the link may be assumed to be

a motion of pure rotation about some centre known as virtual centre or instantaneous

centre.

5. Why is roller follower preferred to knife edge follower?

Because rate of wear is greatly reduced in roller follower. Also side thrust exists

between the follower and guide is less in roller follower.

6. Define ‘under cutting in cam’.




88

7. State the law gearing.




gears.

8. Write the mobility of differential mechanism.

Mobility of differential mechanism is given by

n = 3(L-1)-2j-h

where L = Number of links

j = Number of joints

h = Number of higher pairs.

9. What do you mean by self-locking screw,

T = p × d2

= 2 = W tan (φ − α )

If < α, then torque required is negative.

If > α, then torque required is positive, indicating that an effort is applied

to lower the load. Such as screw is called self- locking screw.

10.Give the effect of centrifugal tension in belt drives.

Centrifugal tension has no effect on the power transmitted. However the

centrifugal tension will increase the tension on both tight and slack sides. Its effect is

considerable at higher belt speeds (> 10m/s).

89

ANNA UNIVERSITYB.E. Degree Examinations, November/ December 2011


130. Explain the term kinematic link. Give the classification of kinematic link

A link or an element is defined as that part of machine which has motion relative to

some other part.

There are three types of links as classified below:

131. Explain the terms: (a) Lower pair, (b) higher pair.




Higher pair : If a pair in motion has a line or point contact between the two elements, it

is called a higher pair.


132. Define transmission angle of the four-bar mechanism. What is the worst value of

transmission angle?

Definition: The angle between the coupler and the follower is a four-bar


Worst value of transmission on angle is less than 45◦.

133. What is coriolis component of acceleration?



component.

90

134. Define pressure angle of a cam mechanism and stat the best value of the

pressure angle.



Best value of the pressure angle is below 30◦.

135. State the advantages of tangent cams.




136. What is epicylic gear train? Give a practical example.



Examples: differential gears of automobile, back gear of lathe, wrist watches, etc.

137. What is the differential in automobile?

The function of a differential gear in an automobile is to:

(i) Transmit motion from engine to rear wheels, and

(ii) Rotate the rear wheels at different speeds while the automobile is taking a turn.

138. What is the difference between sliding friction and rolling friction? Give

example.

Sliding friction occurs in between two sliding surfaces whereas rolling friction

occurs in between two rolling surfaces.

139. What are the advantages and disadvantages of V-belt drive over flat belt drive?

Power transmitted is more due to wedging action in the grooved pulleys.

V-belt is more compact, quiet and shock absorbing.

The V-belt drive is positive because of negligible slip between the belt and the

groove.

High velocity ratio (maximum 10) may be obtained.

91



140. What is the significance of Grashof’s law for a four bar mechanism?

Grashof’s law specifies the order in which the links are connected in a kinematic

chain.

Grashof’s law specifies which link of the four-bar chain is fided.

s + l ≤ p + q

If this inequality is not satisfied, no link will make a complete revolution relative to

another.

141. State the application of an offset slider-crank mechanism.

The offset slider crank mechanism is used to get reciprocating motion of the slider

and is also used as a quick return mechanism.

142. For what kind of relative motion, the Coriolis component of acceleration occurs?

Sketch the links to illustrate.

When a point on one link is sliding along another rotating link, then the point is

known as coincident point. At the coincident point the Coriolis component of

acceleration occurs Refer Fig.1.

92

143. State the relationship between crank angle ‘θ’ and connecting rod angle ‘’ of a

single slider crank mechanism.

sin φ = rl

sin θ = sin θn

144. Sketch the shapes of displacement, velocity and acceleration diagrams for

‘uniform acceleration and retardation’ motion of a follower.

145. Why sometimes the axes of translating roller followers in cam follower

mechanisms are offset from the axis of rotation of cam?

The offset causes a reduction of the side thrust present in the follower

146. Define the following terms used in gear: (a) Pressure angle (b) Module.


point of contact and the common tangent at the pitch pint.

Module is the ratio of the pitch circle diameter to the number of teeth.

93

147. What are the advantages of planetary gear trains?

Because they share load between several gear meshes, epicyclic trains take up less

space and have a lighter weight.

Because they share load between several meshes, epicyclic trains have smaller and

stiffer components that lead to reduced noise and vibration while increasing

efficiency.

The input and output shafts of epicyclic trains are concentric so no bending moments

or torques are created from radial forces that develop from the change of the force’s

line of action.

The input and output shafts of epicyclic trains are concentric so driver and driven

equipment can be mounted in line, providing additional space savings.

148. What is limiting angle of friction?

The limiting angle of friction () is defined as the angle at which the resultant

reaction ‘R’ makes with the normal reaction ‘RN’.

149. State the functional difference between a clutch and a brake.

The functional difference between a clutch and a brake is that a clutch connects two

moving members of a machine, whereas a brake connects a moving member to a

stationary member.

94



150. Write Grashoff’s law for 4-bar mechanism




151. What is meant by indexing mechanism? Where do we use it’?

Indexing mechanism is used when intermittent rotary motion is required generally

in machine tools where turret or work table is required to be indexed.

152. What is a configuration diagram? What is its use?

Configuration diagram is a line sketch of a given mechanism drawn to a suitable scale.

The configuration diagram forms the basis for the construction of both velocity and

acceleration diagrams.

153. Define rubbing velocity. What will be the expression for rubbing velocity at a pin

joint when the two links rotate in opposite direction?


angular velocities of the two links which are connected by pin joints, multiplied

by the radius of the pin.


= (ω1+ω2)×r



95

154. Define rubbing velocity. What will be the expression for rubbing velocity at a pin

joint when the two links rotate in opposite direction?

amax = 2 π S

θ2ω2

Where, S = Follower lift,

= Angular velocity of cam, and

θ = Angle of ascent / descent.

155. Why sometimes the axes of translating roller followers in cam follower

mechanisms are offset from the axis of rotation of cam?

An offset is usually provided to decrease pressure angle and thereby the side thrust

in guides of follower.

156. Define the term ‘arc of contact’ in gears.

The arc of contact is the path traced by a point on the pitch circle for the beginning

to the end of engagement of two meshing teeth.

157. Name two applications of reverted gear train

Back gear of lathes

Automobile gear box

158. Why self locking screws have lesser efficiency?

η = tan αtan (α + φ )

and for self – locking screws, α or α 1.

Efficiency of self-locking screws,

η ≤ tan φtan (φ + φ )

≤ tan φtan 2 φ

≤tan φ (1 − tan2 φ)

2 tan φ≤ 1

2− tan2 φ

2

[∵ tan 2 φ =2 tan φ

1 − tan2 φ ]From this expression, we see that efficiency of self-locking screws is less than

12 or 50%

96

159. What is meant by a self-locking and a self –energised brake?

When the moment of frictional force helps to apply the brake, then the brake is said to

be self-energising brake.

When the frictional force is great enough to apply the brake with no external force,

then the brake is said to be self –locking brake.

97



160. Define sliding connectors.

Sliding connectors are used when one slider (the input) is to drive another slider

(the output). Usually the two slider operate in the same plane but in different directions.

161. Differentiate rotation and translation.

Translation is defined as a stat of motion of body for which the displacement

difference between any two points is zero.

Rotation is a state of motion of the body for which different points of the body are

equal.

162. Define number of instantaneous centre.


n (n−1 )2


163. What is low degree of complexity?

In a complex mechanism if only one radius of path curvature of one motion

transfer point is not known such a mechanism is called a mechanism with low degree of

complexity.

164. Define pressure angle in gears.


point of contact and the common tangent at the pitch point.

165. Write the procedure to draw the cam profile.

98

166. Define gear ratio.

The gear ratio of a gear train is the ratio of the angular velocity of the input gear to

the angular velocity of the output gear.

167. Write short notes on differentials.

The function of a differential gear of an automobile is:

(i) to transmit motion from engine to rear wheels, and

(ii) to rotate the rear wheels at different speeds while the automobile is taking a turn.

168. Define anti – friction bearing.

An antifriction bearing, also known as a rolling contact bearing, is used when very

little friction is needed for low differential surface speeds.

169. Differentiate multiplate clutch and cone clutch.

A cone clutch serves the same purpose as a multiplate clutch. However, instead of

mating two or more spinning disks, the cone clutch uses two conical surfaces to transmit

torque by friction. The cone clutch transfers a higher torque than plate or disk clutches of

the same size due to the wedging action and increased surface area.

99



170. Differentiate between the machine and structure.







171. Classify the constrained motion.


Completely constrained motion (eg. Square bar moving in a square hole)

In completely constrained motion ( eg. Circular shaft in a hole)

Successfully constrained motion (eg. Piston and cylinder)

172. Define instantaneous centre



173. What is the expression for Coriolis component of acceleration?

aBCC = 2 v ω



174. Define tangent cam.

When the flanks of the cam are straight and tangential to the base circle and nose

circle, the cam is known as tangent cam.

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175. What are the different motions of the follower?


Simple harmonic motion SHM


Cycloidal motion

176. State the law of gearing




gears.

177. What are the methods to avoid interference?

The height of the teeth may be reduced.

The pressure angel may be increased.

The radial flank of the pinion may be cut back (undercutting).

178. Define velocity ratio

It is defined as the ratio between velocity of the driver and the follower (or) driven.

179. What is maximum efficiency of the screw jack?

η max = 1 − sin φ1 + sin φ

Where φ = tan−1 μ

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me 6401 kom 2 marks q & a

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bar mechanism

bar crank rocker mechanism

crankrocker mechanism

double crank mechanism

types of relative motion

constrained motion

bar linkage

double rocker mechanism