KINEMATICS OF MACHINERY
Unit 1:
1. Define ‘degrees of freedom’.
It is
defined as the number of input 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.
2. 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.
3. Classify the constrained motion.
There are
three types.
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)
4. 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.
5. What are the some important inversions of four chain
mechanism?
1)
Crank-rocker mechanism.
2)
Crank-crank mechanism.
3)
Rocker-rocker mechanism.
6. 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.
7. 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.
8. What are the 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.
9. Give some examples for kinematics pairs.
1) Crank
and connecting rod
2)
Connecting and piston rod
3) Piston
and engine cylinder.
10. 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.
11. What is movability?
It includes
the 6 degree of freedom of the device as a whole, as though the ground link
were not fixed, and this applies to a kinematic chain.
12. What is mobility?
It neglects
these and considers only the internal relative motions, thus applying a
mechanism.
13. 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.
14. 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.
15. 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 motion between two members.
16. 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.
17. What is meant by motion adjustment mechanism?
The
mechanism used to adjust or modify the motion of the link are known as motion
adjustment mechanism. Motion adjustment is obtained by wedges, levers and rack
and pinion.
18. Whether a cycle chain is kinematic chain or not?
A cycle
chain is a combination of several links with turning pair. Hence it is not a
kinematic chain.
19. Define instantaneous centre.
Instantaneous
centre of a moving body may be defined as that centre which goes on changing
from one instant to another.
20. What is instantaneous axis?
Instantaneous
axis is a line drawn through an instantaneous centre and perpendicular to the
plane of motion.
21. 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.
22. 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.
23. What are the different types of links?
1) Rigid
link.
2) Flexible
link.
3) Fluid
link.
24. 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.
25. What is the use of oldham’s coupling?
It is used for transmitting motion
between two shafts which are parallel but not coaxial.
Unit 2:
1. What is kinematic analysis?
The
objective of the kinematics analysis is to determine the kinematic quantities
such as displacements, velocities and accelerations of the elements in a
mechanism.
2. What is displacement?
It is
defined as the distance moved by a body with respect to a certain fixed point.
3. What is vector?
A vector is
a straight line of a certain length possessing a starting point and a terminal
point at which it carries an arrow head.
4. Write down the different types of motion.
1) Rectilinear
motion.
2)
Curvilinear motion.
3) Circular
motion.
5. What is Rectilinear motion?
In this
motion, the particles of a body move in straight parallel paths. Such a motion
is also known as Translatory motion or straight line motion.
6. What is Curvilinear motion?
In this
motion, the particles of a body move along parallel circular arcs or curved
paths.
7. What is Circular motion?
When all
the particles of a body travel in concentric circles then the motion is said to
be circular motion.
8. What is the difference between velocity and speed/
Velocity is
defined as the rate of change of displacement of a body with respect to the
time.
Speed is
defined as the rate of change of linear displacement of a body with respect to
the time.
9. What are the different methods are used for finding the
velocity?
1) Graphical
method.
2)
Analytical method.
10. Write the different types of graphical method.
1) Relative
velocity method.
2)
Instantaneous centre method.
11. What is configuration diagram?
It is a
skeleton or a line diagram which represents a machine or a mechanism. To study
the velocity and acceleration of any mechanisms, first we have to draw the
configuration diagram. It is also known as space diagram.
12. What is acceleration?
The rate of
change of velocity with respect to time is known as acceleration.
13. What is deceleration?
The
negative acceleration is known as deceleration or retardation.
14. What is meant by coincident points?
When a
point on one link is sliding along another rotating link, then the point is
known as coincident point.
15. What is centrode?
The locus
of all instantaneous centre is known as centrode.
16. What is space centrode?
The locus of the instantaneous
centre in space during a definite motion of the body is called the space
centrode.
17. What is Body centrode?
The locus
of all instantaneous centre relative to the body itself is called the body
centrode.
18. What is Instantaneous axis?
A line
drawn through an instantaneous centre and perpendicular to the plane of motion
is called instantaneous axis.
19. What is axode?
The locus
of Instantaneous axis is known as axode.
20. Write down the different types of Instantaneous centres.
1) Fixed
Instantaneous centres.
2)
Permanent Instantaneous centres.
3) Neither
fixed nor permanent Instantaneous centres.
21. 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.
22. What are properties of instantaneous centre?
1) A rigid
link rotates instantaneously relative to another link at the instantaneous
centre for the configurations of the mechanism.
2) 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.
23. What is angular velocity ratio theorem?
The angular
velocity ratio theorem states that the angular velocity ratio of any two bodies
in planar relative to a third body is inversely proportional to the segments into
which the common instantaneous centre cuts the line of centres.
24. Explain any two methods of reducing interference in
gears.
1. The
height of the teeth may be reduced.
2. The
pressure angle may be increased.
3. The face
of gear tooth may be relieved.
25. What is the effects of centrifugal tension in belt
drives?
1.
Centrifugal tension will increase the tension on both tight and slack sides.
2.
Centrifugal tension has no effect on the power transmitted by the belt drive.
Unit 3:
1. What is a cam?
A cam is a
rotating machine element which gives reciprocating or oscillating motion to
another element known as follower.
2. Give some examples of cam.
1) Radial
or disc cams.
2)
Cylindrical or barrel cams.
3) End or
face cams.
4) Wedge
cams.
3. 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.
4. What ate the different motions of the follower?
1) Uniform
motion.
2) Simple harmonic
motion.
3) Uniform
acceleration and retardation.
4)
Cycloidal motion.
5. 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.
6. 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.
7. Define dwell period?
The period
during which the follower remains at rest is called dwell period.
8. 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.
9. 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.
10. 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.
11. Define lift or stroke in cam.
It is the
maximum travel of the follower from its lowest position to the topmost
position.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. What is cam profile?
The surface
of cam which comes into contact with follower, is known as cam profile.
18. 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.
19. 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.
20. 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.
21. What is prime circle?
The
smallest circle drawn tangent to the pitch curve is known as prime circle.
22. What is 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 cam design as it represents steepness of
the cam profile.
23. What is pitch point?
It is the
point on the pitch curve at which the pressure angle is maximum.
24. What is pitch circle?
It is the
circle passing through the pitch point and concentric with the base circle.
25. What is cam angle?
It is the
angle of rotation of the cam for a definite displacement of the follower.
Unit 4:
1. What is an angle of obliquity in gear?
It is the
angle between the common normal to two gear teeth at the point of contact and
the common tangent at the pitch point. It is also called as pressure angle.
2. What is bevel gearing? Mention its types.
When the
non-parallel or intersecting but coplanar shafts connected by gears, they are
called bevel gears and the arrangement is bevel gearing.
Types.
1) Skew
bevel gearing
2) Spiral
gearing.
3. What is meant by arc of approach?
It is the
portion of the path of contact from the beginning of the engagement to the
pitch point.
4. What is meant by arc of recess?
It is the
position of the path of contact from pitch point to the end of the engagement
to the pitch point.
5. What is meant by Arc of contact?
It is the
path traced by a point on the pitch circle from the beginning to the end of
engagement of a pair of teeth.
6. 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 point, situated on the line joining the centre of rotation of the pair of
mating gears.
7. Define normal and axial pitch in helical gears.
Normal
pitch is the distance between similar faces of adjacent teeth, along a helix on
the pitch cylinder normal to the teeth.
Axial pitch
is the distance measured parallel to the axis between similar faces of a
adjacent teeth.
8. What are the methods to avoid interference?
1. The
height of the teeth may be reduced.
2. The
pressure angle may be increased.
3. The
radial flank of the pinion may be cut back.
9. What is the advantage when arc of recess is equal to arc
of approach in a meshing gears?
When arc of
recess equal to arc of approach, the work wasted by friction is minimum and
efficiency of drive is maximum.
10. What do you know about tumbler gear?
Tumbler
gears are those which are used in lathes for reversing the direction of
rotation of driven gears.
11. Define contact ratio.
It is the
ratio of the length of arc of contact to the circular pitch is known as contact
ratio. The value gives the number of pairs of teeth in contact.
12. Where will the interference occur in an involute pinion
and gear are in mesh having same size of addendum?
There will
be an interference between the tip of pinion and flank of gear.
13. Define interference.
The
phenomenon when the tip of tooth undercuts the roots on its mating gear is
known as interference.
14. What you meant by non standard gear teeth?
The gear
teeth obtained by modifying the standard proportions of gear teeth parameters
is known as non standard gear teeth.
15. Define cycloidel tooth profile and involute tooth
profile.
A cycloid
is the curve traced by a point on the circumference of a circle which rolls without slipping on a
fixed straight line.
Involute
profile is defined as the locus of a point on a straight line which rolls
without slipping on the circumference of a circle.
16. Define Backlash.
It is the
difference between the tooth space and the tooth thickness along the pitch
circle.
Backlash
= Tooth space – Tooth thickness.
17. What is gear train?
Two or more
gears re made to mesh with each other to transmit power from one shaft to
another. Such a combination is called a gear train.
18. What are the types of gear trains?
1. Simple
gear train.
2. Compound
gear train.
3. Reverted
gear train.
4.
Epicyclic gear train.
19. Write velocity ratio in compound train of wheels?
Speed of
last follower- Product of teeth on drives.
Speed of
first driver- Product of teeth on followers.
20. Define simple gear train.
When there
is only one gear on each shaft, it is called as simple gear train.
21. What is meant compound gear train?
When there
are more than one gear on shaft, it is called a compound gear train.
22. What is the advantage of a compound gear train over a
simple gear train?
The
advantage of a compound gear train over a simple gear train is that a much
larger speed reduction from the first shaft to the last shaft can be obtained
with small gears.
23. What is reverted gear train?
When the
axes of the first and last wheels are co-axial the train is known as reverted gear
train.
24. What are the externally applied torques used to keep the
gear train in equilibrium?
1. Impart
torque on the driving member.
2.
Resisting or holding torque on the driven member.
3. Holding
or braking torque on the fixed member.
25. Where the epicyclic gear trains are used?
The
epicyclic gear trains are used in the back gear of lathe, differential gears of
the automobiles, pulley blocks, wrist watches, etc.
Unit 5:
1. What is dry friction?
The
friction that exists between two unlubricated surfaces is known as dry
friction.
2. What is greasy friction?
When the
two surfaces in contact have a minute thin layer of lubricant between them,
then it is called as greasy friction.
3. What is fluid friction?
When the
two surfaces in contact are completely separated by a lubricant, then it is
called as fluid friction.
4. State the laws of dry friction.
1. The
frictional force is directly proportional to the normal reaction between the
surfaces.
2. The
frictional force opposes the motion.
3. The
frictional force is independent of the area and the shape of the contacting
surfaces.
5. State the laws of fluid friction.
1. The
frictional force is almost independent of load.
2. The
frictional force is independent of the substances of the bearing surfaces and
opposing tendency is less.
3. The
frictional force reduces with increase in temperature of the lubricant.
6. What is angle of repose?
The angle
of repose is defined as the maximum inclination of a plane at which a body
remains in equilibrium over the inclined plane by the assistance of friction
only.
7. 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.
8. Define Co-efficient of friction.
It is
defined as the ratio of the limiting friction to the normal reaction between
two bodies.
μ
= F / Rn
9. What is the efficiency of the inclined plane?
The
efficiency of inclined plane is defined as the ratio between effort without
friction and the effort with friction.
10. Why self locking screws have lesser efficiency?
Self locking screws needs some friction on the
thread surface of the screw and nut hence it needs higher effort to lift a body
and hence automatically the efficiency decreases.
11. What are the functions of clutches?
1. It
supplies power to the transmission system.
2. It stops
the vehicle by disconnecting the engine from transmission system.
3. It is
used to change the gear and idling the engine.
4. It gives
gradual increment of speed to the wheels.
12.What is the difference between cone clutch and
centrifugal clutch?
Cone clutch
works on the principle of friction alone. But centrifugal clutch uses principle
of centrifugal force in addition with it.
13. Why friction is called as necessary evil?
Friction is
the important factor in engineering and physical applications such as belt and
ropes, jibs, clutches and brakes, so it is the necessary one.
If the
friction exceeds certain value it will cause heat, damage and wear when
applied. So it is called necessary evil.
14. What are the belt materials?
1. Leather.
2. Cotton
or fabric.
3. Rubber.
4. Balata.
5. Nylon.
15. Explain velocity ratio.
It is
defined as the ratio between velocity of the driver and follower or driven.
16. State the law of belting.
Law of
belting states that the centre line of the belt as it approaches the pulley
must lie in a plane perpendicular to the axis of the pulley or must lie in the
plane of the pulley, otherwise, the belt will runoff the pulley.
17. What is slip?
The
relative motion between belt and pulley due to insufficient friction is called
slip.
18. What is creep?
The
phenomenon of sudden contraction and expansions of belt when it passes from
slack side to tight side is called as creep.
19. What is centrifugal effect on belts?
During
operation, as the belt passes over a pulley the centrifugal effect due to its
self weight to lift the belt from the pulley surface. This reduces the normal
reaction and hence the frictional resistance.
20. What is the cross belt used instead of open belt?
1. Cross
belt is used where the direction of rotation of driven pulley is opposite to
driving pulley.
2. Where we
need more power transmission there we can use cross belt drive.
21. What is wipping?
If the
centre distance between two pulleys are too long then the belt begins to
vibrate in a direction perpendicular to the direction of motion of belt. This
phenomenon is called wipping. It can be avoided by idler pulleys.
22. Why lubrication reduces friction?
In
practical all the mating surfaces are having roughness with it. It causes
friction. If the surfaces are smooth then friction is very less. Lubrication
smoothens the mating surface by introducing oil film between it. The fluids are
having high smoothness than solids and thus lubrication reduces friction.
23. What you meant by crowning in pulley?
The process
of increasing the frictional resistance on the pulley surface is known as
crowning. It is done in order to avoid slipping of the belt.
24. What is brake?
Brake is a
device by means of which motion of a body is retarded for slowing down or to
bring it to rest which works on the principle of frictional force, it acts
against the driving force.
25. Explain self energizing.
When
moments of efforts applied on the break drum and frictional force are in the
same direction, the breaking torque becomes maximum. In such a case the brake
is said to be partially self actuating or self energizing.
