ME 2203 - KINEMATICS OF MACHINERY UNIT I – BASICS OF MECHANISMS 1. Define Kinematic link. It is a resistive body which go to make a part of a machine having relative motion between them. 2. Define Kinematic pair. When two links are in contact with each other it is known as a pair. If the pair makes constrain motion it is known as kinematic pair. 3. Define Kinematic chain. When a number of links connected in space make relative motion of any point on a link with respect to any other point on the other link follow a definite law it is known as kinematic chain.
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ME 2203 - KINEMATICS OF MACHINERY - Erode ... Mark... · Web viewThe mechanism used to adjust or modify any one of the links in a mechanism is known as motion adjustment mechanism.
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ME 2203 - KINEMATICS OF MACHINERY
UNIT I – BASICS OF MECHANISMS
1. Define Kinematic link.
It is a resistive body which go to make a part of a machine having
relative motion between them.
2. Define Kinematic pair.
When two links are in contact with each other it is known as a pair. If the
pair makes constrain motion it is known as kinematic pair.
3. Define Kinematic chain.
When a number of links connected in space make relative motion of
any point on a link with respect to any other point on the other link follow a
definite law it is known as kinematic chain.
4. Write the Grubler’s criterion for determining the degrees of freedom of
a mechanism having plane motion.
n=3(l-1)-2j
h-Higher pair joint
l-Number of links
j-Lower pair joint
5. Define degree of freedom, what is meant by mobility. (Ap/May-2008)
The mobility of a mechanism is defined as the number of input
parameters which must be independently controlled in order to bring the
device into a particular position.
6. Write the Kutzbach’s relation. (Ap/May-2008)
Kutzbach’s criterion for determining the number of degrees of
freedom or movability (n) of a plane mechanism is n=3(l-1)-2j-h
n-Degree of freedom.
l-Number of links.
h-Higher pair joint
j-Lower pair joint.
7. Define Grashoff’s law and state its significance? (Ap/May-2008)
It states that in a planar four bar mechanism, the sum of shortest link
length and longest link length is not greater than the sum of remaining two
links length, if there is to be continuous relative motion between two
members.
Significance:
Grashoff’s law specifies the order in which the links are connected in
a kinematic chain.
Grashoff’s law specifies which link of the four-bar chain is fixed.
(s+1)=(p+q) should be satisfied, if not, no link will make a complete
revolution relative to another.
s= length of the shorter length
l= length of the longest link
p & q are the lengths of the other two links.
8. Define Inversion of mechanism.
The method of obtaining different mechanism by fixing different links
in a kinematic chain is known as inversion of mechanism.
9. What is meant by Mechanical advantage of mechanism?
It is defined as the ratio of output torque to the input torque also
defined as the ratio of load to effort.
M.A ideal = TB / TA
TB =driven (resisting torque)
TA =driving torque
10.Define Transmission angle.
The acute angle between follower and coupler is known as transmission
angle.
11. Define Toggle position.
If the driver and coupler lie in the same straight line at this point
mechanical advantage is maximum. Under this condition the mechanism is
known as toggle position.
12.List out few types of rocking mechanism?
Pendulum motion is called rocking mechanism.
1. Quick return motion mechanism.
2. Crank and rocker mechanism.
3. Cam and follower mechanism.
13.Define pantograph?
It is device which is used to reproduce a displacement exactly in a
enlarged scale. It is used in drawing offices, for duplicating the drawing
maps, plans, etc. It works on the principle of 4 bar chain mechanism.
Eg. Oscillating-Oscillating converter mechanism
14.Name the application of crank and slotted lever quick return motion
mechanism?
1. Shaping machines.
2. Slotting mechanism.
3. Rotary internal combustion engine.
15.Define structure?
It is an assemblage of a number of resistant bodies having no relative
motion between them and meant for carrying loads having straining action.
16.What is simple mechanism?
A mechanism with four links is known as simple mechanism.
17.Define mechanism?
When one of the links of a kinematic chain is fixed, the chain is
known as a mechanism.
18.Define equivalent mechanism; and spatial mechanism?
Equivalent mechanism: The mechanism, that obtained has the same
number of the degree of freedom, as the original mechanism called
equivalent mechanism.
Spatial mechanism: Spatial mechanism have special geometric
characteristics in that all revolute axes are parallel and perpendicular to the
plane of motion and all prism axes lie in the plane of motion.
19.Define double slider crank chain mechanism?
A kinematic chain which consists of two turning pair and two sliding
pair is known as double slider crank mechanism.
20.Define single slider crank chain mechanism?
A single slider crank chain is a modification of the basic four bar
chain. It consists of one sliding pair and three turning pair.
Applications:
Rotary or Gnome engines Crank and slotted lever mechanism
Oscillating cylinder engine Ball engine
Hand pump
21.Define Sliding pair.
In a sliding pair minimum number of degree of freedom is only one.
22.Define Turning pair.
In a turning pair also degree of freedom is one. When two links are
connected such that one link revolves around another link it forms a turning
pair.
23.Define cylindrical pair.
In a cylindrical pair degree of freedom is two. If one link turns and
slides along another link it forms a cylindrical pair.
24.Define Rolling pair.
In a rolling pair degree of freedom is two. The object moves both
linearly and angularly.
25.Define Spherical pair.
In a spherical pair degree of freedom is three. It can both move left
and right,up and down, and rotate along the same point.
26.Define Lower pair.
If contact between two links is surface contact also having degree of
freedom one, then the pair is known as lower pair.
Example: Sliding pair.
27.Define higher pair.
If contact between two links is either point contact or line contact then
the pair is known as higher pair.
Example: Point contact-Rolling pair.
Line contact-Cylindrical pair.
28.Define Mechanical pair.
(a) Open pair.
In this pair everything is open to the atmosphere.
(b) Closed pair.
In this pair everything is closed from the atmosphere
29.Give any two example of Snap action mechanism.
It is used in calling bells, bicycle bells etc.
30.What is meant by motion adjustment mechanism?
The mechanism used to adjust or modify any one of the links in a
mechanism is known as motion adjustment mechanism. Differential screw
used in bench vice, pipe wrench, Lathe chuck and screw jack are some of the
examples of motion adjustment mechanism.
31.What is meant by Scott Russel mechanism?
This is one of the mechanisms to produce straight line motion
mechanism. The mechanism in which the straight line is copied from a
existing straight line constrain is known as Scott Russel mechanism.
32.What are the types of quick return motion mechanism?
Quick return motion mechanisms are of two types. They are,
1) Crank and slotted lever quick return motion mechanism.
2) Whitworth quick return motion mechanism
33.What are the different types of joints?
a. Binary Joint b. Ternary Joint c. Quaternary Joint
34.What is meant by binary Joint?
If two links are connected at the same junction it is called binary joint.
Illustration:
In the above figure ( kinetic Chain)
Number of binary joints j = 4
D Link (3) C
Link (4) Link (2)
A Link (1) B
L = 2/3 (j+2)
L = 4
4=2/3 (6)
4=4
L.H.S. = R.H.S.
It is a kinetic chain based on Kline’s equation.
35.What is meant by Ternary Joint?
If three links are connected to the same junction, then is known
ternary joint.
One ternary joint is equivalent to two binary joints.
Illustration:
In the fig:
No of binary joints = A+B+C = 3
Number of Ternary joints = C+E
Equivalent binary joints = 2+2 = 4
Hence total number of binary joints = 3 + 4 = 7
Based on Kline’s Equation
L = 2/3 (J+2)
6 = 2/3 (9)
D Link(4) Link (3)
E Link (5) C
Link (6) Link (2)
A Link (1) B
6=6
Hence is a Kinematic Chain.
36.What is meant by Quaternary Joint?
If four links are connected to the same joint then it is a Quaternary
joint. One quaternary joint = Three binary joints
In the figure Number of binary joint C = 1
Number of ternary joints = A + B + E + F
Link (11)
Link (5)
Link (3)
Link (4)
Link (1)
Link (2)Link (8)
Link (7)
Link (9)Link (10)
Link (6)
A B
D
C
E
F
G
Equivalent binary joints = 8
Number of quaternary joints = D, G
Equivalent binary joints = 6,
Total Number of Equivalent binary joints
J = 15
Based on Kline’s equation
L = 2/3 (I+2)
11 = 2/3 (17)
L.H.S. R.H.S
Hence it is not a kinematics chain. The chain is represented as locked chain.
In the figure if the link (DG) is deleted then it
would be a kinematic chain.
37.Compare Movability and Mobility.
Movability includes the six degrees of freedom of the device as a
whole, as though the ground link was not fixed and thus applies to a
kinematic chain.
Mobility neglects these and considers only the internal relative
motions, thus applying to a mechanism.
38.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.
39.What are the types of inversion of four Bar Kinematic Chain?
The inversions of four bar kinematic chain are as follows
-Beam engine, coupling rod of a locomotive, Watt’s indicator
mechanism.
40. Differentiate a kinematic chain from a mechanism.