Test: Simple Mechanisms - 3 - Mechanical Engineering MCQ

1 quarternary joint is equivalent to three primary joint and 1 turnery joint is equal to 2 binary joint.

This device is known as telescopic hand.

It has 4 loop and 10 link hence degree of freedom is N - 9 i.e., one.

In Belt and pulley due to line contact they formed higher pair.

Method of obtaining different mechanism by fixing different link of a kinematic chain is known as inversion.

A four-bar chain consists of four revolute pair.

In the equation
f = 3(n -1) - 2j
n = Number of links
j = Number of lower pair

Single slider crank chain is a four-link mechanism. By fixing, in turn, different links in a kinematic chain, an inversion is obtained and we can obtain as many mechanisms as the links in a kinematic chain. There are the following inversions:

1. Pendulum pump or Bull engine

2. Oscillating cylinder engine

3. Rotary internal combustion engine or Gnome engine

4. Crank and slotted lever quick return motion mechanism or Whitworth quick return motion mechanism

Crank and.slotted lever type quick return mechanism is used in slotter machine.

Inversion of single slider crank mechanism are
1. Simple slider crank mechanism
2. Whitworth quick return mechanism
3. Crank and slotted lever mechanism
4. Hand pump mechanism

For toggle conditions mechanical advantage in infinite.

Inversion of double slider crank mechanism
1. Skotch Yoke
2. Elliptical Trammel
3. Oldham Coupling

Degree of freedom
f = 3 (N - 1) - 2p₁
where
N = number of links
p₁ = number of revolute pair
Given, N = 5 , p₁ = 5
Hence f = 3(5 - 1) - 2 x 5 = 2

In this, N = 4
P₁ = 5
DOF = 3(N - 1) - 2P₁
DOF = 3(4 - 1) - 2 x 5
DOF = 9 - 10 = -1

The angle between the output link and the coupler is known as transmission angle.

For a four bar mechanism If S + L ≤ Sum of other two and if smallest link is fixed then crank-crank mechanism can be obtained.

For complete revolution of output link
Shortest link + Largest < Sum of other two link

If coupler is longest link, then
600 + 300 ≤ L + 500 
L ≤ 400
If output is longest link, then
300 + L ≤ 600 + 500
L ≤ 800
Hence 400 < L < 800

P. Higher kinematic pair - Line contact
Q. Lower kinematic pair - Surface contact
R. Quick return mechanism - Shaper
S. Mobility of a linkage - Grubler’s equation

Number of links = 5
Number of lower pair (Joint) = 5
Degree of freedom
f = 3(N - 1) - 2p₁
f = 3(5 - 1) - 2 x 5
f= 2
Since DOF > 1
Hence it is unconstrained kinematic chain.

It is known as elliptical trammel hance, it wiii trace elliptical path.

OC = 7 cm (longest link)

OA = 3 cm (shortest link)

AB = 5 cm and BC = 6 cm

OA + OC = 7 + 3 = 10 cm

AB + BC = 11 cm

Since OA + OC < AB + BC

i.e. the sum of shortest and longest link is less than the sum of other two links. Thus, the given links form a Grashoff chain.

According to Grashoff law:

(i) The double crank mechanism is obtained if the shortest link is fixed.

(ii) Crank – rocker mechanism is obtained if link adjacent to shortest link, is fixed.

(iii) Double rocker mechanism is obtained if link opposite to shortest link, is fixed.

Here the link adjacent to the shortest link is fixed. Thus, the mechanism is a crank-rocker mechanism.

Degree of freedom is given by
f = 3(N - 1) - 2 p₁ = 3(8 - 1) - (2 x 10) = 1

The configuration is a toggle condition and in toggle condition mechanical advantage is infinite.

P. Scott - Russel mechanism - straight line motion
Q. Geneva Mechanism - intermittent motion
R. Off - set slider crank mechanism - quick return motion
S. Scotch yoke mechanism - simple harmonic motion.