Engineering Questions with Answers - Multiple Choice Questions
Machine Kinematics Questions and Answers – Types of Kinematic Chains
Scotch yoke mechanism is used to generate
a) Sine functions
b) Square roots
Explanation: In Scotch Yoke mechanism, the constant rotation of the crank produces harmonic translation of the yoke. Its four binary links are:
1. Fixed link
3. Sliding Block
Which of the following are inversions of a double slider crank chain?
1. Whitworth return motion 2. Scotch Yoke
3. Oldham’s Coupling 4. Rotary engine
Select correct answer using the codes given below:
a) 1 and 2
b) 1, 3 and 4
c) 2 and 3
d) 2, 3 and 4
Explanation: Double slider crank mechanism
It has four binary links, two revolute pairs, two sliding pairs. Its various types are:
1. Scotch Yoke mechanism
2. Oldhams Coupling
3. Elliptical Trammel.
Oldham’s coupling is used to transmit power between two parallel shafts which are slightly offset.
Explanation: It is used for transmitting angular velocity between two parallel but eccentric shafts.
In Oldham’s coupling the condition for maximum speed ratio is
c) w1/W = 1/cosα
d) w1/W = 1/sinα
Explanation: w1/W = cosα/1 – cos2ϴsin2α
For maximum speed ratio cos2ϴ = 1
Therefore, w1/W = 1/cosα.
The relative acceleration of two points which are at variable distance apart on a moving link can be determined by using the
a) three centers in line theorem
b) instantaneous centre of rotation method
c) Coriolis component of acceleration method
d) Klein’s construction
Explanation: The relative acceleration of two variable points on a moving link can be determined by using the instantaneous centre of rotation method.
What is the number of instantaneous centres of rotation for a 6-link mechanism?
Explanation: N = n(n – 1)/2 = 6 x (6 – 1)/2 = 15.
For one degree of freedom planer mechanism having links, which one of the following is the possible combination?
a) Four binary links and two ternary links
b) Four ternary links and two binary links
c) Three ternary links and three binary links
d) One ternary link and five binary links
Explanation: From Grubler’s criteria 1 = 3(l – 1) – 2j
or, j = 3/2l – 2 for six link
j = 3/2 x 6 – 2 = 7 1 ternary link = 2 binary link
a) j = 4 + 2 x 2 ≠ 7
b) j = 4 x 2 + 2 ≠ 7
c) j = 3 x 2 + 2 ≠ 7
d) j = 1 x 2 + 5 ≠ 7 the ans is d.
Inversion of a kinematic chain relative to some other links is a property of the chain and is not that of the mechanism.
Explanation: In a kinematic inversion relative motion does not change but absolute motion change drastically.
In a shaping operation, the average cutting speed is ( Stroke length S, Number of strokes per minute N, Quick return ratio R)
c) NS(1 + R)
d) NS(1 + R)/2
Explanation: Time for forward stroke + Tf
Time for return stroke = Tr
R = Tr/Tf
Therefore, time for only one cutting stroke(T) = 1/N x Tf/(Tf + Tr)
Average cutting speed = S/T = SN(Tf + Tr)/Tf = SN(1 + R).
Ina kinematic inversion, the relative motions between links of the mechanism change as different links are made the frame by turns.
Explanation: Through the process of inversion the relative motions between the various links is not changed in any manner but their absolute motions may be changed drastically.
An elliptical trammel is a mechanism with three prismatic pairs and one revolute pair.
Explanation: Elliptical trammels have two sliding pairs and two turning pairs. It is an instrument used for drawing ellipse.