Machine Kinematics Questions and Answers – Simple Mechanisms – 2

«
»

This set of Machine Kinematics Interview Questions and Answers for Experienced people focuses on “Simple Mechanisms – 2”.

1. The relation between the number of links (l) and the number of binary joints ( j) for a kinematic chain having constrained motion is given by j = 3/2 I -2 If the left hand side of this equation is greater than right hand side, then the chain is
a) locked chain
b) completely constrained chain
c) successfully constrained chain
d) incompletely constrained chain

Explanation: If the left hand side is greater than the right hand side, therefore it is not a kinematic chain and hence no relative motion is possible. Such type of chain is called locked chain and forms a rigid frame or structure which is used in bridges and trusses.

2. In a kinematic chain, a quaternary joint is equivalent to
a) one binary joint
b) two binary joints
c) three binary joints
d) four binary joints

Explanation: When four links are joined at the same connection, the joint is called a quaternary joint. It is equivalent to three binary joints.

3. If n links are connected at the same joint, the joint is equivalent to
a) (n – 1) binary joints
b) (n – 2) binary joints
c) (2n – 1) binary joints
d) none of the mentioned

Explanation: In general, when n number of links are joined at the same connection, the joint is equivalent to (n – 1) binary joints.

4. In a 4 – bar linkage, if the lengths of shortest, longest and the other two links are denoted by s, l, p and q, then it would result in Grashof’s linkage provided that
a) l + p < s + q
b) l + s < p + q
c) l + p = s + q
d) none of the mentioned

Explanation: None

5. A kinematic chain is known as a mechanism when
a) none of the links is fixed
b) one of the links is fixed
c) two of the links are fixed
d) all of the links are fixed

Explanation: When one of the links of a kinematic chain is fixed, the chain is known as mechanism. It may be used for transmitting or transforming motion e.g. engine indicators, typewriter etc.

6. The Grubler’s criterion for determining the degrees of freedom (n) of a mechanism having plane motion is
a) n = (l – 1) – j
b) n = 2 (l – 1) – 2j
c) n = 3 (l – 1) – 2j
d) n = 4 (l – 1) – 3j

Explanation: The Grubler’s criterion applies to mechanisms with only single degree of freedom joints where the overall movability of the mechanism is unity.
i.e. n = 3 (l – 1) – 2j
where l = Number of links, and j = Number of binary joints.

7. The mechanism forms a structure, when the number of degrees of freedom (n) is equal to
a) 0
b) 1
c) 2
d) – 1

Explanation: When n = 0, then the mechanism forms a structure and no relative motion between the links is possible.
When n = 1, then the mechanism can be driven by a single input motion.
When n = 2, then two separate input motions are necessary to produce constrained motion for the mechanism.
When n = – 1 or less, then there are redundant constraints in the chain and it forms a statically indeterminate structure.

8. In a four bar chain or quadric cycle chain
a) each of the four pairs is a turning pair
b) one is a turning pair and three are sliding pairs
c) three are turning pairs and one is sliding pair
d) each of the four pairs is a sliding pair.

Explanation: A very important consideration in designing a mechanism is to ensure that the input crank makes a complete revolution relative to the other links. The mechanism in which no link makes a complete revolution will not be useful. In a four bar chain, one of the links, in particular the shortest link, will make a complete revolution relative to the other three links, if it satisfies the Grashof ’s law. Such a link is known as crank or driver.

9. Which of the following is an inversion of single slider crank chain ?
a) Beam engine
b) Watt’s indicator mechanism
c) Elliptical trammels
d) Whitworth quick return motion mechanism

Explanation: None

10. Which of the following is an inversion of double slider crank chain ?
a) Coupling rod of a locomotive
b) Pendulum pump
c) Elliptical trammels
d) Oscillating cylinder engine