Question

22. A kinematic chain is known as 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 the links are fixed

Hint:

Fixing different links of a single kinematic chain to produce different mechanisms is called kinematic inversion.
For any mechanism to transmit motion, exactly one link must be designated as the fixed frame.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A kinematic chain is a simple assembly of links connected by kinematic pairs that allows relative motion but lacks a defined stationary reference.
To transform a kinematic chain into a mechanism, we must establish a fixed frame of reference from which the relative motion of the remaining links can be measured and utilized.

Step 2: Detailed Explanation:
When none of the links in a kinematic chain are fixed, the entire assembly can move arbitrarily through space as a single body, meaning there is no defined output motion relative to a stationary platform.
Fixing exactly one link of the chain establishes a ground or frame, which serves as a stable reference coordinate system.
This fixed link constrains the movement of the other links, converting arbitrary relative motions into a single, predictable, and useful output path.
If more than one link is fixed, such as fixing two links in a four-bar chain, the degrees of freedom of the assembly drop to zero or negative values.
This turns the entire system into a rigid structure or a redundant frame, completely preventing any relative motion between the links.
Thus, the defining condition that transforms a kinematic chain into a mechanism is the fixing of exactly one link.

Step 3: Final Answer:
A kinematic chain is known as a mechanism when one of its links is fixed.