Whitworth quick-return (crank-and-slotted lever) mechanism from a slider–crank chain: Which link is kept fixed to obtain this inversion? Identify the fixed link choice that produces unequal cutting and return strokes (quick return characteristic). Choose the correct option.

Given data

• We form Whitworth quick-return as an inversion of the slider–crank chain.

Concept / Approach
Different inversions arise by fixing different links.Fixing the shortest link (crank) yields the crank-and-slotted lever/Whitworth mechanism that gives a quick return (shorter time for the return stroke).

Reasoning
The geometry produced by fixing the crank creates non-symmetric angular travel of the slotted lever about its mean, hence different cutting/return times.

Common pitfalls
Confusing with fixing the slider (a different inversion leading to other mechanisms).

Final Answer
Smallest link (crank) is fixed