Question

In the crank and slotted lever type quick return mechanism, if the length of the fixed link AB is 50 cm and that of the crank BC is 20 cm, the quick return ratio is

• A. 1.7
• B. 1.8
• C. 2.0
• D. 2.4

Answer 1

The correct option is A 1.7


At extreme position crank BC becomes perpendicular to link AD thus

$q_r=\frac{\beta }{\alpha }=\frac{\text{time taken in forward stroke}}{\text{time taken in return stroke}}$

$\cos \frac{\alpha }{2}=\frac{BC}{AB}=\frac{20}{50}$

$\frac{\alpha }{2}=66.42$

$\therefore \alpha =132.84$

$\beta =360-132.84=227.16$

$q_r=\frac{\beta }{\alpha }=\frac{227.16}{132.84}=1.71$