Question

In a crank and slotted lever quick-return motion, the distance between the fixed centres is 150 mm and the length of the driving crank is 75mm. the ratio of the time taken on the cutting and return strokes is

(a) 1.5

(b) 2.0

(c) 2.2

(d) 2.93

The question was posed to me during an interview for a job.

My question is based upon Four Bar Chain or Quadric Cycle Chain in chapter Simple Mechanisms of Machine Kinematics

Answer 1

Correct option is (b) 2.0

The best I can explain: OA = 150mm

AB = 75 mm

sin (90 – α/2) = AB/OA

cosα/2 = 1/2

therefore, α = 120^0

β = 360^0 – 120^0 = 240^0

Quick return ratio = β/α = 240/120 = 2.