Question 16.1: A four-link mechanism has the dimensions as: a=1.5 cm, b=4.5...

Procedure:
First limit position
1. Draw points A and B, 6 cm apart representing d=6.0 cm
2. From point A draw an arc of 6 cm (a+b=6.0 cm) and from point B draw an arc of 4.5 cm (c=4.5 cm).
3. These arcs intersect at point C.
4. Locate point D on AC such that AD=a=1.5 cm.
5. AD, DC and BC represent input link, coupler and output link respectively. The angle between AD and DC is 180°. This is the first limit position as shown in Fig.16.5(a).
Second limit position
1. Draw points A and B, 6 cm apart as d=6.0 cm. (Fig.16.5(b)).
2. From point A draw a circle of radius AC=b – a=4.5  1.5=3.0 cm.
3. From B draw a circle of radius 4.5 cm i.e., c=4.5 cm. These circles (arcs) intersect at point C.

4. Join A, C and B. Draw AD=a=1.5 cm
5. Thus angle between AD, input link and AC, the coupler is 360°.

Note: For drawing the dead centre position, arc of radius (b+c) is drawn at point B and another arc is drawn from A with radius ‘a’. Both arcs intersect at point D. This is for first dead centre position.
For the second dead centre position, an arc of radius (b – c) is drawn from point B.