Subject: Kinematics of Machinery

Topic: Special Mechanism

Difficulty: Low

It is a four bar mechanism in which the crossed links OA and $O_{1}$B are of equal length, as shown in fig.9. the point P, which is the mid-point of AB traces out an approximately straight line parallel to $OO_{1}$. The proportion of the links are, usually, such that point P is exactly above O or $O_{1}$ in the extreme positions of the mechanism i.e. when BA lies along OA or when BA lies along $BO_{1}$,It may be noted that the point P will lie on a straight parallel to $OO_{1}$, in the two extreme positions and in the mid position, if the length of the links are in proportions

$AB:OO_{1}:OA =1:2:2.5$