Subject: Kinematics of Machinery

Topic: Kinetics of Rigid Bodies

Difficulty: High

A kinematic chain which consist of two turning pairs and two sliding pairs is known as double slider crank chain, as shown in fig.3,we see that the link 2 and link 1 form one turning pair and link 2 and link 3 from the second turning pair. The link 3 and link 4 form one sliding pair and link 1 and link 4 form the second sliding pair.

The following are three inversions of a double slider crank chain are important from the subject point of view;

1. Elliptical trammels
2. Scotch yoke mechanism
3. oldham’s coupling

Scotch yoke mechanism:

This mechanism is used for converting rotary machine into a reciprocating motion. The inversion is obtained by fixing either the link 1 or link 3. In fig , link 1 is fixed .in this mechanism, when the link 2 (which correspond to crank) rotates about B as centres, the link 4 (which correspond to a frame) reciprocates. The fixed link 1 guides the frame.