The four-bar mechanism is the quintessential example of what Reuleaux called a kinematic chain. In this planar mechanism, four links are constrained by four cylindrical joints. When one link is fixed or grounded, the motion of a second link determines the motion of the third and fourth links.

In this model the linkage is demountable from the pedestal so that the instructor can fix different links thereby obtaining four inversions. These inversions can be realized with the help of the model pedestal H1.(See Fig. 21, Reuleaux's Kinematics of Machinery.) For example in one inversion a rotary motion of the crank link produces an oscillatory motion in the driven link (Fig. 11), while in another inversion a rotary motion of the crank produces a rotary motion of the opposite link, sometimes called a drag link coupling (Fig. 24).

Francis Moon 2003-05-29