Articulated Mechanisms ' Basis. The Four Bar Linkage

The articulated quadrilateral or 4-bar mechanism is a highly adaptable universal mechanism. You'll find it in car steering with the Janteau quadrilateral, in car suspension with the superimposed wishbone, or rigid axle guidance with the Watt three-bar, and in accessories with windshield wiper controls. It should also be remembered that the connecting rod-crank system is only a special case, like the Mac Pherson suspension system or the toggle joint used in amplifiers.

The so-called 4-bar mechanism is one of the reference mechanisms in kinematics. Its first studies and industrial applications are due to Watt's three-bar system. For a long time, the frame was not counted as a bar. These gave rise, and still give rise, to a large number of studies and realizations. Theoretical studies have also spawned a large number of mathematical developments that have spread to other fields. Robotics has provided a new and powerful impetus.

In this first article, we'll set out the general methods. This will be followed by a second article devoted entirely to applications.