Four-Bar Mechanism

INTRODUCTION

The motion of a four-bar linkage is transformed into oscillatory motion.
The four-bar mechanism or quadrilateral linkage is a mechanism consisting on three movable bars and a fourth fixed bar (for example,the floor). The movable bars are linked to the fixed one through pivots. Grashof’s law is a formula used to analyze the type of movement made by the four-bar linkage mechanism: to obtain a continuous movement between the bars, the sum of the shortest bar and the longest bar cannot be greater than the sum of the remaining bars.
The four-bar linkage is one of the most commonly used kinematic mechanisms, for example in window hinges, conveyor belts, folding carts, etc.
The Four-Bar Mechanism, “MCA”, has been designed to demonstrate the action of a four bar mechanism with different geometrical arrangements of joints.

EXERCISES AND PRACTICAL POSSIBILITIES

1. To demonstrate the action of a four-bar mechanism with different geometrical arrangements of joints.
2. To demonstrate Grashof law.
3. To determine graphically the relationship between the angular displacements of the input crank and the output joint of a simple four-bar system.
4. To determine the velocity and acceleration of the output joint by graphical differentiation and compared with the values obtained in velocity and acceleration diagrams.