Four Bar Linkage: Learn the Principle, Inversions, and Applications with Solved Examples

 A four bar linkage is a mechanical linkage that consists of four rigid bars or links connected by four joints to form a closed loop. The linkage can be used to transmit motion and force between the links and can be found in many mechanical devices, from car suspensions to robotic arms.

Grashof's theorem states that in a four bar linkage, the sum of the shortest and longest link lengths should be less than or equal to the sum of the other two link lengths for the linkage to have a complete rotation.

The four bar linkage can be classified into four types based on the arrangement of the links and the position of the input and output links. They are crank-rocker, rocker-crank, double-rocker, and double-crank.

Four bar linkages provide smooth and efficient motion transfer between links, have a simple and compact design, and can be easily modified to adjust the motion and force transmission characteristics.

Four bar linkages have limited motion range and may not be suitable for applications that require more complex motion or high loads. The links and joints may also wear out over time, which can affect the performance of the linkage.