Answer to Question #300909 in Mechanical Engineering for Love

Question

Axes Q2 and Q4 are fixed. Q2A = 1 1/2 inches., AB = 3 inches., Q4B= 2 inches., and Q2Q4=3 inches. crank 2 is the driver turning counterclockwise. the proportions are such that, while 2 makes a complete revolution , 4 oscillates through a certain angle. Find the two extreme positions of the center line Q4B of crank 4.

Answer 1

A four-link mechanism with four revolute joints is commonly called a four-bar mechanism.

Four-bar linkages can be used for many mechanical purposes, including to: convert rotational motion to reciprocating motion (e.g., pumpjack examples below) convert reciprocating motion to rotational motion (e.g., bicycle examples below) constrain motion

Correlation of the angular rotations of the links connected to the fixed link (commonly known as correlation of crank angles or function generation). In such applications we would like to have a certain functional relation such as q₁₄ = f(q₁₂) to be realised by the four-bar mechanism. A simple example will be to convert a linear scale to a logarithmic scale within a certain range.