In analyzing the motion of a machine or mechanism, it is often difficult to visualize the movement of the components in a full assembly drawing. So we need to use kinematic diagrams (kinematic scheme) to illustrate the connectivity of links and joints of a mechanism or machine instead of full assembly drawing.
The purpose of using these kinematic diagrams is similar to electrical circuit schematic or piping diagrams in that they represent variables that affect the primary function of the mechanism.
Below image shows the typical conventions used for representing kinematic diagrams for different components like simple link, complex link, pin joint, slider joint, cam joint and gear joint.
A kinematic diagram should be drawn to a scale proportional to the actual mechanism. For convenient note, the links are numbered, starting with the frame as link number ‘1’ and the joints need to be lettered with alphabets.