Six-point positioning principle

A free object has six possible activities for three mutually perpendicular coordinate systems, three of which are movement and three are rotation. It is customary to call this possibility of activity degree of freedom, so any free object in space has a total of six degrees of freedom.
As shown in the following figure:

The degree of freedom of the workpiece in the air

The position of an unconstrained rigid body in space is uncertain. It has six degrees of freedom: . In order to make the rigid body have a certain
position in space, its six degrees of freedom must be limited.
Positioning is to use various positioning elements of different shapes to limit the degrees of freedom of the workpiece.
Six-point positioning principle: The method of using six support points to limit the six degrees of freedom of the workpiece so that the workpiece can get the correct processing position in the fixture is called the six-point positioning principle.
Emphasis: use six support points, not six positioning elements