Six Degrees of Freedom

The six degrees of freedom for one axis are:

1. Pitch
2. Yaw
3. Roll
4. Linear positioning
5. Side to side straightness
6. Up and down straightness

This picture shows pitch, yaw and roll for X-Axis.  These are the three angular degrees of freedom.



Linear positioning represents the linear displacement for an axis.   In other words if an axis is commanded to move one inch, one inch is how much it has been displaced.   If the axis does not move one inch then the amount it is in error of one inch is called it's linear positioning error.

Straightness for an horizontal axes is represented in two directions, up and down, and side to side.   If an axis does not travel straight (or flat) along it's path, it has straightness errors.

CNC machines normally have more than one linear axis.  Generally the other axes are perpendicular or square to each other.   Once another axis is introduced we also add another degree of freedom for each axis, a squareness degree of freedom.   In the above picture there are three axes directions shown, X, Y, and Z so there are three squareness degrees of freedom, X/Y, X/Z, and Y/Z.   For this three axis example there are now 21 degrees of freedom.   The six degrees of freedom for each axis plus the three squareness degrees of freedom.  6 + 6 + 6 + 3 = 21.