HEIDENHAIN TNC 360 User Manual - Manual (Page 25)

TNC 360 1-7
1 Introduction
1.2 Fundamentals of NC
Reference system
In order to define positions, one needs a reference system. For example,
positions on the earth's surface can be defined "absolutely" by their
geographic coordinates of longitude and latitude. The term "coordinate"
comes from the Latin word for "that which is arranged". The network of
horizontal and vertical lines around the globe constitute an "absolute
reference system" — in contrast to the "relative" definition of a position
that is referenced, for example, to some other, known location.
Cartesian coordinate system
A workpiece is normally machined on a TNC controlled milling machine
according to a workpiece-reference Cartesian coordinate system (a
rectangular coordinate system named after the French mathematician and
philosopher Renatus Cartesius; 1596 to 1650). The Cartesian
coordinate system is based on three coordinate axes X, Y and Z, which are
parallel to the machine guideways. The figure to the right illustrates the
"right hand rule" for remembering the three axis directions: the
middle finger is pointing in the positive direction of the tool axis from the
workpiece toward the tool (the Z axis), the thumb is pointing in the
positive X direction, and the index finger in the positive Y direction.
0
°
90
°
90
°
0
°
30
°
30
°
60
°
60
°
Greenwich
+X
+Y
+Z
+X
+Z
+Y
Fig. 1.10: Designations and directions of the
axes on a milling machine
Fig. 1.9: The geographic coordinate system
is an absolute reference system