
B–63523EN–1/03
6. INTERPOLATION FUNCTION
751
Many computer–aided design (CAD) systems used to design metal dies
for automobiles and airplanes utilize non–uniform rational B–spline
(NURBS) to express a sculptured surface or curve for the metal dies.
This function allows NURBS curve expression to be directly specified to
the CNC. This eliminates the need for approximating the NURBS curve
with small line segments. This offers the following advantages:
1. Elimination of approximation error caused by small line segments
2. Short part program
3. No break between blocks when small blocks are executed at high
speed
4. No need for high–speed transfer from the host computer to the CNC
When this function is used, a computer–aided machining (CAM) system
creates a NURBS curve according to the NURBS expression output from
the CAD system, after compensating for the length of the tool holder, tool
diameter, and other tool elements. The NURBS curve is programmed in
the NC format by using these three defining parameters: control point,
weight, and knot.
CAM (Creating an NC part program)
CAD (Designing a metal die)
Generating a metal die surface
(NURBS surface or curve)
Studying the machining method and others
Tool compensation file
NC part program after tool compensation
(NURBS curve)
CNC
equipment
Machine tool
NURBS curve (control point, weight, knot)
Fig. 6.18 NC part program for machining a metal die
according to a NURBS curve
6.18
NURBS
INTERPOLATION
(M SERIES)
General