Fanuc Series 15i/150i-MA (Programming) Operators Manual

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Many computer-aided design (CAD) systems used to design metal dies
for automobiles utilize non-uniform rational B-spline (NURBS) to
express a sculptured surface or curve for the metal dies.
This function enables NURBS curve expression to be directly specified
to the CNC. This eliminates the need for approximating the NURBS
curve with minute line segments. This offers the following advantages:
1. No error due to approximation of a NURBS curve by small line
2. Short part program
3. No break between blocks when small blocks are executed at high
4. No need for high-speed transfer from the host computer to the
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.
Fig.4.17 (a) NC part program for machining a metal die according to a
NURBS curve
The CNC executes NURBS interpolation while smoothly accelerating
or decelerating the movement so that the acceleration on each axis will
not exceed the allowable maximum acceleration of the machine. In this
CAM (creating an NC part program)
CAD (designing a metal die)
Generating a metal die surface
(NURBS surface or curve)
Studying the machining
method, etc.
Tool compensation file
NC part program after tool compensation
(NURBS curve)
Machine tool
NURBS curve (control point, weight, knot)

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