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

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Either of two types of machining can be selected, depending on the
program command.
1) For those portions where the accuracy of the figure is critical,
such as at corners, machining is performed exactly as specified by
the program command.
2) For those portions having a large radius of curvature where a
smooth figure must be created, points along the machining path
are interpolated with a smooth curve, calculated from the
polygonal lines specified with the program command (smooth
G5.1Q2X0Y0Z0 ; : Starting of smooth interpolation mode
G5.1Q0 ; : Cancellation of smooth interpolation mode
- Characteristics of smooth interpolation
To machine a part having sculptured surfaces, such as metal moldings
used in automobiles and airplanes, a part program usually
approximates the sculptured surfaces with minute line segments. As
shown in the following figure, a sculptured curve is normally
approximated using line segments with a tolerance of about 10 ˚m.
: Specified point
Fig.4.16 (a) Approximation with Line Segments
When a program approximates a sculptured curve with line segments,
the length of each segment differs between those portions that have a
small radius of curvature and those that have a large radius of curvature.
The line segments are short in those portions having a small radius of
curvature, while they are long in those portions having a large radius of
The CNC moves the tool along a programmed path thus enabling
highly precise machining. This means that the tool movement
precisely follows the line segments used to approximate a sculptured
curve. This may result in a non-smooth machined curve when a curve
in which the radius of curvature is large and changes only gradually is
machined. Although this effect is a result of high-precision machining,

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