FANUC Series 16/18/160/180-Model C Machining Center Operators Manual

PROGRAMMING
4. INTERPOLATION FUNCTIONS
B–62764EN/01
68
When a program approximates a sculptured curve with line segments, the
length of each segment differs between those portions that have mainly
a small radius of curvature and those that have mainly a large radius of
curvature. The length of the line segments is short in those portions
having a small radius of curvature, while it is long in those portions
having a large radius of curvature. The high–precision contour control of
the FANUC Series 15 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 if control is
applied to machining a curve where the radius of curvature is large and
changes only gradually. Although this effect is caused by high–precision
machining, which precisely follows a pre–programmed path, the uneven
corners that result will be judged unsatisfactory when smooth surfaces are
required.
Profile Portions having
mainly a small radius
of curvature
Portions having
mainly a large radius
of curvature
Example of machined
parts
Automobile parts Decorative parts, such
as body side moldings
Length of line segment Short Long
Resulting surfaces pro-
duced using high–preci-
sion contour control
Smooth surface even
when machining is per-
formed exactly as speci-
fied by a program
Uneven surfaces may
result when machining
is performed exactly as
specified by a program
Example of uneven surfaces (polygon) resulting from machining that
precisely follows the line segments.
In smooth interpolation mode, the CNC automatically determines,
according to the program command, whether an accurate figure is
required, such as at corners, or a smooth figure is required where the
radius of curvature is large. If a block specifies a travel distance or
direction which differs greatly from that in the preceding block, smooth
interpolation is not performed for that block. Linear interpolation is
performed exactly as specified by the program command. Programming
is thus very simple.

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