# FANUC Series 16/18/160/180-Model C Machining Center Operators Manual PROGRAMMING
B–62764EN/01
4. INTERPOLATION FUNCTIONS
59
An involute curve on the X–Y plane is defined as follows ;
X (θ)=R [cos θ+ (θ-θ
0
) sin θ] +X
0
Y (θ)=R [sin θ- (θ-θ
0
) cos θ] +Y
0
where,
X
0
, Y
0
: Coordinates of the center of a base circle
θ
0
: Angle of the start point of an involute curve
θ : Angle of the point where a tangent from the current position
to the base circle contacts the base circle
X (θ), Y (θ): Current position on the X–axis and Y–axis
(X,Y)
θ0
(X0,Y0)
R
θ
X
Y
Start point
End point
Involute curve
Base circle
Fig.4.8 (a) Involute Curve
Involute curves on the Z–X plane and Y–Z plane are defined in the same
way as an involute curve on the X–Y plane.
The end point of an involute curve is specified using address X, Y, or Z.
An absolute value or incremental value is used to specify an X, Y, or Z
value. When using an incremental value, specify the coordinates of the
end point viewed from the start point of the involute curve.
When no end point is specified, P/S alarm No. 241 is issued.
If the specified start point or end point lies within the base circle, P/S
alarm No. 242 is issued. The same alarm is issued if cutter compensation
C causes the offset vector to enter the base circle. Be particularly careful
when applying an offset to the inside of an involute curve.
The center of a base circle is specified with I, J, and K, corresponding to
X, Y, and Z. The value following I, J, or K is a vector component defined
when the center of the base circle is viewed from the start point of the
involute curve; this value must always be specified as an incremental
value, regardless of the G90/G91 setting. Assign a sign to I, J, and K
according to the direction.
If I, J, and K are all left unspecified, or I0J0K0 is specified, P/S alarm No.
241 or No. 242 is issued.
If R is not specified, or R < 0, P/S alarm No. 241 or No. 242 is issued.
Explanations
D Involute curve
D Start point and end point
D Base circle specification 