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

B-63324EN/01 PROGRAMING 4.INTERPOLATION FUNCTIONS
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- Cases where a spiral results
When an end point does not lie on the arc, a spiral results, as shown
below.
Fig.4.4 (d) Case Where a Spiral Is Produced
The arc radius changes linearly with the center angle θ(t). Spiral
interpolation is performed using a circular command that specifies one
arc radius for the start point and another arc radius for the end point. To
use spiral interpolation, set a large value in parameter No. 2410, used to
specify the limit on the arc radius error.
Limitation
- Simultaneous specification of I, J, K, and R
If I, J, K, and R addresses are specified simultaneously, the arc specified
by address R takes precedence and the other are ignored.
- Commandment of an axis not comprising the specified plane
If an axis not comprising the specified plane is commanded, an alarm is
displayed.
For example, if axis U is specified as a parallel axis to X axis when plane
XY is specified, an P/S alarm (No.0186)is displayed.
- Specifying a semicircle by R
If an arc has a central angle of nearly 180°, an error may occur when the
position of the center is calculated. To avoid this error, specify the
semicircle by R using two arcs having a central angle of nearly 90° or
specify its center position directly by I, J, and K.
γe
γ(t)
γs
Start point
Center
End point
θ(t)
˘
Start point
End point
Center θ
θ
γs
γe
)t(s)e(
s(t)
γ
γ
+γ=γ