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FANUC Series 30i/300i/300is-MODEL A. Machining Center System. User's manual - page 23

4.INTERPOLATION FUNCTIONS

PROGRAMMING

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Example
- The next block to G31 is an incremental programming

G31 G91 X100.0 F100;

Y50.0;

50.0

100.0

Skip signal is input here

Actual motion

Motion without skip signal

Fig. 4.18 (a) The next block is an incremental programming

- The next block to G31 is an absolute programming for 1 axis

G31 G90 X200.0 F100;

Y100.0;

Y100.0

Skip signal is input here

Actual motion

Motion without skip signal

X200.0

Fig. 4.18 (b) The next block is an absolute programming for 1 axis

- The next block to G31 is an absolute programming for 2 axes

100

200

300

Actual motion

Motion without skip signal

Skip signal is input here

(300,100)

100

G31 G90 X200.0 F100;

X300.0 Y100.0;

Fig. 4.18 (c) The next block is an absolute programming for 2 axes

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4.19

MULTI-STEP SKIP (G31)

In a block specifying P1 to P4 after G31, the multi-step skip function
stores coordinates in a custom macro variable when a skip signal
(4-point or 8-point ; 8-point when a high-speed skip signal is used) is
turned on. In the block where Q1 to Q4 are specified after G04, dwell
can be skipped when skip signals (four or eight signals, or eight
signals when high-speed skip signals are used) are input.
A skip signal from equipment such as a fixed-dimension size
measuring instrument can be used to skip programs being executed.
In plunge grinding, for example, a series of operations from rough
machining to spark-out can be performed automatically by applying a
skip signal each time rough machining, semi-fine machining,
fine-machining, or spark-out operation is completed.

Format

Move command

G31

;

_ : End point

F_ : Feedrate
P_ : P1 to P4

Dwell

G04X(U,P)

);

X(U,P)_ : Dwell time
Q_ : Q1 to Q4

Explanation

Multi-step skip is caused by specifying P1, P2, P3, or P4 in a G31
block. For an explanation of selecting (P1, P2, P3, or P4), refer to the
manual supplied by the machine tool builder.
Specifying Q1, Q2, Q3, or Q4 in G04 (dwell command) enables dwell
skip in a similar way to specifying G31. A skip may occur even if Q is
not specified. For an explanation of selecting (Q1, Q2, Q3, or Q4),
refer to the manual supplied by the machine tool builder.

- Correspondence to skip signals

Parameter Nos. 6202 to 6205 can be used to specify whether the
4-point or 8-point skip signal is used (when a high-speed skip signal is
used). Specification is not limited to one-to-one correspondence. It is
possible to specify that one skip signal correspond to two or more Pn's
or Qn's (n=1, 2, 3, 4). Also, bits 0 (DS1) and 7 (DS8) parameter
No.6206 can be used to specify dwell.

CAUTION

Dwell is not skipped when Qn is not specified and
bits 0 (DS1) and 7 (DS8) parameter No.6206 are
not set.

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4.20

HIGH-SPEED SKIP SIGNAL (G31)

The skip function operates based on a high-speed skip signal
(connected directly to the NC; not via the PMC) instead of an ordinary
skip signal. In this case, up to eight signals can be input.
Delay and error of skip signal input is 0 - 2 msec at the NC side (not
considering those at the PMC side).
This high-speed skip signal input function keeps this value to 0.1 msec
or less, thus allowing high precision measurement.
For details, refer to the appropriate manual supplied from the machine
tool builder.

Format

G31

;

G31; One-shot G code (If is effective only in the block in

which it is specified)

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4.21

CONTINUOUS HIGH-SPEED SKIP FUNCTION

Overview

The continuous high-speed skip function is used to read absolute
coordinates using high-speed skip signals HDI0 to HDI7. Inputting a
high-speed skip signal in a G31P90 block causes absolute coordinates
to be stored in custom macro variables #5061 to #5080. For a system
with more than 20 axes, they are stored in variables #100151 to
#100182. An axis movement does not stop even if a signal is input, so
that the coordinates of multiple points can be read.
Using bit 5 (CSE) of parameter No. 6201, it is possible to enable both
the rising and falling edges of a high-speed skip signal.
For details, refer to the manual supplied by the machine tool builder.

Format

G31 P90

IP ;

G31; One-shot G code (If is effective only in the block in

which it is specified)

Explanation
- Custom macro variables

If a high-speed skip signal is input when G31P90 is issued, absolute
coordinates are stored in custom macro variables #5061 to #5080. For
a system exceeding 20 axes, they are stored in variables #100151 to
#100182.
These variables are updated as soon as the axis reaches a new skip
position. It is, therefore, necessary to specify a speed so that the axis
reaches the next skip position in a period of time longer than it takes
for the application to read the variable values.

System with 20 or less axes

System with more than 20 axes

#5061

Coordinates on the first
axis

#100151

Coordinates on the first
axis

#5062

Coordinates on the
second axis

#100152

Coordinates on the
second axis

#5063

Coordinates on the third
axis

#100153

Coordinates on the third
axis

: :

#5079

Coordinates on the 19th
axis

#100181

Coordinates on the 31st
axis

#5080

Coordinates on the 20th
axis

#100182

Coordinates on the
32nd axis

- High-speed skip signal

This function works with a high-speed skip signal only.
Select a high-speed skip signal with bits 0 to 7 (9S1 to 9S8) of
parameter No. 6208.

- Ending a block

A G31P90 block is ended when the axis reaches the end point.

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Limitation

The continuous high-speed skip function (G31P90) block must be a
command for a single axis only. If an attempt is made to specify two
or more axes, P/S alarm No. 5068 is issued.

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4.22

TORQUE LIMIT SKIP

Overview

Executing the move command following G31P99 (or G31P98) while
overriding the torque limit

on the servo motor enables cutting feed in

to be performed in the same way as in linear interpolation (G01). If,
during the movement with this command, the torque of the servo
motor reaches the torque limit value (torque limit on the servo motor
multiplied by the override) due to pressing or other causes or a skip
signal (including a high-speed skip signal) is input, any remaining
move commands will be canceled, and the next block is executed.
(The operation of canceling any remaining move commands and
executing the next block is called a skip operation in the remainder of
this document.)
It is possible to override the torque limit on the servo motor with the
following command methods:
(1) Execute the torque limit override command in the PMC window.
(2) Execute an address Q command in the same block as that

containing a G31P99 (or G31P98) command.

*1 : The torque limit on the servo motor is automatically set to a

value conforming to the motor type setting.

Format

G31 P98 Q_

_ F_

G31 P99 Q_

_ F_

G31 : Skip command (one-shot G code)
P98 : Performs a skip operation if the torque of the servo motor

reaches the limit value.

P99 : Performs a skip operation if the torque of the servo motor

reaches the limit value or if a skip signal is input.

: Override value for the torque limit

Range of valid settings: 1 to 254 (%)
0 to 255 correspond to 0% to 100%.
The Q command is optional. If omitting it, specify the torque
limit command in the PMC window beforehand. If it is
omitted, and no torque limit override is set beforehand,
alarm PS0035 is issued.
If an attempt is made to specify a value out of range, alarm
PS0366 is issued.
The specified override value is effective only to the block in
which it is specified.
At the end of the skip operation, the override value returns to
the one assumed immediately before the G31 command.

: Axis address on any one axis

F :

Feedrate

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- Conditions for performing a skip operation

Command

Condition

G31P98 G31P99

The torque limit value is reached.

A skip operation is

performed.

A skip operation

is performed.

A skip signal is input.

No skip operation

is performed.

A skip operation

is performed.

- Operation during a torque limit skip

A torque limit skip presses a specified axis against a previously
prepared part or other item while the torque limit command is being
executed on the servo motor, and then performs a skip operation when
the servo motor reaches the torque limit value. A skip operation is
performed with the fact that the torque limit value as detected in the
servo motor is reached. It is, therefore, not necessary to input a skip
signal using a separate sensor or other device unlike with normal skip
functions.
(1) At point A, the machine comes in contact with the object under

measurement and stops. At this time, because the torque limit
value is not reached, no skip operation is performed, move
commands are continuously output, and the current position of
the CNC is updated.

(2) Because move commands are output but the machine remains

stopped, there occurs a difference (error amount) between the
current position of the CNC and the machine position, and torque
is applied to the servo motor.

(3) When the torque limit value is reached, a skip operation is

performed at machine stop position, point A, and the N2
command is executed. Assuming that the current position of the
CNC when the torque limit is reached is point B, the error
amount during the torque limit skip is (A - B).

(Example)

N1 G31 P99 Q50 Z400.0 F100.0 ;
N2 G01 X300.0 F500.0 ;

100.0 200.0 300.0 400.0

100.0

200.0

300.0

Error amount

A : Machine stop position

B : Current position of the CNC when the

torque limit is reached

C : N1 command end point position

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- Torque limit command

If, with the torque limit skip command, no torque limit override value
is specified with address Q and no torque limit command is issued
from the PMC window, etc., alarm PS0035 is issued.

When no toque limit command is issued, the torque limit override
value is either 0% or 100%.

If, in a torque limit skip command block, no torque limit override
value is specified with address Q, a torque limit is to be specified as in
the program example below.

(Program example)
O0012

Mxx (Specify a torque limit from the PMC via the window)

:
G31 P99 X200. F100.

（

Torque limit skip command

）

:
G01 X100. F500.

（

Move command with the torque limit being still

effective

）

:
Myy (Cancel the torque limit from the PMC)
:
M30

- Positional deviation limit during the torque limit command

While the torque limit skip command is being executed, the positional
deviation limit check with the settings of parameters Nos. 1828 and
1829 is not performed. Instead, the positional deviation limit check
with the settings of parameter No. 6287 is performed. If the positional
deviation exceeds the limit, alarm SV0004 is issued and an
instantaneous stop occurs.

- Custom macro variables

When the torque limit skip command is executed, the custom macro
system variables #5061 to #5080 (skip signal position; for a system
with more than 20 axes, variables #100151 to #100182 are used) store
the coordinate position assumed at the end of the skip. In reality, there
is a deviation due to the delay of the servo system between the
machine position and the current position of the CNC when a skip
operation is executed. This deviation can be determined from the
positional deviation of the servo. By setting bit 2 (TSE) of parameter
No. 6201, it is possible to select whether or not the skip signal
position to be stored in system variables should be compensated for
with the error (positional deviation) of the servo system.

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