FANUC Series 30i/300i/300is-MODEL A. Machining Center System. User's manual - page 100

21.AXIS CONTROL FUNCTIONS

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21.7.4.2 

Description of commands compatible with those for a 

hobbing machine (G80, G81) 

 
A command compatible with that for a hobbing machine can be used 
as a synchronization command. 
Usually, a hobbing machine performs machining by synchronizing the 
workpiece axis (usually, the C-axis) to the hobbing axis (spindle). 
If there are two synchronization sets with the EGB, which 
synchronization set to start with this specification method can be 
specified with parameter No. 7710. 
 

Format 

 

Parameter EFX(No.7731#0)=1 

 

Parameter EFX 

(No.7731#0)=0 

Parameter HBR 

(No.7731#5)=1 

Parameter HBR 

(No.7731#5)=0 

Start of synchronization 

G81 T

＿

 ( L

＿

 ) 

( Q

＿

  P

＿

 ) ; 

G81.4 R

＿

 ( L

＿

 ) 

( Q

＿

  P

＿

 ) ; 

G81.4 T

＿

 ( L

＿

  )

( Q

＿

  P

＿

 ) ; 

Cancellation of 

synchronization 

G80 ; 

G80.4 ; 

G80.4 ; 

 

(*1) (*2) (*3) 

 

T(or R) : Number of teeth (Specifiable range: 1 to 1000) 
L : Number of hob threads (Specifiable range: -200 to +200) 
      The sign of L determines the direction of rotation for the workpiece 

axis. 
When L is positive, the direction of rotation for the workpiece axis 
is positive (+ direction). 
When L is negative, the direction of rotation for the workpiece axis 
is negative (- direction). 
When L is 0, it follows the setting of bit 3 (LZR) of parameter 
No.7701. 
If L is not specified, the number of hob threads is assumed 1. 

Q : Module or diametral pitch 
      Specify a module in the case of metric input. 
      (Unit: 0.00001mm, Specifiable range: 0.01 to 25.0mm) 
      Specify a diametral pitch in the case of inch input. 
   (Unit: 0.00001inch

-1

, Specifiable range: 0.01 to 254.0 inch

-1

) 

P :  Gear helix angle 
 

(Unit: 0.0001deg, Specifiable range: -90.0 to 90.0deg) 

*1  Use it for machining centers. 
*2  Use it for lathes. 
*3  Use it for machining centers. 
        This format enables specification of the same G codes as those 

for lathes. 

*4  When specifying Q and P, the user can use a decimal point. 

 

NOTE 

 

Specify G81, G80, G81.4, and G80.4 in a single block. 

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Explanation 
 - Synchronization start 

Specify P and Q to use helical gear compensation. In this case, if only 
one of P and Q is specified, alarm PS1594 is generated. 
When G81 is issued so that the machine enters synchronization mode, 
the synchronization of the workpiece axis to the spindle is started. 
During synchronization, control is performed such that the ratio of the 
spindle speed to the workpiece-axis speed is the same as that of T 
(number of teeth) to L (number of hob threads). 
If, during synchronization, G81 is issued again without 
synchronization cancellation, alarm PS1595 is generated if ECN, bit 3 
of parameter No. 7731, is 0.    If ECN, bit 3 of parameter No. 7731, is 
1, helical gear compensation is conducted with the synchronization 
coefficient being changed to the one newly specified with T and L 
commands if T and L commands are issued, and if T and L commands 
are not issued and only P and Q commands are issued, helical gear 
compensation is conducted with the synchronization coefficient kept 
intact.    This allows consecutive fabrication of helical gears and super 
gears. 
 

 - Synchronization end 

Synchronization of all synchronized axes is canceled. 
When a synchronization cancellation command is issued, the absolute 
coordinates for the slave axis are updated according to the amount of 
travel during synchronization. 
For a rotation axis, the value obtained by rounding off the amount of 
travel during synchronization to the nearest 360 degrees is added to 
the absolute coordinates. 
In a G80 block, do not specify addresses other than O or N. 
 

 CAUTION 

1  Feed hold, interlock, and machine lock are invalid 

to a slave axis in EGB synchronization. 

2  Even if an OT alarm is issued for a slave axis in 

EGB synchronization, synchronization will not be 
canceled. 

3  During synchronization, it is possible to execute a 

move command for a slave axis and other axes, 
using a program. The move command for a slave 
command must be an incremental one. 

 

NOTE 

1  If bit 0 (HBR) of parameter No. 7700 is set to 1, 

EGB synchronization will not be canceled due to a 
reset. Usually, set this parameter bit to 1. 

2  In synchronous mode, it is not possible to specify 

G27, G28, G29, G30, G30.1, and G53 for a slave 
axis. 

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NOTE 

3  It is not possible to use controled axis detach for a 

slave axis 

4  During synchronization, manual handle interruption 

can be performed on the slave and other axes. 

5  In synchronization mode, no inch/metric conversion 

commands (G20 and G21) cannot be issued. 

6  In synchronous mode, only the machine 

coordinates on a slave axis are updated. 

7  If bit 0 (EFX) of parameter No. 7731 is 0, no drilling 

canned cycle can be used. To use a drilling canned 
cycle, set bit 0 (EFX) of parameter No. 7731 to 1 
and use G81.4 instead of G81 and G80.4 instead 
of G80. 

8  If bit 0 (TDP) of parameter No. 7702, is 1, the 

permissible range of T is 0.1 to 100 (1/10 of the 
specified value). 

9  If, at the start of EGB synchronization (G81), L is 

specified as 0, synchronization starts with L 
assumed to be 1 if bit 3 (LZR) of parameter 
No.7701, is 0; if bit 3 (LZR) of parameter No.7701, 
is 1, synchronization is not started with L assumed 
to be 0.    At this time, helical gear compensation is 
performed. 

10 Feed per revolution is performed on the feedback 

pulses on the spindle. By setting bit 0 (ERV) of 
parameter No. 7703, to 1, feed per revolution can 
be performed based on the speed on the 
synchronous slave axis. 

11 Actual cutting feedrate display does not take 

synchronization pulses into consideration. 

12 For an EGB slave axis, synchronous and 

cpmposite control cannot be executed. 

13 In EGB synchronization mode, AI contour control 

mode is temporarily canceled. 

 

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  - Helical gear compensation 

For a helical gear, the workpiece axis is subjected to compensation for 
movement along the Z axis (axial feed axis) according to the twisted 
angle of the gear. 
Helical gear compensation is performed with the following data. 
 

Compensation angle =         

×

360 (for metric input) 

 

Compensation angle =                       

×

360 (for inch input) 

 
where 

  Compensation angle:  Absolute value with sign (degrees) 

Z : Amount of travel along the Z axis after a G81 command is 

issued (mm or inch) 

P :   Twisted angle of the gear with sign (degrees) 

π

 : Circular constant 

T  :  Number of teeth 
Q  :  Module (mm) or diametral pitch (inch

-1

) 

 

Use P, T, and Q specified in the G81 block. 

In helical compensation, the machine coordinates on the workpiece 
axis and the absolute coordinates are updated with helical 
compensation. 
 

Q

T

sin(P)

×

×

×

π

Z

T

sin(P)

Q

Z

×

×

×

π

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  - Direction of helical gear compensation 

The direction depends on bit 2 (HDR) of parameter No. 7700. 

When HDR is set to 1.

 

+C

C:+, Z:+, P:+ 

Compensation direction : + 

(a) 

-

Z

 

+

Z

 

+C

C:+, Z:+, P:- 

Compensation direction : -

(b) 

+C

C:+, Z:-, P:+ 

Compensation direction : -

(c)

+C

C:+, Z:-, P:- 

Compensation direction : +

(d) 

-

Z

 

+

Z

 

C:-, Z:+, P:+ 

Compensation direction : - 

(e) 

-

C

C:-, Z:+, P:- 

Compensation direction : +

(f) 

-

C

 

C:-, Z:-, P:+ 

Compensation direction : +

(g) 

-

C

C:-, Z:-, P:- 

Compensation direction : -

(h) 

-

C

 

When HDR is set to 0. (In (a), (b), (c), and (d), the same as that if HDR is 1)

 

-Z 

+

Z

 

C:-, Z:+, P:+ 

Compensation direction : + 

(e) 

-

C

C:-, Z:+, P:- 

Compensation direction : -

(f) 

-

C

C:-, Z:-, P:+ 

Compensation direction : -

(g) 

-

C

C:-, Z:-, P:- 

Compensation direction : +

(h) 

-

C

 

 

 
 

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21.7.4.3 

Controlled axis configuration example 

 

  - For gear grinders 

Spindle  :  EGB master axis : Tool axis 
1st axis  :  X axis 
2nd axis  :  Y axis 
3rd axis  :  C axis (EGB slave axis : Workpiece axis) 
4th axis  : C axis (EGB dummy axis : Cannot be used as a normal 

controlled axis) 

5th axis  :  V axis (EGB slave axis : Dressing axis) 
6th axis  : V axis (EGB dummy axis : Cannot be used as a normal 

controlled axis) 

 
Cannot be used as a normal controlled axis) 

Spindle amp.

Motor 

Spindle (master axis)

 

1st axis X (omitted) 
2nd axis Y (omitted)

 

Tool axis 

3rd axis C 
slave axis

 

4th axis 
dummy axis

 

EGB 

- 

+ 

+ 

- 

K

1

:  Sync coefficient

K

1

 

Error counter 

Sync switch

 

Motor

Detector 

Velocity/current control

Servo amp.

Position control 

Workpiece axis

C axis

 

Separate detector

FFG 

+ 

Follow-up 

Spindle Detector

CNC 

5th axis V 
slave axis

 

6th axis 
dummy axis

 

EGB 

- 

+ 

+ 

- 

K

2

:  Sync coefficient

K

2

 

Error counter 

Sync switch

 

Motor

Detector 

Velocity/current control

Servo amp.

Position control 

Workpiece axis

V axis

 

Separate detector

FFG 

+ 

Follow-up 

 

Fig. 21.7.4.3 (a)     

 

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21.7.4.4 

Sample programs 

 

  - When the master axis is the spindle, and the slave axis is the C-axis 

(1)  G81.5  T10  C0  L1  ; 

Synchronization between the master axis and C-axis is 
started at the ratio of one rotation about the C-axis to ten 
rotations about the master axis. 

(2)  G81.5  T10  C0  L-1  ; 

Synchronization between the master axis and C-axis is 
started at the ratio of one rotation about the C-axis to ten 
rotations about the master axis. 
In this case, however, the direction of rotation is opposite to 
that of (1). 

(3)  G81.5  T1  C3.26  ; 

Synchronization between the master axis and C-axis is 
started at the ratio of a 3.26-degree rotation about the C-axis 
per one rotation about the master axis. 

(4)  G81.5  P10000  C-0.214  ; 

Synchronization between the master axis and C-axis is 
started at the ratio of a -0.214 degree rotation about the 
C-axis to 10,000 feedback pulses from the pulse coder of 
the master axis. 

 

  - When the master axis is the spindle, the slave axis is the V-axis (linear axis), and 

inch/metric conversion is performed 

(1)  For a millimeter machine and metric input 

G81.5  T1  V1.0  ; 
Synchronization between the master axis and V-axis is 
started at the ratio of a 1.00 mm movement along the V-axis 
per rotation about the master axis. 

(2)  For a millimeter machine and inch input 

G81.5  T1  V1.0  ; 
Synchronization between the master axis and V-axis is 
started at the ratio of a 1.0 inch movement (25.4 mm) along 
the V-axis per rotation about the master axis. 

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  - When two groups of axes are synchronized simultaneously 

Based on the controlled axis configuration described in Fig. 21.7.4.3 
(a), the sample program below synchronizes the spindle with the 
V-axis while the spindle is synchronized with the C-axis. 

Grinding 

Dressing 

Grinding 

O0100 ; 
............... 
N01  M19 ; 

Performs spindle orientation. 
Positions the C-axis. 
Starts synchronization at the ratio of one rotation about the
C-axis to ten spindle rotations. 

N02  G00  G90  C... ; 

N03  G81.5  T10  C0  L1 ; 

N04  M03  S300 ; 

Rotates the spindle. 
Makes movements for grinding. 
 
Stops the spindle. 

N05  G01  G91  X... Y... F... ; 

....... 

N06  M05 ; 
....... 
N10  G00  G90  V... ; 

Positions the dressing axis. 
Starts synchronization at the ratio of a   
0.5 mm movement along the V-axis   
every 12,000 pulses on the spindle. 
Rotates the spindle. 
A subprogram for dressing is called. (Note) 
 
Stops the spindle. 

N11  G81.5  P12000  V0.5 ; 

N12  M03 S300 ; 
N20  M98  P9500 ; 

N21  M05 ; 

N30  G80.5  V0 ; 

Cancels V-axis synchronization. 

....... 
....... 
N31  M03  S300 ; 

Rotates the spindle. 
Makes movements for grinding. 

N32  G01  G91  X... Y... F... ; 
....... 
....... 

N40  M05 ; 

Stops the spindle. 
Cancels C-axis synchronization. 

N41  G80.5  C0 ; 

V-axis synchronization mode 

C-axis synchronization mode 

 

 
Thus, the synchronizations of two groups can be started and canceled 
independently of each other.