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FANUC Series 30i/300i/300is-MODEL A. Machining Center System. User's manual - page 92

21.AXIS CONTROL FUNCTIONS

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21.1

AXIS SYNCHRONOUS CONTROL

Overview

When a movement is made along one axis by using two servo motors
as in the case of a large gantry machine, a command for one axis can
drive the two motors by synchronizing one motor with the other.
Moreover, by using a feedback signal from each motor, a positional
difference (synchronous error) between the two motors is detected to
compensate for the synchronous error. When a synchronous error
exceeding a set value occurs, a synchronous error check can be made
to issue an alarm and stop a movement along the axis.

An axis used as the reference for axis synchronous control is referred
to as a master axis (M-axis), and an axis along which a movement is
made in synchronism with the master axis is referred to as a slave axis
(S-axis).

(Slave axis)

(Master axis)

Fig. 21.1 (a) Example of machine with X and A being synchronous axes

Even when synchronous error compensation is not used, the
synchronous establishment function can be used for automatic
compensation to eliminate a machine coordinate error in cases such as
emergency stop cancellation.

An external signal can be used to turn synchronization on and off.
When synchronization is turned on and off using an external signal,
synchronous error compensation cannot be used.

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21.1.1

Axis Configuration for Axis Synchronous Control

Explanation
- Master axis and slave axis for axis synchronous control

An axis used as the reference for axis synchronous control is referred
to as a master axis (M-axis), and an axis along which a movement is
made in synchronism with the master axis is referred to as a slave axis
(S-axis).
By setting the axis number of a master axis in the parameter No. 8311
of the slave axis, the axis configuration for axis synchronous control is
determined.

- Synchronous operation and normal operation

Operation where axis synchronous control is turned on (enabled) to
make a movement along the slave axis in synchronism with the master
axis is referred to as synchronous operation. Operation where axis
synchronous control is turned off (disabled) to make movements along
the master axis and slave axis independently of each other is referred
to as normal operation.

(Example)
Automatic operation when the master axis is the X-axis and the slave
axis is the A-axis

In synchronous operation, movements are made along the X-axis
and A-axis according to the programmed command Xxxxx for
the master axis.

In normal operation, movements are made along the master axis
and slave axis independently of each other as in the case of
normal CNC control. The programmed command Xxxxx
makes a movement along the X-axis. The programmed
command Aaaaa makes a movement along the A-axis. The
programmed command Xxxxx Aaaaa makes movements along
the X-axis and A-axis at the same time.

The mode of operation can be switched between synchronous
operation and normal operation by an input signal, or synchronous
operation can be performed at all times. Which mode to use can be
set using bit 5 (SCA) of parameter No. 8304.

- Switching between synchronous operation and normal operation by using an

input signal

When bit 5 (SCA) of parameter No. 8304 is set to 0 for the slave axis,
the signal SYNCx/SYNCJx (with x representing a slave axis number)
is used to switch between synchronous operation and normal
operation. When SYNCx/SYNCJx = 1, synchronous operation is
selected. When SYNCx/SYNCJx = 0, normal operation is selected.
Synchronous error compensation cannot be used when the mode of
operation is switched between synchronous operation and normal
operation.
During feed axis synchronization control, the output signal SYNOx is
set to "1".

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- Setting for using synchronous operation at all times

When bit 5 (SCA) of parameter No. 8304 for the slave axis is set to 1,
synchronous operation is performed at all times, regardless of the
setting of the signal SYNCx/SYNCJx.

- Synchronous control axis name

The name of a master axis and the name of a slave axis may be the
same or may be different from each other.

- Restrictions on using the same name for the master axis and slave axis

If the same axis name is assigned to the master axis and slave axis,
manual operation only is allowed in normal operation. Automatic
operation and manual numeric command cannot be performed.

- Setting of an axis name subscript

A subscript can be attached to an axis name like X1, X2, XM, and XS.
If the same axis name is used for multiple axes, and a unique subscript
is assigned to each of those axes, the axes can be distinguished from
each other on the screen display, or which of those axes issued an
alarm can be identified.
Set a subscript in parameter No. 3131.

- Setting of multiple slave axes

One master axis can have multiple slave axes.

(Example)

In the example below, movements along the X1-axis and X2-axis
are made in synchronism with the XM-axis.

Axis name

indication

Controlled

axis number

Axis name

Parameter

(No. 1020)

Subscript

Parameter

(No.3131)

Master axis

number

Parameter

(No.8311)

Operation

XM 1 88 77 0

Y 2 89

0 0

X1 3 88

49 1

A movement is made
in synchronism with
the XM-axis.

X2 4 88

50 1

A movement is made
in synchronism with
the XM-axis.

When one master axis has multiple slave axes, synchronous error
compensation, synchronous establishment, and synchronous error
check are performed for each slave axis independently.

- Combination with tandem control

Tandem control can be used with each of the master and slave axes.
The same restriction on axis arrangement as imposed in the case of
normal tandem control is imposed. No particular restriction is
imposed on axis synchronous control.

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- Axis selection on the screen display

On a screen such as the current position display screen, a slave axis is
also displayed. The display of a slave axis can be disabled by setting
bit 0 (NDP) of parameter No. 3115 to 1 and setting bit 1 (NDA) of
parameter No. 3115 to 1.

- Axis selection in actual cutting feedrate display

By setting bit 2 (SAF) of parameter No. 8303 to 1 for a slave axis, the
slave axis can be included in an actual cutting feedrate display
calculation during synchronous operation.

- Axis synchronous control with an absolute-position detector

When bit 7 (SMA) of parameter No. 8302 is set to 1 to attach an
absolute-position detector, and bit 4 (APZ) of parameter No. 1815 for
an axis placed in synchronous operation is turned off, APZ for the axis
(axes) placed together in synchronous operation is also turned off.

- Slave axis mirror image

By setting parameter No. 8312, a mirror image can be applied to a
slave axis placed in synchronous operation. When the mirror image
function is enabled, the direction in which the absolute and relative
coordinates change is the same as for the machine coordinates.
At this time, synchronization error compensation, synchronization
establishment, synchronization error check, and correction mode
cannot be used.
The mirror image set by bit 0 (MIR) of parameter No. 0012 cannot be
applied to the slave axis. Because this mirror image differs from the
mirror image set by parameter MIR, it does not affect input signal MIx
<G106> or output signal MMIx <F108>.

- External machine coordinate system shift

Bit 7 (SYE) of parameter No. 8304 can be set to 1 for the slave axis to
shift the slave axis by the same amount as specified for the master axis
when external machine coordinate system shift is specified by external
data input/output for the master axis in synchronous control.

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21.1.2

Synchronous Error Compensation

Explanation

When a synchronous error value exceeding the zero width set in
parameter No. 8333 is detected, compensation pulses for synchronous
error reduction are calculated and added onto the command pulses
output for the slave axis. This compensation is not performed in
servo-off state, servo alarm state, follow-up operation, and
modification mode.
Compensation pulses are calculated by multiplying the synchronous
error value between master and slave axes by a compensation gain.

Compensation pulses = synchronous error

(Ci/1024)

Ci: Compensation gain (parameter No. 8334)

Before synchronous error compensation can be performed, bit 5
(SCA) of parameter No. 8304 must be set to 1 to perform synchronous
operation at all times. Furthermore, the first synchronous
establishment after power-up must already be performed by a manual
reference position return or another operation.

Compensation

pulse counter

Added to command for

slave axis

Master axis

machine position

Slave axis machine
position

Compensation gain

Compensation pulses

Synchronous
error counter

- Synchronous error compensation smooth suppress function

When bit 6 (SMS) of parameter No. 8304 is set to 1, the synchronous
error compensation smooth suppress function is enabled. With this
function, another set of parameters for a synchronous error zero width
and synchronous error compensation gain (B and Ks in the figure
below) can be set. So, even a small synchronous error can be
reduced smoothly as shown below.

Synchronous error compensation gain

Synchronous error value

A: Synchronous error zero width (parameter No. 8333)
B: Synchronous error zero width 2 (parameter No. 8335)

(0 < B < A)

Kd: Synchronous error compensation gain (parameter No. 8334)

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Ks: Synchronous error compensation gain 2 (parameter No.

8336) (0 < Ks < Kd)

Er: Synchronous error value between the current master axis

and slave axis

K: Current synchronous error compensation gain for Er

1. When Er < B, compensation is not performed. (K = 0)
2. When B < Er < A

Ks +

(Er - B)(Kd - Ks)

A - B

Compensation is performed with the above gain:

3. When Er > A, compensation is performed with a gain of K = Kd.

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21.1.3

Synchronous Establishment

Explanation

Upon power-up or after emergency stop cancellation, the machine
positions on the master axis and slave axis under axis synchronous
control are not always the same. In such a case, the synchronous
establishment function matches the machine position on the master
with that on the slave axis.

- Synchronous establishment method

The method of synchronous establishment used when synchronous
error compensation is performed differs from that used when
synchronous error is not performed.

- Synchronous establishment based on synchronous error compensation

When synchronous error compensation is performed (when bit 3
(CLP) of parameter No. 8304 for the slave axis is set to 1),
synchronous establishment is performed in the same way as
synchronous error compensation. This means that the positional
difference between the master axis and slave axis is regarded as a
synchronous error, and pulses produced by multiplying the positional
difference by a synchronous error compensation gain are output for
the slave axis. So, the parameter No. 8334 for specifying a
synchronous error compensation gain must be set before synchronous
establishment can be performed.
If the parameter No. 8333 for specifying a synchronous error
compensation zero width is set, no further synchronous establishment
is performed after the positional difference between the master axis
and slave axis becomes the zero width or below.

- Synchronous establishment based on machine coordinates

To perform synchronous establishment when synchronous error
compensation is disabled (when bit 3 (CLP) of parameter No. 8304 for
the slave axis is set to 0), enable synchronous establishment based on
machine coordinates by setting bit 7 (SOF) of parameter No. 8303 to 1.
This method of synchronous establishment outputs the machine
coordinate difference between the master axis and slave axis as
command pulses for the slave axis to establish synchronization.  A
machine coordinate difference is output at a time as command pulses.
So, if the compensation value is large, the machine abruptly makes a
large movement. Taking this into consideration, set a maximum
allowable compensation value to be used for synchronous
establishment in parameter No. 8325. As a maximum allowable
compensation value, set a maximum allowable value by which the
machine may move abruptly.    If a compensation value is larger than
the value set in this parameter, an alarm SV0001 is issued, and
synchronous establishment is not performed. Moreover, when
parameter No. 8325 is set to 0, synchronous establishment is not
performed.
The result of comparing the positional difference between the master
axis and slave axis with a maximum allowable compensation value for
synchronous establishment can be checked using the synchronous
establishment enable state output signal SYNOF <F0211>.

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- First synchronous establishment after power-up

Two methods of performing the first synchronous establishment after
power-up are available. One method is based on manual reference
position return operation, and the other is based on absolute position
detection.
Until this synchronous establishment is completed, synchronous error
compensation is disabled. However, a synchronous error check is
made.

- Synchronous establishment based on manual reference position return operation

When manual reference position return operation is performed along
axes under axis synchronous control, the machine is placed at the
reference position on the master axis and slave axis according to the
same sequence as for normal reference position return operation.
When synchronous error compensation is used, the synchronous error
counter is reset and synchronous error compensation is started upon
completion of reference position return along both axes.
The sequence is the same as the grid method for one axis only.
However, only the deceleration signal for the master axis is used.
When the deceleration signal is set to 0, the machine gradually stops
along the master axis and slave axis, then an FL feedrate is set.
When the deceleration signal is set to 1, the machine moves to a grid
point along each of the master axis and slave axis, then stops.

NOTE

When the grid position difference between the master axis and
slave axis is large, a reference position shift can occur,
depending on the timing of the *DEC signal set to 1. In the
example below, the shift along the slave axis is so large that
the position shifted one grid point from the actual reference
position is regarded as the reference position.

*DEC

Master axis feedrate

Master axis grid

Slave axis feedrate

Slave axis grid

Actual reference position

Stop at position shifted one
grid point

(Example) When the reference position on the slave axis is shifted one grid point

Actual reference position

In such a case, match the grid position according to Subsection
21.1.4, "Automatic Setting for Grid Position Matching."

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