FANUC Series 30i/300i/300is-MODEL A. Machining Center System. User's manual - page 88

PROGRAMMING

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20. HIGH-SPEED CUTTING

FUNCTIONS

- Speed control based on the feedrate difference on each axis at a corner

By using the speed control based on the feedrate difference on each
axis at a corner, if a feedrate change occurs on an axis on each axis at
a corner, the feedrate is determined so that any feedrate difference
exceeding the permissible feedrate difference on that axis that has
been set for parameter No. 1783 does not occur, and deceleration is
automatically performed.

(Example)

Program
N1 G01 G91 X100. F5000

N2 Y100.

Tangent feedrate

X-axis feedrate

Y-axis feedrate

The deceleration
based on the feedrate
difference is used.

Tangent feedrate

X-axis feedrate

Y-axis feedrate

The feedrate difference becomes
small, and the feedrate on each

axis becomes smooth.

The tangent feedrate is
smooth, but the feedrate

on each axis is not.

The method of deceleration based on the feedrate difference differs
depending on the setting made for bit 6 (FNW) of parameter No.
19500.
If "0" is set, the largest feedrate that does not exceed the permissible
feedrate difference set for parameter No. 1783 is assumed to be the
deceleration feedrate.

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20.HIGH-SPEED CUTTING

FUNCTIONS

In this case, the deceleration feedrate differs if the travel direction
differs, even if the shape is the same.

Deceleration to

500 mm/min

Deceleration to

354 mm/min

(Example)
If parameter FNW (bit 6 of No. 19500) = 0 and the

permissible feedrate difference = 500 mm/min (on all axes)

If "1" is set, the feedrate is determined not only with the condition that
the permissible feedrate difference and permissible acceleration on
each axis are not exceeded, but also that the deceleration feedrate is
constant regardless of the travel direction if the shape is the same.
If 1 is set for this parameter, the deceleration feedrate determined with
the feedrate difference may be up to 30% lower than that determined
if 0 is set.

Deceleration to

354 mm/min

Deceleration to

354 mm/min

(Example)
If parameter FNW (bit 6 of No. 19500) = 1 and

permissible feedrate difference = 500 mm/min (on all axes)

PROGRAMMING

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20. HIGH-SPEED CUTTING

FUNCTIONS

- Speed control with acceleration in circular interpolation

When high-speed cutting is performed in circular interpolation, helical
interpolation, or spiral interpolation, the actual tool path has an error
with respect to the programmed path. In circular interpolation, this
error can be approximated from the equation given below.

Specified path

Actual path

∆

r : Maximum radius error (mm)

: Feedrate (mm/sec)

: Arc radius (mm)

: Acceleration (mm/sec

)

: Time constant of

acceleration/deceleration after
interpolation at cutting (sec)

: Time constant of servo motor (sec)

∆

r : Error

)

(

)

(

⋅

∆

................................ (Equation 1)

In actual machining, permissible error

∆

r is given, so the maximum

permissible acceleration a (mm/sec

) in equation 1 is determined.

When a specified feedrate causes the radial error from an arc having a
programmed radius to exceed the permissible error, speed control with
acceleration in circular interpolation automatically clamps the
arc-cutting feedrate by using parameter settings.

Let the permissible acceleration calculated from the permissible
acceleration set for each axis be A. Then, maximum permissible
feedrate v with programmed radius r is expressed as follows:

⋅

........................................................................... (Equation 2)

If a specified feedrate exceeds feedrate v obtained from equation 2,
the feedrate is clamped at feedrate v automatically.
The permissible acceleration is specified in parameter No. 1735. If
there is a difference in permissible acceleration between two axes for
circular interpolation, the lower acceleration is regarded as the
permissible acceleration.
If the radius of an arc is small, too small value can be calculated as
deceleration v. In such a case, the lower feedrate limit can be set in
parameter No. 1732 to prevent the feedrate from being decreased too
much.

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20.HIGH-SPEED CUTTING

FUNCTIONS

- Speed control with the acceleration on each axis

When consecutive small lines are used to form a curve, as in the
example shown in the figure below, the feedrate differences on each
axis at the individual corners are not very large. Thus, deceleration
with the feedrate differences is not effective. Consecutive small
feedrate differences, however, cause a large acceleration on each axis,
as a whole.
In such a case, deceleration can be performed to reduce the impact on
the machine and the machining error caused by too large an
acceleration. The deceleration feedrate is determined to be the feedrate
that does not cause the acceleration on each axis to exceed the
permissible acceleration set for parameter No. 1737.
The deceleration feedrate is determined for each corner. The actual
feedrate is the smaller of the deceleration feedrate determined at the
start point of the block and that determined at the end point.
Depending on the specified figure, a very low deceleration feedrate
may be calculated. In such a case, the lower feedrate limit can be set in
parameter No. 1738 to prevent the feedrate from being decreased too
much.
In the following example, the acceleration (gradient of the broken line
in the feedrate graph) at too large at corners N2 to N4 and N6 to N8
and, therefore, deceleration is performed.

X-axis
feedrate

Y-axis
feedrate

Tangent
feedrate

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20. HIGH-SPEED CUTTING

FUNCTIONS

The method of determining the feedrate with the acceleration differs
depending on the setting of bit 6 (FNW) of parameter No. 19500.
If "0" is set, the highest feedrate that does not cause the permissible
acceleration set for parameter No. 1737 to be exceeded is assumed to
be the deceleration feedrate. In this case, the deceleration feedrate
differs depending on the travel direction even if the shape is the same,
as shown in the figure below.

(Example) If a circular shape with a radius of 10 mm is specified with small

line blocks

Parameter FNW (bit 6 of No. 19500) = 0

Permissible acceleration = 1000 mm/s

(on all axes)

The feedrate is
higher in these

directions.

Tangent feedrate

Time

F6000

If "1" is set, the feedrate is determined with not only the condition that
the permissible acceleration on each axis is not exceeded but also the
condition that the deceleration feedrate is constant regardless of the
travel direction if the shape is the same.
If 1 is set for this parameter, the deceleration feedrate determined with
the feedrate difference or acceleration may be up to 30% lower than
that determined if 0 is set.

(Example) If a circular shape with a radius of 10 mm is specified with small

line blocks

Parameter FNW (bit 6 of No. 19500) = 1,

radius = 10 mm, permissible acceleration = 1000 mm/s

(on all axes)

The tangent
feedrate is

constant.

Tangent feedrate

Time

F6000

NOTE

In circular interpolation, the tangent feedrate is
constant regardless of the setting of the parameter.

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20.HIGH-SPEED CUTTING

FUNCTIONS

- Smooth speed control

In speed control with acceleration, the smooth speed control function
recognizes the entire figure from preceding and following blocks
including blocks read ahead to make a smooth feedrate determination.
When a curve is specified with successive minute straight lines,
programmed values are rounded to the least input increment before
issued, so the machining profile is approximated with a broken line.
When the feedrate is determined with acceleration in an ordinary
manner, an optimum feedrate is automatically calculated exactly for a
programmed figure, so a large acceleration may result depending on
the command, which can lead to deceleration.
In such a case, the use of smooth speed control enables speed control
by recognizing the entire figure, which provides smooth speed control
while suppressing local deceleration, therefore increasing the feedrate.

Large acceleration

: Programmed path

: Recognized figure

Also for a part of a programmed figure in which a large acceleration
would be required, the acceleration is obtained based on the figure
recognized from multiple blocks, and the feedrate is determined so
that the acceleration is within the permissible acceleration set in
parameter No. 1737.

Tangential feedrate

Deceleration with acceleration
in ordinary manner

Smooth speed control

Time

Command with large acceleration

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20. HIGH-SPEED CUTTING

FUNCTIONS

Smooth speed control obtains the acceleration by using the figure
recognized from the preceding and following blocks including blocks
read ahead, so smooth speed control is enabled even in parts in which
the acceleration increases.
Smooth speed control is enabled under the following conditions:
<1> Speed control with acceleration is enabled in the AI contour

control mode.

<2> Successive linear interpolation commands are specified.
<3> Bit 0 (HPF) of parameter No. 19503 is set to 1.

CAUTION

When smooth speed control is used, the feedrate in
a certain figure such as a corner may become
larger than the feedrate obtained by ordinary speed
control with acceleration. For corners, set
parameter No. 1783, which is the permissible
feedrate difference parameter for speed control with
the feedrate difference at corners, to perform
appropriate deceleration by speed control with the
corner feedrate difference.

- Speed control with the cutting load

Usually, the cutting resistance produced when machining is performed
with the bottom of the cutter as the tool lowers along the Z-axis is
greater than the cutting resistance produced when machining is
performed with the side of the cutter as the tool rises along the Z-axis.
Therefore, deceleration is required.
In AI contour control, the tool travel direction on the Z-axis is used as
a condition for calculating the machining feedrate.
This function is enabled when bit 4 (ZAG) of parameter No. 8451 is
set to 1.

During ascent on the Z-axis

During descent on the Z-axis

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PROGRAMMING

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20.HIGH-SPEED CUTTING

FUNCTIONS

The descent angle

during descent on the Z-axis (angle formed by the

XY plane and the tool center path) is as shown in the figure. The
descent angle is divided into four areas, and the override values for the
individual areas are set for the following parameters:

Parameter No. 8456 for area 2
Parameter No. 8457 for area 3
Parameter No. 8458 for area 4

For area 1, however, no parameter is available, and an override of
100% is used at all times. The feedrate obtained according to other
feedrate control is multiplied by the override value of the area to
which descent angle

belongs.

Area1 0º

≤

< 30º

Area2 30º

≤

< 45º

Area3 45º

≤

< 60º

Area4 60º

≤

< 90º

The feedrate can be overridden with an inclination by setting bit 1
(ZG2) of parameter No. 19515 to 1. In this case, specify the override
value for area 1 in parameter No. 19516.

XY plane

Area1

Area2

Area3

Area4

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