
B–64113EN–1/01
7. FEEDRATE CONTROL/ACCELERATION
AND DECELERATION CONTROL
396
When a given arc radius R and the maximum permissible speed V for that
arc radius are set as parameters, the maximum permissible speed v for an
arc with a programmed radius r can be obtained from expression 3. Then,
if a specified feedrate exceeds the speed v, the feedrate is automatically
clamped to the speed v.
The maximum permissible speed v obtained from expression 3 decreases
with the specified arc radius. To prevent the maximum permissible speed
from decreasing excessively, the lower limit imposed on the maximum
permissible speed v can be set in parameter 1732.
Provided the specified feedrate does not exceed the maximum
permissible speed v obtained from expression 3, arc cutting is performed
at the specified feedrate.
When the cutting feed linear acceleration/deceleration function is used,
an approximate error in arc cutting can be obtained from expression 4.
Programmed
path
Actual path
Dr : Maximum radius error (mm)
v : Feedrate (mm/s)
r : Arc radius (mm)
T
1
: Time constant for cutting
feed linear acceleration/
deceleration (s)
T
2
: Servo motor time constant
(s)
Dr : Error
0
Y
X
r
Dr + (
1
24
T
1
2
)
1
2
T
2
2
)
V
2
r
(Expression 4). . . . . . . .
As can be seen from expression 4, expression 3 also holds for linear
acceleration/deceleration after interpolation. Therefore, feedrate
clamping by the arc radius is enabled.
Expressions 1, 2, and 4 logically denote an approximate error in the CNC.
They do not denote an actual error in machining.
Let the actual error in machining be Dr all. Then, it is expressed as
follows:
Dr all + Dr NC ) Dr machine
(Expression 5). . . . . . . .
Error caused by the machine
Error caused by the acceleration/
deceleration time constant (T
1
) and
servo motor time constant (T
2
)
This function controls only the first term on the right side of expression
5. In other words, this function suppresses only the error caused by the
acceleration/deceleration time constant (T
1
) and servo motor time
constant (T
2
) to a certain level. This function does not control the error
caused by the machine.
D Cutting feed linear
acceleration/deceleration
D Actual error