
4. REFERENCE POSITION ESTABLISHMENT
B–63833EN–1/02
178
D L
DW
: Deceleration dog width (mm or inch)
L
DW
u
V
R
(
T
R
2
) 30 ) T
S
) ) 4V
L
T
S
60 1000
V
R
: Rapid traverse (mm/min or inch/min)
T
R
: Rapid traverse time constant (ms)
T
S
: Servo time constant (ms)
V
L
: FL speed for reference position return (mm/min or inch /min)
D L
DA
: Distance between deceleration limit switch released position
and reference position
L
DA:
Move amount of 1/2 revolution of motor
Since the above conditions do not include the limit switch operation
variations, this point must also be considered at installation.
To perform the first manual reference position return after power on, the
tool must be fed in manual reference position return mode, in the reference
position return direction at a speed so that the servo position error exceeds
the value set in parameter No. 1836. At that time, the tool must cross the
grid line corresponding to a one–rotation signal from the position
detector.
The servo position error is calculated from the following formula:
Servo position error amount=
F 1000
60
1
G
1
U
F: Feedrate
G: Servo loop gain [s
–1
]
U: Detection unit [mm]
(Example)
When the tool is fed at a feedrate F of 6000 mm/min with a servo loop gain
G of 30 s
–1
and a detection unit U of 1 mm, the servo position error is
calculated as follows:
Servo position error +
6000 1000
60
1
30
1
1
=3,333
By reversing the formula above, the following formula gives the feedrate
F needed to obtain a servo position error of 128, when the servo loop gain
G is 30 s
–1
and the detection unit U is 1 mm:
F=
128 60
1000
30
= 230 [mm/min]
Therefore, when the servo loop gain is 30 s
–1
, the detection unit is 1 mm,
and parameter No. 1836 is set to 128, the tool must be fed in the reference
position return direction at a speed of at least 230 mm/min before
completing manual reference position return.
The electronic grid can be shifted by the distance set in parameter 1850,
thus shifting the reference position. The grid shift to be set in the
parameter must not exceed the reference counter capacity (parameter No.
1821) (grid interval).
Servo position error and
one–rotation signal
Grid shift