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11.SELECTION
11-8 Precautions for zeroing
To return the system to the home position, use a zeroing dog or actuator. The method and
precautions for setting the mechanical origin are given below.
In the following zeroing, an actuator and the zero pulse signal (encoder Z-phase pulse OP) of a
servo motor encoder are used to set the mechanical origin.The state of ON/OFF of encoder Z-
phase pulse signal (OP) can be confirmed by using external I/Q signal display function. When a
general positioning unit is used, the sequence of events is as shown in Fig. 11-1.
Zero pulse signal
Clear signal
Considering the variations of the
actuator signal, adjust the actuator
so that it switches off near the center
of the High of the zero pulse signal.
(1) When determining the ON duration of the actuator, consider the delay time of the control section
and the deceleration time so that the creep speed is attained. If the actuator signal switches off
during deceleration, precise home position return cannot be performed.
Travel distance gained after
detecting the zeroing dog until
Zeroing speed V
1
the creep speed is reached L
Deceleration time t
Control delay
time t
ON duration of the actuator L
1
(2) Set the end (OFF position) of the actuator signal at the middle of two ON positions (Lows) of the
zero pulse signal. If it is set near either ON position of the zero pulse signal, the positioning unit
is liable to misdetect the zero pulse signal. In this case, a fault will occur, e.g. the home position
will shift by one revolution of the servo motor.
The zero pulse output position can be confirmed by OP (encoder Z-phase pulse) on the external
I/O signal display.
(3) Set the creep speed at which the machine is not shocked at a stop.
The machine will stop suddenly as the clear (CR) signal is given to the servo amplifier on
detection of the zero pulse signal.
Zeroing speed V
1
Deceleration started by actuator signal
Actuator signal
ON
OFF
Fig. 11-1 Zeroing Using the Actuator
• Travel distance L1 in the chart can be obtained by
• ON duration of the actuator LD [mm] must be longer
1
Creep speed V
2
L
=
1
d
L
D
D
where,
V
t
L
L
Creep speed V
2
When determining the ON duration of the
actuator, consider the deceleration time so
that the speed reaches the creep speed.
About 15ms
Equation 11-28
than L1 obtained by Equation 11-28, as indicated
in Equation 11-29.
{
1
1
•
V
• t
+
•
V
• t
•
1 -
1
1
1
d
60
120
> L
.................................................................. (11-29)
1
, V
: As shown in the chart [mm/min]
1
2
, t
: As shown in the chart [s]
1
d
: As shown in the chart [mm]
1
: As shown in the chart [mm]
D
11– 10
2
( )
}
V
1
2
........ (11-28)
+
•
V
• Tp
1
V
60
1
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