YASKAWA Sigma-7 Series Product Manual page 140

6.3 Troubleshooting Based on the Operation and Conditions of the Servomotor
Problem
Absolute
Encoder
Position
Deviation
Error (The
position
that was
saved in the
host con-
troller when
the power
was turned
OFF is dif-
ferent from
the posi-
tion when
the power
was next
turned ON.)
6-52
Possible Cause
Noise interference occurred
because of incorrect Encoder
Cable specifications.
Noise interference occurred
because the Encoder Cable
is too long.
Noise interference occurred
because the Encoder Cable
is damaged.
The Encoder Cable was sub-
ject to excessive noise inter-
ference.
There is variation in the FG
potential because of the
influence of machines on the
Servomotor side, such as a
welder.
There is a SERVOPACK
pulse counting error due to
noise.
The encoder was subjected
to excessive vibration or
shock.
Confirmation
Turn OFF the power sup-
ply to the servo system.
Check the Encoder Cable
to see if it satisfies speci-
fications. Use shielded
twisted-pair cables or
screened twisted-pair
cables with conductors of
2
at least 0.12 mm
(stranded wire).
Turn OFF the power sup-
ply to the servo system.
Check the length of the
Encoder Cable.
Turn OFF the power sup-
ply to the servo system.
Check the Encoder Cable
to see if it is pinched or
the sheath is damaged.
Turn OFF the power sup-
ply to the servo system.
Check to see if the
Encoder Cable is bundled
with a high-current line or
installed near a high-cur-
rent line.
Turn OFF the power sup-
ply to the servo system.
Check to see if the
machines are correctly
grounded.
Turn OFF the power sup-
ply to the servo system.
Check to see if there is
noise interference on the
I/O signal line from the
encoder or Serial Con-
verter Unit.
Turn OFF the power sup-
ply to the servo system.
Check to see if vibration
from the machine
occurred.
Check the Servomotor
installation (mounting sur-
face precision, securing
state, and alignment).
Check the linear encoder
installation (mounting sur-
face precision and secur-
ing method).
Continued from previous page.
Correction Reference
Use cables that satisfy
–
the specifications.
• Rotary Servomotors:
The Encoder Cable
length must be 50 m
max.
• Linear Servomotors:
Make sure that the
Serial Converter Unit
–
cable is no longer
than 20 m and that
the Linear Encoder
Cable and the Sensor
Cable are no longer
than 15 m each.
Replace the Encoder
Cable and correct the
–
cable installation envi-
ronment.
Correct the cable lay-
out so that no surge is
–
applied by high-current
lines.
Properly ground the
machines to separate
–
them from the FG of
the encoder.
Implement counter-
measures against noise
for the encoder or –
Serial Converter Unit
wiring.
Reduce machine vibra-
tion. Improve the
mounting state of the
–
Servomotor or linear
encoder.
Continued on next page.