YASKAWA UAK series User Manual page 298

11 Inspection, Maintenance, and Troubleshooting
Problem
High Motor Speed
Overshoot on
Starting and
Stopping
Absolute Encoder
Position
Difference Error
(The position
saved in the host
controller when
the power was
turned OFF is
different from the
position when the
power was next
turned ON.)
11-44
Probable Cause
Unbalanced servo gains
Speed loop gain value (Pn100) too
high
Position loop gain value (Pn102)
too high
Incorrect speed loop integral time
constant (Pn101)
Incorrect moment of inertia ratio
data (Pn103)
Noise interference due to improper
encoder cable specifications
Noise interference due to length of
encoder cable
Noise interference due to damaged
encoder cable
Excessive noise interference at the
encoder cable
FG potential varies because of
influence of machines such as weld-
ers at the servomotor.
SERVOPACK pulse counting error
due to noise interference
Excessive vibration and shock to
the encoder
Encoder failure
SERVOPACK failure
(The pulse count does not change.)
Host controller multiturn data read-
ing error
Investigative Actions
Check to see if the servo gains have
been correctly adjusted.
Check the speed loop gain (Pn100).
Factory setting: Kv = 40.0 Hz
Check the position loop gain
(Pn102).
Factory setting: Kp = 40.0/s
Check the speed loop integral time
constant (Pn101).
Factory setting: Ti = 20.0 ms
Check the moment of inertia ratio
(Pn103).
The encoder cable must be tinned
annealed copper shielded twisted-
pair or screened unshielded twisted-
pair cable with a core of 0.12 mm
min.
Check the encoder cable length.
Check if the encoder cable is bent or
if its sheath is damaged.
Check if the encoder cable is bun-
dled with a high-current line or near
high-current line.
Check if the machines are correctly
grounded.
Check if there is noise interference
on the I/O signal line from the
encoder.
Check if vibration from the machine
occurred or motor installation is
incorrect (mounting surface accu-
racy, fixing, alignment, etc.).
−
−
Check the error detection section of
the host controller.
Check if the host controller is exe-
cuting data parity checks.
Check noise in the cable between
the SERVOPACK and the host con-
troller.
Corrective Actions
Execute the advanced autotuning.
Reduce the speed loop gain
(Pn100).
Reduce the position loop gain
(Pn102).
Correct the speed loop integral time
constant (Pn101).
Correct the moment of inertia ratio
(Pn103).
Use the specified encoder cable.
2
The encoder cable length must be
no more than 20 m.
Replace the encoder cable and cor-
rect the encoder cable layout.
Change the encoder cable layout so
that no surge is applied.
Ground machines correctly, and
prevent diversion to the FG on the
encoder side.
Take measures against noise in the
encoder wiring.
Reduce vibration from the machine,
or secure the motor installation.
Replace the motor.
Replace the SERVOPACK.
Correct the error detection section
of the host controller.
Execute a multiturn data parity
check.
Take measures against noise, and
again execute a multiturn data par-
ity check.
(cont'd)