NS system Tango-B series, User Manual

Page: 93 / 123

CHAPTER 15. SERVO GAIN TUNING
15-1. MANUAL GAIN TUNING
The position P-gain, speed P-gain and speed I-gain is set to satisfy no-load condition at factory
setting. Therefore, when the motor is installed to the machine, the gain must be adjusted to satisfy the
load inertia condition. The auto tuning function get the optimal gains (position P-gain, speed P-gain,
speed I-gain) automatically. When the machine rigidity is low (timing belt or disc without reduction
gear), set smaller value than the normal condition.
(Adjustment of position P-gain)
The position P-gain determines the responsibility of position control.
If the value is bigger, the response is getting better to reduce the position determination time.
However, the high limit value depends upon the response of the machine (inherent frequency) and
rigidity. If the value is too big to make the vibration, there is a acoustic noise in the mechanical part.
Because the position P-gain is inverse proportional to the load inertia, the gain must be adjusted to
satisfy following formula according to the load inertia. The load inertia is total value including the
motor inertia. Load inertia ratio=(Load Motor inertia)/Motor inertia
Position P-gain Factory setting value / Load inertia ratio ※ ≤
(Adjustment of speed P-gain)
The speed P-gain determines the transient responsibility of speed control.
Because the speed P-gain is directly proportional to the load inertia, the gain must be adjusted to
satisfy following formula according to the load inertia. The load inertia is total value including the
motor inertia.
Speed P-gain Factory setting value X Load inertia ratio ※ ≤
(Adjustment of speed I-gain)
The speed I-gain determines the steady state responsibility of speed control.
The bigger the value the better the steady state error. If the value is too big, the transient overshoot
or undershoot is getting bigger, and so it shall be used in the proper range. Because the speed I-gain
is directly proportional to the load friction and is slightly proportional to load inertia, the gain must be
adjusted some highly to the satisfaction of good tuning with consideration of load friction and inertia.
Especially in case of ultra low speed, the intermittent revolution phenomena disappear due to I-gain of
the speed loop.
Speed I-gain = Factory setting value X Load constant ※
Load constant (above 1) is the coefficient of load friction and inertia.
(
Adjustment of feed forward gain
)
Sometimes, the feed forward function is used for ultra fine tuning of the position loop.
The feed forward function shorten the settling time of position control with minimum overshoot. If the
value is bigger, the response of the position loop is faster. But it is too big, there occurs the vibration
of system. Generally, this function is not used.
(Inhibition of speed I (integral) action)
The speed I-gain function is disabled when the Svpar-05 "SPDIC" is set in "1". In the result, the
structure of speed controller is changed from PI to P control regardless of speed I-gain value.
If the servo motor at a stop is rotated even one pulse due to an external factor, it generates torque to
compensate for a position mismatch. When the shaft is mechanically locked at a stop after
positioning end, the setting value "1" suppress the unnecessary torque which attempts to compensate
for
position mismatch. If the speed I-gain function is valid under the mechanically locked
condition, the servo motor and amplifier may be damaged by the over load.