(
(
Start-Up
and
Adjustments
Autc;tune implements a simple "self-tuning" algorithm that adjusts the tuning parameters P GAIN and I
GAIN
by
computing the effect
of
the user's load as applied
to
the servo motor shaft. This method operates
by commanding a constant current
to
the motor that produces a constant motor torque. The acceleration
of
the motor is measured and used
to
compute the gain
of
the system. Once the actual gain
of
the system
is measured, the values
of
the tuning parameters P GAIN and I GAIN are adjusted
to
compensate
for
the
change in gain. Auto-tune mode
is
selected by moving the cursor
to
the Mode line on the Setup page
of
the User interface (refer
to
Section 5.2.3.2.3). Once selected, enabling the BRU-Series drive starts auto-
tune which causes the servo motor
to
rapidly accelerate and decelerate. After 5 seconds, the current
command
to
the motor
is
set
to
· zero which should haft ·motion:· ·- -
--
WARNING
AT
THE COMPLETION
OF
AUTO-TUNE,
VOLTAGE
REMAINS
APPUED
TO
THE MOTOR UNTIL THE BRU-500
OR
BRU-200 IS
DISABLED.
Three parameters control the operation
of
auto-tune mode: Dist, Max
Vel
, and Step L The Dist parameter
is used
to
limit the distance moved from the starting position. The maximum value for Dist is 4 motor
rotations. Due
to
the open-loop nature
of
the auto-tune and the unpredictable affects
of
gravity, friction,
etc., the distance may be exceeded. During auto-tune, exceeding the Dist value will not generate a fault
condition. The Max
Vel
parameter
is
used
to
set a maximum velocity during auto-tune. It can be a positive
or negative value. If Dist is set
to
0,
the servo motor will move in one direction with the sign
of
Max
Vel
determining the direction. Step I determines the value of motor current used
to
accelerate and decelerate
the motor. The maximum allowed value
of
Step I is limited
to
rated current
of
the motor. These three
parameters are set
to
default values upon entering auto-tune mode which should be sufficient for most
loads.
The parameters adjusted by auto-tune are P GAIN, I GAIN, and D
GAIN.
D GAIN is always set to
0.
P
GAIN and I GAIN are adjusted proportionally
to
the change
in
gain
of
the system. There are certain
conditions where erroneous values are computed
for
P GAIN and I GAIN. These conditions are as follows:
1.) Dist is set
too
low. This condition results in very rapid reversal
of
the servo motor
rotation and causes
it
to
make a buzzing sound.
2.) Max
Vel
is set
too
low. This condition results
in
very rapid reversal
of
the servo
motor rotation and causes it
to
make a buzzing sound.
3.) Step I is set
too
low. There
is
no
servo motor motion.
4
.)
FAC
andj or
RAC
enabled. This condition can be checked by observing the Status
page on the user terminal
to
see if
FAC
andj or
RAC
are displayed. The condition
is evidenced
by
no
motion
or
a halting
of
the back-and-forth motion.
These conditions will generally result in very high values for P
GAIN
(999
is maximum) and I GAIN (999 is
maximum) which may result in instability when returned
to
the velocity mode of operation.
The procedure
for
using auto-tune
is
as follows:
1
.)
Make sure the system is connected and is operating
proper1
y
by
following the initial start-up
procedure
in
Sec. 5.1.
2.)
Connect the user terminal
to
connector P6 on the
BRU
-Series drive.
3.) With the drive disabled, apply power.
BRU-200/BRU-500 Brushless
Dri
ves In
st
ruction Manual
37
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