T
EST
S
YSTEM
6-3
C
lo
se
d
-L
o
o
p
S
y
st
em
s
S
te
p
5
: V
er
ify
M
o
to
r/
E
n
co
d
er
P
h
a
si
n
g
Next, disconnect the amplifier connections to the controller and use a voltmeter to verify that
the controller
is
outputting a motor signal. Remember that the voltmeter will at best pick up an
average value for the step output.
Note that +/-32,767 counts, corresponds to +/-10V and +/- full scale step output. If no voltage
is present, contact Motion Engineering for assistance.
Step 5: Verify Motor/Encoder Phasing
With the motor turning slowly under a manually applied offset, check the
Actual
position field
in the
Axis
Operation
window to see if the encoder counts are increasing or decreasing.
If the phasing is incorrect, set the offset to zero, turn off the servo amplifier/step drive and the
host computer, and swap the A and B leads (A+ for B+ and A- for B-) to the encoder. Then
repeat Steps 4-5 to verify proper motor/encoder phasing.
Step 6: Exercise the System
Setting the tuning parameters is part science and part art. Closed loop performance depends on
the tuning parameters, servo amp/step drive, and the mechanical system. Finding optimum tun-
ing parameters requires experimentation, theoretical understanding of PID control loops, and
practical experience.
Before tuning, verify the settings for the axis in the
Axis Configuration
property page. Double-
click on the axis to open the
Axis Operation
window and refer to the
Tuning Parameters
dis-
play. Start with the parameters in the next table.
Tip!
Motor Doesn’t Turn
If the motor will not turn when an offset is applied, check the motor and
amplifier connections, and also check that the
State
field reads
Abort
Event
, to make sure the PID control is disabled.
Table 6-1
Correct Motor/Encoder Phasing
Offset
Encoder Counts
Phasing
Positive (+ Value)
Increasing
Correct
Positive (+ Value)
Decreasing
Wrong
Negative (- Value)
Decreasing
Correct
Negative (- Value)
Increasing
Wrong
Tip!
Tune It TWICE
We highly recommend tuning the system
twice
.
First tune the system
with the motor disconnected from the mechanical
system
, to gain familiarity with the procedure.
Second,
connect the motor to the mechanical system
and re-tune.
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