30
6250 Servo Controller User Guide
S t e p 6
Observe the 6250's analog output noise level on the oscilloscope. The ideal noise level
should be below 3.0mV (1/2-bit resolution of the 6250's digital-to-analog converter), but
anything up to 10mV is acceptable in most cases.
If the noise level is acceptable, proceed to Step 7. If the noise level is too high:
a.
Turn all the power off and tie the grounds of all the electrical components of your system
to a single point, and connect this point to the ground of one of the drives.
b .
Shield the drive(s) properly and shield all the wiring that interconnect the components.
c.
After you have completed a and b above, turn on the controller only and start over from
Step 2. If the noise level is still unacceptable, consult the noise suppression techniques
described in Appendix A.
S t e p 7
The purpose of this step is to ensure that a positive voltage on the 6250's analog control
signal output (from the
C M D +
and
C M D -
terminals) results in the encoder counting in the
positive direction.
C A U T I O N
This offset may cause a torque drive to accelerate the motor to a high speed, if little or no
load (vs. rotor inertia) is attached.
a.
Using the
SMPER
command, set the maximum allowable position error to a step value
equivalent to 1 rev. For instance, if the resolution value you entered for the
ERES
command was
4ØØØ
(4,000 counts per rev), then you should enter the
SMPER4ØØØ
command.
b .
Enter the
TPE
command to check the current position of the encoder. Record this number
for later use.
c.
Enter the
SOFFSØ.2
command to introduce an offset servo analog output value of 0.2V
to make the motor turn slowly in the positive (clockwise) direction. (The motor will
stop when the maximum allowable position error is exceeded.) If the load has a large
friction component, you may need to use a larger offset (
SOFFS
command) to affect
motion.
d.
Use the
TPE
command again to observe the encoder position value. The value should
have increased from the value observed in Step 7.b.
If the encoder reading decreases when using a positive
SOFFS
setting, turn off the drive
and the 6250 and swap the wires connected to the 6250's
C M D + and C M D -
terminals,
or the wires connected to the drive's analog control signal input and signal
ground/common, whichever are more accessible. Then turn on the 6250 again, enter the
DRIVE11
command, and repeat Steps 4 through 7.d. before proceeding to Step 8.
e.
Enter the
SOFFSØ
command to stop the motor, and enter the
DRIVE11
command to re-
enable the drives.
S t e p 8
Having set the servo output offset to zero with the
SOFFSØ
command (see Step 7.e.), read the
6250's analog output with the DVM to determine if there is any offset caused by the electrical
interconnections between the 6250 and the drive.
If the DVM reads anything other than zero volts, enter the DVM's reading (but with the opposite
polarity) as the offset adjustment with the
SOFFS
command. For example, if the DVM reading
is 0.015V, then enter
SOFFS-Ø.Ø15
. If, after doing this, the reading is still not zero, then
fine-tune it by trying
SOFFS
entries of slightly different values until the DVM reading is
between
±
3.0mV.
S t e p 9
If you have a velocity drive, the motor may still be turning due to the drive's balance/offset
setting. If so, adjust the drive's balance/offset until the motor stops. Consult the drive's user
documentation for instructions.
S t e p 1 0
Proceed to the Drive Tuning Procedure section to tune the velocity drive (if you are using a
torque drive, skip to the Controller Tuning Procedure).
