Rockwell Automation 8510 AC Spindle Drive System User Manual - Manual (Page 105)

Start-Up
Chapter 9
9-101
Ideally, if the drive will be operated within a position loop, the final
tuning should be performed with the position loop closed by the
CNC or other control system. This will allow for the highest overall
gains and system stiffness. Independently tuning the velocity loop
with step velocity commands leads to a conservative set of tuning
parameters.
With an integrator in the velocity loop, a very small command from
the position loop will be integrated until it is large enough to cause
spindle movement to null the error. If there is a difference between
static and dynamic friction, it is possible the spindle will suddenly
move too far when it finally moves and a stop/move limit cycle will
result. To guard against this, the droop parameter places a maximum
limit on the integrator gain to prevent very small inputs from
causing motion. The Droop In Run parameter is used during very
low speed servo operation when the drive is being controlled by an
external position loop control. The Droop In Hold parameter is used
during spindle orient operation. These parameters should be set as
low as possible while still giving satisfactory operation on the
machine. Effectively, droop assures smooth, quiet operation at rest
or very low speeds and tends to minimize small shaft disturbances.
o 16. If two servo mode speed ranges are being used, remove the 24V DC
from the Servo Input Scaling input to select the low operating speed
range. Repeat step 15.
o 17. If the 8510 drive must perform the spindle orient operation, verify
that all of the ORIENT SETUP – FEEDBACK DEFN parameters are
correctly set for the type of feedback device being used. Verify that
the GEAR RANGES – SET RATIO parameters accurately define the
ratio between the motor and the spindle being oriented. Incorrect
settings for either of these parameter groups will cause a drive fault
when orient is attempted.
While the drive is running, apply 24V DC to the Orient Command
input. The motor should slow to orient speed and then orient to the
target position (either preset or entered via the optional digital
inputs). If it continues to run at the low orient speed, the feedback
phasing must be reversed. Use the ORIENT SETUP – FEEDBACK
DEFN – Encdr Phasing parameter to reverse the feedback phasing.
The orient function gives an exponential deceleration to the target
position. The effective position loop gain is defined by the setting of
the ORIENT TUNE – Orient Speed and ORIENT TUNE – Orient
Start parameters.
The effective gain can be increased by either increasing the Orient
Speed parameter or reducing the Orient Start parameter value. To
assure that the drive will always orient the spindle without
overshoot, setup should be done with the largest expected reflected
load inertia. If expected maximum load inertias are not known,
always leave sufficient torque margin to assure successful operation
with high inertias.
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