
4. SERVO FUNCTION DETAILS B-65150E/04
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4.18 SERVO AUTO TUNING
(1) Overview
The FANUC auto tuning system uses a personal computer to
automatically determine servo-related parameter values. Data such as
the move commands required for auto tuning is sent to the NC from the
personal computer via the RS-232C interface (DNC operation). Servo
data (such as position and velocity data) generated during operation is
fed to the personal computer via an interface board manufactured by
FANUC; the optimum parameter values for the system are determined
by analyzing the data and comparing with a specified figure. The
parameter values determined by the auto tuning function are sent to the
NC via the RS-232C interface.
(2) Scope
This system allows the adjustments described below to be made.
<1> Velocity loop gain adjustment
The velocity loop gain parameter is automatically adjusted to an
optimum value by gradually increasing the gain while monitoring
the resonance of the machine system.
<2> Automatic estimation of machine inertia
By repeatedly accelerating/decelerating a machine, the inertia of
that machine can be automatically estimated to determine the
values of the parameters related to machine inertia. Thus, the
acceleration torque of the machine can be separated from the
friction torque to facilitate backlash acceleration and unexpected
disturbance detection adjustments.
<3> Feed-forward coefficient adjustment
The advanced preview feed-forward coefficient is automatically
adjusted to allow the user to eliminate figure errors caused by
servo system delay while viewing a circular trace error. (To
enable this adjustment, the advanced preview control option is
required.)
<4> Quadrant protrusion compensation adjustment
The two-stage backlash acceleration function is adjusted to
eliminate quadrant protrusion in circular cutting at both low and
high speeds. (To enable this adjustment, the advanced preview
control option is not required.)
<5> Measurement of machine system velocity loop frequency
characteristics
Even without the use of a special measuring instrument, the
frequency characteristics (gain diagram) of a velocity loop
involving a machine system can be measured easily.
<6> Creation of initial parameter values
Initial digital servo parameter values can be automatically created
using the personal computer. The initial parameters include those
parameters that are set on the servo setting screen of the NC,
which are automatically set by entering data such as the gear
reduction ratio, the motor used, and so forth on the personal
computer.