
B-65222EN/03 START-UP 4.PARAMETER SETTING
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4.2 VELOCITY LOOP GAIN
The velocity loop gain of a linear motor is based not on the concept of
load inertia but on the ratio of load mass to coil slider mass. For
15000C, for example, suppose that the mass of the coil slider is 48 kg,
and the load (the mass of the movable section including the coil
slider) is 1500 kg. The mass ratio is about 31 times. This means that
the reference velocity loop gain is 3100%.
If a very low velocity loop gain (200% or less) is set initially,
oscillation with a large amplitude can occur. For velocity loop gain
adjustment, first set a half of the reference value, then check the state
of oscillation by operating the manual pulse generator. If oscillation
still occurs, the point of resonance is very low.
Increase the velocity loop gain by 300% to 500% from this state, then
observe oscillation and sound by operating the manual pulse generator.
If no problem is found, increase the velocity loop gain furthermore.
If oscillation occurs, return the velocity loop gain to the previous
setting, then combine the following functions so that a high
oscillation limit can be set:
- Proportional term high-speed processing function or 250 µs
acceleration feedback
- Torque command filter
- Vibration suppression filter
The oscillation limit may be increased by changing the frequency
characteristics of the current loop.
No. 1852 (FS15)/No. 2040 (FS16) PK1 Current loop integral gain
As a guideline, about a half of the standard value should be set.
After determining an oscillation limit by using various functions, set
70% of the oscillation limit as a velocity loop gain. When a machine
with a long stroke is used, finally check that no oscillation occurs
across the stroke.
If the use of HRV2 or HRV3 causes the absolute value of the current
loop gain PK2 to exceed 16000, the maximum force can decrease.
In this case, set the following:
Bit 2 of No. 1750 (FS15)/No. 2210 (FS16) = 1
Then, set the current loop gain (PK1, PK2) to 1/4.
With both the linear motor and rotary motor, a higher velocity loop
gain needs to be set in order to ensure precision.
NOTE
For the functions described in this section, refer to
"FANUC AC SERVO MOTOR αi series Parameter
Manual (B-65270EN)".