Tuning Servo Loops U511 User’s Manual
8-24 Aerotech, Inc. Version 1.1
Adjusting “Aff” is optional. The user’s application may not need it.
8. Turn the Position Error, Integral Error, and Velocity Error traps on by returning
to the U511 Parameters Editor window and selecting the Parameter tab called
“Faults.” Turn the “Position Error,” the “Integral Error,” and the “Velocity
Error” back on by checking the boxes. This will reactivate these traps.
Save and exit the Parameter Editor window.
Reinitialize the UNIDEX 511.
8.6. Tuning Tips
Some tips for tuning AC brushless motors and low resolution encoders are given below.
• AC brushless motors usually have cyclic position error. Most Aerotech AC
brushless rotary motor systems will have a disturbance of 4 cycles per motor
revolution (8 pole motor). Aerotech linear motors have a pitch of 2.4 in and will
generate a cyclic error with a period of 2.4 in. These errors are due to gain or
offset differences in the amplifier phases.
• A low resolution encoder (1000 lines/rev) and a high servo loop sampling rate (4
kHz) may cause high frequency noise or squealing sounds. These systems will
usually perform quieter by changing the “Loop update rate (*.25 ms)” (axis
parameter x62) from zero to four. The “Kp” gain should be decreased by a factor
of four and “Kpos” increased by a factor of four when doing this. The “Ki”
should remain unchanged.
• The position loop bandwidth can be calculated from the “Kpos” and servo loop
update frequency. The calculation is as follows:
FHz
KF
BW
pos servo
()=
⋅
⋅⋅4096 2
where:
Fservo = servo loop update frequency (Hz) (typically 1000 or 4000)
F
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