bnp-b2365(eng)b.pdf - 第233页
4. Servo Adjustment 4 - 34 4-4-2 Speed loop delay compensation Generally, the tool end position follows the operation later than the motor end positio n. With full closed loop position loop control, the tool end position…
4. Servo Adjustment
4 - 33
4-4 Adjustment during full closed loop control
4-4-1 Outline
(1) Full closed loop control
The servo control is all closed loop control using the detector's feedback. "Full closed loop control"
is the system that directly detects the machine position using a linear scale, whereas the general
"semi-closed loop" is the one that detects the motor end position.
In a machine that drives a table with a ball screw, the following factors exist between the motor and
table end:
[1] Coupling or ball screw table bracket's backlash
[2] Ball screw pitch error
These can adversely affect the accuracy. If the table position, which is the tool end, is directly
detected with a linear scale, high-accuracy position control which is not affected by backlash or
pitch error is possible. However, with the full closed loop system, the machine system is also
directly included in the position loop control. Thus, if the machine's rigidity is not high, the gain
cannot be increased, and the required high accuracy cannot be attained.
The procedures for adjusting the servo with the full closed loop system are the same as the
semi-closed loop system. Vibration or overshooting will occur easily, so the position loop gain is
generally lower than the semi-closed loop.
(2) Overrun detection
With the full closed system, the tool end position feedback (FB) detected with the linear scale is
used for the position control. However, the motor end position FB is detected at the same time, and
the error of both FB is observed. If this FB error exceeds the servo parameter SV054 setting value,
alarm 43 will be detected and the system will stop to prevent overrunning due to a scale FB error
from occurring.
Overrun detection c ontrol
No. Abbrev. Parameter name Explanation Setting range
SV054 ORE Overrun detection
width in closed loop
control
Set the overrun detection width in the full-closed loop control.
If the gap between the motor end detector and the linear scale (tool end
detector) exceeds the value set by this parameter, it is judged to be
overrun and Alarm 43 will be detected.
When "-1" is set, the alarm detection won’t be performed. When "0" is
set, overrun is detected with a 2mm width.
-1 to 32767
(mm)
Position
command
PGN
+
-
FB error
Position droop
Servo-
motor
ENC
Linear scale
Table
Speed command
Machine end
p
osition FB
Motor end position FB
+
-
4. Servo Adjustment
4 - 34
4-4-2 Speed loop delay compensation
Generally, the tool end position follows the operation later than the motor end position. With full closed
loop position loop control, the tool end position is used for position feedback, so the motor end position
could advance too far and cause the tool end position to overshoot easily. Speed loop delay
compensation suppresses overshooting by weakening the speed loop PI control (weakening advance
compensation = delaying). If the compensation is too large and PI control is weakened too far, the
positioning time could increase, or the position droop will remain when the motor is stopped.
<Adjustment method>
[1] Set the servo function selection 1 (SV027: SSF1)/bit1, bit0 to 10. (Select delay compensation
changeover type 2)
[2] Set the axis unbalance torque to the torque offset (SV032: TOF). (Refer to "4-3-5 (1) Unbalance
torque and frictional torque" for details on measuring the unbalance torque.)
[3] Observe the position droop waveform, and confirm the overshooting. Increase SV007 (VIL) in
increments of 5, and adjust so that the overshooting is improved. If set too high, the position
droop will remain when the axis is stopped.
No. Abbrev. Parameter name Explanation Setting range
Set this when the limit cycle occurs in the full-closed loop, or overshooting
occurs in positioning.
Select the control method with SV027 (SSF1)/bit1, 0 (vcnt).
Normally, use "Changeover type 2".
When you set this parameter, make sure to set the torque offset SV032
(TOF). When not using, set to "0".
SV007 VIL
Speed loop delay
compensation
Changeover type 2 When SV027 (SSF1)/ bit1, 0 (vcnt)=10
The delay compensation control works when the command from the
NC is "0" and the position droop is "0". Overshooting or the limit cycle
that occurs during pulse feeding or positioning can be suppressed.
0 to 32767
SV032 TOF Torque offset
Set the unbalance torque of vertical axis and inclined axis.
-100 to 100
(Stall [rated]
current %)
SV027 SSF1 Servo function
selection 1 F E D C B A 9 8 7 6 5 4 3 2 1 0
aflt zrn2 afse ovs lmc omr zrn3 vfct upc vcnt
bit Meaning when "0" is set Meaning when "1" is set
0
Set the execution changeover type of the speed loop delay
compensation.
1
vcnt
00:
Delay compensation changeover
invalid
10: Delay compensation
changeover type 2
01:
Delay compensation changeover
type 1
11: Setting prohibited
CAUTION
The position droop will remain if SV007 is set too high.
4. Servo Adjustment
4 - 35
4-4-3 Dual feedback control (Optional function)
If the motor and machine coupling or machine system's rigidity is low (ex. large machine, etc.) when
using a closed loop system, the response during acceleration/deceleration will vibrate and cause
overshooting. This can cause the position loop gain from increasing. The dual feedback function is
effective in this case.
To validate the dual feedback function, use position feedback with a motor end detector in ranges with
high acceleration to enable stable control. In ranges with low acceleration, use position feedback with
the tool end detector (scale). This will make it possible to increase the position loop gain.
Dual feedback control
The state will approach the semi-closed loop system as the primary delay filter's time constant
increases, so the position loop gain limit will increase. Note that the limit of the position loop gain
increased with the dual feedback function is the same as the position loop gain limit for a semi-closed
system that does not use a tool end detector(scale, etc.). In addition, the positioning time will increase
as the primary delay filter time constant increases.
POINT
1. Dual feedback control is a function that compensates symptoms resulting
from insufficient machine rigidity. If there are items that can be improved on
the machine (improvement of scale installation position, etc.) improve those
first.
2. The position loop gain limit will not increase compared to the semi-closed
loop system even when using dual feedback control.
3. Dual feedback control is an optional function. If the option is not set in the
NC, alarm 37 (at power ON), or warning E4 and error parameter No. 103
(2303 for M60S/E60 Series NC) will be output.
Position control
Primary
delay filter
High frequency
FB element
Low frequency
FB element
dead band
SV052
SV051
Position
command
+
-
Position droop
Servo-
motor
ENC
Linear scale
Table
Speed
command
Tool end
p
osition FB
Motor end position FB
+
-
+
-