bnp-b2365(eng)b.pdf - 第231页

4. Servo Adjustment 4 - 32 <Adjustment methods> [1] Confirm that the motor end circle accuracy measured with the NC sampling functio n is appropriate. [2] In this state, measure the tool end low-spe ed and high-spe…

4. Servo Adjustment

4 - 31

4-3-7 Improvement of the interpolation control path

(1) Tool end compensation

The tool end compensation function compensates the shape of the tool end during high-speed and

high-speed acceleration/deceleration. The spring effect from the tool (spindle) end to the motor

(scale) end is compensated. If the machine has a large spring effect, the shape may be fine during

low-speed operation. However, at high speeds (specially when using a small radius), the section

from the tool (shaft) end to the outer sides of the motor (scale) end could swell, and cause the

shape to become elliptical during measurement of the roundness. The tool end compensation

function compensates the motor end position according to the acceleration size, so the tool end

position is always controlled to the commanded position.

POINT

1. Always evaluate the roundness accuracy at the tool end.

2. Adjust the parameter after adjusting the roundness accuracy at the motor

end.

Without tool end compensation With tool e nd compensation

During high acceleration,

the end section swells

outward due to the spring

effect.

The inner side is driven by the amount

that the end section swells due to the

spring effect.

Tool end roundness

(machining surface)

Elliptical shape fault

Tool end roundness

(machining surface)

Elliptical shape is

improved

Low speed:

Example:

R25mm

F1000mm/min

High speed

(high acceleration):

Example:

R25mm

F10000mm/min

Both low speed and

high speed are on

the same path.

Command path

(ideal path)

Tool end path

(machining surface)

Tool end path

(machining surface)

Command path

(ideal path)

4. Servo Adjustment

4 - 32

[1] Confirm that the motor end circle accuracy measured with the NC sampling function is

appropriate.

[2] In this state, measure the tool end low-speed and high-speed circle path without tool end

compensation. The difference of the high-speed circle path and low-speed circle path is the

amount that path has swelled due to the spring effect of the machine system. Calculate the

SV065 setting value with the following expression using this amount as the compensation

amount.

SV065 =

Compensation amount [µm] × radius R [mm] ×10

(command speed F [mm/min])

[3] Set SV027/bit7 to 1, and input the value calculated in step 2 into SV065. Measure the

high-speed circle path. If the shape is still elliptical, adjust by increasing/decreasing the SV065

value in 1/10 units.

[4] Confirm that there is no problem with the low-speed circle path.

Example of low-speed and high-speed roundness measurement for adjusting tool end compensation

When using grid encoder When using DBB measurement Acceleration

Low speed (reference circle) R=25 [mm], F=500 [mm/min] R=100 [mm], F=1000 [mm/min] 0.00028G

High-speed (when adjusting

compensation amount)

R=25 [mm], F=10000 [mm/min] R=100 [mm], F=20000 [mm/min] 0.11G

No. Abbrev. Parameter name Explanation Setting range

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

7 omr Tool end compensation invalid Tool end compensation valid

SV065 TLC Tool end

compensation spring

constant

Set the spring constant of the tool end compensation.

In the semi-closed loop control, the tool end compensation amount is

calculated with the following equation.

Compensation amount =

Commanded speed F (mm/min)

SV065

Radius R (mm)

(µm)

When not using, set to "0".

-32768 to

32767

POINT

1. To confirm the machine's spring element, adjust the electrical end

roundness, and then tool end roundness while changing the cutting speed.

Confirm that the error increases with the speed.

2. The electrical end roundness will have an error on the inner side when tool

end compensation is used.

CAUTION

If an excessive value is set in the tool end compensation spring constant

(SV065), the machine could vibrate when stopping, resulting in a dangerous

state.

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

osition FB

Motor end position FB