bnp-b2365(eng)b.pdf - 第225页

4. Servo Adjustment 4 - 26 (4) Adjusting for feed for ward control In LMC compensation, a model position considering the position lo op gain is calculated based on the position command sent from the CNC, and compensation…

4. Servo Adjustment

4 - 25

(3) Adjusting the lost motion compensation timing

If the speed loop gain has been lowered from the standard setting value because the machine

rigidity is low or because machine resonance occurs easily, or when cutting at high speeds, the

quadrant protrusion may appear later than the quadrant changeover point on the servo control. In

this case, suppress the quadrant protrusion by setting the lost motion compensation timing

(SV039: LMCD) to delay the LMC compensation.

If a delay occurs in the quadrant protrusion in the circle or arc cutting as shown below in respect to

the cutting direction when CNC sampling measurement (DBB measurement) or actual cutting is

carried out, and the compensation appears before the protrusion position, set the lost motion

compensation timing (SV039: LMCD).

While measuring the arc path, increase LMCD by 10 ms at a time, to find the timing that the

protrusion and compensation position match.

Before timing delay compensation After timing delay compensation

No. Abbrev. Parameter name Explanation Setting range

SV039 LMCD Lost motion

compensation timing

Set this when the lost motion compensation timing does not match. Adjust

while increasing the value by 10 at a time.

0 to 2000

(ms)

When the LMCD is gradually raised, a two-peaked contour may occur at the motor FB position

DBB measurement. However, due to the influence of the cutter diameter in cutting such as end

milling, the actual cutting surface becomes smooth.

Because satisfactory cutting can be achieved even if this two-peaked contour occurs, consider the

point where the protrusion becomes the smallest and finest possible without over compensating

(bite-in) as the optimum setting.

Cutter center path

ctual cutting surface

Cutting direction

Quadrant changeover point

Point of LMC compensation execution

Cutter diameter

fter

compensation

Cutting

direction

4. Servo Adjustment

4 - 26

(4) Adjusting for feed forward control

In LMC compensation, a model position considering the position loop gain is calculated based on

the position command sent from the CNC, and compensation is carried out when the feed changes

to that direction. When the CNC carries out feed forward (fwd) control, overshooting equivalent to

the operation fraction unit occurs in the position commands, and the timing of the model position

direction change may be mistaken. As a result, the LMC compensation timing may deviate, or

compensation may be carried out twice or more.

If feed forward control is carried out and the compensation does not operate correctly, adjust with

the non-sensitive band (SV040 (LMCT)) during feed forward control. In this non-sensitive band

control, the overshooting set with LMCT is ignored during feed forward control. Instead the model

position direction change point is correctly recognized to correctly compensate LMC.

This parameter is meaningless when feed forward control is not being carried out.

If the compensation timing deviates during feed forward control, increase the LMCT setting by 1µm

at a time.

Note that 2µm are set even when the LMCT is set to 0.

No. Abbrev. Parameter name Explanation Setting range

SV040 LMCT

Lost motion

compensation

non-sensitive band

Set the non-sensitive band of the lost motion compensation in the feed

forward control.

When "0" is set, the actual value that is set is 2µm. Adjust by increasing by

1µm at a time.

0 to 100

(µm)

4. Servo Adjustment

4 - 27

(5) Setting and adjusting LMC compensation type 3

LCM compensation type 3 can be used to accommodate quadrant projection changes that

accompany feed rate and circular radius changes which could not be accommodated by LCM

compensation type 2. In this case, on a machine model where the travel direction is reversed, the

viscosity component is also considered in addition to the friction, with compensation occurring in

accordance with the changes in the cutting conditions.

Adjust Compensation parameter (SV016, SV041), a basis of compensation, while measuring

roundness at low speed. Then adjust viscous coefficient (SV086) while measuring roundness at

high speed.

LMC compensation type 3 parameter adjustments should be made while performing a machine

end roundness measurement such as a DDB measurement, etc.

[1] Set the bit1=1 to servo function selection 5 (SV082). (The LMC compensation type 3 will start).

[2] Set a value double the friction torque to the lost motion compensation 1 (SV016). The SV016 setting

value will be used for compensation in the positive and negative directions when the lost motion

compensation 2 (SV041) is 0.

[3] Set the initial value, 1000 to the lost motion compensation viscous coefficient (SV086).

[4] Perform a roundness measurement at such speed as radius R=100mm and feedrate F=1000mm/min

and adjust SV016 value.

[5] Set SV041, when changing the compensation amount in the direction for compensation. The setting

of the compensation direction is shown below with the setting of CW/CCW in the NC parameter. If

compensating only one direction, set –1 to the side not to be compensated.

Compensation

point

CW CCW

A X axis: SV041 X axis: SV016

B Y axis: SV016 Y axis: SV041

C X axis: SV016 X axis: SV041

D Y axis: SV041 Y axis: SV016

[6] Perform a roundness measurement at such speed as radius, R=100mm and feedrate,

F=5000mm/min. (Select a condition to be used for the actual cutting according to the machine's

specification.) Adjust viscous coefficient (SV086) by reducing it gradually to have minimum quadrant

protrusion.

[7] After adjusting SV086, verify its accuracy by performing roundness measurement at low speed again.

POINT

1. As the acceleration of circular feed increases, the quadrant protrusion tends to

get larger. Therefore, the quadrant protrusion gets larger as the circular feedrate

increases for the same radius and as radius gets smaller for the same feedrate.

2. Torque offset (SV032) does not work for LMC compensation type 3.

3. Always set 0 to the lost motion compensation timing (SV039:LMCD).

-Y

-X

The X axis command direction

chan

es from + to -.

The Y axis command direction

changes from + to -.

The Y axis command direction

changes from - to +.

The X axis command direction

changes from - to +.