Improving The Cutting Surface Precision - Mitsubishi Electric MELDAS MDS-B-SVJ2 Series Specifications And Instruction Manual

5-3-3 Improving the cutting surface precision

If the cutting surface precision is poor, it can be
improved by adjusting the speed loop gain or by
using the voltage dead zone compensation or
disturbance observer function.
<Examples of faults>
• The surface precision in the 45° direction of a
taper or arc is poor.
• The load fluctuation during cutting is large, causing
vibration or surface precision defects to occur.
POINT
(1) Adjusting the speed loop gain (VGN1)
If the speed loop gain is increased, the cutting surface precision will be improved but the machine
will resonate easily.
The final VGN1 setting should be approx. 70 to 80% of the maximum value where resonance
does not occur. (Refer to "5-2-2 (1) Setting the speed loop gain")
(2) Adjusting the speed loop leading compensation (VIA)
The VIA has a large influence on the position trackability, particularly during high-speed cutting
(generally F1000 or more). Raising the setting value improves the position trackability, and the
contour precision during cutting can be improved. For high-speed high-precision cutting machines,
adjust so that a value equal to or higher than the standard value can be set.
When VIA is set lower than the standard value and set to a value differing between interpolation
axes, the roundness may worsen (the circle may distort). This is due to differences occurring in
the position trackability between interpolation axes. The distortion can be improved by matching
the VIA with the smaller of the values. Note that because the position trackability is not improved,
the surface precision will not be improved.
(Refer to "5-2-2 (2) Setting the speed loop leading compensation")
No. Abbrev. Parameter name
SV005 VGN1 Speed loop gain
SV008 VIA Speed loop lead
compensation
(3) Voltage non-sensitive zone (Td) compensation (Compatible from software version C3)
With the PWM control of the inverter, a dead time
(non-energized time) is set to prevent short-circuits
caused by simultaneous energizing of the P side and
N side transistors having the same phase. The dead
time has a non-sensitive zone for particularly low
voltage commands. Thus, when feeding with a low
speed and a low torque, the control may be unstable.
When an unbalanced axis is lowering, the frictional
torque and unbalance torque, and the frictional
torque and deceleration torque before the quadrant
changes during circle cutting, are balanced. The
motor output torque will be approximately zero, and
the control accuracy may drop. In this case, the
control accuracy can be improved by using the
voltage non-sensitive band compensation. Note that
this may cause vibration to increased while the motor
is running.
No. Abbrev. Parameter name
SV030 IVC Voltage dead-time
compensation
Chapter 5 Adjustment
Adjust by raising the speed loop gain equivalently to improve cutting surface
precision, even if the measures differ. In this case, it is important how much the
machine resonance can be controlled, so adjust making sufficient use of
vibration suppression functions.
Increase the value by 20 to 30% at a time.
If the machine starts resonating, lower the value by 20 to 30% at a time.
The setting value should be 70 to 80% of the value where resonance
does not occur.
1364 is set as a standard. 1900 is set as a standard during SHG control.
Adjust in increments of approx. 100.
Raise the VIA and adjust to improve the contour tracking precision in
high-speed cutting. If the position droop vibrates (10 to 20Hz), lower the
VIA and adjust.
When 100% is set, the voltage equivalent to the logical non-energized
time will be compensated. Adjust in increments of 10% from the default
value 100%. If increased too much, vibration or vibration noise may be
generated.
Y
Explanation
Deceleration torque =
For circle cutting
Explanation
5-14
X
Setting range
1 ~ 999
1 ~ 9999
Cutting
Motor torque
direction
Frictional
torque
Unbalance
torque
Lowering
frictional torque
For unbalance torque
Setting range
0 ~ 200
≒ 0
Balanced