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Chapter 10 Adjustment
10–19
10-3-5 Improvement of overshooting
The phenomenon when the machine position goes past or exceeds the command during feed
stopping is called overshooting. Overshooting is compensated by overshooting compensation (OVS
compensation).
Overshooting occurs due to the following two causes.
1) Machine system torsion: Overshooting will occur mainly during rapid traverse positioning
2) Machine system friction: Overshooting will occur mainly during one pulse feed
Either phenomenon can be confirmed by measuring the position droop.
1) Overshooting during rapid traverse positioning 2) Overshooting during pulse feed
(1) Overshooting compensation (OVS compensation)
In OVS compensation, the overshooting is suppressed by subtracting the thrust command set in
the parameters when the motor stops. There are two types of OVS compensation. The standard
method is type 2.
OVS compensation type 3 has a compensation effect for the overshooting during either rapid
traverse positioning or pulse feed. Note that there is no compensation if the next feed command
has been issued before the motor positioning (stop). (Therefore, there is no compensation during
circle cutting.) There is no compensation in the non-sensitive band when the CNC is carrying out
feed forward control. To compensate overshooting during feed forward control, refer to the
following section "(2) Adjusting for feed forward control".
<Setting and adjustment methods>
1) Set the special servo function selection 1 (SV027:SSF1) bit 11 (ovs2). (OVS compensation
type 2 will start.)
2) Observe the position droop waveform using the D/A output, and increase the overshoot
compensation 1 (SV031: OVS1) value 1% at a time. Set the smallest value where the
overshooting does not occur. If SV042:OVS2 is 0, the overshooting will be compensated in
both the positive/negative directions with the OVS1 setting value.
3) If the compensation amount is to be changed in the direction to be compensated, set the +
direction compensation value in OVS1 and the – direction compensation value in OVS2. If only
one direction is to be compensated, set the side not to be compensated as -1. The
compensation direction setting will be as reversed with the CNC parameter CW/CCW setting.
POINT
In OVS compensation type 2, there is no compensation in the following cases.
1. There is no compensation if the next feed command has been issued before
the motor positioning (stop). (There is no compensation in circle cutting.)
2. There is no compensation when the CNC is carrying out feed forward (fwd)
control.
0
Position
command
0
Position
droop
Time
Overshoot
0
Speed
FB
0
Position
droop
Time
Overshoot