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9. Adjustment
9 - 24
9-3-5 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 settling
<2> Machine system friction: Overshooting will occur mainly during one pulse feed
<2> Machine system friction: Overshooting will occur mainly during one pulse feed
Either phenomenon can be confirmed by measuring the position droop.
0
Position
command
command
0
Position
droop
droop
Time
Overshoot
0
Speed
FB
FB
0
Position
droop
droop
Time
Overshoot
<1> Overshooting during rapid traverse settling
<2> Overshooting during pulse feed
(1) Overshooting compensation (OVS compensation)
In OVS compensation, the overshooting is suppressed by subtracting the torque command set in
the parameters when the motor stops.
the parameters when the motor stops.
<Setting and adjustment method>
<1> Set the special servo function selection 1 (SV027 (SSF1)) bit 10, 11. (OVS compensation type 3 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
forward/reverse directions with the OVS1 setting value.
does not occur. If SV042 (OVS2) is 0, the overshooting will be compensated in both the
forward/reverse 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 NC parameter CW/CCW setting.
to be compensated, set the side not to be compensated as -1. The compensation direction setting will
be as reversed with the NC parameter CW/CCW setting.
(2) Adjusting for feed forward control
If OVS compensation type 3 is used to attempt to compensate overshooting, the overshooting may
conversely become larger, or projections may appear during arc cutting. This is because overshooting
equivalent to the operation fraction unit occurs in the position commands when the NC is carrying out
feed forward (fwd) control. Because of this, the OVS compensation recognizes a change in the
command direction, and executes the compensation in the opposite direction.
conversely become larger, or projections may appear during arc cutting. This is because overshooting
equivalent to the operation fraction unit occurs in the position commands when the NC is carrying out
feed forward (fwd) control. Because of this, the OVS compensation recognizes a change in the
command direction, and executes the compensation in the opposite direction.
If the compensation is in the opposite direction when carrying out feed forward control, adjust with
the dead band (SV034 (SSF3) bit C to F: ovsn) during feed forward control. By ignoring
overshooting of a set width in the ovsn or less, the command direction change point is correctly
recognized, and the OVS compensation is correctly executed.
the dead band (SV034 (SSF3) bit C to F: ovsn) during feed forward control. By ignoring
overshooting of a set width in the ovsn or less, the command direction change point is correctly
recognized, and the OVS compensation is correctly executed.
This parameter is insignificant when feed forward control is not used.
<Adjustment method>
If the OVS compensation is carried out in reverse 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.
setting by 1µm at a time. Note that 2µm are set even when the LMCT is set to 0.