32
Rev. 1.0
0006302011
SSM24C User Manual
+86-400-820-9661
VP and VI parameters and observe the results. VP and VI shold be adjusted at the same time and
in small increments. The following two figures shows responses with different VP and VI settings.
This first plot is performed with the default tuning values and no load added to the motor.
The second plot is performed with higher gain values for the VP (25000) and VI (3000), as can be
seen the velocity error decreases as the gains are increased.
To get a good comparison between different plots where the gains have been changed, turn off
the
Auto Scale
by clearing that check box below the plot screen. When auto scaling is turned off,
the difference can be seen more clearly.
5.5.4 Adding in the FF Gain (KK) parameter
The Acceleration Feed Forward (KK) applies more current to the motor to help compensate
for high inertia in the system. In a servo system more current is typically required during the
acceleration and deceleration phases of the move profile.
A reduction in the Velocity Error peak values should then be seen. As seen in this plot with the KK
set to 3000 the peaks in the Velocity error have been reduced. With loads that have greater inertia
this can provide a significant improvement.
NOTE: The FF Term (KK) is not available when operating in the Pulse & Direction Control
Mode. Setting this value will have no effect.
If the Velocity Error goes too positive during acceleration, the adjustment was too large and the
value should be adjusted in smaller amounts until there is as near to zero error as possible. The
Rescale
button next to the
Auto Scale
may be clicked at any time to re-scale the plot on the new
Velocity Error value.
5.5.5 Filter parameter
Step-servo has a control loop filter for special situations where the motor may resonate or may
have significant audible noise. This filter is designed as a low pass type for the control loop output.
When a system is subject to mechanical resonance, this low pass filter can be set below the
natural frequency of the system so that the control loop output does not excite the resonance.
With a large inertial load, the gain parameters, especially the VP and VI terms, may need to be set
high to get a good response. The filter may then need to be decreased in value (lower frequency)
to prevent ringing or oscillation. The default of 15000 works well in many cases but can be
increased or decreased with little risk.
5.5.6 Verify the Drive Current
The amount of drive current can be verified at any time during the tuning process to make sure the
current supplied to the motor is not being limited by the drive. If too much current is being required
changes may be made to the move profile. Select
Current
in one of the
Plot
selection lists and
repeat the move, from this the current can be evaluated.
5.5.7 Finishing up
If the SSM will only be operated in a
Velocity Control Mode
with a
Speed only
Control Type, the
