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setting the bandwidth too high can result in ringing (audible
ringing) in the velocity loop. The units for Velocity Loop
Bandwidth are Hz.
Position Loop Response
The Position Loop Response directly impacts the stiffness
of the position loop. Position Loop Response is effectively
the Proportional gain term for the position loop controller.
Higher Position Loop Response values will result in less
following error throughout a motion profile, however setting
the response too high can result in instability in the position
loop.
Enable Velocity Feedforward
The Velocity Feedforward applies the calculated velocity
command directly to the drive’s velocity loop. Enabling the
Velocity Feedforward will generally yield faster velocity
response, however the feedforward will introduce some
overshoot. It is vital in applications that require the use of
Jog profiles to enable the Velocity Feedforward signal.
Current Demand Filter
The Current Demand Filter is a first-order low pass filter
applied to the current command of the Unidrive SP. The
parameter entered by the user is a time constant, t, in the
filter formula. The frequency of the filter, f, can be derived
as follows:
The units for the parameter are milliseconds. This
parameter is written directly to parameter 4.12 of the
Unidrive SP parameter database.
Simple Tuning Procedure
1. Select the desired Drive Type and Motor Type on
the Drive/Encoder view in PowerTools Pro EZ.
2. Verify that the values of each of the motor
parameters have been entered correctly, paying
close attention to the Motor Rotor Inertia and the
Motor Ke.
3. Enter the calculated Inertia Ratio into the edit box
on the Tuning view.
4. Set the Position Loop Response to zero.
5. Enable the Velocity Feedforward parameter.
6. Configure an index that will simulate a step signal
(make sure not to configure accel/decel values that
you cause the motor to be current limited)
7. Initiate the index while recording velocity
feedback on an oscilloscope.
8. Gradually increase the Velocity Loop Bandwidth
until the velocity plot shows less than 20% velocity
overshoot with no ringing (instability).
9. Audible noise may be introduced by increasing the
Velocity Loop Bandwidth due to velocity jitter.
The Current Demand Filter can be used to reduce
the noise. Begin with a 1 ms value in the Current
Demand Filter and gradually increase until the
noise is reduced.
10. After adding the Current Demand Filter, you may
be able to slightly increase the Velocity Loop
Bandwidth again.
11. Gradually increase the Position Loop Response
until Following Error is minimized. Often, a value
approximately 1/4th of the Velocity Loop
Bandwidth will work well. Increase until
oscillation is introduced and then slightly decrease.
12. Save file.
7.3.9 Errors View
The Errors View contains information about Drive Trips
and Module Errors that are currently active as well as a log
of the last ten drive trips. PowerTools Pro must be online
with the module to obtain this information. Figure 73 shows
an example of the Errors View when Online with the
module.
Figure 73: Errors View
Active Errors
The Active Errors box shows any drive trips or module
errors that are currently active. The user can reset any
drive trip or module error by clicking on the Reset control
button underneath the Active Errors box. If the situation
that caused the trip or error has not been fixed, then the trip
or error will activate again immediately.
f
1
2πt()
-------------=