User guide

Configuring an Application www.controltechniques.com 55
Figure 76: Tuning View
7.3.8.1 Load
7.3.8.1.1 Inertia Ratio
This parameter is the ratio between the load inertia and the
motor rotor inertia. The formula is defined as follows:
In order to calculate the Inertia Ratio, the user must first
calculate the load inertia. The load inertia is the inertia of
the load reflected to the motor shaft. Control Techniques
offers a free sizing software called CTSize that helps the
user calculate the load inertia. CTSize can be downloaded
from the Control Techniques’ website at no charge
(www.emersonct.com).
When entering the inertia ratio, if the exact ratio is not
known, it is better to enter a lower (more conservative)
value than to enter a “higher-than-actual” value. Higher
numbers in the Inertia Ratio amplify the gains of the
Velocity and Position Loop parameters described below.
The motor rotor inertia used in this calculation can be found
on the Motor Tab on the Motor/Encoder view in
PowerTools Pro or in the SPMotor.ddf file that is installed
with PowerTools Pro software.
7.3.8.2 Tuning
7.3.8.2.1 Velocity Loop Bandwidth
The Velocity Loop Bandwidth is the theoretical bandwidth
of the velocity controller. It is important for the motor data
file to be accurate for ideal velocity performance, in
particular the Motor Inertia and Motor Current Constant
(Ke). Higher Velocity Loop Bandwidth values will result in
better response to change in velocity command, however
setting the bandwidth too high can result in ringing (audible
ringing) in the velocity loop. The units for Velocity Loop
Bandwidth are Hz.
7.3.8.2.2 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.
7.3.8.2.3 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.
7.3.8.3 Filter
7.3.8.3.1 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.
7.3.8.4 Module Gains Enable Checkbox
Under normal operation, the SM-EZMotion module
calculates Current Loop and Velocity Loop gains based on
information provided by the user on the Motor Tab and
Tuning view. These calculated gains are sent by the
SM-EZMotion module to the Unidrive SP on every
power-up or warmstart, overwriting any gain values stored
in the drive. In some cases, a user may decide to use their
own values for Current Loop and Velocity Loop gains
rather than the values calculated by the SM-EZMotion
module. Therefore, it is necessary to be able to prevent the
SM-EZMotion module from sending its calculated gain
values to the Unidrive SP.
By default, the “Module Gains Enable” checkbox will be
selected so that the values calculated by the SM-EZMotion
are sent to the Unidrive SP. To disable this function, simply
clear the “Module Gains Enable” checkbox.
If the user decides to enter their own gain values, the
values are entered using the Unidrive SP Keypad (or Drive
Menu Watch Window in Power Tools Pro). Once the values
are entered using the keypad, the values must be saved so
that they are not lost the next time power is cycled. This is
done by navigating to parameter number zero in any menu
(MM.00), entering the value 1000, and then pressing the
InertiaRatio
LoadInertia
RotorInertia
-----------------------------------=
f
1
2πt()
-------------
=