8-50 Functions ECODRIVE03-FL*-04VRS
DOK-ECODR3-FL*-04VRS**-FK01-EN-P
Setting the Acceleration Feedforward
For servo applications requiring high precision at high speeds, it is
possible to greatly improve the precision of an axis during the acceleration
and deceleration phases by activating the acceleration feed forward.
Typical applications for the use of the acceleration feed forward:
• Free-form surface milling
• Grinding
To set the acceleration feed forward, use the following parameter
• CR08, Acceleration feedforward gain
Requirements for a Correct Setting for Acceleration
Feedforward
• Velocity and position loops must be set properly.
Setting the Acceleration Feedforward
Since it is dependent on the moment of inertia, the correct acceleration
feedforward can only be set by the user.
Setting this value involves two steps:
• Calculation of an approximate value for acceleration feedforward. To
make this calculation, take the total moment of inertia transferred from
the axis to the motor shaft (J
Motor+JLoad). This approximate value is
known from the size and set-up of the axis. Then take the torque
constant of the motor used. This data can be retrieved from the motor
data sheet or parameter CM05, Torque/force constant. The
approximate value is calculated as follows:
1000
LoadMotor
×
+
=
Kt
JJ
dFeedforwaronAccelerati
Acceleration feedforward [mA\rad\s²)]
J
Motor: Moment of inertia of the motor [kg m²]
J
Load: Moment of inertia of the load [kg m²]
Kt: Torque constant of the motor [Nm/A]
Fig. 8-27: Approximate Value for Acceleration Feedforward
Enter the approximate value calculated in parameter CR08, Acceleration
feedforward gain.
• Verification of the effect of the acceleration feedforward and fine
tuning of parameter CR08, Acceleration Feedforward Proportional
Gain if necessary. The deviation between the actual feedback value
and the position command can be displayed via the analog diagnostic
outputs of the drive controller or using the oscilloscope function. To
verify the effect of the acceleration feedforward, this signal must be
viewed on an oscilloscope while the axis traverses the desired
operating cycle. In the acceleration and deceleration phases, the
acceleration feedforward must reduce the dynamic control deviation
significantly.
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