Acceleration feedforward

Configuration

In order to use acceleration feedforward in P-AXIS-00223 acceleration feedforward and output of acceleration feedforward as additional command value has to be configured:

vorsteuer.vorsteuerung 0x202 #0x002: Activation acceleration feedforward
#0x200: Output as additive torque command
#value

The additive torque/current command value has to be configured in the cyclic process data.

Acceleration feedforward 1:

If output of acceleration feedforward as additive command value is configured and there is no additive torque/current command value configured in the cyclic process data error message 70351 (see P-ERR-70351removed link: P-ERR-70351) is output.

Torque calculation

When acceleration feedforward with an additive torque/current command value is used the required torque of the motor is calculated with the formula

Acceleration feedforward 2:

This torque is scaled in the motor format and output to the drive.

For the calculation of the angular acceleration, it is necessary to know the mechanical configuration of the axis. Because of this it is necessary to configure the path resolution of the axis with the parameters P-AXIS-00092, P-AXIS-00363, P-AXIS-00362, P-AXIS-00334 and P-AXIS-00223.

When one of the parameters P-AXIS-00363 and P-AXIS-00362 has assigned a value unequal one path resolution is calculated according to the formula:

Acceleration feedforward 3:

Parameter set

For an axis with a motor encoder resolution of 220 increments per Revolution, a gearbox ratio of 3 and a spindle pich of 5 mm/rev the following parameter set follows:

antr.feed_const_num 50000 #feedconstant 5mm per revolution
antr.feed_const_denom 1 #
getriebe[].incr_per_rev 10485676 #2**20 increments per motor
#revolution
getriebe[].wegaufz 3 #gearbox ratio: input
#revolutions
getriebe[].wegaufn 1 #gearbox ratio: output
#revolutions

As a further parameter total motor load (Jt) is needed. Jt consists of the sum of the moment of inertia of the motor and the motor related moment of inertia of the load. The resulting value in dimension kg*m2 must be inserted in parameter P-AXIS-00391.

getriebe[].load 0.48  #Total motor load 0.48 kg*m**2

With the available parameters it is possible to calculate the required motor torque.

To calculate the command value that must be output to the drive the following parameters are necessary:

The nominal torque of the motor as a reference value for torque scaling in P-AXIS-00392 and the torque scaling factor in parameters P-AXIS-00325 and P-AXIS-00326.

The value for P-AXIS-00392 can be extracted from the motor data sheet:

antr.acc_reference_value 0.45  #nominal torque in Nm

For parameters P-AXIS-00325 and P-AXIS-00326 the value has to be entered, which has to be output to the motor in order to deliver its nominal torque. This value depends on the torque scaling that is set up in the drive.

If for example percentual weighting in 0.1% of the maximum current of the drive amplifier is used, for a maximum current of 3.16 A and a nominal current of 1.58 A parameters P-AXIS-00325 und P-AXIS-00326 result in:

Acceleration feedforward 4:

Possible values for P-AXIS-00325 and P-AXIS-00326 would be:

antr.torque_scale_num        500
antr.torque_scale_denom        1

Additionally, the output of the acceleration feedforward value can be delayed with respect to the command position. This delay can be set up with parameter P-AXIS-00390.

Acceleration feedforward 5:

The maximum delay time that can be set up is one interpolator cycle. If a bigger delay time is set up an error message 70348 (see P-ERR-70348) is output and the delay time is set to zero..

With parameters P-AXIS-00225 and P-AXIS-00226 the feedforward value can be weighted. In the following example the weighting factor is 1.2.

vorsteuer.vs_a_faktor 12 # Weighting acceleration feedforward
# numerator
vorsteuer.vs_a_nenner 10 # Weighting acceleration feedforward
# denominator

So the resulting, complete parameter set is:

vorsteuer.vorsteuerung 0x202 #0x002: Activation acceleration feedforward
#0x200: Output as additive torque command value
antr.feed_const_num 50000 #feedconstant 5mm per revolution
antr.feed_const_denom 1 #
getriebe[].incr_per_rev 10485676 #2**20 increments per motor revolution
getriebe[].wegaufz 3 #gearbox ratio: input revolutions
getriebe[].wegaufn 1 #gearbox ratio: output revolutions
antr.acc_reference_value 0.45 #nominal torque in Nm
antr.torque_scale_num 500
antr.torque_scale_denom 1
vorsteuer.acceleration_delay_time 150 # Delay acceleration feedforward against
# position command value in us
vorsteuer.vs_a_faktor 12 # Weighting acceleration feedforward numerator
vorsteuer.vs_a_nenner 10 # Weighting acceleration feedforward denominator