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XtrapulsPac - User Guide
Chapter 3 – Reference
The
Speed measurement filter
is a 1st order, low-pass type filter, with 3 selectable time constant values. The
higher the time constant value, the lower the speed measurement noise, but also the lower the speed loop gains
because of the increased speed measurement delay. The
Speed measurement filter
time constant is selected
according to the motor position sensor resolution and the acceptable noise level in the speed measurement.
Position loop
gains mainly influence the servo motor behaviour during the displacements (following error,
position overshoot, audible noise, ...).
- Proportional position gain KPp)
: defines the proportional gain of the controller which acts on the position
error. The higher this parameter value, the better the axis stiffness and the lower the following error.
- Feedforward speed 1 gain (KFp)
: defines the feedforward speed amplitude corresponding to the speed input
command. This term allows reducing the following error during the motor displacement. Its value is set at the
maximum (65536) after the auto-tuning procedure, if a following error as small as possible is required.
- Feedforward speed 2 gain (KBv)
: defines the feedforward speed amplitude corresponding to the viscous
frictions. This term allows reducing the viscous friction effect during the motor displacement. The gain value is
equal to the damping gain value + the viscous friction compensation term. After the auto-tuning procedure, the
feedforward speed 2 gain is set equal to the damping gain value, if a following error as small as possible is
required. The viscous friction compensation term can be calculated by measuring the current/speed ratio at
various motor speed values.
- Feedforward acceleration gain (KAv)
: defines the feedforward acceleration amplitude corresponding to the
acceleration input command. This term allows reducing the following error during the motor acceleration and
deceleration phases. Its value is calculated by the amplifier during the auto-tuning procedure, if a following error
as small as possible is required.
When the
auto-tuning
procedure is executed, the motor + mechanical load specifications are identified and the
appropriate gain values are calculated according to the user selected requirements (controller type, filter type,
bandwidth value, ...). All gain values can then be manually modified by the user, if required.
The choice of the time interval for speed measurement (speed measurement filter) allows selecting the speed
measurement resolution value according to the position sensor resolution value:
speed resolution (rpm) = 60000 / position sensor resolution (ppr) / time interval (ms).
The higher the time interval value, the better the resolution, but also the lower the servo loop gains because of the
increased speed measurement delay.
The choice of the anti-resonance filter is necessary in case of loud noise in the motor due to the motor/load
coupling elasticity.
The choice of the maximum stiffness filter allows getting the maximum stiffness on the motor shaft with regard to
the torque disturbances. However, this choice is only possible without any resonance due to the motor/load
coupling elasticity.
The choice of the speed loop bandwidth defines the cut-off frequency value of the closed loop frequency
response (Low = 50 Hz, Medium = 75 Hz, High = 100 Hz).
The choice “
minimum following error
” allows getting an accurate following of the position reference value during
the whole motor displacement. In this case, all feedforward gain values are calculated.
