Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 150)

Publication 1784-UM003A-EN-P – June 2003
142 Naming & Configuring Your Motion Axis
Velocity Scaling
The Velocity Scaling attribute is used to convert the output of the servo loop
into equivalent voltage to an external velocity servo drive. This has the effect
of “normalizing” the units of the servo loop gain parameters so that their
values are not affected by variations in feedback resolution, drive scaling, or
mechanical gear ratios. The Velocity Scaling value is typically established by
servo’s automatic tuning procedure but these values can be calculated, if
necessary, using the following guidelines.
If the axis is configured for a velocity external servo drive (in the Servo tab of
this dialog), the software velocity loop in the servo module is disabled. In this
case the Velocity Scaling value can be calculated by the following formula:
Velocity Scaling = 100% / (Speed @ 100%)
For example, if this axis is using position units of motor revolutions (revs), and
the servo drive is scaled such that with an input of 100% (e.g. 10 Volts) the
motor goes 5,000 RPM (or 83.3 RPS), the Velocity Scaling attribute value
would be calculated as:
Velocity Scaling = 100% / (83.3 RPS) = 1.2% / Revs Per Second
Torque Scaling
The Torque Scaling attribute is used to convert the acceleration of the servo
loop into equivalent % rated torque to the motor. This has the effect of
“normalizing” the units of the servo loops gain parameters so that their values
are not affected by variations in feedback resolution, drive scaling, motor and
load inertia, and mechanical gear ratios. The Torque Scaling value is typically
established by the controller’s automatic tuning procedure but the value can be
manually calculated, if necessary, using the following guidelines:
Torque Scaling = 100% Rated Torque / (Acceleration @ 100% Rated
Torque)
For example, if this axis is using position units of motor revolutions (revs),
with 100% rated torque applied to the motor, if the motor accelerates at a rate
of 3000 Revs/Sec2, the Torque Scaling attribute value would be calculated as
shown below:
Torque Scaling = 100% Rated / (3000 RPS2) = 0.0333% Rated/ Revs
Per Second2
Note: If the Torque Scaling value does not reflect the true torque to
acceleration characteristic of the system, the gains also does not reflect
the true performance of the system.