Torque scaling – Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual User Manual

Page 344

Publication 1784-UM003A-EN-P – June 2003

336 Motion Object Attributes

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 Torque Scaling attribute value would
be calculated as shown below.

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. In fact, the Torque Scaling value, when
properly established, represents the inertia of the system and is related to the
Tune Inertia attribute value by a factor of the Conversion Constant. The
Torque Scaling value is typically established by the MAAT instruction as part
of 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), and
that with 100% rated torque applied to the motor, the motor accelerates at a
rate of 3000 Revs/Sec

, the Torque Scaling attribute value would be calculated

as shown below.

Torque Scaling = 100 % Rated / (3000 RPS

) = 0.0333 % Rated/

Revs

Per Second

Note: If the Torque Scaling value does not reflect the true torque to
acceleration characteristic of the system, the gains will also not reflect
the true performance of the system.

GSV/SSV Access

Attribute Name

Data Type

Values

SSV/GSV

Velocity Scaling

REAL

% / Position Units Per Second