Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 394)

Publication 1784-UM003A-EN-P – June 2003
386 Motion Object Attributes
Motor Dual Command Servo The Motor Dual Command Servo configuration provides full position servo
control using only the motor mounted feedback device to provide position
and velocity feedback. Unlike the Motor Position Servo configuration,
however, both command position and command velocity are applied to the
loop to provide smoother feedforward behavior. This servo configuration is a
good choice in applications where smoothness and stability are important.
Positioning accuracy is limited due to the fact that the controller has no way of
compensating for non-linearities in the mechanics external to the motor. Note
that the motor mounted feedback device also provides motor position
information necessary for commutation. Synchronous input data to the servo
loop includes Position Command, Velocity Command, and Velocity Offset.
These values are updated at the coarse update rate of the associated motion
group. The Position and Velocity Command values are derived directly from
the output of the motion planner, while the Velocity Offset value is derived
from the current value of the corresponding attributes. The velocity offset
attribute may be changed programmatically via SSV instructions or direct Tag
access which, when used in conjunction with future Function Block programs,
provides custom “outer” control loop capability.
Figure 13.21 Motor Dual Command Servo
Pos P
Gain
Pos I
Gain
Vel
FF
Gain
Error
Accum
-ulator
Position
Error
Low
Pass
Filter
Vel P
Gain
Σ Σ Σ
Position
Command
(Coarse)
Fine
Interpolator
Position
Command
Velocity
Command Velocity
Error
Velocity
Feedback
Hardware
Feedback
Position
Position
Integrator
Error
Acc
FF
Gain
d/dt
Σ
Vel I
Gain
Velocity
Integrator
Error
Torque
Limit
Position
Feedback
(Coarse)
Position
Feedback
Error
Accum
-ulator
Notch
Filter
Output
Notch
Filter
BW
Feedback
Polarity
Velocity
Command
(Coarse)
Velocity
Offset
Motor
Feedback
Channel
Servo Config = Motor Dual Command
Σ Torque
Scaling
Σ
Pos/Neg
Torque
Limit
Low
Pass
Filter
Output
Low Pass
Filter
BW
Torque
Command
Motor
Feedback
Aux
Feedback
Motor
Torque
Amplifier
Hardware
Feedback
Position
Aux
Feedback
Channel Position
Accum-
ulator
Accel
Command
Fine
Interpolator
Torque
Offset
Frict.
Comp