Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 392)

Publication 1784-UM003A-EN-P – June 2003
384 Motion Object Attributes
Auxiliary Position Servo The Auxiliary Position Servo configuration provides full position servo
control using an auxiliary (i.e., external to the motor) feedback device to
provide position and velocity feedback. This servo configuration is a good
choice in applications positioning accuracy is important. The smoothness and
stability may be limited, however, due to the mechanical non-linearities
external to the motor. Note, that the motor mounted feedback device is still
required to provide motor position information necessary for commutation.
Synchronous input data to the servo loop includes Position Command,
Velocity Offset, and Torque Offset. These values are updated at the coarse
update rate of the associated motion group. The Position Command value is
derived directly from the output of the motion planner, while the Velocity
Offset and Torque Offset values are derived from the current value of the
corresponding attributes. These offset attributes 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 13.19 Auxiliary Position Servo
Pos P
Gain
Pos I
Gain
Vel
FF
Gain
d/dt
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 2 /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
Offset
Torque
Offset
Motor
Feedback
Channel
Servo Config = Aux Position Servo
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
Frict.
Comp