Chapter 2
Behavior models used in CIP Motion
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Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018
While a Ramp Generator function could be included in each of the Fine
Command Generator position, velocity, and acceleration commands, this version
includes a Ramp Generator only within the Velocity Fine Command Generator.
When operating in Frequency Control mode, the Ramp Generator function is
integrated into the Frequency Control system.
The Ramp Generator enforces directional velocity limits on the Command Data,
ensuring that the Velocity Command never exceeds the configured Maximum
Velocity Pos/Neg values.
The Ramp Generator also supports Flying Start functionality. When enabling the
drive while the motor is still moving, the Ramp Generator output is initialized to
the current speed of the motor. From there, the Ramp Generator smoothly
accelerates or decelerates the motor to the current Controller Velocity Command.
Finally, the Ramp Generator supports Skip Bands that are most frequently used in
Frequency Control applications when certain speeds excite mechanical resonance
frequencies of the motor and load. The Skip Band feature allows three separate
Skip Speeds to be defined that shift the Velocity Command signal to avoid, or
skip, these problematic speeds. The Skip Speed Band determines the range of
speeds centered on the three Skip Speeds that the device avoids:
•
If the Velocity Command is within the Skip Band, but below the Skip
Speed, the Velocity Command output is set to the Skip Speed, minus half
the Skip Speed Band.
•
If the Fine Velocity Command is within the Skip Band, but above the Skip
Speed, the Velocity Command output is set to the Skip Speed, plus half the
Skip Speed Band.
When operating in Frequency Control mode, the Skip Band function is integrated
into the Frequency Control system.
See also
The Fine Command Generators can generate higher derivatives of the command
data input to serve as feedforward signals. The units for the velocity and
acceleration feedforward signals are generally different than the derivative units,
hence the derivative signals are scaled appropriately. Superior signal quality,
however, can be provided by the Motion Planner trajectory generators. The
feedforward selection blocks pick the best feedforward signal to apply based on the
bits set in the Command Data Set attribute. The best signal is defined as the signal
derived by using the fewest differencing operations.
Feedforward Signal Selection