Behavior models used in CIP Motion
Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018 81
be used in conjunction with an outer control loop to make minor adjustments to
the velocity of the motor.
When serving as an inner velocity loop in Position Control Mode, the device
applies the Position Loop Output signal to the input of the velocity command
summing junction. Input signals that are not applicable to the configured control
mode are generally set to zero.
Velocity Limiter
The output of the velocity command summing junction signal passes through a
limiter to produce the Velocity Reference signal into the velocity loop. The
Velocity Limiter applies a directional velocity limit, either Velocity Limit - Pos or
Velocity Limit - Neg, to the velocity command signal input that is based on the
sign.
Velocity Feedback Selection
Feedback to the PI regulator can be derived from either of the two available
feedback transducers, Feedback 1 or Feedback 2. Which feedback source is used by
the loop is governed by the Feedback Mode enumeration. If Feedback Mode is No
Feedback, indicating sensorless operation, the Velocity Feedback signal is
estimated by the Sensorless Velocity signal generated by the sensorless control
algorithm. If an optional Load Observer is configured for Velocity Estimate
operation, the Velocity Feedback signal is the Load Observer Velocity Estimate.
Velocity Error Filter
A low pass filter can be optionally applied to the velocity error signal generated by
the velocity loop summing junction. The output of this filter becomes the Velocity
Error signal that is subsequently operated on by the velocity loop PI control
algorithm. When used, the filter is typically set between 5 to 10 times the velocity
loop bandwidth. It is recommended that this filter be a two pole IIR filter to
maximum its effectiveness at quantization noise filtering.
Velocity Gains
The velocity loop generates a Velocity Loop Output signal to the next inner loop
through a PI control loop structure. The Proportional Gain of the controller sets
the unity gain bandwidth of the velocity loop in radians/second, while the Integral
Gain is used to drive the Velocity Error signal to zero to compensate for any static
and quasi-static torque or forces applied to the load. The integrator path includes a
Proportional Gain so that units of the Integral Gain represent the bandwidth of
the integrator in radians/second.
The integral section of the velocity regulator includes an anti-windup feature. The
anti-windup feature automatically holds the regulator's integral term when a limit
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