User manual

166 Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015
Chapter 7 Commission
Load Observer
Acceleration Control can optionally include a Load Observer. Feeding the
Acceleration Reference (Kinetix 350 drive not supported) into a Load Observer,
along with the velocity feedback signal, has been found to be effective in
compensating for mechanical backlash, mechanical compliance, and various load
disturbances. For example, the effectiveness of the Load Observer can be thought
of as a result of the Observer adding virtual inertia to the motor.
The Load Observer functions as an inner feedback loop, like the current loop, but
unlike the current loop in that the observer’s control loop includes the motor
mechanics. Due to the work of the Load Observer, variations in load inertia,
mass, and even the motor’s torque/force constant can be nearly eliminated as seen
by the velocity loop.
Because the Load Observer includes the Acceleration Reference signal as an
input, it can provide a velocity estimate signal that has less delay than the velocity
feedback estimate generated by the actual feedback device. Thus, applying the
Load Observer’s velocity estimate to the velocity loop can be used to improve the
performance of the velocity loop.
Acceleration Feedback Selection
Feedback to the Load Observer can be derived from either feedback device,
Feedback 1 or Feedback 2. Which feedback source is used by the loop is governed
by Feedback Mode. In general, the Load Observer works best when using a high
resolution feedback device.
Acceleration and Torque Estimates
The output of the Load Observer is the Acceleration Estimate signal that is
subsequently applied to the acceleration reference summing junction.