Rockwell Automation Publication MOTION-UM003K-EN-P - January 2019 241
Commission an Axis Chapter 11
Load Observer
The Load Observer feature is a control loop inside the drive that estimates the
mechanical load on the motor and compensates for it. This feature lets the
control loops to treat the motor as if it is unloaded and relatively easy to
control. The Load Observer automatically compensates for disturbances and
load dynamics, such as sudden inertia changes, compliance, backlash, and
resonances that are within the bandwidth of the Load Observer.
Benefits of Load Observer
You can use the Load Observer with out-of-box control loop gains, where the
load is unknown and thus the Load Inertia Ratio is equal to zero. You can also
use the Load Observer with auto-tuned control loop gains, where the Load
Inertia Ratio is known or calculated by performing an autotune procedure.
When you enable Load Observer with the recommended out-of-box control
loop gains, the Load Observer perform the following:
• Provides relatively high-performance motion control without tuning
• Minimizes the need to retune to account for machine wear over time
• Automatically compensates for changes in vibration and resonance that
are within the bandwidth of the Load Observer
• Mitigates periodic identification of in-band resonance to compensate for
them
When you use autotuned control loop gains, the Load Observer performs the
following:
• Increases system bandwidth
• Reduces tracking errors, so that line speeds can increase
• Provides tighter control of moving parts, which reduces wear and saves
on material costs
How Load Observer Functions
The Load Observer acts on the acceleration signal within the control loops and
monitors the Acceleration Reference and the Actual Position feedback. The
Load Observer models an ideal unloaded motor and generates a load Torque
Estimate that represents any deviation in response of the actual motor and
mechanics from the ideal model. This deviation represents the reaction torque
that is placed on the motor shaft by the load mechanics. Closed-loop operation
compensates the deviation, which is estimated in real time. See Figure 104 on
page 242 for an example Load Observer block diagram.
To Next Page
Loading...
Need help?
General
