Adaptive control algorithms are continuing to advance the state-of-the-art
in digital servo drives. In May, we reported on "Servo
Drives Utilizing Adaptive Control for Advanced Algorithms." But now we're
finding additional innovative products that are using real-time autotuning and
sophisticated electronic nameplates on motors to extend the performance of
adaptive tuning in servo drives.
The
MR-J3 drive from Mitsubishi Electric
uses a combination of a 900Hz frequency response and 18-bit encoder resolution
to implement robust, real-time autotuning.
Beyond adaptive tuning, the drives offer other servo tuning features that
simplify eliminating machine vibrations and resonances.
One control function, Vibration Suppression Tuning, automatically
determines vibration suppression parameters and makes it feasible to achieve higher
response for low stiffness machines. The
amplifier has load model blocks that stimulate a machine structure, and describe
the structural relation between the motor and load. The tuning section then estimates
the frequency of load vibration from the encoder position signal and calculates
the structural parameters and optimized feedback gains.
"Features like this are possible because of
the adaptive tuning capabilities in the drive which provides real-time, dynamic
autotuning of the system," says Sunny Ainapure, product manager for Servos and
Motion at Mitsubishi. He also says an adaptive filter algorithm provides software to deal with machine resonances
that can be difficult to resolve using traditional architectures.
A Robust
Disturbance Compensation algorithm is effective for an axis where the load
inertia is bigger than the motor inertia like the roller axis in a printing
press. Synchronizing the motor that has
a bigger inertia mismatch with smaller motors in the system is often a
problem. The algorithm monitors the low
frequencies on the machine and matches the gains to what is required for the
smaller size motors, so all three motors can be effectively synchronized.
With new Siemens S110 and S120 drives,
adaptive tuning algorithms offer improved performance by incorporating "electronic
nameplate" parameters along with factory measurements not typically found on a
nameplate.
"The DRIVE-CLiQ interface between SINAMICS
S110 drive and motor not only supplies the motor feedback to the drive
(including temperature) but also the electronic nameplate information," says
Craig Nelson, product marketing manager for SINAMICS Drives at Siemens Energy
& Automation.
Nelson says this
alleviates the need to parameterize motor data in the drive, forming a plug-and-play servo system as this information is automatically read up into the
drive. The performance of the drive is
also increased since auto-tuning algorithms have access to factory measurements
of the motor and important functions such as the resistance and inductance of the
stator and rotor.
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