Thane Heins Perepiteia.

[markzpeiverson]

Stumbled across this interesting read at this location:

http://twinkle_toes_engineering.home.comcast.net/~twinkle_toes_engineering/induction_motor.htm

about why induction motors were not fully understood until someone attempted to use them as you would a servo motor. Torque 'ringing' due to the rotor time constant...

Excerpt from the full article is below...
-Mark

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Baffled by the rotor time constant
        For several years all attempts at getting servo-like performance from the induction motor failed.  A step of torque (really a fast ramp) would be requested, but the motor if it made the torque step at all would  then 'ring' the torque for a half second or so. No one could figure out how to stop the ringing.

        All conductors have resistance (R) and inductance (L). Inductance is a measure of the strength of the magnetic field generated by the current flowing in the conductor. The ratio of L/R has the units of time and forms a natural time constant that is a measure of how fast  the current and magnetic field of the conductor can change. The rotor of an induction motor has embedded in it a conducting loop of copper in which current flows round and around. It was known that the 'ringing' seen in the induction motor matched the rotor time constant, so it was pretty clear the rotor time constant was in some way causing the ringing.  The rotor time constant of the typical induction motors is about 0.1 to 0.3 seconds.

No one really understands how the induction motor works
        The failure to tame the rotor time constant was indicative of the fact that even the experts did not 'really' understand how the induction motor worked. At least they didn't understand it dynamically. The induction motor, while complicated, had long been written up in the motor text books, and the text books were accurate as long as things didn't change too fast. Think how remarkable this is. The world's most common motor and almost a century since its invention, and no one really understands how it works!

         One of the difficulties in understanding the induction motor is that it is not a linear device; it often operates with partial saturation in its iron. This non linearity in the motor frustrated the efforts of the mathematically oriented researchers to understand the motor  by writing out its equations. They had some limited success. Their equations would be valid for small signal changes about an operating point, so in those limited regions the desired fast, clean torque step was obtained, but in the general case the torque response remained contaminated by the dreaded rotor time constant ring.

Dynamics are figured out
        Here is where my work comes in.... I solved the ring problem, and by doing so improved the understanding of the induction motor dynamically. My employer at the time, Draper Laboratory, a large research and development laboratory in Cambridge MA, filed for a patent on this work in 1980 with me as sole inventor and in 1982 the patent was granted. (US patent 4,348,627).

[i_ron]

I_RON HAS A NEW FAN IN ME!!!

CHEERIOS
Thane

You are too kind, mon ami

Ron

[JustMe]

.

[CRANKYpants]

Some fantastic work to date Thane.

Can I just make sure I understand this... and ask you kindly to fill in the gaps (no pun intended )

thanks

Lee

DEAR LEE,

I HOPE THE NEW PHOTOS POSTED BY JUSTME ANSWER YOUR QUESTIONS?
THE AIR GAP IS ABOUT 1/4 INCH.
THERE IS NO AIR GAP BETWEEN THE TOROIDS.
EVERYTHING ELSE YOU GOT RIGHT.

THANKS
Thane

[CRANKYpants]

HEY,

HAS ANYONE NOTICED THE SMILEY IN THE BOTTOM TORIOD IN THE PHOTO? 

A SIGN PERHAPS?

CHEERS
Thane