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Why Servo Motor Is Used?


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#1 AB2005

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Posted 15 May 2007 - 07:01 AM

Dear All,

I want to know why servo motor (with Encoder) is used for controlling any device, as we can use the general Asynchronous motor with encoder and drive. Actually I havenít the basic information of Servo Motor. Can any body explain what the difference between servo motor and Asynchronous motor is?



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#2 jraef

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Posted 15 May 2007 - 04:57 PM

QUOTE(AB2005 @ May 15 2007, 12:01 AM) View Post

Dear All,

I want to know why servo motor (with Encoder) is used for controlling any device, as we can use the general Asynchronous motor with encoder and drive. Actually I havenít the basic information of Servo Motor. Can any body explain what the difference between servo motor and Asynchronous motor is?


The basic theory is actually close to being the same. The differences are precision and size.
Generally a servo is more precise, making it preferable for fine motor movements as you would find in machine tool applications. Servos can be made that will support movements of fractions of a radian. But servo motors get exponentially more expensive as the total power increases, so at around 10HP (7.5kW) it begins to be less expensive to use vector drives with asynchronous motors and encoders. Also, at the higher power ratings, high precision often becomes less important.
"He's not dead, he's just pinin' for the fjords!"

#3 Mike

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Posted 16 May 2007 - 12:22 PM

My basic understanding is
servo motor - permanant magnet rotor
Asynchronous motor - wound rotor typically squirrel cage.

The servo motor has a faster response to changes in stator because of the delay time in the wound rotor responding.

I have found it possible to get both systems to be very accurate however I can get a servo to position faster with a shorter settling time.









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