7/23/2019 Ac Servo Motors

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AC Servo Motors

Timing Electric Motors (cont.) Ac and dc electric motors can be used as timing motors. Dc

electric timing motors are used for portable applications, or where high acceleration and low

speed variations are required. These electric motors offer advantages, which include startingtorque as high as ten times running torque, efficiency from 50 to 70, and relatively easy speed

control. !ut some form of speed governor, either mechanical or electronic, is required.

Ac motors use readily available power, are lower in cost, have improved life, and do not generate"#$. %owever, ac motors cannot be readily adapted to portable applications, have relatively low

starting torques, and are much less efficient than dc motors.

AC Servo Motors: Ac servo motors are used in ac servomechanisms and computers which

require rapid and accurate response characteristics. To obtain these characteristics, servo motorshave small&diameter high&resistance rotors. The small diameter provides low inertia for fast

starts, stops, and reversals, while the high resistance provides a nearly linear speed&torquerelationship for accurate control.

'ervo motors are wound with two phases physically at right angles or in space quadrature. 'ervomotors feature a fi(ed or reference winding is e(cited from a fi(ed voltage source, while the

control winding is e(cited by an ad)ustable or variable control voltage, usually from a

servoamplifier. The servo motor windings are usually designed with the same voltage&turns ratio,so that power inputs at ma(imum fi(ed&phase e(citation and at ma(imum control&phase signal

are in balance.

$n an ideal servo motor, torque at any speed is directly proportional to the servo motor*s control&

winding voltage. $n practice, however, this relationship e(ists only at +ero speed because of theinherent inability of an induction servo motor to respond to voltage input changes under

conditions of light load.

The inherent damping of servo motors decreases as ratings increase, and the servo motors have a

reasonable efficiency at the sacrifice of speed&torque linearity. ost larger servo motors haveintegral au(iliary blowers to maintain temperatures within safe operating ranges. 'ervo motors

are available in power ratings from less than - to 750 , in si+es ranging from 0.5 to 7&in. /D.

ost servo motors are available with modular or built&in gearheads.