ac motor,servo motor and stepper motor

8/10/2019 AC Motor,Servo Motor and Stepper Motor

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AC Motors

AC motors are used worldwide in many applications to

transform electrical energy into mechanical energy. There are manytypes of AC motors, but this course focuses on threephase AC

induction motors, the most common type of motor used in

industrial applications.

An AC motor of this type may be part of a pump or fan or

connected to some other form of mechanical equipment such as a

winder, conveyor, or mixer.

Siemens manufactures a wide variety of AC motors. In addition to

providing basic information about AC motors in general, this course

also includes an overview of Siemens AC motors.


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AC Motor Construction

Three-phase AC induction motors are commonly used in

industrial applications. This type of motor has three main parts,rotor, stator, and enclosure. The stator and rotor do the work,

and the enclosure protects the stator and rotor.

Stator Core

The stator is the stationary part of the

motors electromagnetic circuit. The

stator core is made up of many thin

metal sheets,called laminations.Laminations are used to reduce energy

loses that would result if a solid core

were used.


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Stator Windings

Stator laminations are stacked together forming a hollow

cylinder. Coils of insulated wire are inserted into slots of thestator core.

When the assembled motor is in operation, the stator windings

are connected directly to the power source. Each grouping of

coils, together with the steel core it surrounds, becomes an

electromagnet when current is applied. Electromagnetism is

the basic principle behind motor operation.


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Rotor Construction

The rotor is the rotating part of the motors electromagnetic

circuit. The most common type of rotor used in a three-phaseinduction motor is a squirrel cage rotor. Other types of rotor

construction is discussed later in the course. The squirrel cage

rotor is so called because its construction is reminiscent of the

rotating exercise wheels found in some pet cages.

A squirrel cage rotor core is made by stacking thin steel

laminations to form a cylinder.


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Rather than using coils of wire as conductors, conductor bars

are die cast into the slots evenly spaced around the cylinder.

Most squirrel cage rotors are made by die casting aluminum toform the conductor bars. Siemens also makes motors with die

cast copper rotor conductors.

Advantages of AC Motor

Low cost

Speed variation

High power factor

Reliable operation

Disadvantages of AC Motor

Inability to operate at low speeds

Poor positioning control


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Servo Motors

What is a servo motor?

Servo motors (or servos) are self-contained electric devices that rotate

or push parts of a machine with great precision. Servos are found in

many places: from toys to home electronics to cars and airplanes. If

you have a radio-controlled model car, airplane, or helicopter, you are

using at least a few servos. In a model car or aircraft, servos move

levers back and forth to control steering or adjust wing surfaces. By

rotating a shaft connected to the engine throttle, a servo regulates the

speed of a fuel-powered car or aircraft. Servos also appear behind the

scenes in devices we use every day. Electronic devices such as DVD

and Blu-ray DiscTM players use servos to extend or retract the disc

trays. In 21st-century automobiles, servos manage the car's speed:

The gas pedal, similar to the volume control on a radio, sends an

electrical signal that tells the car's computer how far down it is

pressed. The car's computer calculates that information and other data

from other sensors and sends a signal to the servo attached to the

throttle to adjust the engine speed. Commercial aircraft use servos anda related hydraulic technology to push and pull just about everything

in the plane.


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Design of Motor

The magnetic force is be made by permanent magnet and the current

is used to generate torque. Then high torqueand efficiency are available at low current and small size.

It has no brush so there is little noise/vibration and no dirt. And high

precision control is available with high resolution encoder.

How does a servo motor work?

The simplicity of a servo is among the features that make them so

reliable. The heart of a servo is a small direct current (DC) motor,

similar to what you might find in an inexpensive toy. These motors

run on electricity from a battery and spin at high RPM (rotations per

minute) but put out very low torque (a twisting force used to do

workyou apply torque when you open a jar). An arrangement of

gears takes the high speed of the motor and slows it down while at the


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same time increasing the torque. (Basic law of physics: work = force

x distance.) A tiny electric motor does not have much torque, but it

can spin really fast (small force, big distance). The gear design inside

the servo case converts the output to a much slower rotation speed but

with more torque (big force, little distance). The amount of actual

work is the same, just more useful. Gears in an inexpensive servo

motor are generally made of plastic to keep it lighter and less costly

.On a servo designed to provide more torque for heavier work, the

gears are made of metal and are harder to damage.

Advantages

high performance, higher speeds, accurate positioning (becauseof feedback)

Disadvantages

higher cost (less of an issue today), requires setup/tuning


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Stepper motor

A stepper motor is an electromechanical device which converts

electrical pulses into discrete mechanical movements.

The shaft or spindle of a stepper motor rotates in discrete step

increments when electrical command pulses are applied to it in the

proper sequence. The motors rotation has several direct relationships

to these applied input pulses. The sequence of the applied pulses is

directly related to the direction of motor shafts rotation.

The speed of the motor shafts rotation is directly related to the

frequency of the input pulses and the length of rotation is directly

related to the number of input pulses applied.


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How Stepper Motors Work

Stepper motors consist of a permanent magnetic rotating shaft, called

the rotor, and electromagnets on the stationary portion that surroundsthe motor, called the stator.Figure 1 illustrates one complete rotation

of a stepper motor. At position 1, we can see that the rotor is

beginning at the upper electromagnet, which is currently active (has

voltage applied to it). To move the rotor clockwise (CW), the upper

electromagnet is deactivated and the right electromagnet is activated,

causing the rotor to move 90 degrees CW, aligning itself with the

active magnet. This process is repeated in the same manner at the

south and west electromagnets until we once again reach the starting

position.

Types of Stepper Motor

By construction the step motors come into three broad classes:

1. Permanent Magnet Stepper

2. Variable Reluctance Stepper

3. Hybrid Step Motor

These three types have been explained in detail in the following

sections.
http://www.imagesco.com/articles/picstepper/02.html#fig1http://www.imagesco.com/articles/picstepper/02.html#fig1


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ac motor,servo motor and stepper motor

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