stepper motor (3)

7/30/2019 Stepper Motor (3)

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STEPPER MOTOR

Presented by: 1) Supriya Rakshit

2) Monika Soni


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Contents1. Introduction2. Comparison Between Servo & Stepper Motor

3. Types Of Stepper Motor

a. Variable Reluctance Stepper Motorb. Permanent Magnet Stepper Motor

c. Hybrid Stepper Motor

4. Applications

5. Advantages & Disadvantages

6. Simulation in Matlab


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1. Introduction A stepper motor is a pulse-driven motor that changes

the angular position of the rotor in steps.Rotor

Stator

Coils

2

1

S

N

1

2

Outside Casing

Stator

Rotor

Internal components of a Stepper

Motor


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Cont. A stepper (or, stepping) motor is an electromechanical

device which converts electrical pulses into discretemechanical movements.

Stepper motors work on the principle of

electromagnetism. There is a soft iron or magnetic rotor

shaft surrounded by the electromagnetic stators. The

rotor and stator have poles which may be teethed or not

depending upon the type of stepper. When the stators are

energized the rotor moves to align itself along with the

stator (in case of a permanent magnet type stepper) or

moves to have a minimum gap with the stator (in case of

a variable reluctance stepper). This way the stators are

energized in a sequence to rotate the stepper motor.


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2. Compare With a Servo Stepper motors are similar to servo motors as we can

perform position control with both. However, Servo motors require some form of analog

feedback whereas stepper motors are often open loop.

Stepping motors can be used in simple open-loop

control systems; these are generally adequate forsystems that operate at low accelerations with staticloads, but closed loop control may be essential for highaccelerations.

For high accelerations with variable loads, all rotor

information is lost, and we require closed loop for

accurate control

Servo motors are not subject to this problem


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3. Types Of Servo MotorPERMENANT MAGNET

MOTOR

VARIABLE RELUCTANCE

MOTOR

STEPPER MOTOR

HYBRID MOTOR


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Cont.

Permanent Magnet Employ permanent magnet

Low speed, relatively high torque

Variable Reluctance Does not have permanent magnet

Low torque

Hybrid multi-toothed stator poles and a permanent magnet

rotor

High static and dynamic torque


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PERMANENT MAGNET MOTOR

Cutaway diagram of a typical

permanent magnet stepper

motor.

Canstack rotor that is used in

permanent magnet stepper motors.


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The rotor and stator poles of a permanent magnet stepper are not

teethed. Instead the rotor have alternative north and south polesparallel to the axis of the rotor shaft.

When a stator is energized, it develops electromagnetic poles.

The magnetic rotor aligns along the magnetic field of the stator.

The other stator is then energized in the sequence so that the

rotor moves and aligns itself to the new magnetic field. This way

energizing the stators in a fixed sequence rotates the stepper

motor by fixed angles.

The resolution of a permanent magnet stepper can be increased

by increasing number of poles in the rotor or increasing the

number of phases.

Cont.


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The variable reluctance stepper has a toothed non-magnetic softiron rotor. When the stator coil is energized the rotor moves to

have a minimum gap between the stator and its teeth.

VARIABLE RELUCTANCE STEPPER

MOTORS


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The teeth of the rotor are designed so that when they arealigned with one stator they get misaligned with the next

stator. Now when the next stator is energized, the rotor

moves to align its teeth with the next stator. This way

energizing stators in a fixed sequence completes the

rotation of the step motor.

The resolution of a variable reluctance stepper can be

increased by increasing the number of teeth in the rotorand by increasing the number of phases.

Cont..


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A hybrid stepper is a combination of both permanentmagnet and the variable reluctance. It has a magnetic

teethed rotor which better guides magnetic flux to

preferred location in the air gap.

HYBRID MOTOR


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The magnetic rotor has two cups. One for north polesand second for the south poles. The rotor cups are

designed so that that the north and south poles

arrange in alternative manner. Check out the insight

of a Hybrid Stepper Motor.

The Hybrid motor rotates on same principle of

energizing the stator coils in a sequence.

Cont.
http://www.engineersgarage.com/insight/how-stepper-motor-workshttp://www.engineersgarage.com/insight/how-stepper-motor-workshttp://www.engineersgarage.com/insight/how-stepper-motor-workshttp://www.engineersgarage.com/insight/how-stepper-motor-works


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4. APPLICATIONS Stepper motors are also used for cruise control, military

antenna positioners, automated sensing devices


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1.Step motors are used inside

medical scanners, multi-axis

stepper motor microscopic or

nanoscopic motion control ofautomated devices, dispensing

pumps,

2.samplers, and chromatograph

auto-injectors. Also found insidedigital dental photography, fluid

pumps, respirators, and blood

analysis machinery.

Cont.


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Stepper motors are incorporatedinside PC based scanning

equipment, data storage tape

drives, optical disk drive head

driving mechanism, printers,bar-code printers, scanners.

Stepper motors in cameras for

automatic digital camera focus

and zoom functions.

Cont..


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The rotation angle of the motor is proportional to the

input pulse.

The motor has full torque at standstill (if the windings

are energized).

Precise positioning and repeatability of movement sincegood stepper motors have an accuracy of 3 to 5% of a

step and this error is non-cumulative from one step to the

next.

Excellent response to starting/stopping/reversing.

Very reliable since there are no contact brushes in the

motor. Therefore the life of the step motor is simply

dependent on the life of the bearing.

5. STEPPER MOTOR ADVANTAGEC


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The stepper motors response to digital input pulses

provides open-loop control, making the motor

simpler and less costly to control.

It is possible to achieve very low speed synchronousrotation with a load that is directly coupled to the

shaft.

A wide range of rotational speeds can be realized as

the speed is proportional to the frequency of the input

pulses.

Cont..


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Require a dedicated control circuit

Use more current than D.C. motors

High torque output achieved at low speeds

5. STEPPER MOTOR disadvantage


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6. SIMULATION cIRCUIT


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Output Waveforms

Phase Current of A


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Cont.

Phase Voltage


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Torque

Cont.


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Cont.

Angular Speed


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Cont.

Angular Position


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Thank You

stepper motor (3)

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