stepper motors seminar

8/3/2019 Stepper Motors Seminar

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Stepper MotorsBy

NAVEENKUMAR R

1ST M.Tech

N.I.T.K Surathkal


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CONTENTS

Introduction

Components

Types of Stepper Motors>Variable Reluctance

>Permanent Magnet

>Hybrid Applications


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What is a Stepper Motor?

A stepper motor is an electromechanical devicewhich converts electrical pulses into discretemechanical movements.

The sequence of the applied pulses is directlyrelated to the direction of motor shafts rotation.

The speed of the motor shafts rotation is directlyrelated to the frequency of the input pulses and

the length of rotation is directly related to thenumber of input pulses applied.


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Stepper Motors Types

There are three basic steppermotor types. They are:

Variable-reluctance

Permanent-magnet

Hybrid


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N S

N

S

S

N

N S

S

N

SN

S N

S

N

S

N

S N

N

S

S

N

N S

N

S

S

N

N S

S

N

SN

S N

S

N

S

N

for the next step invert magnetic field in the other coil

one step invert magnetic field in 1 coil

rotor follows the stator field

Movement Generation

S N

N

S

S

N

A stepper motor always needs electronic control.

step angle depends on number of poles -> fixed by construction


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Stepper motor operation

Step angle angle through which motor shaft rotates for

each command pulse

= 360 / (m*Nr)where

Nr=No. of rotor poles (teeth)m=No. of phases

Displacement = * No of control pulses

(Rotation) Speed =(60*f) / SR rpm

step resolutionSR=360 / step/rev


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Variable ReluctanceStepper motors

No permanent magnet

Free wheeling possible less torque


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Working of variable reluctancemotor


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Methods to increase resolutionof VR


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Permanent Magnet Stepper motors

Rotor is made of permanentmagnetic Material

No teeth on rotor

No freewheeling

more torque during rotation

Less acceleration

Difficult to make small step pmrotors with a large number of poles.


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Working of pm motor


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Hybrid Stepper motors

A hybrid stepping motor hascharacteristics of both PM and VRmotors

the rotor is a permanent magnet buthas blades like VR motors

Rotor is magnetised axially to create

the poles motor has very high torque and very

small, precise step increments


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Step ModeFull Step Mode

Step angle = catalogue value

N S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

S

NN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

S

N

0

-1

1

I1/ I1max

I2/ I2max

1

0

-1

coil current in a bipolar motor


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Step ModeHalf Step Mode

Step angle = half catalogue value

N S

N

S

S

NN SS NN S

S

N

S

N

S

N

S

N

S N

S

N

S

NS NS

NS N

N

S

S

N

N

S

S

N

0

-1

1

I1/ I1max

I2 / I2max

1

0

-1

coil current in a bipolar motor


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CharacteristicsOutput Power

torque

frequency

power

Motor output power : P = M with

M...torque

...angular velocity

z

f2

f...step frequency

z...steps per revolution


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Advantages

They produce the highest torque at low speeds

It is possible to achieve very low speedsynchronous rotation with a load that is directly

coupled to the shaft. The motors response to digital input pulses

provides open-loop control, making the motorsimpler and less costly to control.

holding torque (not present in DC motors)

Rotor has no winding, commutator or brushes quite, robust and reliable operation


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Applications

Precise positioning and speed control

Open loop position control

Torque : 1Nm to 40 Nm Power : 1w to 2500w


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Applications


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Applications cont


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Applications cont


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THANK YOU

stepper motors seminar

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