stepper motors1

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Stepper MotorsStepper MotorsBy

SURESHA S B2nd M.Tech

C.A.I.D


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What is a Stepper Motor?What is a Stepper Motor?

The stepper motor is a motor whichThe stepper motor is a motor whichtakes input pulses andtakes input pulses and thenthen takestakes

proportional steps to inputproportional steps to input thesethesesignals. You can use forsignals. You can use for positioningpositioning and/orand/or speedspeed control forcontrol for mostmost anyany

applications. The stepper motor needsapplications. The stepper motor needsaa power circuit and a sequence circuitpower circuit and a sequence circuitfor changing phase.for changing phase.


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Stepper Step

per MotorsMotors

MovementMovement GenerationGeneration Step ModeStep Mode

TorqueTorque GenerationGenerationCharacteristicsCharacteristicsReduced Duty CycleReduced Duty Cycle

Synchronous MotorSynchronous Motor


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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

SN

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 GenerationMovement Generation

S N

N

S

SN

A stepper motor always needs electronic control.step angle depends on number of poles -> fixed by construction


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PhA1 (=GND) PhA2 (=open)+

SN

PhA1 (=open) PhA2 (=GND)+

NS

Movement GenerationMovement GenerationUnipolar PrincipleUnipolar Principle

every coil end has only one polarity (+ or ground (-))

motor coils are unipolar


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PhA1 PhA2

S

GND+

N

Movement GenerationMovement GenerationBipolar PrincipleBipolar Principle

every coil end will be positive (+) or ground (-)

motor coils are bipolar

S

GND +

N


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CoilStator Core

Shaft

Permanent Magnet

Bobbin

Movement GenerationTin Can Motor


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S N

S

N

S

N

Rotor follows the stator field

Rotor reaches the end stop noise

Rotor is not able to follow the stator field

Rotor swings back

Movement GenerationMovement GenerationStep LossStep Loss

S N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SN

Motor will always loose n4 steps


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S N

S

N

S

N

Rotor follows the stator field

Rotor reaches the end stop noise

Rotor is not able to follow the stator field

Rotor swings back

Movement GenerationMovement GenerationStep LossStep Loss

S N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SN

Motor will always loose n4 steps


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Step ModeStep ModeFull Step ModeFull Step Mode

Step angle = catalogue value

N S

N

S

S

NN S

S

N

S

NS N

S

N

S

N

S N

N

S

S

NN S

N

S

S

NN S

S

N

S

NS N

S

N

S

N

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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Step ModeStep ModeHalf Step ModeHalf Step Mode

Step angle = half catalogue value

NN S

NN

S

S

NNN SS NNN S

S

NN

S

N

S

NN

S

NS NN

S

NN

S

N

S NNS NS NN

NN

S

S

N

NN

S

S

N

0

-1

1

I1 / I1max

I2 / I2max

1

0

-1

coil current in a bipolar motor


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Mel(torque)

S

1 2 3-1-2 4

MH(holding torque)

-MH

Mel

Torque GenerationTorque GenerationPositioning AccurancyPositioning Accurancy

...Step Angle Tolerance

(torque)

S

2

Friction

Tolerance exists at every position, but it will not sum up!Accuracy depends on friction and motor tolerances (5-7% of step angle).


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CharacteristicsCharacteristicsTorqueTorque

with chopper (pull out graph)

reduced duty cycle =increased power consumption(pull out graph)

pull-out

f A f B

pull-in

t o r q u e

frequencyf 2f 1

Resonances may influence application!


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CharacteristicsCharacteristicsOutput Power Output Power

t o r q u e

frequency

p o w e r

Motor output power : P = M with

M...torque

...angular velocity

z f

=2

f ...step frequency z ...steps per revolution


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Speed

Torque

Glossary -4Glossary -4

Pull-Output Torque Pull-in

Torque

Max. StartingFrequency

HoldingTorque


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AdvantagesAdvantages

They produce the highest torque at low speeds

holding torque (not present in DC motors)

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


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ApplicationsApplications

Precise positioning and speed controlPrecise positioning and speed controlOpen loop position controlOpen loop position control

Torque : 1Torque : 1 Nm to 40 NmNm to 40 NmPower : 1w to 2500wPower : 1w to 2500w


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Film DriveFilm Drive

Optical ScannerOptical ScannerPrintersPrintersATM MachinesATM Machines

Computer peripheralsComputer peripheralsIC fabricationIC fabrication


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robotics

digital control systemstape driversdisk drivestool positioningprocess controlX-Y recorders


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THANK YOUTHANK YOU

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