MICRO STEPPING MODE FOR

STEPPER MOTOR

OVERVIEW

• INTRODUCTION

• OPERATION

• TYPES OF STEPPER MOTOR

• MODES OF OPERATION

• MICRO STEPPING MODE

• DRIVER OVERVIEW

• MICRO STEPPING CONTROL

SYSTEM

• EXPERIMENTAL RESULTS

• CONCLUSION

• REFERENCE

INTRODUCTION

Stepper Motor

“A stepper motor (or step motor) is a brushless,

synchronous electric motor that can divide a full

rotation into a large number of steps”

Multiple "toothed" electromagnets arranged around a central

gear-shaped piece of iron.

The electromagnets are energized by an external control

circuit, such as (eg;microcontroller )

Rotor

Stator

Coils

2

1

S

N

1

2

Outside Casing

Stator

Rotor

Internal components of a stepper motor

Step angle θs

“Step angle of the stepper motor is defined as the

angle traversed by the motor in one step.”

θs=360/S

s=m*N

m= no of phases

N=no of rotor teeth

OPERATION

Basic stepper motor operation

TYPES OF STEPPER MOTOR

1 Variable reluctance

2 Permanent magnet

3 Hybrid

CHARACTERISTICS

Constant power devices.

Speed increases, torque decreases.

Steppers exhibit more vibration than other motor types, as the

discrete step tends to snap the rotor from one position to

another (called a detent).

“Ringing" effect can be mitigated by accelerating quickly using

a micro-stepping driver.

ADVANTAGES & DISADVANTAGES

ADVANTAGES DISADVANTAGES

• High accuracy of motion • High vibration levels due

to stepwise motion

• Easily adaptable to

digital control applications

•Dynamic instability, low

frequency oscillations

around Fs non linear

assembly of the control

system

• No stability problem

-----------------------------------

• Response can be

controlled by electronic

switching

-----------------------------------

Full Step Operation

Half Step Operation

Single-Coil excitation Two-Coil excitation

Micro stepping

MODES OF OPERATION

MICRO STEPPING MODE

“An electronic control technique that proportions the current

in a step motor’s windings to provide additional intermediate

positions between poles.”

Produces smooth rotation over a wide speed range and high

positional resolution.

It allows even smaller steps by using different

currents through the two motor windings.

h = ( a2 + b2 )0.5

x = ( S / (π / 2) ) arctan( b / a )

a -- torque applied by winding with equilibrium at 0 radians.

b -- torque applied by winding with equilibrium at S radians.

h -- holding torque of composite.

x -- equilibrium position, in radians.

S -- step angle, in radians.

Sine cosine microstepping

a= h1 sin((( π/2)/s)θ))h1 = single winding holding current((( π/2)/s)θ))=electric shaft angle

To hold motor rotor to angle θ

Ia=Imax sin((( π/2)/s)θ)) Ib=Imax cos((( π/2)/s)θ))

Ia= current through winding with equilibrium at angle 0’

Ib= current through winding with equilibrium at angle S’

MA=KM*Ia=Imax sin((( π/2)/s)θ))

MB=KM*Ib=Imax sin((( π/2)/s)θ))

Mo=KM*Imax

b= h1 cos((( π/2)/s)θ))

Example 1

Example 2

DRIVER OVERVIEW

USER

INTERFACEINDEXE

R

DRIVERMOTO

R

HIGH LEVEL

COMMANDS STEP

PULSESMOTOR CURRENT

Stepper motor with drive circuit

“Stepper motor performance is strongly dependent

on the drive circuit”

MICRO STEPPING CONTROL SYSTEM

Block

diagram

Electronic scheme of digital command block

EXPERIMENTAL RESULTS

1 Resonance are significantly reduced

11 Noise generation is considerably reduced

111 Precise position control

1V Very high step resolution

• Experimental results prove that a smooth and

continuous rotation is achieved.

• Velocity ripples are eliminated.

• Greatly improves performance at low rotational

speeds and helps avoid resonance problems.

• The method is found to be less complex and cheap

also

CONCLUSION

REFERENCES

[1] P. Acarnley, Stepping Motors: a Guide to Modern Theory and Practice, 4th ed.,IEE Control Engineering Series 63, ISBN: 0-85296-029-8, Michael Faraday House,2002, pp.48-5 1.

[2] T. Kenjo and A. Sugawara, Stepping Motors and Microprocessor Control, 2nded., ISBN:0-19-859385-6, Oxford: Clarendon Press, 2003, pp.113-120.

[3] H. Maczala, Elektrische Kleinmotoren, ISBN: 3-8169-0909-4, Expert Verlag,1993, pp.261-263.

[4] Gh. Baluta., Electrical Drives with Stepper Motors (in Romanian), ISBN:973-621-034-0, Iasi: Gh. Asachi, 2003, pp.63-85.

[5] Gh. Baluta, Low Power Electrical Drives. Applications (in Romanian), IS.B.N:973-621-072-3, Iasi: Politehnium, 2004, pp.40-48.

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