Stepper Motor PDF

Electromechanical Electromechanical Systems & ActuatorsSystems & Actuators

STEPPER MOTORSSTEPPER MOTORS

Dr. Adel Gastli

Dr. Adel Gastli Stepper Motors 2

ROTATING IN STEPS


CONTENTS

Introduction

Components

Types of Stepper MotorsVariable Reluctance

Permanent Magnet

Hybrid

Linear

Applications


INTRODUCTION

Stepper motors are highly accurate pulse-driven motors that change their angular position in steps, in response to input pulses from digitally controlled systems.

The stepper motor makes a step for each applied pulse.

The size of the step (step angle) depends on the type and design of the stepper motor.

The input pulses to the stepper motor must be in a proper sequence with acceptable frequency and must provide the phase windings with sufficient current.

Typical applications of stepper motors requiring incremental motion are printers, disk drives, robotics, X-Y plotters.


COMPONENTS


TYPES OF STEPPER MOTORS

Variable Reluctance

VR

Variable Reluctance

VR

Single stackSSVR

Single stackSSVR

Multi-stackMSVR

Multi-stackMSVR

Permanent Magnet

Permanent Magnet HybridHybrid


VARIABLE RELUCTANCE MOTORS

Principle of AlignmentPrinciple of Alignment

Pieces of highly permeable materials such as iron, situated in an ambient medium of low permeability such as air in which magnetic field is established, experience mechanical forces that tend to align them in such a way to minimize the reluctance of the system

F

Ferromagnetic pieces

Magnetic flux lines

F


VARIABLE RELUCTANCE (Cont’d)Single-Stack Variable Reluctance (SSVR)

Construction:Construction:

A basic circuit configuration of a four-phase, 2-pole, single-stake, variable reluctance stepper motor is shown in the figure. When the winding on a certain phase is excited (energized) the rotor will rotate, seeking alignment with the excited phase winding, such that maximizing the inductance of that phase. This position is the stable equilibrium position of rotor where the net torque is zero.

44--phase, 2 pole SSVRphase, 2 pole SSVR

SD

SC

SB

SA


VARIABLE RELUCTANCE (Cont’d)Single-Stake Variable Reluctance (SSVR)

Modes of operation:Modes of operation:This figure shows the mode of operation for a 45° step in clockwise direction. The winding are energized in the sequence A, A+B, B, B+C, and so forth and the sequence is repeated.

C

B

A

D

Ia

ΦA

C

B

A

D

Ia

ΦR

ΦA

ΦB

45o

C

B

A

D

Ia

ΦB



Reversing rotationReversing rotation’’s direction:s direction:The direction of rotation can be reversed by reversing the sequence of switching the windings, that is, A, A+D,D, D+C, etc. Multi-pole rotor construction is required in order to obtain smaller step sizes.

C

B

A

D

Ia

ΦA



Phases 1, 2 and 3 are energized in sequence making the rotor rotating in steps of 30o.

A

C

B

A

B

C

X

X

YY0

A

B

C

33--phase, 4phase, 4--pole VR Motorpole VR Motor



360001533010030001027000142401002100101800013150100120010900012601003001000011

Position δoCBACyclePhase

A

C

B

A

B

C

X

X

YY

0

A

B

C


Unipolar


VARIABLE RELUCTANCE (Cont’d)Single-Stack Variable Reluctance (SSVR)This figure shows a single stack variable reluctance stepper motor with the following design parameters:

Number of phases; m=3

Number of stator poles; Ns=12

Number of stator poles / phase; X=Ns/m

(i.e the windings on 4 stator poles are connected in series to form one phase).

- X must be even number - X =12/3=4

Number of rotor poles; Nr =16

SSVR motor with 16 rotor poles



°=== 3012

360360

SS N

τ

°=== 5.2216

360360

rr N

τ

Step angle calculation

Stator pole pitch;

Rotor pole pitch;

Step angle;

Relation between :

°=×

==Θ°=−=−=Θ 5.7163

360360or 5.75.2230

rSrSS Nm

ττ

rS N,N,m

XNm

NN

NNmN

SSr

rSr

rSS

±=±=∴

−=±

−=Θ±

)1

1(

360360360

ττ


VARIABLE RELUCTANCE (Cont’d)Multi-Stack Variable Reluctance (MSVR)


Multi-stack variable-reluctance motors are widely used to give smaller step sizes. The motor is divided along its axial length into magnetically isolated sections “stacks”, and each of these sections can be excited by a separate winding. The figure shows a three stack arrangements.

3-stack VR stepper motor


VARIABLE RELUCTANCE (Cont’d)Multi-Stack Variable Reluctance (MSVR)Principle of Operation:Principle of Operation:

The stator of each stack consists of “N”poles and each pole has a number of teeth ”x” and carries a phase winding. The teeth on the different stator stacks are misaligned. The rotor stacks have number of teeth equals to stator teeth number but they are aligned.

NxrevstepsofNoNxN

pitchToothsizeStep

xpitchTooth .

360./ ,

.

360 ,

360=

ΔΘ===ΔΘ==


PERMANENT MAGNET STEPPER MOTOR PERMANENT MAGNET STEPPER MOTOR (PMSM)(PMSM)


The permanent magnet stepper motor has a stator construction similar to that of the single-stack variable-reluctance type, but the rotor is made of a permanent magnet material. The figure shows a 2-pole permanent stepper motor. The rotor poles align with two stator pole according to the winding excitation.

2-Pole PMSM


PMSM (Cont’d): Full Step Motor

This animation demonstrates the principle for a stepper motor using full step commutation. The rotor of a permanent magnet stepper motor consists of permanent magnets and the stator has two pairs of windings. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off and also reverse polarity. There are four steps.

http://www.freescale.com/files/microcontrollers/doc/train_ref_material/MOTORSTEPTUT.html


PMSM (Cont’d): Full Step Motor

One phase lags the other phase by one step. This is equivalent to one forth of an electrical cycle or 90°.This stepper motor is very simplified. The rotor of a real stepper motor usually has many poles. The animation has only ten poles, however a real stepper motor might have a hundred.



PMSM (Cont’d)Full Step Motor

These are formed using a single magnet mounted inline with the rotor axis and two pole pieces with many teeth.

The teeth are staggered to produce many poles.

The stator poles of a real stepper motor also has many teeth.

The teeth are arranged so that the two phases are still 90° out of phase.



PMSM (Cont’d): Half Step Motor

This animation shows the stepping pattern for a half-step stepper motor. The commutation sequence for a half-step stepper motor has eight steps instead of four. The main difference is that the second phase is turned on before the first phase is turned off.



PMSM (Cont’d): Half Step Motor

Both phases can be energized at the same time so the rotor is held in between the two full-step positions.Interleaving the two sequences will cause the motor to half-step

A half-step motor has twice the resolution of a full step motor. It is very popular for this reason.


PMSM (Cont’d): Control Circuit


Clockwise rotation


Anticlockwise Rotation


PMSM (Cont’d): Bipolar


PMSM (Cont’d): More Steps

On the left, there are 8 magnets, but only 4 circuits. Sequencing through the four circuits gives half of a rotation. One more run through the sequence completes the rotation. This setup requires that both ends of the compass needle be north-seeking.

On the right, the same 4 circuits energize 16 magnets. This setup requires 16 steps (4 repetitions of a 4-step cycle) to complete one rotation. In actual practice, just four control wires can provide just about as many steps as you might want. One of the characteristics of a given stepper motor is the number of steps necessary to make a complete circle, usually expressed as number of degrees per step.


PMSM (Cont’d): Direction Control

Since computers are great at turning things on and off, let's look at the four electromagnet circuits as a computer might see them.

Take a step back.0100

Wait right here!1000

another step clockwise1000



take a step clockwise0001

CommentDCBA


PMSM (Cont’d): One More Example

PMSMs have the following properties: Permanent Magnet Stepper Motors

(PMSMs) are restricted to step sizes (the range 30 to 90 degrees).

PMSMs have higher inertia and therefore slower acceleration than Variable-Reluctance Stepper Motors.

PMSM produces more torque per ampere stator current than Variable-Reluctance Stepper Motors.

This figure shows 4-phase (8-stator poles) PMSM in which step angle θ = 45°

4-phase PMSM


HYBRID STEPPER MOTOR

A hybrid stepper motor in which the rotor has an axial permanent magnet at the middle and ferromagnetic teeth at the outer section is shown in the figure. A hybrid stepper motor combines the characteristics of both PMSM and VR Stepper Motors. Hybrid motors have a small step length (typically 1.8°).

Hybrid stepper motor


HYBRID STEPPER MOTOR (Cont’d)

Torque producing capability for a given motor volume is greater in the hybrid than in the variable reluctance motor, so the hybrid is a natural choice for applications requiring a small step length and high torque, but hybrid stepper motor is more expensive than the variable-reluctance-type stepper motor. Hybrid stepper motor


Linear Stepper Motor


APPLICATIONS

Computer Peripherals

paper feedPlotter

X-Y-Z positioningPlotter

index tapeTape Reader

position matrix print headPrinter

ribbon wind/rewindPrinter

paper feedPrinter

rotate character wheelPrinter

carriage drivePrinter

position magnetic pickupFloppy Disc

UseApplication


Stepper Motor Applications (Cont’d)


APPLICATIONS (Cont’d)

Business Machines

route card flowCard Sorter

lens positioningCopy Machine

paper feedTypewriters (automatic)

head positioningTypewriters (automatic)

paper feedBanking Systems

credit card positioningBanking Systems

paper feedCopy Machine

position cardsCard Reader

UseApplication



Process Control

feeding and positioning letterMail Handling Systems

valve cover positioningLiquid Gasket Dispensing

X-Y positioningLaser Trimming

chip positioningI. C. Bonding

I. C. wafer slicingSilicon Processing

parts positioningAssembly Lines

parts positioningIn-Process Gaging

main driveConveyor

fluid gas meteringValve Control

air-fuel mixture adjustCarburetor Adjusting

UseApplication



Machine Tool

X-Y table positioningSewing

X-Y positioningLathes

X-Y-Z positioningLaser Cutting

X-Y-Z positioningElectron Beam Welder

automatic wheel dressingGrinding Machines

downfeed grinding wheelGrinding Machines

X-Y table positioningDrilling Machines

X-Y-Z table positioningMilling Machines

UseApplication


STEPPING MOTOR/GEARHEAD ROBOTICS ASSEMBLY




CNC Machines



CNC Machines



This motor is very much like the other stepper motors mentioned above, except that it is 2D and very small

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Stepper Motor PDF