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Sean DeHart

Smriti Chopra

Hannes Daepp

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2

Overview

DC Motors (Brushed and Brushless)

Brief Introduction to AC Motors

Stepper Motors Linear Motors

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3

Electric Motor Basic Principles

Interaction between magnetic field and currentcarrying wire produces a force

Opposite of a generator

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4

Conventional (Brushed) DC Motors

Permanent magnets forouter stator

Rotating coils for innerrotor

Commutationperformed with metalcontact brushes andcontacts designed to

reverse the polarity ofthe rotor as it reacheshorizontal

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5

2 pole brushed DC motor commutation

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Conventional (Brushed) DC Motors

Common Applications:

Small/cheap devices such as toys, electric tooth brushes,small drills

Lab 3

Pros: Cheap, simple

Easy to control - speed is governed by the voltage andtorque by the current through the armature

Cons: Mechanical brushes - electrical noise, arcing, sparking,

friction, wear, inefficient, shorting

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DC Motor considerations

Back EMF - every motor is also a generator More current = more torque; more voltage = more speed

Load, torque, speed characteristics

Shunt-wound, series-wound (aka universal motor),compound DC motors

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Brushless DC Motors

Essential difference - commutation is performedelectronically with controller rather thanmechanically with brushes

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Brushless DC Motor Commutation

Commutation is performed electronically using acontroller (e.g. HCS12 or logic circuit)

Similarity with stepper motor, but with less #poles

Needs rotor positional closed loop feedback: halleffect sensors, back EMF, photo transistors

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Delta Wye

BLDC (3-Pole) Motor Connections

Has 3 leads instead of 2 like brushed DC

Delta (greater speed) and Wye (greater torque)stator windings

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Brushless DC Motors

Applications

CPU cooling fans

CD/DVD Players

Electric automobiles

Pros (compared to brushed DC)

Higher efficiency

Longer lifespan, low maintenance

Clean, fast, no sparking/issues with brushed contacts

Cons

Higher cost

More complex circuitry and requires a controller

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AC Motors Two main types of AC motor, Synchronous and

Induction.

Synchronous motors supply power to both the rotorand the stator, where induction motors only supplypower to the stator coils, and rely on induction togenerate torque.

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AC Induction Motors (3 Phase)

Use poly-phase (usually 3) AC current to create a rotatingmagnetic field on the stator

This induces a magnetic field on the rotor, which tries tofollow stator - slipping required to produce torque

Workhorses of the industry - high powered applications

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AC induction Motors Induction motors only supply current to the stator,

and rely on a second induced current in the rotorcoils.

This requires a relative speed between the rotatingmagnetic field and the rotor. If the rotor somehowmatches or exceeds the magnetic field speed, there iscondition called slip.

Slip is required to produce torque, if there is no slip,there is no difference between the induced pole andthe powered pole, and therefore no torque on the

shaft. 14Sean DeHart

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Synchronous AC Motors Current is applied to both the Rotor and the Stator.

This allows for precise control (stepper motors), but

requires mechanical brushes or slip rings to supplyDC current to the rotor.

There is no slip since the rotor does not rely oninduction to produce torque.

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Stepper Motor

A stepper motor is an electromechanical device whichconverts electrical pulses into discrete mechanicalmovements. The shaft or spindle of a stepper motor

rotates in discrete step increments when electricalcommand pulses are applied to it in the proper sequence.

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Main features

The sequence of the applied pulses is directly related tothe direction of motor shafts rotation.

The speed of the motor shafts rotation is directly relatedto the frequency of the input pulses.

The length of rotation is directly related to the number ofinput pulses applied.

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Stepper Motor Characteristics

Open loopThe motors response to digital input pulses provides open-loop

control, making the motor simpler and less costly to control.

BrushlessVery reliable since there are no contact brushes in the motor.

Therefore the life of the motor is simply dependant on the life of

the bearing.

Incremental steps/changesThe rotation angle of the motor is proportional to the inputpulse.

Speed increases -> torque decreasesSmriti Chopra

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Torque vs. SpeedTorque varies inversely withspeed.

Current is proportional totorque.

Torque means Current, which leads to motor damage.

Torque thus needs to be limitedto rated value of motor.

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Disadvantages of stepper motorsThere are two main disadvantages of stepper motors:

Resonance can occur if not properly controlled.This can be seen as a sudden loss or drop in torque at certain speeds which canresult in missed steps or loss of synchronism. It occurs when the input step pulse rate

coincides with the natural oscillation frequency of the rotor. Resonance can be

minimised by using half stepping or microstepping.

Not easy to operate at extremely high speeds.

20

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Working principle

Stepper motors consist of a permanent magnet rotatingshaft, called the rotor, and electromagnets on thestationary portion that surrounds the motor, called the

stator.

When a phase winding of a stepper

motor is energized with current, a

magnetic flux is developed in thestator. The direction of this flux is

determined by the Right Hand

Rule.

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At position 1, the rotor isbeginning at the upperelectromagnet, which iscurrently active (has voltageapplied to it).

To move the rotor clockwise(CW), the upper electromagnet

is deactivated and the rightelectromagnet is activated,causing the rotor to move 90degrees CW, aligning itselfwith the active magnet.

This process is repeated in thesame manner at the south andwest electromagnets until weonce again reach the starting

position.Smriti Chopra

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Understanding resolution

Resolution is the number of degrees rotated per step.

Step angle = 360/(NPh * Ph) = 360/N

NPh = Number of equivalent poles per phase = number of rotorpoles.

Ph = Number of phases.

N = Total number of poles for all phases together.

Example: for a three winding motor with a rotor having 4 teeth,the resolution is 30 degrees.

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Two phase stepper motors

There are two basic winding arrangements for theelectromagnetic coils in a two phase stepper motor:bipolar and unipolar.

unipolar bipolarSmriti Chopra

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A unipolar stepper motor has two windings per phase, onefor each direction of magnetic field. In this arrangement amagnetic pole can be reversed without switching the

direction of current.

Bipolar motors have a single winding per phase. Thecurrent in a winding needs to be reversed in order toreverse a magnetic pole.

Bipolar motors have higher torque but need more complexdriver circuits.

Main difference

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Stepping modesWave Drive (1 phase on)

A1 B2 A2 B1(25% of unipolar windings , 50% of bipolar)

Full Step Drive (2 phases on)A1B2 B2A2 A2B1 B1A1

(50% of unipolar windings , full bipolarwindings utilization)

Half Step Drive (1 & 2 phases on)A1B2 B2 B2A2 A2 ----(increases resolution)

Microstepping (Continuouslyvarying motor currents)A microstep driver may split a full step into as many as 256 microsteps.

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Types of Stepper Motors

There are three main types of stepper motors:

Variable Reluctance stepper motor

Permanent Magnet stepper motor

Hybrid Synchronous stepper motor

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This type of motor consists of a soft iron multi-toothedrotor and a wound stator.

When the stator windings are energized

with DC Current, the poles become magnetized.

Rotation occurs when the rotor teeth

are attracted to the energized statorpoles.

Variable Reluctance motor

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Permanent Magnet motor

The rotor no longer has teeth as withthe VR motor.

Instead the rotor ismagnetized with alternating northand south poles situated in a straightline parallel to the rotor shaft.

These magnetized rotor poles provide an increased

magnetic flux intensity and because of this

the PM motor exhibits improved torque characteristics

when compared with the VR type.

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Hybrid Synchronous motor

The rotor is multi-toothed like the VR motor and

contains an axially magnetized concentric

magnet around its shaft.

The teeth on the rotor provide an even

better path which helps guide the

magnetic flux to preferred locations inthe air gap.

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Applications

Stepper motors can be a good choice whenever controlledmovement is required.

They can be used to advantage in applications where youneed to control rotation angle, speed, position andsynchronism.

These include

printers

plotters

medical equipment

fax machines

automotive and scientific equipment etc.

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Linear MotorsHannes Daepp

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Hannes Daepp

Basics of Linear Motors [1],[4]

I

Analogous to Unrolled DC Motor

Force (F) is generated

when the current (I)(along vector L) and theflux density (B) interact

F = LI x B

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Hannes Daepp

Linear Motors in Action

http://www.parkermotion.com/video/Braas_Trilogy_T3E_Video.MPG

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Hannes Daepp

Analysis of Linear Motors [1],[5]

Analysis is similar to that of rotary machines Linear dimension and displacements replace

angular ones

Forces replace torques Commutation cycle is distance between two

consecutive pole pairs instead of 360 degrees

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Hannes Daepp

Benefits of Linear Motors [2] High Maximum Speed

Limited primarily by bus voltage, control electronics

High Precision Accuracy, resolution, repeatability limited by feedback device, budget

Zero backlash: No mechanical transmission components.

Fast Response Response rate can be over 100 times that of a mechanical

transmission faster accelerations, settling time (more throughput)

Stiffness No mechanical linkage, stiffness depends mostly on gain & current

Durable Modern linear motors have few/no contacting parts no wear

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Hannes Daepp

Downsides of Linear Motors [2] Cost

Low production volume (relative to demand)

High price of magnets

Linear encoders (feedback) are much more expensive than rotaryencoders, cost increases with length

Higher Bandwidth Drives and Controls

Lower force per package size

Heating issues Forcer is usually attached to load I2R losses are directly coupled to

load

No (minimal) Friction No automatic brake

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Hannes Daepp

Components of Linear Motors[2],[3]

Forcer (Motor Coil) Windings (coils) provide current (I) Windings are encapsulated within core

material Mounting Plate on top Usually contains sensors (hall effect

and thermal)

Magnet Rail

Iron Plate / Base Plate Rare Earth Magnets of alternating

polarity provide flux (B) Single or double rail

F =

lIx B

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Hannes Daepp

Types of Linear Motors [1],[2],[3]

Iron Core Coils wound aroundteeth of laminationson forcer

Ironless Core Dual back ironseparated by spacer Coils held togetherwith epoxy

Slotless Coil and back ironheld together withepoxy

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Hannes Daepp Iron PlateRare earth magnets

Laminated forcer

assembly and mounting

plate

Coil wound Around

Forcer lamination

Hall effect

and thermal

sensors

Linear Motor Types: Iron Core [1],[2]Distinguishing Feature Copper windings around forcer laminations over a single magnet rail

Advantages: Highest force available per unit volume Efficient Cooling Lower cost

Disadvantages: High attractive force between forcer & magnet track Cogging: iron forcer affects thrust

force as it passes over each

magnet (aka velocity ripple)

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Hannes Daepp

Distinguishing Feature Forcer constructed of wound coils held

together with epoxy and runningbetween two rails (North and South)

Also known as Aircore or U-channelmotors

Advantages: No attractive forces in forcer No Cogging Low weight forcer - No iron means

higher accel/decel rates

Top View

ForcerMounting

Plate

Rare

Earth

Magnets

HorseshoeShaped

backiron

Winding, held

by epoxy

Hall Effect and

Thermal

Sensors in coil

Front View

Linear Motor Types: Ironless [1],[2]

Disadvantages: Low force per package size Lower Stiffness; limited max load without improved structure Poor heat dissipation Higher cost (2x Magnets!)

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Hannes Daepp

Distinguishing Feature Mix of ironless and iron core: coils with

back iron contained within aluminumhousing over a single magnet rail

Advantages over ironless: Lower cost (1x magnets)

Better heat dissipation

Structurally stronger forcer

More force per package size

Advantages over iron core: Lighter weight and lower inertia forcer

Lower attractive forces

Less cogging

Side View

Front View

Back

iron

Mounting

plate

Coil

assemblyThermal

sensor

Rare

Earth

Magnets

Iron

plate

Linear Motor Types: Slotless [1],[2]

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Hannes Daepp

Disadvantages Some attractive force and cogging

Less efficient than iron core andironless - more heat to do the same job

Side View

Front View

Back

iron

Mounting

plate

Coil

assemblyThermal

sensor

Rare

Earth

Magnets

Iron

plate

Linear Motor Types: Slotless [2],[3]

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Hannes Daepp

Linear Brushless DC Motor Type

Feature Iron Core Ironless Slotless

Attraction Force Most None Moderate

Cost Medium High Lowest

Force Cogging Highest None Medium

Power Density Highest Medium Medium

Forcer Weight Heaviest Lightest Moderate

Linear Motor Type Comparison [2]

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Hannes Daepp

Components of a Complete Linear

Motor System [3]

1. Motor components

2. Base/Bearings

3. Servo controller/feedbackelements

Typical sensors include HallEffect (for position) and thermalsensors

4. Cable management

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Hannes Daepp

Sample Pricing

$3529 Trilogy T1S Ironless linear

motor

110V, 1 pole motor

Single bearing rail

~12 travel

magnetic encoder

Peak Velocity = 7 m/s

Resolution = 5m

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Hannes Daepp

Applications [3],[5],[6] Small Linear Motors

Packaging and Material Handling

Automated Assembly

Reciprocating compressors andalternators

Large Linear Induction Machines(3 phase)

Transportation

Materials handling

Extrusion presses

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References[1] S. Cetinkunt, Mechatronics, John Wiley & Sons, Inc., Hoboken 2007.[2] J. Barrett, T. Harned, J. Monnich, Linear Motor Basics, Parker

Hannifin Corporation,http://www.parkermotion.com/whitepages/linearmotorarticle.pdf

[3] Trilogy Linear Motor & Linear Motor Positioners, Parker Hannifin

Corporation, 2008,http://www.parkermotion.com/pdfs/Trilogy_Catalog.pdf

[4] Rockwell Automation,http://www.rockwellautomation.com/anorad/products/linearmotors/questions.html

[5] J. Marsh,Motor Parameters Application Note, Parker-Trilogy LinearMotors, 2003. http://www.parkermotion.com/whitepages/Linear_Motor_Parameter_Application_Note.pdf

[6] Greg Paula, Linear motors take center stage, The American Societyof Mechanical Engineers, 1998.

http://www.parkermotion.com/whitepages/linearmotorarticle.pdfhttp://www.parkermotion.com/pdfs/Trilogy_Catalog.pdfhttp://www.rockwellautomation.com/anorad/products/linearmotors/questions.htmlhttp://www.rockwellautomation.com/anorad/products/linearmotors/questions.htmlhttp://www.parkermotion.com/whitepages/%0BLinear_Motor_Parameter_Application_Note.pdfhttp://www.parkermotion.com/whitepages/%0BLinear_Motor_Parameter_Application_Note.pdfhttp://www.parkermotion.com/whitepages/%0BLinear_Motor_Parameter_Application_Note.pdfhttp://www.parkermotion.com/whitepages/%0BLinear_Motor_Parameter_Application_Note.pdfhttp://www.parkermotion.com/whitepages/%0BLinear_Motor_Parameter_Application_Note.pdfhttp://www.rockwellautomation.com/anorad/products/linearmotors/questions.htmlhttp://www.rockwellautomation.com/anorad/products/linearmotors/questions.htmlhttp://www.rockwellautomation.com/anorad/products/linearmotors/questions.htmlhttp://www.parkermotion.com/pdfs/Trilogy_Catalog.pdfhttp://www.parkermotion.com/whitepages/linearmotorarticle.pdf

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References (continued)

http://www.physclips.unsw.edu.au/jw/electricmotors.html

http://www.speedace.info/solar_car_motor_and_drivet

rain.htm

http://www.allaboutcircuits.com/vol_2/chpt_13/1.html http://www.tpub.com/neets/book5/18d.htm single

phase induction motor

http://www.stefanv.com/rcstuff/qf200212.html

Brushless DC motors https://www.geckodrive.com/upload/Step_motor_basic

s.pdf

http://www.solarbotics.net/library/pdflib/pdf/motorbas

http://www.physclips.unsw.edu.au/jw/electricmotors.htmlhttp://www.physclips.unsw.edu.au/jw/electricmotors.htmlhttps://www.geckodrive.com/upload/Step_motor_basics.pdfhttps://www.geckodrive.com/upload/Step_motor_basics.pdfhttps://www.geckodrive.com/upload/Step_motor_basics.pdfhttps://www.geckodrive.com/upload/Step_motor_basics.pdfhttp://www.physclips.unsw.edu.au/jw/electricmotors.htmlhttp://www.physclips.unsw.edu.au/jw/electricmotors.html