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lINEAR MOTOR

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a little history In 1947 Linear motor was commercially

invented by professor Eric Laithwait , the British Electrical

Engineer......................

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Basics of Linear MotorsAnalogous to Unrolled DC Motor

• F = LI x B• Force (F) is generated when the

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

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Working principle

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Analysis of Linear Motors Analysis is similar to that of rotary

machines› Linear dimension and displacements

replace angular ones› Forces replace torques

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Components of Linear Motors

Forcer

Stator

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Components of Linear Motors (continued)

Linear guide way

FORCE PLATE

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Components of Linear Motors

Posistion encoder

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Types of linear motor

Iron Core

Ironless Core

Slotless

• Coils wound around teeth of laminations on forcer

• Dual back iron separated by spacer

• Coils held together with epoxy

• Coil and back iron held together with epoxy

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Iron coreCopper windings around forcer laminations over a single magnet rail

Iron PlateRare earth magnets

Laminated forcer assembly and mounting plate

Coil wound AroundForcer lamination

Hall effectand thermalsensors

o

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Ironless Linear motorForcer constructed of wound

coils held together with epoxy and running between two rails (North and South)

Also known as “Aircore” or “U-channel” motors

ForcerMountingPlateRare EarthMagnetsHorseshoeShapedbackiron

Winding, heldby epoxy

Hall Effect and ThermalSensors in coil

Front View

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Slotless linear motorMix of ironless and iron core: coils with back iron contained within aluminum housing over a single magnet rail

Backiron

Mountingplate

Coilassembly

Thermalsensor

Rare EarthMagnets

Ironplate

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Linear motor types comparison

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

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Types of linear motor according to application

Voice coil......Speed: Very highForce: 35 lbf (160 N)Accuracy: Encoder dependentCost: Low

StepperSpeed: 1 to 100 ips (25 to 2,500 mm/sec.)Force: 2 to 50 lbf (9 to 220 N)Accuracy: 2 to 250 um.Cost: Low

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Types of linear motor according to application (continued)

Hybrid linear MotorSpeed: 60 in/sec (1.5 meters/sec)Force: 180 lbf (800 N)Accuracy: Encoder dependentCost: High.

DC Brush Speed: 75 in/sec (3.8 meters/sec)Force: 171 lbf (1070 N)Accuracy: Encoder dependent.Cost: Moderate.

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Types of linear motor according to application (continued)

AC InductionSpeed: 270 in/sec (6.85 meters/sec)Force: 500 lbf (2,225 N)Accuracy: Encoder dependent.Cost: Moderate.

Iron Core AC SynchronousSpeed: 400 ips (10 meters/sec)Force: 2,500 lbf (11,000N)Accuracy: Encoder dependent.Cost: High.

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Rs. 300000.00 Trilogy T1S Ironless

linear motor 110V, 1 pole motor Single bearing rail ~12’’ travel magnetic encoder Peak Velocity = 7

m/s Resolution = 5μm

Sample Pricing

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advantage 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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dis-advantage

Cost› High price of magnets› Low production volume (relative to demand) Linear encoders (feedback) are much more expensive than

rotary encoders, 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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pplications Small Linear Motors

› Packaging and Material Handling› Automated Assembly› Reciprocating compressors and

alternators Large Linear Induction Machines

(3 phase)› Transportation› Materials handling› Extrusion presses

a

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

http://www.speedace.info/solar_car_motor_and_drivetrain.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_basics.pdf

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

References

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Contributed by....................

Suman Singha, B-Tech

Electrical and Electronics Engg.

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