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EEE 1317
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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