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Jiasheng HeScott Koziol

Kelvin Chen Chih PengME6405

Motors

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Overview

DC Motors (Brushed and Brushless) Brief Introduction to AC Motors Stepper Motors Linear Motors

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Electric Motor Basic Principles Interaction between magnetic field and current

carrying wire produces a force Opposite of a generator

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Conventional (Brushed) DC Motors

Permanent magnets for outer stator

Rotating coils for inner rotor 

Commutation performed with metal contact brushes and contacts designed to reverse the polarity of the rotor as it reaches horizontal

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2 pole brushed DC motor commutation

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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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Conventional (Brushed) DC Motors

Common Applications:Small/cheap devices such as toys, electric tooth

brushes, small drillsLab 3

Pros:Cheap, simpleEasy to control - speed is governed by the voltage

and torque by the current through the armature Cons:

Mechanical brushes - electrical noise, arcing, sparking, friction, wear, inefficient, shorting

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Brushless DC Motors

Essential difference - commutation is performed electronically with controller rather than mechanically with brushes

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Brushless DC Motor Commutation

Commutation is performed electronically using a controller (e.g. HCS12 or logic circuit)Similarity with stepper motor, but with less #

polesNeeds rotor positional closed loop feedback:

hall effect 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

ApplicationsCPU cooling fansCD/DVD PlayersElectric automobiles

Pros (compared to brushed DC)Higher efficiencyLonger lifespan, low maintenanceClean, fast, no sparking/issues with brushed contacts

ConsHigher costMore complex circuitry and requires a controller

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AC Motors

Synchronous and Induction (Asynchronous) Synchronous: rotor rotation frequency = AC

current frequency

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AC Induction Motors (3 Phase) Use poly-phase (usually 3) AC current to create a

rotating magnetic field on the stator This induces a magnetic field on the rotor, which tries to

follow stator - slipping required to produce torque Workhorses of the industry - high powered applications

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Stepper Motors

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Stepper Motor Characteristics

Brushless

Incremental steps/changes

Holding Torque at zero speed

Speed increase -> torque decreases

Usually open loop

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Stepper Speed Characteristics

Torque varies inversely with speed

Current is proportional to torque

Torque → ∞ means

Current → ∞, which leads to motor damage

Torque thus needs to be limited to rated value of motor

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Types of Stepper Motors

Permanent Magnet

Variable Reluctance

Hybrid Synchronous

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Permanent Magnet Stepper Motor

Rotor has permanent magnets The teeth on the rotor and stator are offset Number of teeth determine step angle Holding, Residual Torques

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Unipolar

Two coils, each with a center tap Center tap is connected to positive supply Ends of each coil are alternately grounded Low Torque

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Bipolar

Two coils, no center taps Able to reverse polarity of current across coils Higher Torque than Unipolar

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Bipolar

More complex control and drive circuit

Coils are connected to an H-Bridge circuit Voltage applied across load in either direction

H-Bridge required for each coil

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Variable Reluctance

No permanent magnet – soft iron cylinder Less rotor teeth than stator pole pairs Rotor teeth align with energized stator coils

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Variable Reluctance

Magnetic flux seeks lowest reluctance path through magnetic circuit

Stator coils energized in groups called Phases

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Hybrid Synchronous

Combines both permanent magnet and variable reluctance features

Smaller step angle than permanent magnet and variable reluctance

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Applications

Printers Floppy disk drives Laser Cutting Milling Machines Typewriters Assembly Lines

Jiasheng He

Linear Motors

Scott Koziol

Introduction to Linear Motors How they work Comparison to Rotary motors Types System level design Advantages/ Disadvantages Applications

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Key Points you’ll learn:

The Good:○High linear position accuracy○Highly dynamic applications○High Speeds

The Bad:○Expensive! (>$3500)

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Split a rotary servo motor radially along its axis of rotation:

Flatten it out:

Result: a flat linear motor that produces direct linear force instead of torque

How Linear Brushless DC Motors work [4],[6],[8] ,[3, p. 6]

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Analysis Method

Analysis is similar to that of rotary machines [1]

Linear dimension and displacements replace angular ones

Forces replace torques

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Two Motor Components [3][6, p. 480],[7],[8]

• Motor coil (i.e. “forcer”)– encapsulates copper windings within a core material– copper windings conduct current (I).

• Magnet rail– single row of magnets or a double-sided (as below)– rare earth magnets, mounted in alternating polarity on a steel

plate, generate magnetic flux density (B)

Motor coil

Magnetic rail

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Generating Force [7] : force (F) is generated when the current (I) and

the flux density (B) interact F = I x B

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Types of Linear Motors [3] Iron core

Ironless

slotless

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Type 1: Iron Core [3],[6],[8]Forcer rides over a single magnet rail made of copper windings wrapped around iron

laminationsAdvantages: efficient cooling highest force available per unit volume [3, p.8] Low cost Disadvantages: High attractive force between the forcer and the magnet track Cogging

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Type 2: Ironless Motors [3],[6],[8]

Forcer rides between dual magnet rails known as “Aircore” or “U-channel”

motors no iron laminations in the coil Advantages: No Attractive Force- Balanced dual

magnet track No Cogging Low Weight Forcer - No iron means

higher accel/decel rates Easy to align and install.Disadvantages: Heat dissipation Lower RMS power when compared to

iron core designs. Higher cost (2x Magnets!)

ForcerMountingPlate

Rare EarthMagnets

HorseshoeShapedbackiron

Winding, heldby epoxy

Hall Effect and ThermalSensors in coil

Top View

Front View

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Type 3: Slotless [3],[6],[8]

Forcer: has no iron toothed laminations

Advantages over ironless: Lower cost (1x magnets) Better heat dissipation More force per package size

Advantages over iron core: Lighter weight and lower inertia forcer Lower attractive forces Less cogging

Disadvantages: Some attractive force and cogging Air gap is critical Less efficient than iron core and ironless more heat to do the same job

Side View

Front View

Backiron

Mountingplate

Coilassembly

Thermalsensor

Rare EarthMagnets

Ironplate

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Comparing Linear Motor Types [6, p. 479],[8]

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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Direct-drive linear motor No mechanical transmission

elements converting rotary into linear movement

simpler mechanical construction

low-inertia drive for highly dynamic applications

Differences in linear and rotary motor construction [3]

Conventional rotary drive systemmotor coupled to the load by means of intermediate mechanical components:

Gears Ballscrews Belt drives

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Components of “complete” linear motor system [3]

1. motor components2. Base/Bearings3. Servo

controller/feedback elements

4. cable management

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System Components: Base/Bearings [3]

Design Considerations: speed and acceleration capability Service life Accuracy maintenance costs Stiffness noise.

Most Popular Bearings [3] Slide bearings Rolling-contact bearings Air bearings

Others Track rollers (steel or plastic roller wheels) Magnetic bearings

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System Components: feedback control loop [3]

Advantage position sensor can be located at or closer to the loadDisadvantages: effects of external forces are significantly greater Factors influencing ability to determine correct

position:• quality of the position signal• performance of the servo controller

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System Components: Motor Commutation [3]

Conventional rotary servo systems: Important to know the position of the rotor to properly switch

current through the motor phases in order to achieve the desired rotation of the shaft

Linear Motors must know the position of the forcer in relationship to the

magnet rail in order to properly switch the windings forcer position need only be determined upon power up and

enabling of the driveScott Koziol

System Components: Positional Feedback [3]

analog transducers rack-and-pinion

potentiometers laser interferometers [9]

Linear encoder (Most Popular!)Optical (nanometer

resolution)Magnetic (1-5 micron

resolution)Sine encoder

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System Components: Servo Control [3]

Extremely important to have a controller with fast trajectory update rates

no intermediate mechanical components or gear reductions to absorb external disturbances or shock loading

disturbances have a significantly greater impact on the control loop than they would when using other technologies

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Linear Motor Advantages [3],[4]

Zero Backlash low-inertia drive High Speeds High Accelerations Fast Response High repeatability Highly accurate Clean Room compatibility

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Linear Motor Advantages cont… [3],[4]

Stiffness Maintenance Free Operation Long Travels Without Performance Loss Suitable for Vacuum and Extreme

Environments Better reliability and lower frictional

losses than traditional rotary drive systems

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Linear Motor Disadvantage COST!

In most cases, the upfront cost of purchasing a linear motor system will be more expensive than belt- or screw-driven systems

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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 = 5μm

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Applications Small Linear Motors [2], [3]

Automation & Robotics [1][3]

Semiconductor and Electronics

Flat Panel and Solar Panel Manufacturing

Machine tool industry [1]Optics and PhotonicsLarge Format Printing,

Scanning and Digital Fabrication

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Optics Polishing System [9]

Applications cont… Small Linear Motors [2],

[3]

Packaging and Material Handling

Automated AssemblyReciprocating

compressors and alternators [1]

Large Linear Induction Machines (3 phase) [2]

TransportationMaterials handlingExtrusion presses

“Most widely known use of linear motors is in the transportation field [1, p. 227]”

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References [1] A.E. Fitzgerald, C. Kingsley, Jr, S. Umans, Electric

Machinery, Sixth Edition, McGraw Hill, Boston, 2003. [2] M.S. Sarma, Electric Machines, Steady-State Theory

and Dynamic Performance, Second Edition, West Publishing Company, Minneapolis/St. Paul, 1985.

[3] Trilogy Linear Motor & Linear Motor Positioners, Parker Hannifin Corporation, 2007

[4] Baldor's Motion Solutions Catalogs, Linear Motors and Stages – Brochure, Literature Number: BR1202-G

[5] Greg Paula, Linear motors take center stage, The American Society of Mechanical Engineers, 1998.

References (continued) [6] S. Cetinkunt, Mechatronics, John Wiley & Sons, Inc.,

Hoboken 2007. [7] Rockwell Automation,

http://www.rockwellautomation.com/anorad/products/linearmotors/questions.html

[8] J. Barrett, T. Harned, J. Monnich, Linear Motor Basics, Parker Hannifin Corporation, http://www.parkermotion.com/whitepages/linearmotorarticle.pdf

[9] Aerotech Engineering Reference, http://www.aerotech.com/products/PDF/EngineeringRef.pdf

[10]http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee3/bdeee3_7.aspx

[11] http://en.wikipedia.org/wiki/Rare-earth_magnet

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References (continued)

http://zone.ni.com/devzone/cda/ph/p/id/287 http://zone.ni.com/devzone/cda/ph/p/id/286 http://www.cs.uiowa.edu/~jones/step/types.html http://en.wikipedia.org/wiki/H-bridge http://www.stepperworld.com/Tutorials/

pgBipolarTutorial.htm http://electojects.com/motors/stepper-motors-1.htm http://www.howstuffworks.com/motor.htm http://hyperphysics.phy-astr.gsu.edu/hbase/

magnetic/mothow.html#c1 http://en.wikipedia.org/wiki/Electric_motor

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References (continued)

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