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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
Kelvin Peng
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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
Kelvin Peng
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2 pole brushed DC motor commutation
Kelvin Peng
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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
Kelvin Peng
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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
Kelvin Peng
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Brushless DC Motors
Essential difference - commutation is performed electronically with controller rather than mechanically with brushes
Kelvin Peng
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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
Kelvin Peng
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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
Kelvin Peng
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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
Kelvin Peng
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AC Motors
Synchronous and Induction (Asynchronous) Synchronous: rotor rotation frequency = AC
current frequency
Kelvin Peng
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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
Kelvin Peng
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Stepper Motors
Jiasheng He
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Stepper Motor Characteristics
Brushless
Incremental steps/changes
Holding Torque at zero speed
Speed increase -> torque decreases
Usually open loop
Jiasheng He
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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
Jiasheng He
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Types of Stepper Motors
Permanent Magnet
Variable Reluctance
Hybrid Synchronous
Jiasheng He
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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
Jiasheng He
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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
Jiasheng He
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Bipolar
Two coils, no center taps Able to reverse polarity of current across coils Higher Torque than Unipolar
Jiasheng He
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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
Jiasheng He
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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
Jiasheng He
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Variable Reluctance
Magnetic flux seeks lowest reluctance path through magnetic circuit
Stator coils energized in groups called Phases
Jiasheng He
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Hybrid Synchronous
Combines both permanent magnet and variable reluctance features
Smaller step angle than permanent magnet and variable reluctance
Jiasheng He
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
Scott Koziol
Key Points you’ll learn:
The Good:○High linear position accuracy○Highly dynamic applications○High Speeds
The Bad:○Expensive! (>$3500)
Scott Koziol
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]
Scott Koziol
Analysis Method
Analysis is similar to that of rotary machines [1]
Linear dimension and displacements replace angular ones
Forces replace torques
Scott Koziol
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
Scott Koziol
Generating Force [7] : force (F) is generated when the current (I) and
the flux density (B) interact F = I x B
Scott Koziol
Types of Linear Motors [3] Iron core
Ironless
slotless
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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
Scott Koziol
Components of “complete” linear motor system [3]
1. motor components2. Base/Bearings3. Servo
controller/feedback elements
4. cable management
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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
Scott Koziol
Linear Motor Advantages [3],[4]
Zero Backlash low-inertia drive High Speeds High Accelerations Fast Response High repeatability Highly accurate Clean Room compatibility
Scott Koziol
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
Scott Koziol
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
Scott Koziol
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]”
Scott Koziol
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
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