Motors
Jiasheng He
Scott Koziol
Kelvin Chen Chih Peng
ME6405
1
Overview




DC Motors (Brushed and Brushless)
Brief Introduction to AC Motors
Stepper Motors
Linear Motors
2
Electric Motor Basic Principles
Interaction between magnetic field and current
carrying wire produces a force
 Opposite of a generator

Kelvin Peng
3
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
4
2 pole brushed DC motor commutation
Kelvin Peng
5
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
6
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
and torque by the current through the armature
 Cons:
 Mechanical brushes - electrical noise, arcing,
sparking, friction, wear, inefficient, shorting
Kelvin Peng
7
Brushless DC Motors

Essential difference - commutation is performed
electronically with controller rather than
mechanically with brushes
Kelvin Peng
8
Brushless DC Motor Commutation

Commutation is performed electronically using a
controller (e.g. HCS12 or logic circuit)
 Similarity with stepper motor, but with less #
poles
 Needs rotor positional closed loop feedback:
hall effect sensors, back EMF, photo transistors
Kelvin Peng
9
BLDC (3-Pole) Motor Connections
Has 3 leads instead of 2 like brushed DC
 Delta (greater speed) and Wye (greater torque)
stator windings

Delta
Kelvin Peng
Wye
10
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
Kelvin Peng
11
AC Motors
Synchronous and Induction (Asynchronous)
 Synchronous: rotor rotation frequency = AC
current frequency

Kelvin Peng
12
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
13
Stepper Motors
Jiasheng He
14
Stepper Motor Characteristics

Brushless

Incremental steps/changes

Holding Torque at zero speed

Speed increase -> torque decreases

Usually open loop
Jiasheng He
15
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
16
Types of Stepper Motors

Permanent Magnet

Variable Reluctance

Hybrid Synchronous
Jiasheng He
17
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
18
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
19
Bipolar
Two coils, no center taps
 Able to reverse polarity of current across coils
 Higher Torque than Unipolar

Jiasheng He
20
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
21
Variable Reluctance
No permanent magnet – soft iron cylinder
 Less rotor teeth than stator pole pairs
 Rotor teeth align with energized stator coils

Jiasheng He
22
Variable Reluctance
Magnetic flux seeks lowest reluctance path
through magnetic circuit
 Stator coils energized in groups called Phases

Jiasheng He
23
Hybrid Synchronous
Combines both permanent magnet and variable
reluctance features
 Smaller step angle than permanent magnet and
variable reluctance

Jiasheng He
24
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
How Linear Brushless DC Motors work [4],[6],[8]
,[3, p. 6]

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
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=IxB

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
laminations
Advantages:
 efficient cooling
 highest force available per unit volume [3, p.8]
 Low cost
Disadvantages:
 High attractive force between the
Laminated forcer assembly
forcer and the magnet track
and mounting plate
 Cogging
Hall effect
and thermal
sensors
Coil wound Around
Forcer lamination
Scott Koziol
Rare earth magnets
Iron Plate
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!)
Scott Koziol
Top View
Front View
Winding, held
by epoxy
Hall Effect and
Thermal
Sensors in coil
Forcer
Mounting
Plate
Rare
Earth
Magnets
Horseshoe
Shaped
backiron
Type 3: Slotless [3],[6],[8]
Forcer: has no iron toothed laminations
Side View
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
Front View
Thermal
sensor
Coil
assembly
Back Mounting
iron
plate
Disadvantages:

Some attractive force and cogging

Air gap is critical

Less efficient than iron core and ironless

more heat to do the same job
Rare
Earth
Magnets
Iron
plate
Scott Koziol
Comparing Linear Motor Types
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
[6, p. 479],[8]
Differences in linear and rotary motor construction [3]
Conventional rotary drive
system

motor coupled to the load
by means of intermediate
mechanical components:

Gears

Ballscrews

Belt drives
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
Components of “complete” linear
motor system
1. motor components
2. Base/Bearings
3. Servo
controller/feedback
elements
4. cable management
[3]
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 load
Disadvantages:
 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 drive
Scott 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
46
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
47
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 Photonics
 Large Format Printing,
Scanning and Digital
Fabrication
Scott Koziol
Optics Polishing System [9]
Applications cont…

Small Linear Motors [2],

Large Linear Induction
Machines (3 phase) [2]
 Transportation
 Materials handling
 Extrusion presses

“Most widely known use of
linear motors is in the
transportation field [1, p.
227]”
[3]
 Packaging and
Material Handling
 Automated Assembly
 Reciprocating
compressors and
alternators [1]
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/lin
earmotors/questions.html
[8] J. Barrett, T. Harned, J. Monnich, Linear Motor Basics,
Parker Hannifin Corporation,
http://www.parkermotion.com/whitepages/linearmotorar
ticle.pdf
[9] Aerotech Engineering Reference,
http://www.aerotech.com/products/PDF/EngineeringRef.
pdf
[10]http://www.electricmotors.machinedesign.com/guiEdi
ts/Content/bdeee3/bdeee3_7.aspx
[11] http://en.wikipedia.org/wiki/Rare-earth_magnet
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/pgBipolarTutori
al.htm
 http://electojects.com/motors/stepper-motors-1.htm
 http://www.howstuffworks.com/motor.htm
 http://hyperphysics.phyastr.gsu.edu/hbase/magnetic/mothow.html#c1
 http://en.wikipedia.org/wiki/Electric_motor

53
References (continued)






http://www.physclips.unsw.edu.au/jw/electricmotors.ht
ml
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
54