1. Motors
Jiasheng He
Scott Koziol
Kelvin Chen Chih Peng
ME6405 1

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

3. Electric Motor Basic Principles
Interaction between magnetic field and current carrying wire produces a force
Opposite of a generator
left: current carrying wire
F=BIL
pair of force produces torque - spins the rotor 
right: electromagnet with metal core wrapped by wire coils
coil creates N and S poles - becomes attracted to S and N poles on stator, respectively 
the idea, is then how to create a dynamically changing magnetic flux to keep the rotor spinning constantly
faraday's law concerning generators:
generated emf = rate of change of magnetic flux
Kelvin Peng

4. 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
2 pole DC electric motor
Direct Current
a better picture of rotation/commutation next slide
Kelvin Peng

5. 2 pole brushed DC motor commutation
important to note that with this simple 2 pole motor, when rotor rotates 90 degrees from this picture, there will be 0 torque.
Unable to start from rest at that 90deg position
in practice, a real DC motor use more than 2 poles to eliminate - zero torque zone, and shorting of battery
2 pole brushed DC motor commutation
Kelvin Peng

6. 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
under no load conditions, motor will rotate at a speed such that the back emf equals the applied voltage plus voltage drop across armature 
generally highest torque at zero speed, zero torque at max speed 
increase current to increase torque
increase voltage to increase speed 
shunt wound, series wound DC motors: Here, the stator is an electromagnet instead of permanent magnet.
shunt has stator and armature connected in parallel. series has stators and armature connected in series. 
Has different loading characteristics 
series wound DC is also known as universal motor and can run on both AC and DC because both stator and rotor polarity can be switched
Kelvin Peng

7. 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
mechanical brushes could be metallic or carbon
Kelvin Peng

8. Brushless DC Motors
Essential difference - commutation is performed electronically with controller rather than mechanically with brushes
Brushed DC motor 
- 'conventional'/'inrunner' configuration: 
flipped inside out - stator is now coil, rotor is permanent magnet that spins on the inside
typically less torque, but high RPM 
'outrunner' configuration - rotor spins on the outside around stator.
typically high torque but lower RPM
Energize the stator electromagnet coils sequentially (very much like a stepper motor) to make the rotor rotate
Kelvin Peng

9. 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
How to know when to energize coils? 
cannot do this in open loop like stepper due to smaller number of poles on stator; needs feedback 
2 ways to sense rotor position: -hall effect sensor (detects magnetic fields)
-sensorless (back emf on the un-energized coils)
-photo transistors (encoders, lab3 slot and detector)
Kelvin Peng

10. BLDC (3-Pole) Motor Connections
Has 3 leads instead of 2 like brushed DC
Delta (greater speed) and Wye (greater torque) stator windings 
left diagram (delta):
sequentially energize each of the 3 leads to make rotor turn
if more poles/windings on stator, typically still arranged into 3 groups - hence still 3 leads
wye - greater torque at low speeds
delta - greater speed 
delta, wye in AC transformers - neutral wires - 
phase to neutral voltages available for wye. 
only phase to phase voltage available for delta 
Delta               Wye
Kelvin Peng

11. 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

12. AC Motors Synchronous and Induction (Asynchronous)
Synchronous: rotor rotation frequency = AC current frequency
no need for commutation! coil magnetic field reverses by itself with AC current. In theory the rotor will rotate at same speed with AC sinewave
Kelvin Peng

13. 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
There are also single phase - require external starter
AC current through the stator windings creates a time varying magnetic field.
This induces an emf across the conductive rotor (often a 'squirrel cage'
This makes the rotor a magnet, which then interacts with the magnetic field of the stator.
The goal is to make a rotating magnetic field with the stator.Induction motors require (slip)
workhorse of industry - rugged construction; no brushes to wear out - reliable, low maintenance
Kelvin Peng

14. Stepper Motors
Jiasheng He

15. Stepper Motor Characteristics
Brushless
Incremental steps/changes
Holding Torque at zero speed
Speed increase -> torque decreases
Usually open loop
Jiasheng He

16. 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

17. Types of Stepper Motors
Permanent Magnet
Variable Reluctance
Hybrid Synchronous
Jiasheng He

18. 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

19. 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

20. Bipolar Two coils, no center taps
Able to reverse polarity of current across coils
Higher Torque than Unipolar
Jiasheng He

21. 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

22. Variable Reluctance No permanent magnet – soft iron cylinder
Less rotor teeth than stator pole pairs
Rotor teeth align with energized stator coils
Jiasheng He

23. Variable Reluctance
Magnetic flux seeks lowest reluctance path through magnetic circuit
Stator coils energized in groups called Phases
Jiasheng He

24. Hybrid Synchronous
Combines both permanent magnet and variable reluctance features
Smaller step angle than permanent magnet and variable reluctance
Jiasheng He

25. Applications Printers Floppy disk drives Laser Cutting
Milling Machines
Typewriters
Assembly Lines
Jiasheng He

26. Linear Motors Scott Koziol
Our class text, Mechatronics, by Sabri Cetinkunt, is an excellent source for information on motors.
Scott Koziol

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

28. Key Points you’ll learn:
The Good:
High linear position accuracy
Highly dynamic applications
High Speeds
The Bad:
Expensive! (>$3500)
High linear position accuracy because of Zero Backlash.
Zero backlash b/c of direct drive technology (direct linear motion without mechanical linkages)
Backlash ~ elasticity from the moving elements [3]
Good for highly dynamic applications b/c Low-inertia drive
Cost: Permanent magnets are expensive!
Also 5 micron magnetic encoder ~$400
Scott Koziol

29. 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
A brushless DC linear motor is similar to an “unwrapped” brushless DC rotary motor [3, p. 6]
Linear DC Motors
A linear dc motor, like a rotating dc motor, generates mechanical force by the interaction of current in conductors and magnetic flux provided by permanent rare-earth magnets. It is constructed of a stator assembly and a slider. The stator assembly serves as the body and contains a laminated steel structure with conductors wound in transverse slots. The slider contains one or more sets of magnets, commutation components, a bearing surface, and its body completes the magnetic flux path between the magnets.
The brushless slider contains an additional set of magnets which activate Hall-effect sensors and solid-state switches to commutate the motor windings. A dc linear motor positioning system is extremely stiff, fast, and efficient. It is capable of precision accuracy to 0.1 micron and does not deteriorate with wear. It can drive loads directly, obviating the need for gears and lead screws. Its typical range of thrust and travel is 2.5 to 2,500 lb and a few inches to about 4 ft.
Scott Koziol

30. Analysis Method Analysis is similar to that of rotary machines [1]
Linear dimension and displacements replace angular ones
Forces replace torques
Scott Koziol

31. 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
Stator becomes forcer
Rotor becomes Magnetic rail [8]
Rare-earth magnets are strong, permanent magnets made from alloys of rare earth elements. Rare-earth magnets are substantially stronger than ferrite or alnico magnets.
Scott Koziol

32. Generating Force [7] :
force (F) is generated when the current (I) and the flux density (B) interact
F = I x B
Like stepper motors: For a given excitation state of the forcer’s coils there is a stable position “as a result of the attraction between electromagnetic poles of the” forcer and permanent magnets of the magnetic rail. [6, p. 395]
In order to maintain perpendicular relationship between the forcer’s magnetic field the and magnetic rail’s magnetic field, the current in the forcer must be controlled as a vector quantity (both magnitude and direction) relative to the magnetic rail position….(This description is based on our text’s description brushless DC motors on [6, p. 430]) …doing this is called commutation
As the forcer moves, the magnetic field moves with it. Based on [6, p. 430]
The normal force of the magnetic attraction can be up to 10 times the continuous force rating of the motor [6, p. 480], [7]
“In a two-pole rotary brushless DC motor, the commutation cycle is 360 degrees, whereas the commutation cycle in a linear brushless motor is the distance between two consecutive pole pairs (i.e., distance between two north or two south pole magnets, total length of a north and a south pole magnet).” [6, p 479]
Scott Koziol

33. Types of Linear Motors [3]
Iron core
Ironless
slotless
Scott Koziol

34. 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
forcer and the magnet track
Cogging
This design comes straight from a DC brushless rotary motor! [8]
Additional info on Advantages:
One row of magnets => Lower cost!
Additional info on Disadvantages:
Since the forcer consists of iron, it is attracted to the permanent
magnets. Bearings are used to support the force.
“Cogging: Since the forcer is made of iron and it passes over magnets, there is a
variation in the thrust force as it passes each magnet. This is referred to as cogging and
affects low speed smoothness (velocity ripple) [8]”
Iron Plate
Rare earth magnets
Laminated forcer assembly and mounting plate
Coil wound Around
Forcer lamination
Hall effect
and thermal
sensors
Scott Koziol

35. 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!)
Top View
Front View
Forcer
Mounting
Plate
Rare
Earth
Magnets
Horseshoe
Shaped
backiron
Winding, held
by epoxy
Hall Effect and
Thermal
Sensors in coil
Advantages:
No Iron in Forcer => No cogging!
No Iron in Forcer => Low forcer weight and higher acceleration/deceleration!
“Cogging: Since the forcer is made of iron and it passes over magnets, there is a
variation in the thrust force as it passes each magnet. This is referred to as cogging and
affects low speed smoothness (velocity ripple) [8]”
Scott Koziol

36. 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
Back
iron
Mounting
plate
Coil
assembly
Thermal
sensor
Rare
Earth
Magnets
Iron
Hybrid between iron core and ironless linear motor designs
Scott Koziol

37. 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
Power Density
Forcer Weight
Heaviest
Lightest
Scott Koziol

38. 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
Direct-drive linear motor
No mechanical transmission elements converting rotary into linear movement
simpler mechanical construction
low-inertia drive for highly dynamic applications
No Backdrive ability: Linear motors need to be powered or counterweighted to hold their position
Scott Koziol

39. Components of “complete” linear motor system [3]
motor components
Base/Bearings
Servo controller/feedback elements
cable management
Scott Koziol

40. 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

41. 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
Overall comments on the feedback control loop
Additional info on:
Advantage:
Position sensor at load (not at end of transmission) => improves overall system accuracy
Disadvantage:
lack of a traditional mechanical transmission => external forces have greater effect on control
quality of the position signal == resolution & accuracy
performance of the servo controller == sampling time, trajectory update, control algorithms
Scott Koziol

42. 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
Part of the feedback control loop: motor commutation
Commutation == distribution of current into appropriate coils as function of rotor position.
Scott Koziol

43. 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
Part of the feedback control loop: position feedback
Scott Koziol

44. 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
Part of the feedback control loop: control law
Scott Koziol

45. Linear Motor Advantages [3],[4]
Zero Backlash
low-inertia drive
High Speeds
High Accelerations
Fast Response
High repeatability
Highly accurate
Clean Room compatibility
More detail of Advantages:
Zero Backlash -> Provides higher accuracy
low-inertia drive for highly dynamic applications
High Speeds: speeds to over 8 me/sec
High Accelerations: from 1 to over 10 g’s
Fast Response – 100x that of a mechanical system
High repeatability – resolution to 0.1 microns
Highly accurate – to 2.5 micron
Clean Room compatibility
“In many applications, linear motors offer distinct advantages over
conventional rotary drive systems. When using a linear motor, there
is no need to couple the motor to the load by means of intermediate
mechanical components such as gears, ballscrews, or belt drives. The
load is directly connected to the motor. Therefore, there is no backlash or
elasticity from the moving elements. Thus, the dynamic behavior of the
servo control is improved and higher levels of accuracy are achieved.
The absence of a mechanical transmission component results in a drive
system with low inertia and noise. In addition, mechanical wear only
occurs in the guidance system. As a result, linear motors have better
reliability and lower frictional losses than traditional rotary drive systems. ”
[3]
Scott Koziol

46. 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
More info on Advantages:
Stiffness – spring rate better than a mechanical system
Maintenance Free Operation – mechanical simplicity due to reduced component count
Long Travels Without Performance Loss
Suitable for Vacuum and Extreme Environments
Better reliability and lower frictional losses than traditional rotary drive systems

47. 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

48. 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
8-pole 117’’ travel dual rail ~$15,000 (Trilogy)
Scott Koziol

49. 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
Optics Polishing System [9]
Scott Koziol

50. Applications cont… Small Linear Motors [2], [3]
Packaging and Material Handling
Automated Assembly
Reciprocating compressors and alternators [1]
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]”
Scott Koziol

51. 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.

52. References (continued)
[6] S. Cetinkunt, Mechatronics, John Wiley & Sons, Inc., Hoboken 2007.
[7] Rockwell Automation, earmotors/questions.html
[8] J. Barrett, T. Harned, J. Monnich, Linear Motor Basics, Parker Hannifin Corporation, ticle.pdf
[9] Aerotech Engineering Reference, pdf
[10] ts/Content/bdeee3/bdeee3_7.aspx
[11]

53. References (continued)
al.htm
astr.gsu.edu/hbase/magnetic/mothow.html#c1

54. References (continued)ml
rain.htm
single phase induction motor
Brushless DC motors
s.pdf