1. Sean DeHart Smriti Chopra Hannes Daepp
Motors
Sean DeHart
Smriti Chopra
Hannes Daepp

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

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
Sean DeHart 3 3

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
Sean DeHart 4 4

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 5
Sean DeHart 5

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
mechanical brushes could be metallic or carbon
Sean DeHart 6 6

7. 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
Sean DeHart 7 7

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
Sean DeHart 8 8

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)
Sean DeHart 9 9

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
Sean DeHart 10 10

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
Sean DeHart 11

12. AC Motors Two main types of AC motor, Synchronous and Induction.
Synchronous motors supply power to both the rotor and the stator, where induction motors only supply power to the stator coils, and rely on induction to generate torque. 12
Sean DeHart

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
Sean DeHart 13 13

14. AC induction Motors
Induction motors only supply current to the stator, and rely on a second induced current in the rotor coils.
This requires a relative speed between the rotating magnetic field and the rotor. If the rotor somehow matches or exceeds the magnetic field speed, there is condition called slip.
Slip is required to produce torque, if there is no slip, there is no difference between the induced pole and the powered pole, and therefore no torque on the shaft. 14
Sean DeHart

15. Synchronous AC Motors
Current is applied to both the Rotor and the Stator.
This allows for precise control (stepper motors), but requires mechanical brushes or slip rings to supply DC current to the rotor.
There is no slip since the rotor does not rely on induction to produce torque. 15
Sean DeHart

16. Stepper Motor
A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied to it in the proper sequence.
Smriti Chopra

17. Main features
The sequence of the applied pulses is directly related to the direction of motor shafts rotation. The speed of the motor shafts rotation is directly related to the frequency of the input pulses. The length of rotation is directly related to the number of input pulses applied.
Smriti Chopra

18. Stepper Motor Characteristics
Open loop
The motors response to digital input pulses provides open-loop
control, making the motor simpler and less costly to control.
Brushless
Very reliable since there are no contact brushes in the motor. Therefore the life of the motor is simply dependant on the life of the bearing.
Incremental steps/changes
The rotation angle of the motor is proportional to the input pulse.
Speed increases -> torque decreases
Smriti Chopra

19. Torque vs. Speed 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.
Smriti Chopra

20. Disadvantages of stepper motors
There are two main disadvantages of stepper motors:
Resonance can occur if not properly controlled.
This can be seen as a sudden loss or drop in torque at certain speeds which can result in missed steps or loss of synchronism. It occurs when the input step pulse rate coincides with the natural oscillation frequency of the rotor. Resonance can be minimised by using half stepping or microstepping.
Not easy to operate at extremely high speeds.

21. Working principle
Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and electromagnets on the stationary portion that surrounds the motor, called the stator.
When a phase winding of a stepper
motor is energized with current, a
magnetic flux is developed in the
stator. The direction of this flux is
determined by the “Right Hand
Rule”.
Smriti Chopra

22. At position 1, the rotor is beginning at the upper electromagnet, which is currently active (has voltage applied to it).
To move the rotor clockwise (CW), the upper electromagnet is deactivated and the right electromagnet is activated, causing the rotor to move 90 degrees CW, aligning itself with the active magnet.
This process is repeated in the same manner at the south and west electromagnets until we once again reach the starting position.
Smriti Chopra

23. Understanding resolution
Resolution is the number of degrees rotated per step.
Step angle = 360/(NPh * Ph) = 360/N
NPh = Number of equivalent poles per phase = number of rotor poles.
Ph = Number of phases.
N = Total number of poles for all phases together.
Example: for a three winding motor with a rotor having 4 teeth, the resolution is 30 degrees.
Smriti Chopra

24. Two phase stepper motors
There are two basic winding arrangements for the electromagnetic coils in a two phase stepper motor: bipolar and unipolar.
bipolar
unipolar
Smriti Chopra

25. Main difference
A unipolar stepper motor has two windings per phase, one for each direction of magnetic field. In this arrangement a magnetic pole can be reversed without switching the direction of current.
Bipolar motors have a single winding per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole.
Bipolar motors have higher torque but need more complex driver circuits.
Smriti Chopra

26. Stepping modes Wave Drive (1 phase on) A1 – B2 – A2 – B1
(25% of unipolar windings , 50% of bipolar)
Full Step Drive (2 phases on)
A1B2 – B2A2 – A2B1 – B1A1
(50% of unipolar windings , full bipolar
windings utilization)
Half Step Drive (1 & 2 phases on)
A1B2 – B2 – B2A2 – A2 ----
(increases resolution)
Microstepping (Continuously
varying motor currents)
A microstep driver may split a full step into as many as 256 microsteps.
Smriti Chopra

27. Types of Stepper Motors
There are three main types of stepper motors:
Variable Reluctance stepper motor
Permanent Magnet stepper motor
Hybrid Synchronous stepper motor
Smriti Chopra

28. Variable Reluctance motor
This type of motor consists of a soft iron multi-toothed rotor and a wound stator. When the stator windings are energized with DC Current, the poles become magnetized. Rotation occurs when the rotor teeth are attracted to the energized stator poles.
Smriti Chopra

29. Permanent Magnet motor
The rotor no longer has teeth as with
the VR motor.
Instead the rotor is
magnetized with alternating north
and south poles situated in a straight
line parallel to the rotor shaft.
These magnetized rotor poles provide an increased
magnetic flux intensity and because of this
the PM motor exhibits improved torque characteristics
when compared with the VR type.
Smriti Chopra

30. Hybrid Synchronous motor
The rotor is multi-toothed like the VR motor and
contains an axially magnetized concentric
magnet around its shaft.
The teeth on the rotor provide an even
better path which helps guide the
magnetic flux to preferred locations in
the air gap.
Smriti Chopra

31. Applications
Stepper motors can be a good choice whenever controlled movement is required.
They can be used to advantage in applications where you need to control rotation angle, speed, position and synchronism.
These include
printers
plotters
medical equipment
fax machines
automotive and scientific equipment etc.
Smriti Chopra

32. Linear Motors Hannes Daepp

33. Basics of Linear Motors [1],[4]
Analogous to Unrolled DC Motor
Force (F) is generated when the current (I) (along vector L) and the flux density (B) interact
F = LI x B I
Hannes Daepp

34. Linear Motors in Action
Hannes Daepp

35. Analysis of Linear Motors [1],[5]
Analysis is similar to that of rotary machines
Linear dimension and displacements replace angular ones
Forces replace torques
Commutation cycle is distance between two consecutive pole pairs instead of 360 degrees
Commutation cycle in rotary brushless motor is 360 degrees
Hannes Daepp

36. Benefits of Linear Motors [2]
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
Typical max speeds: 3-5 m/s with 1 micron resolution, 5+ m/s (>200 ips) with less resolution
Budget is main restraint on controller bandwidth
Higher stiffness (spring rate), though limited by motor peak force, available current, and feedbakc resolution
Hannes Daepp

37. Downsides of Linear Motors [2]
Cost
Low production volume (relative to demand)
High price of magnets
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
Linear encoders are usually around $500 for 100 mm travel encoder, cost increases with length. Rotary encoders are relatively inexpensive – tend to be under 100 dollars
No mechanical reduction between motor and load, thus servo response (bandwidth) must be faster. Includes higher encoder bandwidth and servo update rates
Linear motors are not compact force generators when compared to rotary motor with transmission offering mechanical advantage. Example 3/8” diam. Ball screw produces 100 lb of thrust, while 15 lb of linear thrust typically requires 2” x 1.5” cross section.
Heat management techniques such as air and water cooling options (both common, popular) have to be applied
Suppose it’s traveling at 3 m/s and loses power. Without resistance, it will quickly reach end of end of system, mechanical stops.
Hannes Daepp

38. Components of Linear Motors [2],[3]
Forcer (Motor Coil)
Windings (coils) provide current (I)
Windings are encapsulated within core material
Mounting Plate on top
Usually contains sensors (hall effect and thermal)
Magnet Rail
Iron Plate / Base Plate
Rare Earth Magnets of alternating polarity provide flux (B)
Single or double rail
F = lI x B
Hannes Daepp

39. Types of Linear Motors [1],[2],[3]
Iron Core
Coils wound around teeth of laminations on forcer
Ironless Core
Dual back iron separated by spacer
Coils held together with epoxy
Slotless
Coil and back iron held together with epoxy
Iron core: base plate with magnets, basically a brushless DC motor laid out. Magnetic back iron keeps it down by maintaining magnetic attraction to place
Ironless: NO back iron.
Slotless: Just one rail, often uses non-ferrous housing to support coil assembly (so that it’s not limited purely to epoxy, but isn’t magnetic)
Hannes Daepp

40. Linear Motor Types: Iron Core [1],[2]
Distinguishing Feature
Copper windings around forcer laminations over a single magnet rail
Advantages:
Highest force available per unit volume
Efficient Cooling
Lower cost
Disadvantages:
High attractive force between forcer & magnet track
Cogging: iron forcer affects thrust force as it passes over each magnet (aka velocity ripple)
Iron Plate
Rare earth magnets
Laminated forcer assembly and mounting plate
Coil wound Around
Forcer lamination
Hall effect
and thermal
sensors
-- Highest force per unit volume is because laminations concentrate flux field
-- iron forcer also aids in heat dissipation. Cooling tubes can be routed through laminations to improve thermal managment
-- only 1 row of magnets  lower cost
Disadvantages:
-- Since the forcer consists of iron, it is attracted to the permanent
magnets. Bearings are used to support the force. Can be up to 10 x thrust force, meaning that choice of bearings is critical.
-- “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]”
Hannes Daepp 40

41. Linear Motor Types: Ironless [1],[2]
Top View
Distinguishing Feature
Forcer constructed of wound coils held together with epoxy and running between two rails (North and South)
Also known as “Aircore” or “U-channel” motors
Advantages:
No attractive forces in forcer
No Cogging
Low weight forcer - No iron means higher accel/decel rates
Forcer
Mounting
Plate
Rare
Earth
Magnets
Horseshoe
Shaped
backiron
Winding, held
by epoxy
Hall Effect and
Thermal
Sensors in coil
Front View
-- No back iron in forcer, but is usually topped with an aluminum bar for mounting the load and for heat removal
Advantages:
-- No attractive forces (no iron in forcer), so no additional forces on bearings. Motor is also easier to handle, install
-- ironless forcer  no cogging. Great for extreme velocity control. Usually used with air bearings due to their “ultra-smooth characteristics”
Disadvantages:
-- since forcer is just coils with epoxy below plate, heat must leave the coil to aluminum plate via coil or through the air gap in magnet rail. High thermal resistance makes heat dissipation an issue.
-- Weak structure relative to iron core, since forcer is made of coils and epoxy (as opposed to iron). Also limits max sizes and forces to which these motors can be manufactured without adding additional structural members
-- Double rail, along with thermal and structural limitations, contributes to lower force per package size
Disadvantages:
Low force per package size
Lower Stiffness; limited max load without improved structure
Poor heat dissipation
Higher cost (2x Magnets!)
Hannes Daepp 41

42. Linear Motor Types: Slotless [1],[2]
Side View
Distinguishing Feature
Mix of ironless and iron core: coils with back iron contained within aluminum housing over a single magnet rail
Advantages over ironless:
Lower cost (1x magnets)
Better heat dissipation
Structurally stronger forcer
More force per package size
Advantages over iron core:
Lighter weight and lower inertia forcer
Lower attractive forces
Less cogging
Front View
Back
iron
Mounting
plate
Coil
assembly
Thermal
sensor
Rare
Earth
Magnets
Iron
Hybrid between iron core and ironless linear motor designs
v. Ironless
-- less weight than ironless. Higher accelerations
-- Housing provides considerably improved heat dissipation
-- housing makes structure better than ironless; can handle larger loads
-- force per package size between ironless and iron core. Better thermal management also means that it can handle higher currents than ironless and thus generate higher forces
v. Iron Core
-- Light weight forcer (aluminum v. iron) means higher throughput in light load applications
-- back iron causes 5-7 times less attractive force than with iron core
-- larger magnetic gap between magnets and forcer backiron results in less cogging  better velocity control
Hannes Daepp 42

43. Linear Motor Types: Slotless [2],[3]
Side View
Disadvantages
Some attractive force and cogging
Less efficient than iron core and ironless - more heat to do the same job
Front View
Back
iron
Mounting
plate
Coil
assembly
Thermal
sensor
Rare
Earth
Magnets
Iron
Hybrid between iron core and ironless linear motor designs
Hannes Daepp 43

44. Linear Brushless DC Motor Type
Linear Motor Type Comparison [2]
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
Hannes Daepp 44

45. Components of a “Complete” Linear Motor System [3]
Motor components
Base/Bearings
Servo controller/feedback elements
Typical sensors include Hall Effect (for position) and thermal sensors
Cable management
Hannes Daepp 45

46. 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)
Hannes Daepp 46

47. Applications [3],[5],[6] Small Linear Motors
Packaging and Material Handling
Automated Assembly
Reciprocating compressors and alternators
Large Linear Induction Machines (3 phase)
Transportation
Materials handling
Extrusion presses
Packaging: Particular notice in semiconductor industry, where precision is critical and motions of under 1 micron are often desired
Most widely known use of linear motors is in transportation
Automotive indsutry has been quick to pick up on linear motors because it allows more flexibility – can simply change fixtures for different cars instead of customizing assembly to one vehicle [6]
Hannes Daepp 47

48. References
[1] S. Cetinkunt, Mechatronics, John Wiley & Sons, Inc., Hoboken 2007.
[2] J. Barrett, T. Harned, J. Monnich, Linear Motor Basics, Parker Hannifin Corporation,
[3] Trilogy Linear Motor & Linear Motor Positioners, Parker Hannifin Corporation, 2008,
[4] Rockwell Automation, products/linearmotors/questions.html
[5] J. Marsh, Motor Parameters Application Note, Parker-Trilogy Linear Motors, Linear_Motor_Parameter_Application_Note.pdf
[6] Greg Paula, Linear motors take center stage, The American Society of Mechanical Engineers, 1998.

49. References (continued)ml
rain.htm
single phase induction motor
Brushless DC motors
s.pdf
.pdf 49 49