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

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  • Slide 1
  • 1 Jiasheng He Scott Koziol Kelvin Chen Chih Peng ME6405 Motors
  • Slide 2
  • 2 Overview  DC Motors (Brushed and Brushless)  Brief Introduction to AC Motors  Stepper Motors  Linear Motors
  • Slide 3
  • 3 Electric Motor Basic Principles  Interaction between magnetic field and current carrying wire produces a force  Opposite of a generator Kelvin Peng
  • Slide 4
  • 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 Kelvin Peng
  • Slide 5
  • 5 2 pole brushed DC motor commutation Kelvin Peng
  • Slide 6
  • 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 Kelvin Peng
  • Slide 7
  • 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 Kelvin Peng
  • Slide 8
  • 8 Brushless DC Motors  Essential difference - commutation is performed electronically with controller rather than mechanically with brushes Kelvin Peng
  • Slide 9
  • 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 Kelvin Peng
  • Slide 10
  • 10 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
  • Slide 11
  • 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
  • Slide 12
  • 12 AC Motors  Synchronous and Induction (Asynchronous)  Synchronous: rotor rotation frequency = AC current frequency Kelvin Peng
  • Slide 13
  • 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 Kelvin Peng
  • Slide 14
  • 14 Stepper Motors Jiasheng He
  • Slide 15
  • 15 Stepper Motor Characteristics  Brushless  Incremental steps/changes  Holding Torque at zero speed  Speed increase -> torque decreases  Usually open loop Jiasheng He
  • Slide 16
  • 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
  • Slide 17
  • 17 Types of Stepper Motors  Permanent Magnet  Variable Reluctance  Hybrid Synchronous Jiasheng He
  • Slide 18
  • 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
  • Slide 19
  • 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
  • Slide 20
  • 20 Bipolar  Two coils, no center taps  Able to reverse polarity of current across coils  Higher Torque than Unipolar Jiasheng He
  • Slide 21
  • 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
  • Slide 22
  • 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
  • Slide 23
  • 23 Variable Reluctance  Magnetic flux seeks lowest reluctance path through magnetic circuit  Stator coils energized in groups called Phases Jiasheng He
  • Slide 24
  • 24 Hybrid Synchronous  Combines both permanent magnet and variable reluctance features  Smaller step angle than permanent magnet and variable reluctance Jiasheng He
  • Slide 25
  • Applications  Printers  Floppy disk drives  Laser Cutting  Milling Machines  Typewriters  Assembly Lines Jiasheng He
  • Slide 26
  • Linear Motors Scott Koziol
  • Slide 27
  • Introduction to Linear Motors  How they work  Comparison to Rotary motors  Types  System level design  Advantages/ Disadvantages  Applications Scott Koziol
  • Slide 28
  • Key Points you’ll learn: The Good: ○ High linear position accuracy ○ Highly dynamic applications ○ High Speeds The Bad: ○ Expensive! (>$3500) Scott Koziol
  • Slide 29
  •  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
  • Slide 30
  • Analysis Method  Analysis is similar to that of rotary machines [1] Linear dimension and displacements replace angular ones Forces replace torques Scott Koziol
  • Slide 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 Scott Koziol
  • Slide 32
  • Generating Force [7] :  force (F) is generated when the current (I) and the flux density (B) interact  F = I x B Scott Koziol
  • Slide 33
  • Types of Linear Motors [3]  Iron core  Ironless  slotless Scott Koziol
  • Slide 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 Iron Plate Rare earth magnets Laminated forcer assembly and mounting plate Coil wound Around Forcer lamination Hall effect and thermal sensors Scott Koziol
  • Slide 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!) Forcer Mounting Plate Rare Earth Magnets Horseshoe Shaped backiron Winding, held by epoxy Hall Effect and Thermal Sensors in coil Top View Front View Scott Koziol
  • Slide 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 plate Scott Koziol
  • Slide 37
  • Comparing Linear Motor Types [6, p. 479],[8] Linear Brushless DC Motor Type FeatureIron CoreIronlessSlotless Attraction ForceMostNoneModerate CostMediumHighLowest Force CoggingHighestNoneMedium Power DensityHighestMedium Forcer WeightHeaviestLightestModerate Scott Koziol
  • Slide 38
  • 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 system  motor coupled to the load by means of intermediate mechanical components:  Gears  Ballscrews  Belt drives Scott Koziol
  • Slide 39
  • Components of “complete” linear motor system [3] 1. motor components 2. Base/Bearings 3. Servo controller/feedback elements 4. cable management Scott Koziol
  • Slide 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
  • Slide 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 Scott Koziol
  • Slide 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 Scott Koziol
  • Slide 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 Scott Koziol
  • Slide 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 Scott Koziol
  • Slide 45
  • 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
  • Slide 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 46
  • Slide 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 47
  • Slide 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 Scott Koziol
  • Slide 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 Scott Koziol Optics Polishing System [9]
  • Slide 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
  • Slide 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-GLinear Motors and Stages – Brochure  [5] Greg Paula, Linear motors take center stage, The American Society of Mechanical Engineers, 1998.
  • Slide 52
  • 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 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 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
  • Slide 53
  • 53 References (continued)  http://zone.ni.com/devzone/cda/ph/p/id/287 http://zone.ni.com/devzone/cda/ph/p/id/287  http://zone.ni.com/devzone/cda/ph/p/id/286 http://zone.ni.com/devzone/cda/ph/p/id/286  http://www.cs.uiowa.edu/~jones/step/types.html http://www.cs.uiowa.edu/~jones/step/types.html  http://en.wikipedia.org/wiki/H-bridge http://en.wikipedia.org/wiki/H-bridge  http://www.stepperworld.com/Tutorials/pgBipolarTutori al.htm http://www.stepperworld.com/Tutorials/pgBipolarTutori al.htm  http://electojects.com/motors/stepper-motors-1.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://hyperphysics.phy- astr.gsu.edu/hbase/magnetic/mothow.html#c1  http://en.wikipedia.org/wiki/Electric_motor http://en.wikipedia.org/wiki/Electric_motor
  • Slide 54
  • 54 References (continued)  http://www.physclips.unsw.edu.au/jw/electricmotors.ht ml 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

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