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 youll 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 = 5m 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