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Prepared by: Mike Tyger Dept. of Electrical and Computer Engineering Utah State University

ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: AC induction motor. Prepared by: Mike Tyger Dept. of Electrical and Computer Engineering Utah State University. 3/06/2009. Outline . Reference List Explore Further Major applications Overview

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Prepared by: Mike Tyger Dept. of Electrical and Computer Engineering Utah State University

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  1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: AC induction motor Prepared by: Mike Tyger Dept. of Electrical and Computer Engineering Utah State University 3/06/2009

  2. Outline • Reference List • Explore Further • Major applications • Overview • Basic working principles • Typical Application • Major specifications • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Reference list • Wikipedia, ‘Induction motor ’, en.wikipedia.org/wiki/AC_induction_motor. • Wikipedia, ‘Squirrel-cage rotor’, en.wikipedia.org/wiki/Squirrel-cage_rotor. • Wikipedia, ‘Slip Ring’, en.wikipedia.org/wiki/Slip_ring. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. To explore further (survival pointers of web references etc) • http://www.physclips.unsw.edu.au/jw/electricmotors.html#ACmotors • Animations of how an AC motor operates • http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/indmot.html • Physics of an AC motor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. Major Applications • Drive motor for small household appliances • Fans • Blenders • Vacuums • Drive motor for larger applications • Pumps • Compressors • Treadmills • Forced air heating system ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. Overview • A polyphase sinusoidal voltage passed though the stators of a motor produces a rotating magnetic field. • By placing conductive material in the rotor the rotating magnetic field will induce a current in the rotor which will in turn create a magnetic field in the rotor. • The rotor magnetic field is opposed by the stator magnetic filed so a torque is generated. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Overview - General A 3-Phase power supply creates a rotating magnetic field in an induction motor. Illustration courtesy of wikipedia.org http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Rotatingfield.png/180px-Rotatingfield.png ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. Overview – Slip For a current to be induced the magnetic field in relation to the rotor must be changing so the speed of the rotor will never be the same as the rotational speed of the magnetic field. This difference is known as slip. F = supply frequency P = Number of Stator Poles Ns = speed of the rotating field S = slip ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Principle – General Operation An AC induction motor does not have any direct supply onto the rotor. A secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energized with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern induces a current in the rotor conductors. These currents create a magnetic field which interacts with the rotating magnetic field created by the stator and the rotor will turn. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. Principle – Slip For a current to be induced in the rotor, the speed of the rotor and the speed of the rotating magnetic field in the stator must be different. If the rotor reaches the speed of the rotating magnetic field the current will stop being induced and the rotor will slow slightly until a current is re-induced and then the rotor continues as before. The difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It is the ratio between the relative speed of the magnetic field as seen by the rotor (the slip speed) to the speed of the rotating stator field. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. Rotor Types • Squirrel Cage Rotor • Most common type of rotor • Slip Ring Rotor • Least common type of rotor • Solid Core Rotor • Simplest rotor to manufacture ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. Squirrel Cage Rotor http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Squirrel_cage.jpg/180px-Squirrel_cage.jpg The core of the rotor is built of a stack of iron laminations. The image above shows only three laminations of the stack but many more are used. Longitudinal conductive bars of aluminum or copper are set into grooves in the laminations and connected together at both ends by shorting rings forming a cage-like shape. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. Slip Ring Rotor A slip ring rotor replaces the bars of the squirrel cage rotor with windings that are connected to slip rings. A slip ring is a conductive band mounted to and insulated from the motor shaft. If the slip rings are shorted to each other the rotor behaves similarly to the squirrel cage rotor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. Solid Core Rotor A solid core rotor uses a solid piece of mild steel for the rotor. The rotation is caused by the induced current ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. Principle – Single Phase Starting In a single phase induction motor a starting circuit must be used to start rotation of the rotor. A single phase induction motor can rotate in either direction. The starting circuit determines the rotational direction. For small motors it is usual to "shade" the stator poles by means of a single turn of heavy copper wire around one corner of the pole. The current induced in the single turn is out of phase with the supply current and so causes an out-of-phase component in the magnetic field. This imparts sufficient torque to start the motor. Starting torque is very low and efficiency is also reduced. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Principle – Starting Larger Motors Larger motors commonly have a second stator winding which is fed with an out-of-phase current to create a rotating magnetic field. The out-of-phase current may be obtained by putting a capacitor inline with the winding, or the winding may have different values of inductance and resistance from the main winding. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Typical Application http://www.traderscity.com/board/userpix12/12733-shade-pole-motor-wahsing-machine-pump-ac-1.jpg Washing machine shaded pole pump motor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Major Specifications • Poles • Power (Horsepower or Watts) • Voltage • Drive Frequency ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Limitations • Speed is not synchronous to drive signal frequency • High starting current ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  20. Cost and availability • Cost • AC induction motors are not complex to manufacture so cost is extremely reasonable • availability • Due to large demand AC induction motors are widely available ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  21. Nonlinearities • ADC nonlinearities • A High-performance ADC is required since ADC nonlinearity cannot be compensated for. • Magnet nonlinearities • The Hall elements of the array must be in the linear range of the magnetic field. This range is larger for larger diameter magnets but the field distribution curve is more shallow, resulting in a smaller differential signal. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  22. Limitations • Highly susceptible to stray magnetic fields • Requires precise assembly • Possible need for magnetic shielding ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  23. Limitations • Sensors must be placed very accurately around the centerline of the rotational axis. • Multiple sensors are typically contained in a single package • Sensor must be very accurately placed on PCB • Small tolerances of sensor PCB mounting fixtures can increase cost ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  24. Other Considerations • Robustness • The non-contact nature of a magnetic encoder makes it fairly robust. The CORDIC can be used to eliminate the effect of stray magnetic fields • Hall effect sensors are used in a wide variety of applications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  25. Other Considerations • The ratio of sensor accuracy to sensor cost is very good for a hall effect rotary encoder ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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