Jiasheng He Scott Koziol Kelvin Chen Chih Peng ME6405

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

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 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 Kelvin Peng

5. 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 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 Kelvin Peng

8. Brushless DC Motors • Essential difference - commutation is performed electronically with controller rather than mechanically with brushes 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 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  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 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 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

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) 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 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 Scott Koziol

32. Generating Force [7] : • force (F) is generated when the current (I) and the flux density (B) interact • F = I x B 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 Laminated forcer assembly and mounting plate Hall effect and thermal sensors Coil wound Around Forcer lamination Iron Plate Rare earth magnets Scott Koziol

35. Type 2: Ironless Motors [3],[6],[8] Top View 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!) Front View Forcer Mounting Plate Winding, held by epoxy Rare Earth Magnets Hall Effect and Thermal Sensors in coil Horseshoe Shaped backiron Scott Koziol

36. Type 3: Slotless [3],[6],[8] Side View 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 Front View Coil assembly Back iron Mounting plate Thermal sensor Rare Earth Magnets Iron plate Scott Koziol

37. Comparing Linear Motor Types [6, p. 479],[8] 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 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 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 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 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 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 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

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 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