Principles of Special Motors

Different Types of Special Motors In Engineering

1. Principles of : AC Series motors Universal motor Stepper motor Shaded pole motor SPECIAL MOTORS

2. A series ac motor is the same electrically as a dc series motor but construction differs slightly. Special metals, laminations, and windings are used which reduce losses caused by eddy currents, hysteresis, and high reactance. Dc power can be used to drive an ac series motor efficiently, but the opposite is not true. The characteristics of a series ac motor are similar to those of a series dc motor. It is a varying-speed machine.  It has low speeds for large loads and high speeds for light loads .  AC SERIES MOTOR

3. SPEED –TORQUE CHARACTERISTICS OF AC AND DC SERIES MOTORS

4. Motor that can be used with a single-phase ac source as well as a dc source of supply voltages are called universal motor. The stator and rotor windings of the motor are connected in series through the rotor commutator . The universal motor is also known as an AC series motor or an AC commutator motor. UNIVERSAL MOTOR

5. MOTORS 5 Universal Motor

6. Universal Motor Series-connected Rotor and Stator are connected in series Operates on either ac or dc MOTORS 6

7. ECE 441 7 Equivalent Circuit

8. ECE 441 8 A Closer Look Armature (Rotor) Field Winding Field (Stator)

9. ECE 441 9 The Commutator Bar and Brushes are a switch that reverses the current in the armature coil as it rotates

10. ECE 441 10 Check the Direction of Rotation Force on conductor B is upwards, rotation is counter-clockwise (CCW) Flux “Bunching” +Positive Half-Cycle+

11. ECE 441 11 Opposite Half-Cycle Force on Conductor B is upwards, rotation is counter-clockwise (CCW) Flux “Bunching” -Negative Half-Cycle-

12. How do you reverse the direction of rotation? Reverse the direction of the current in either the field or in the armature, but not both! How do you control the speed of the motor? Reduce the voltage applied to the motor Use an autotransformer or SCR/Triac This reduces the armature current, reducing the torque, reducing the speed Applications Portable power tools Small appliances ECE 441 12 Other Considerations

13. A special type of synchronous motor which is designed to rotate a specific number of degrees for every electric pulse received by its control unit. It is a motor that can rotate in both directions, move in precise angular increments, sustain a holding torque at zero speed, and be controlled with digital circuits. It moves in accurate angular increments known as steps, in response to the application of digital pulses to the electric drive circuit. Step motors are either bipolar, requiring two power sources or uni polar requiring only one power source. STEPPER MOTORS

14. TYPES OF STEPPER MOTORS

15. Stators Rotor Cross Section of a Stepper Motor

16. Winding number 1 Winding number 2 One step 6 pole rotor

17. The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet 2 The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6° in this example. Practical Stepper motor operation

18. The bottom electromagnet (3) is energized; another 3.6° rotation occurs. The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.

19. Stepping Motor to move read-write head Stepper motor applications

20. Paper feeder on printers CNC lathes Stepper motors Stepper motor applications

21. Rotor Stator coils CNC Stepping Motor

22. Advantages:- Low cost for control achieved Ruggedness Simplicity of construction Can operate in an open loop control system Low maintenance Less likely to stall or slip Will work in any environment Disadvantages:- Require a dedicated control circuit Use more current than D.C. motors High torque output achieved at low speeds Advantages / Disadvantages