stepper motor electrical machines - 2 ppt
- 2. Stepper Motor Stepper Motor A A stepper motor is a motor that moves in steps stepper motor is a motor that moves in steps. . A A stepper motor is stepper motor is one whose shaft moves in precise angular increments for each electrical input. Typical step sizes are 2°, 2.5° ,3°, 7.5° , 15°, 30°.
- 3. Stepper Motor… Stepper Motor… salient poles on both stator and rotor. The stator poles are wound with coils which carry relatively long pulses of current. The rotor poles are made from either magnetically soft or hard iron. Ns always different from Nr.
- 5. Stepper motor operation Stepper motor operation Step angle Step angle β β angle through which motor shaft rotates for each angle through which motor shaft rotates for each command pulse command pulse β β = (Ns~Nr)*360 / (Ns*Nr) = (Ns~Nr)*360 / (Ns*Nr) or or β β = 360 / (m*Nr) = 360 / (m*Nr) where Ns=No. of stator poles (teeth) where Ns=No. of stator poles (teeth) Nr=No. of rotor poles (teeth) Nr=No. of rotor poles (teeth) m=No. of phases m=No. of phases Displacement = Displacement = β β * No of control pulses * No of control pulses (Rotation) (Rotation) Speed =(60*f) / SR Speed =(60*f) / SR rpm rpm step resolution step resolution SR=360 / SR=360 / β β step/rev step/rev
- 6. Comparison to Servo Motors Servo Motor Servo Motor Stepper Motor Stepper Motor Position Control Position Control require some form of require some form of analog feedback analog feedback not subject to this not subject to this problem problem Position Control Position Control often open loop often open loop at high accelerations at high accelerations with variable loads, all with variable loads, all rotor information is lost, rotor information is lost, and closed loop is and closed loop is required for accurate required for accurate control control
- 7. Types of Stepper Motors Types of Stepper Motors Permanent Magnet Permanent Magnet Variable Reluctance Variable Reluctance Hybrid Hybrid
- 8. Permanent Magnet Stepper motors Permanent Magnet Stepper motors Rotor is made of permanent magnetic Material No teeth on rotor No freewheeling No freewheeling more torque during rotation Less acceleration Difficult to make small step pm rotors with a large number of poles. i.e. step sizes are limited to 30° - 90°.
- 9. Permanent Magnet Permanent Magnet Stepper motors… Stepper motors… Full Stepping Full Stepping A-C A-C 0 0˚ ˚ B-D B-D 90˚ 90˚ Half stepping Half stepping A-C A-C 0 0˚ ˚ A-C,B-D 45˚ A-C,B-D 45˚ B-D B-D 90˚ 90˚
- 10. Variable Reluctance Variable Reluctance Stepper motors Stepper motors No permanent magnet No permanent magnet Free wheeling Free wheeling possible possible A - 0 A - 0˚ ˚ C - 15˚ C - 15˚ B - 30˚ B - 30˚
- 11. Variable Reluctance Variable Reluctance Stepper motors…. Stepper motors…. less torque less torque
- 12. Hybrid Stepper motors Hybrid Stepper motors A hybrid stepping motor has characteristics of both PM and VR motors the rotor is a permanent magnet but has blades like VR motors Rotor is magnetised axially to create the poles motor has very high torque and very small, precise step increments
- 13. Hybrid Stepper motors Hybrid Stepper motors
- 14. Hybrid Stepper motors…. Hybrid Stepper motors…. 200 rotor teeth and rotate at 1.80 step angles. Also available in 0.9ºand 3.6º step angle configurations. used in a wide variety of industrial applications.
- 15. Full step Mode • One phase is energized at a time
- 16. Full step Mode Full step Mode
- 17. Full step Mode Full step Mode Animation shows how coils are energized for full steps
- 18. Half Step mode
- 19. Half Step mode Half Step mode the second phase is turned on before the first the second phase is turned on before the first phase is turned off. Thus, sometimes both phase is turned off. Thus, sometimes both phases are energized at the same time. phases are energized at the same time. During the half-steps the rotor is held in between During the half-steps the rotor is held in between the two full-step positions. the two full-step positions. A half-step motor has twice the resolution of a A half-step motor has twice the resolution of a full step motor. full step motor. Fast response Fast response Absence of detent torque Absence of detent torque
- 20. Half Step mode Half Step mode
- 21. Micro Stepping Mode Micro Stepping Mode Smooth and low speed operation with high Smooth and low speed operation with high resolution resolution Printing, photo type setting Printing, photo type setting A – constant B –increased by very small A – constant B –increased by very small increments increments till 1 or max. till 1 or max. A -decreased by very A -decreased by very B – constant B – constant small steps small steps till 0 or min till 0 or min
- 22. Advantages Advantages They produce the highest torque at low speeds holding torque (not present in DC motors) Rotor has no winding, commutator or brushes – quite, robust and reliable operation
- 23. Applications Applications Precise positioning and speed control Precise positioning and speed control Open loop position control Open loop position control Torque : 1 Torque : 1µNm to 40 Nm µNm to 40 Nm Power : 1w to 2500w Power : 1w to 2500w
- 24. Applications Applications Film Drive Film Drive Optical Scanner Optical Scanner Printers Printers ATM Machines ATM Machines Computer peripherals Computer peripherals IC fabrication IC fabrication
- 25. Applications Applications robotics digital control systems tape drivers disk drives tool positioning process control X-Y recorders