Stepper Motors
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Transcript of Stepper Motors
Stepper MotorsStepper Motors
Stepper MotorStepper Motor
A A stepper motor is a motor that moves in stepsstepper 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°.
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.
Stepper motor operationStepper motor operation
Step angle Step angle ββangle through which motor shaft rotates for each angle through which motor shaft rotates for each
command pulsecommand pulse ββ = (Ns~Nr)*360 / (Ns*Nr) = (Ns~Nr)*360 / (Ns*Nr)
or or ββ = 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 phasesm=No. of phases
Displacement = Displacement = ββ * No of control pulses * No of control pulses
(Rotation) (Rotation) Speed =(60*f) / SRSpeed =(60*f) / SR rpm rpm
step resolutionstep resolution SR=360 / SR=360 / ββ step/rev step/rev
Comparison to Servo Motors
Servo MotorServo Motor Stepper MotorStepper Motor
Position ControlPosition Control require some form of require some form of analog feedbackanalog feedback not subject to this not subject to this problemproblem
Position ControlPosition Control often open loopoften 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 controlcontrol
Types of Stepper MotorsTypes of Stepper Motors
Permanent MagnetPermanent Magnet
Variable ReluctanceVariable Reluctance
HybridHybrid
Permanent Magnet Stepper motorsPermanent 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°.
Permanent Magnet Permanent Magnet Stepper motors…Stepper motors…
Full SteppingFull Stepping
A-CA-C 0 0˚̊B-DB-D 90˚ 90˚
Half steppingHalf stepping
A-CA-C 0 0˚̊A-C,B-D 45˚A-C,B-D 45˚B-DB-D 90˚ 90˚
Variable Reluctance Variable Reluctance Stepper motors Stepper motors
No permanent magnetNo permanent magnetFree wheeling Free wheeling
possiblepossible
A - 0A - 0˚̊
C - 15˚C - 15˚
B - 30˚B - 30˚
Variable Reluctance Variable Reluctance Stepper motors….Stepper motors….
less torqueless torque
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
Hybrid Stepper motorsHybrid Stepper motors
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.
Full step Mode
• One phase is energized at a time
Full step ModeFull step Mode
Full step ModeFull step Mode
Animation shows how coils are energized for full steps
Half Step mode
Half Step modeHalf 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 responseFast response Absence of detent torqueAbsence of detent torque
Half Step modeHalf Step mode
Micro Stepping ModeMicro Stepping Mode
Smooth and low speed operation with high Smooth and low speed operation with high resolutionresolution
Printing, photo type settingPrinting, photo type setting
A – constant B –increased by very small A – constant B –increased by very small
incrementsincrements till 1 or max.till 1 or max.
A -decreased by very A -decreased by very B – constant B – constant
small stepssmall steps till 0 or mintill 0 or min
AdvantagesAdvantages
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
ApplicationsApplications
Precise positioning and speed controlPrecise positioning and speed controlOpen loop position controlOpen loop position controlTorque : 1Torque : 1µNm to 40 NmµNm to 40 NmPower : 1w to 2500wPower : 1w to 2500w
ApplicationsApplications
Film DriveFilm DriveOptical ScannerOptical ScannerPrintersPrintersATM MachinesATM MachinesComputer peripheralsComputer peripherals IC fabricationIC fabrication
ApplicationsApplications
robotics
digital control systems tape drivers disk drives tool positioning process control X-Y recorders