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Types of Stepper Motors
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There are few types of stepper motors:
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Unipolar motor
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Bipolar motor
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Variable Reluctance motor
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Permanent Magnet motor
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Hybrid motor
Unipolar Motor
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Two windings per phase, one for each direction
of current.
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A magnetic unipolar stepper motor requires only
one power source.
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It has logically pole that can be reversed without
switching the direction of current.
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The commutation circuit can be made very
simple for each winding using a single transistor.
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There are three leads per phase and six leads
for a typical two phase motor.
Unipolar Motor (Cont..)
Fig-1: Unipolar Motor
Bipolar Motor
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Bipolar motors require two power sources.
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They have logically a single winding per phase.
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The current in a winding needs to be reversed in
order to reverse a magnetic pole, so the driving
circuit must be more complicated.
There are two leads per phase.
Because windings are better utilized, they are
more powerful than a unipolar motor of the
same weight.
Bipolar Motor (Cont..)
Fig-2: Bipolar Motor
Variable Reluctance Motor
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Variable Reluctance (VR) motors have a soft
iron multiple rotor and a wound stator.
They generally operate with step angles from
5 degrees to 15 degrees at relatively high step
rates, and have no detent torque.
Variable Reluctance Motor (Cont..)
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When phase A is energized, four rotor
teeth line up with the four stator teeth
of phase A by magnetic attraction.
In the next step A is turned off and
phase B is energized, rotating the
rotor clockwise 15 degrees.
Continuing the sequence, C is turned on next
and then A again.
Counter clockwise rotation is achieved when the
phase order is reversed.
Permanent Magnet Motor
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Permanent magnet motors has permanent
magnet rotors with no teeth, and are
magnetized perpendicular to the axis.
In energizing the four phases in
sequence, the rotor rotates as it is
attracted to the magnetic poles.
Permanent Magnet Motor (Cont..)
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The motor take 90 degree steps as the windings
are energized in sequence ABCD.
PM's generally have step angles of 45 or 90
degrees and step at relatively low rates, but
they exhibit high torque and good damping
characteristics.
Hybrid Motor
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Combining the qualities of the VR and the PM,
the hybrid motor has some of the desirable
features of each.
They have high detent torque
and excellent holding and
dynamic torque, and they
can operate at high stepping
speeds.
Normally, they exhibit step angle
of 0.9 to 5 degrees.
Hybrid Motor (Cont..)
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Bi-filar windings are generally supplied, so that a
single-source power supply can be used .
If the phases are energized one at a time, in the
order indicated, the rotor would rotate in
increments of 1.8 degrees.
This motor can also be driven two phases at a
time to yield more torque, or alternately one
then two then one phase, to produce half steps
or 0.9 degree increments.
Motor Stepping
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There are three commonly used excitation
stepping modes:

Full-step

Half-step

Micro-step
Full-Step
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This is the usual method for driving the motor.
Both phases are always on.
Each stepping covers 90 degree
of rotation.
In single phase full-step excitation
the motor is operated with only one
energized phase at-a-time.
This mode should only be used
where torque and speed performance are not
important.
Full-Step (Cont..)
Full-Step (Cont..)
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In dual phase full-step excitation the motor is
operated with two energized phase’s at-a-time.
This mode provides good torque and speed
performance with a minimum of resonance
problems.
Full-Step (Cont..)
Half-Step
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Half-step excitation is alternate single and dual
phase operation resulting in steps one half the
normal step size.
Each step completes 45 degree of rotation.
Motors can be operated over a wide range of
speeds.
Half-Step (Cont..)
Half-Step (Cont..)
Micro-Step
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In the micro-step mode, a motor's natural step
angle can be divided into much smaller angles.
Typically, micro-step modes range from divide-by10 to divide-by-256.
This mode is only used where smoother motion or
more resolution is required.
Step Angle Calculation
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The number of degrees a rotor will turn per step
is called step angle.
It is denoted by s.
It is calculated by
Step angle, s =360°/S
where S=m*Nr
m=number of phases
Nr=number of rotor teeth
Step Angle Calculation (Cont..)
For this motor,
m=3
Nr=4
so S=3*4=12
Step angle,
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s =360°/12
=30°
step
per
Fig-6: Cross Section of Stepper Motor
Working Procedure of Unipolar Motor
Fig-7:Single Phase
Working Procedure of Unipolar Motor
(Cont..)
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Four voltage sources are connected using wire
to the stators of motors through transistors.
Current goes to the stators through coil.
As a result a magnetic field is created at the at
the charging pole.
For magnetism the charging pole attract the
permanent magnet of the motor.
Working Procedure of Unipolar Motor
(Cont..)
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Though there are four voltages sources with
stepper motor there can be 8 input combination.
In the previous figure input combination
highlighted is 0001 i.e. inputs comes through
first wire.
Corresponding pole becomes
attracts the magnetic pole to it.
charged
and
The right sided picture shows the position of the
magnet.
Working Procedure of Unipolar Motor
(Cont..)
Fig-8: Dual Phase
Working Procedure of Unipolar Motor
(Cont..)
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In the previous figure input combination
highlighted is 1010 i.e. inputs comes through
second & fourth wires.
Corresponding poles become charged
attract the magnetic pole to them.
and
Though both charging poles attract the magnet,
the magnet positions in the middle of them
which is shown in the right sided figure.
Working Procedure of Unipolar Motor
(Cont..)
Fig-9: Working procedure of Unipolar Motor.
Interfacing with Computer
Fig-10:Interfacing a unipolar stepper motor with computer using
parallel port
Interfacing with Computer (Cont..)
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ULN2003:
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The ULN2003 is a monolithic high voltage and
high current Darlington transistor arrays.
It consists of seven NPN Darlington pairs that
features high-voltage outputs with commoncathode clamp diode for switching inductive
loads.
The collector-current rating of a single
Darlington pair is 500mA.
High-voltage outputs: 50V
Interfacing with Computer (Cont..)
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ULN2003:
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The ULN2003 has a 2.7kW series base resistor for
each Darlington pair for operation directly with TTL
or 5V CMOS devices.
Interfacing with Computer (Cont..)
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25 –pin parallel port:
Fig: Pin Configuration of 25-pin parallel port
Variants of Stepper Motor
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Small Stepper Motor - PM20S
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Small Compact Size.
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Good Torque Characteristics.
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Step Angle: 18°.
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Ideal for small projects and robots.
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Dimensions: 20mm Wide, 14mm High .
Variants of Stepper Motor (Cont..)
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Small Stepper Motor - PM25S
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Good output characteristics .
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Step Angle: 7.5°.
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Ideal for small projects and robots.
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Dimensions: 25mm Wide, 12.5mm High.
Variants of Stepper Motor (Cont..)
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Small Stepper Motor - MP24GA
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High Torque .
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Superior running quietness and stability .
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Step angle: 7.5°, 4 Phase, 12Vdc, Unipolar .
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Dimensions: 24mm Wide, 20mm High .
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Used in car mirror controls and automated door
windows .
Variants of Stepper Motor (Cont..)
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Medium Stepper Motor - PM35S
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High Output Torque .
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Step angle: 7.5°, 4 Phase, 24Vdc, Unipolar .
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Dimensions: 35mm Wide, 15.5mm High .
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Easy to drive with accurate step control .
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Used in printers, scanners and small toys .
Variants of Stepper Motor (Cont..)
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Large Stepper Motor - M55SP-1
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High Output Torque.
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Heavy duty for large applications.
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Dimensions: 55mm diameter, 23mm high.
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Step Angle 7.5°, 48 Steps, 24Vdc, Unipolar type.
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Ideal for use in cutting machines and large robots.
Advantages of Stepper Motor
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A high accuracy of motion is possible, even
under open-loop control.
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Large savings in controller costs are possible
when the open-loop mode is used.
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Because of the incremental nature of command
and motion, stepper motors are easily adaptable
to digital control applications.
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No serious stability problems exist, even under
open-loop control.
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Low power requirement.
Disadvantages of Stepper Motor
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They have low torque capacity compared to DC
motors.
They have limited speed (limited by torque
capacity and by pulse-missing problems due to
faulty switching systems and drive circuits).
They have high vibration levels due to stepwise
motion.
Large errors and oscillations can result when a
pulse is missed under open-loop control.
Applications of Stepper Motor
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Factory Automation:
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Semiconductor fabrication equipment:
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X-Y plotters, laser processors, electric discharge
processors, NC machines, sewing machines, etc.
Wafer processing devices, wafer conveyors, IC
bonders, dicing machines, IC inspection devices,
etc.
Automation and labor-saving devices:
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ATMs, ticket machines, postal sorters, laboratory
systems, bill counters, vending machines, etc.
Applications of Stepper Motor (Cont..)
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Medical equipment:
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Analytical instruments, blood pumps, centrifuges,
spectrographs, etc.
Office automation:
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Copiers, faxes, word processors, printers, optical
and magnetic disk devices, etc.