1. Types of Stepper Motors
There are few types of stepper motors:
Unipolar motor
Bipolar motor
Variable Reluctance motor
Permanent Magnet motor
Hybrid motor

2. Unipolar Motor
Two windings per phase, one for each direction of current.
A magnetic unipolar stepper motor requires only one power source.
It has logically pole that can be reversed without switching the direction of current.
The commutation circuit can be made very simple for each winding using a single transistor.
There are three leads per phase and six leads for a typical two phase motor.

3. Unipolar Motor (Cont..)
Fig-1: Unipolar Motor

4. Bipolar Motor Bipolar motors require two power sources.
They have logically a single winding per phase.
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.

5. Bipolar Motor (Cont..)
Fig-2: Bipolar Motor

6. Variable Reluctance Motor
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.

7. Variable Reluctance Motor (Cont..)
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.

8. Permanent Magnet Motor
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.

9. Permanent Magnet Motor (Cont..)
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.

10. Hybrid Motor
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.

11. Hybrid Motor (Cont..)
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.

12. Motor Stepping
There are three commonly used excitation stepping modes:
Full-step
Half-step
Micro-step

13. Full-Step
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.

14. Full-Step (Cont..)

15. Full-Step (Cont..)
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.

16. Full-Step (Cont..)

17. Half-Step
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.

18. Half-Step (Cont..)

19. Half-Step (Cont..)

20. Micro-Step
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-by-10 to divide-by-256.
This mode is only used where smoother motion or more resolution is required.

21. Step Angle Calculation
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

22. Step Angle Calculation (Cont..)
For this motor,
m=3
Nr=4
so S=3*4=12
Step angle,
s =360°/12
=30° per step
Fig-6: Cross Section of Stepper Motor

23. Working Procedure of Unipolar Motor
Fig-7:Single Phase

24. Working Procedure of Unipolar Motor (Cont..)
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.

25. Working Procedure of Unipolar Motor (Cont..)
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 charged and attracts the magnetic pole to it.
The right sided picture shows the position of the magnet.

26. Working Procedure of Unipolar Motor (Cont..)
Fig-8: Dual Phase

27. Working Procedure of Unipolar Motor (Cont..)
In the previous figure input combination highlighted is 1010 i.e. inputs comes through second & fourth wires.
Corresponding poles become charged and attract the magnetic pole to them.
Though both charging poles attract the magnet, the magnet positions in the middle of them which is shown in the right sided figure.

28. Working Procedure of Unipolar Motor (Cont..)
Fig-9: Working procedure of Unipolar Motor.

29. Interfacing with Computer
Fig-10:Interfacing a unipolar stepper motor with computer using parallel port

30. Interfacing with Computer (Cont..)
ULN2003:
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 common-cathode clamp diode for switching inductive loads.
The collector-current rating of a single
Darlington pair is 500mA.
High-voltage outputs: 50V

31. Interfacing with Computer (Cont..)
ULN2003:
The ULN2003 has a 2.7kW series base resistor for each Darlington pair for operation directly with TTL or 5V CMOS devices.

32. Interfacing with Computer (Cont..)
25 –pin parallel port:
Fig: Pin Configuration of 25-pin parallel port

33. Variants of Stepper Motor
Small Stepper Motor - PM20S
Small Compact Size.
Good Torque Characteristics.
Step Angle: 18°.
Ideal for small projects and robots.
Dimensions: 20mm Wide, 14mm High .

34. Variants of Stepper Motor (Cont..)
Small Stepper Motor - PM25S
Good output characteristics .
Step Angle: 7.5°.
Ideal for small projects and robots.
Dimensions: 25mm Wide, 12.5mm High.

35. Variants of Stepper Motor (Cont..)
Small Stepper Motor - MP24GA
High Torque .
Superior running quietness and stability .
Step angle: 7.5°, 4 Phase, 12Vdc, Unipolar .
Dimensions: 24mm Wide, 20mm High .
Used in car mirror controls and automated door windows .

36. Variants of Stepper Motor (Cont..)
Medium Stepper Motor - PM35S
High Output Torque .
Step angle: 7.5°, 4 Phase, 24Vdc, Unipolar .
Dimensions: 35mm Wide, 15.5mm High .
Easy to drive with accurate step control .
Used in printers, scanners and small toys .

37. Variants of Stepper Motor (Cont..)
Large Stepper Motor - M55SP-1
High Output Torque.
Heavy duty for large applications.
Dimensions: 55mm diameter, 23mm high.
Step Angle 7.5°, 48 Steps, 24Vdc, Unipolar type.
Ideal for use in cutting machines and large robots.

38. Advantages of Stepper Motor
A high accuracy of motion is possible, even under open-loop control.
Large savings in controller costs are possible when the open-loop mode is used.
Because of the incremental nature of command and motion, stepper motors are easily adaptable to digital control applications.
No serious stability problems exist, even under open-loop control.
Low power requirement.

39. Disadvantages of Stepper Motor
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.

40. Applications of Stepper Motor
Factory Automation:
X-Y plotters, laser processors, electric discharge processors, NC machines, sewing machines, etc.
Semiconductor fabrication equipment:
Wafer processing devices, wafer conveyors, IC bonders, dicing machines, IC inspection devices, etc.
Automation and labor-saving devices:
ATMs, ticket machines, postal sorters, laboratory systems, bill counters, vending machines, etc.

41. Applications of Stepper Motor (Cont..)
Medical equipment:
Analytical instruments, blood pumps, centrifuges, spectrographs, etc.
Office automation:
Copiers, faxes, word processors, printers, optical and magnetic disk devices, etc.