A stepper motor is a digital device which is like a computer that runs on pulses. It can be directly connected with digital computer unlike D.C. motor for which A/D or D/A converters are needed. In fact, stepper motor is an electric motor which moves or rotates in series of small discrete steps. A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. In this chapter, the authors discuss the stepper motor. It starts with the definition of stepper motor, its basic function, and principle of working. They then discuss the types and construction of stepper motor. Finally, this chapter concludes with the applications of stepper motor.
Top12.1 Construction Of Stepper Motor
A stepper motor basically consists of yoke, stator and a rotor. The yoke is made up of cast iron. The stator is made up of silicon steel having poles, while rotor of the stepper motor also has poles. It is important to note that stator have always two greater poles than rotor. Figure 1 shows the construction of stepper motor.
We now discuss the general working principal of stepper motor.
Top12.2 Principal Of Operation Of Stepper Motor
The working principal of stepper motor is as follows. First, the phase winding of the stepper motor is energized with the current. As a result, magnetic flux is developed. Direction of this magnetic flux can be determined with the help of “Right Hand Rule”. Note that both the stator and rotor has North pole and South pole. As we know, when same poles are closer, they will repel. Once the magnetic flux is developed, in the second step, the rotor tries to align itself so that the flux opposition is minimized. Consequently, the motor would rotate clockwise in order to align its South pole to the North pole of stator. In this manner, the motor will rotate one step. In order to rotate the motor continuously, we need to provide the current in a sequence to the windings of the motor.
The relationship between the poles and angle of Stator and Rotor is shown in Table 1.
Table 1. Poles and angle of stator and rotor
| Stator | Rotor | Angle of Step |
| Poles | Angle | Poles | Angle | Rotor – Stator = Step |
| 4 | 90° | 2 | 180° | 180-90 = 90° |
| 8 | 45° | 6 | 60° | 60-45 = 15° |
| 10 | 36° | 8 | 45° | 45-36 = 9° |
| 12 | 30° | 10 | 36° | 36-30 = 6° |
| 14 | 25.7° | 12 | 30° | 30-25.7 = 4.3° |
| 16 | 22.5° | 14 | 25.7° | 25.7-22.5 = 3.2° |
| 18 | 20° | 16 | 22.5° | 22.5-20 = 2.5° |
| 20 | 18° | 18 | 20° | 20-18 = 2° |
| 22 | 16.3° | 20 | 18° | 18-16.3 = 1.3° |