- The stepper motor contains a slid stator of several phased curving and a rotor structure without coiling. They characteristically use only three or four phase windings. Therefore the number of poles in it is responsible for maintaining per input pulse required angular change.
- The rotors can be permanent magnet or also of variable reluctance type,
- Stepper motors come into action with a peripheral drive logic circuit. When a series of the pulse is functional to the participation of the drive circuit.The circuit thus provides currents to the stator curls of the motor to convert the axis of the air-slitpart round the input pulses.
- Permanent magnet stepper motor:
- The rotor is composed of ferrite or rareearth material which is considered as a permanent magnet.
- The stator stack of phase II is stunned from that of phase ‘I’ by an angle of 90°.
- When the phase’I’ is agitated, the rotor comes into line as represented in Fig. 28 (i). However, now if the phase ‘II’ is also excited, the active stator poles shift anti-clockwise by 22.5° which is also represented in figure Fig, 28 (ii) that causes the rotor to transfer accordingly. Keeping the phase ‘II’ still energized, if the phase ‘I’ is now de-energised the rotor will move another step of 22,5°. The setback of phase ‘I’ winding current further causes advancing movement of 22.5°, and so on. The movement or the path can be revolted, and that can be readily envisioned.
- Thus each phase is delivered with double coils to shorten the switching arrangement phenomenon.
- Variable reluctance stepper motor:
- In this motor,there is the absence of a permanent magnet and the rotor generally utilized a ferromagnetic multi-toothed one.
- The significant alterations in magnetic reluctances that occuramongst the direct and quadrature axes improve the torque. Coils create a stationary field that enhances torque which in turn enhances-the rotor to change the location of the reluctance of the flux path which is considered as minimum value.
Stepping angle regardless of the type of stepper motor is given as following:
- Hybrid stepper motor:
- This consists of a permanent-magnet stepper motor with toothed and stacked rotor implemented from the variable-reluctance motor.
- The permanent magnet is positioned axially length ways the rotor is placed as an annular cylinder over the motor shaft.
- This stator has only a single set of winding that is capable of exciting the poles which cooperate with duo rotor stacks.
- One major advantage is that if stator agitation is banished,then the rotor will continue to remain protected into the same position, as it was before it was not agitated or brought into excitement.
- The stacks of the rotor are toothed at the terminals. The stack teeth at one end, obtains equivalent polarity whereas the teeth of the stack at the other end of the rotor consist the opposite polarity. Thus the two sets of the teeth are evacuated from the tooth field which is also called pole pitch.
Due to the permanent magnetic exitation, torque prevents rotation of the rotor.
- The large step angles for stepper motors are 15°, 7.5°, 2° and 0.72°. Angle selection depends on the angular resolution.