1. What is stepper motor ?
The stepper motor is essentially a synchronous motor that converts control signals in the form of successive discrete electrical pulses into angular motion.
2. Structure of stepper motor
In terms of the stepper motor structure, there are stator parts, the rotor is a permanent magnet or, in the case of a variable reluctance stepper motor, tooth blocks are made of lightweight magnetic materials. Stepper motor is controlled by external controller. Stepper motor and controller are designed so that the motor can hold any fixed position as well as rotate to any position.
+ The rotor is a series of carefully placed permanent magnet leaves. On these leaves the magnet is divided into pairs of polar poles arranged symmetrically.
+ The stator is made of ferromagnet divided into grooves to place a coil.
– Characteristics of stepper motor:
+ The stepper motor operates under the effect of discrete and successive pulses. When there is current or voltage applied to the armature of the stepper motor, the rotor of the motor rotates at a certain angle called the step of the motor.
+ The step angle is the rotation angle of the motor shaft corresponding to a control pulse. The step angle is determined based on the structure of the stepper motor and the stepping motor control method.
+ The motor’s opening feature is characterized by the maximum pulse frequency that can open the engine without making the rotor asynchronous
+ The direction of rotation of the stepper motor does not depend on the direction of the current but on the order of the impulses to the windings.
3. Classification of stepper motors:
There are three main types of stepper motors, they are: Permanent magnet stepper, Variable reluctance stepper, Hybrid synchronous stepper.
+ Permanent magnet stepper: The permanent magnet stepper has a rotor that is a permanent magnet, the stator has multiple teeth on each winding tooth. The phase windings have different polarities.
+ Variable reluctance stepper: The reciprocating stepper motor has the same structure as the permanent magnet stepper motor. The stator construction also has symmetrical phase coils, but the symmetric phase coils have the same polarity as the permanent magnet stepper motors. The step angle of stator is Ss.
The rotor of the rheostat stepper motor is composed of high steel with high magnetic conductivity, so when the motor is out of power, the rotor continues to spin freely before stopping completely.
+ Hybrid synchronous stepper: Hybrid synchronous stepper features the structure of the two types of motors mentioned above. The stator and the rotor are similar in structure to the Variable reluctance stepper, but the number of stator and rotor teeth is not equal.
The rotor of the stepper motor usually has two parts: the inner part is a permanent magnet that is fastened on the motor shaft, the outer part is the two rotor segments made from young steel leaves and the teeth of the two rotor segments are placed at a distance.
4. Method of stepping motor control
+ Wave control: is a method of controlling pulse level in turn according to the order of each phase winding.
+ Full step control: is the method of controlling the pulse level simultaneously for two successive phase coils.
+ Half step control: is a control method that combines both methods of waveform control and step control. When driven by this method. The step angle value is two times smaller and the number of steps of the stepper motor is increased by 2 times. Compared with the step control method enough. However, this method has a complex control pulse generator.
+ Microstep control: is a new method applied in stepping motor control. Allow the stepping motor to stop and position in a half-step position between 2 sufficient steps. The advantage of this method is that the motor can operate with small step angle and high precision. Because the pulse level has waveform, the motor operates more smoothly. Limiting the resonance problem when the engine is operating.
5. The working principle of stepper motor
Here is the working principle of a six poles stepper motor. In a variable reluctance stepper motor, the rotor moves to minimize magnetic reluctance each time the next pair of coils is energized. At each step, the coils have been energized a moment before the rotor has had time to respond.
5.1 Advantages and disadvantages of stepper motor
+ Ability to provide extremely high torque at low and medium speed ranges.
+ Durable, relatively low price.
+ Stepping motor often has the phenomenon of slipping. The reason is because the magnetic force is weak or the power supply is not enough.
+ Does not run at high speed
+ When operating, the Step Motor often causes noise and has a warming phenomenon. With the new generation Step Motor, the noise and heat of the engine is significantly reduced.
5.2 Application of Step Motor
Stepper motors are now mainly used for digital motion control. It is performed by commands encoded in digital form.
Application in automation industry, especially for equipment where precision is required. For example, industrial machines for mechanical processing such as: CNC cutting machine, cnc plasma cutting machine, etc.
Also in computer technology, the Step motor is used for all types of hard drives, floppy drives, printers, etc.