Dc Stepper Motor for Better and Faster Types, Constructions, Characteristics

Hello everyone, I hope that you all are doing well in your life. The topic for today is Special Dc motor i.e. stepper motor. There are many other special motors as well but today the main focus is on stepper type. In this article, we are going to go through the basic introduction, its types, characteristics, principle, construction, working, and basic advantages and disadvantages. Before starting just get a simple idea that what a simple motor is? It is an electronic device that is use to convert electrical energy into mechanical. Its working principle is that whenever a current-carrying conductor is kept in a magnetic field is undergoes or feels pressure.

What is a DC Stepper Motor?

As the name suggest these are the types of motor that rotate through a fix angular step for each input current pulse obtain by the controller.

These motors also go by the name stepping motors or step motors. However, these are the type of motor that can directly work on the commands of the computer or microprocessors. A stepper motor converts excitations into precisely define increments of the rotor. They are doubly salient machines i.e. they have teeth on both the stator as well as the rotor.

Such motors are mostly suitable for conditions where accurate positioning or exact speed is require. As industrial motors can do the work of motors by converting the energies but they cannot provide speed control. This was when the stepper motors can into existence.

Step Angle

One of the important factor in discussing dc stepper motor is step angle.

The angle through which the shaft of the rotor rotates for each command pulse is called a step angle β. The smaller the step angle, the greater the number of steps per revolution, and the higher the accuracy of positioning will be there. However, the step angle can be as small as 0.72 or as large as 90 degrees. But the most common available step size is 1.8, 2.5, 7.5, and 15 degrees.

Mathematically the value of step angle is;

   

   

However, the resolution is given by the number of steps require to complete one complete revolution of the rotor shaft. Higher the resolution greater the accuracy. Mathematically it is express as;

   

   

Thus the motor shaft speed is;

   

Construction

It consists of a rotor that is of a permanent magnet and a stator that is of an electromagnet. The Stepper motor having multiple toothed electromagnets is arranged around a central gear shape piece of iron.

These electromagnets are energize by the driver circuit

Firstly one of the electromagnets is given power; Which in turn attracts the gear teeth. When these gear teeth align with the first electromagnet, they are a bit offset from the next electromagnet. Whenever the second magnet is given the power the first losses it. And thus the gear rotates and tries to align with the second electromagnet.

These processes repeat themselves for the 3rd and 4th magnet also. Each rotation is refer to be as a step. To make a full rotation integer number of steps is require.

A stepping motor can operate at very high stepping rates and still remain in synch with the command pulse. Whenever the pulse rate is high, the shaft rotation seems to be continuous. Slewing is the name of the operation when the speed is high. However, If the stepping rate suddenly rises the motor may lose its synchronism and stop.

Types of DC Stepper Motor

However, there are three main types of stepper motor that are;

1. Variable reluctance stepper motor.
2. Permanent magnet stepper motor.
3. And lastly hybrid stepper motor.

Variable Reluctance Stepper Motor (VR)

The VR stepper motor is one of the most basic types of stepper motor. helps to explain the principle of operation of stepper motor. It goes by the name variable reluctance stepper motor because of the reluctance of the magnetic circuit due to the angular changes in the location of the rotor.

It consists of poles on the stator that have winding but the rotor poles consist of ferromagnetic material.

The stator has six salient poles with focus excitation windings around each one of them. The stator construction assembles in a single stack for protection and ease. In stepper motors, the number of poles is different on stator and rotor. In VR motors the stator and the rotor get align in such a way that the magnetic reluctance becomes minimum.

Types of VR stepper Motor

1. Single stack Type
2. And Multi stack Type.

A stack is nothing but the number of stator and rotor poles that must be there in a single row is called a stack. It is observe that during comparison the multi-stack stepper motor is more efficient and provides more torque to volume ratio than single stack VR motor.

Full Step Operation

In a full-step mode of operation, the stepper mode goes through or makes a step angle of about 200 steps per revolution i.e. it takes 1.8 steps.

There are two variation of full step operation

1. Single phase full step operation.
2. And dual phase full step operation.

In single-phase full-step operation the motor is in the state of excitation when there’s only one phase energized at a time. These operations are mainly in use where the torque and the speed of the motor don’t really matter. Besides the need for power for the operation of these motors are also quite less.

However, in dual phase full step operation the motor is in the state of excitation when two phases are energize.

While comparison dual phase full step motor gives about 30 to 40 percent more torque than that of single phase. But this simultaneously also increases the power requirements.

Half Step Operation

These is a type of stepper motor in which the phase of operation is basically half of the normal step size. Thus it is named as half step operation.

Therefore this type of model provides double the resolution and the output torque changes at every alternate step. These are applicable in cases where a wide range of speed and efficiency is require.

Permanent Magnet Stepper Motor

It has wound stator poles i.e. stator poles have focus winding and are of salient type. Whereas the rotor is cylindrical in shape and permanently magnetized this is the main difference between the permanent magnet stepper motor and VR stepper motor. Diametrically opposite poles are in series connection to form a two-phase winding on the stator. On the other hand, the rotor aligns themselves with the stator poles depending on the excitations.

Consider a motor with two rotor poles and 4 stator poles in such a way that the two stator poles are energize by one winding which are mark as A and B. Thus there step angle will be;

   

Thus from above, we can say that mostly the step angle of a two-phase permanent stepper motor has a step angle in the range of 45 to 90 degrees.

Hybrid Stepper motor

It combines the features of both VR stepper motor and Permanent magnet stepper motor. These types of motors can have desirable high torque, less power consumption, efficiency, high stepping speed and also small step lengths.

It basic working principle is the rotor consists of permanent magnet that is magnetize axially to create a pair of poles with marking N and S whereas the stator poles are electromagnetically energize.

DC Stepper Motor Characteristics

There are mainly two variations in the characteristics of the stepper motor;

1. Static characteristics
2. and Dynamic Characteristics

Static is when the motor is at stationary position and dynamic when its in motion.

Static characteristics

Torque Displacement character

This gives the relationship between the electromagnetic torque development and the displacement factor in the steady-state condition. The increase in the torque is sinusoidal to displacement

Q_m is the maximum angle

Q_s is the step angle

Torque current character

It gives the relationship between the holding torque and the excitation current.

Dynamic Character

It is also known as torque Vs speed character. The max slew rate increases as the load become lighter.

Conclusion

Here we are the end of the blog. I hope that you like the content and have a insightful information. If you do like the article then do share it with others and also let us know the part which you like the most. Besides if have any doubt regarding the topic then feel free to comment down below or to reach us.

Regards;

Have a nice day 🙂

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