The Basics of a Stepper Motor

Introduction

A stepper motor is a simple electromechanical device that generates mechanical power from electrical power. It is also a synchronous, brushless electric motor that divides one full rotation into a number of expansive steps. One can easily control the motor’s position accurately, without the need for a feedback mechanism. This can occur only if the motor is sized accurately to the machine. These motors are from the same family of switched reluctance motors.

The theory of operation behind the motor is the use of magnets that can turn the motor shaft to a precise distance under the provision of a pulse of electricity. The rotor is installed with six poles while the stator is equipped with eight poles. The rotor requires a total of 24 pulsations of electricity in order to move 24 steps that account for one complete revolution. In other words, with each pulse of current the motor receives, it moves precisely 15°. There are three different types of motors that are described as follows.

Different types of a stepper motor

  1. Hybrid synchronous stepper
  2. Permanent synchronous stepper
  3. Variable synchronous stepper

Each of these types is briefly described and their characteristics are presented-

  1. Hybrid synchronous stepper: These motors are given the name Hybrid synchronous motors since they make use of a combination of variable reluctance (VR) and permanent magnet (PM) procedures to acquire small packages of maximum power.
  1. Permanent magnet stepper: These magnet motors make use of a permanent magnet in their rotors. Their operation is based on attraction and repulsion caused between the stator electromagnets and rotor permanent magnets.
  1. Variable reluctance stepper: The variable reluctance motors contain a plain iron rotor. The concept of minimum reluctance occurring with a minimum gap is their principle of operation. For this reason, the rotor points are attached to the magnet poles.

There are a lot of advantages of a stepper motor some of which are listed as follows.

Advantages of using a stepping motor

  • The main advantage of a stepper motor is that its rotation angle is proportional to the input pulse.
  • At standstill position, the motor contains full torque.
  • Repeatability of movement and precise positioning since good motors often have an accuracy around 3-5% of a single step and this error is step is non-cumulative from one cyclic step to another one.
  • Stepper motors contain an exceptional response to reversing, starting and stopping.
  • They are extremely reliable since they do not contain any brushes in contact with the motor. Hence, the life of the stepper motors is solely dependent on the bearing.
  • The stepper motor’s response towards a digital input pulse consists of an open-loop control that makes the motor structure less complicated and easy to control.
  • By maintaining a load directly coupled to the shaft, we can achieve a very low-speed synchronous rotation.
  • One can realize a variety of rotational speeds since the speed is directly proportional to the input pulses’ frequency.



Source by Shalini M

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