A motor is an electrical device that converts electrical energy into mechanical energy.
Generally, motors output rotational motion by utilizing the force generated by the interaction between a magnetic field and an electric current – known as the Lorentz force.
A motor consists of a rotor, which has a rotating shaft, a stator, which rotates the rotor, a bearing, which supports the rotating shaft, and a cooling system, which cools the heat generated by the losses. The part of the rotor and stator that generates the magnetic field is called the field magnet, and the part that interacts with the field magnet and generates the magnetic field to obtain torque is called the armature.
Linear motors, as well as other variations of linear motors, are also available.
The following is an explanation of the most basic brushed DC motor mechanism.
First, a coil is placed in a magnetic field between the S and N poles. The current flowing through the coil generates a magnetic field in the coil, which repels one pole and attracts the other pole, causing the coil to rotate. By reversing the current flowing through the coil during rotation, the forces of repulsion and attraction are interchanged, and rotation is sustained.
There is an element called a commutator in the motor, and when the commutator hits the brushes, power is supplied from the brushes. The commutator rotates with the shaft, and the position where the commutator contacts the brush moves with the rotation. The direction of the electric current changes as the position of the commutator changes.
The basic structure of a simple DC motor consists of a coiled wire, brushes, and commutator fixed to the rotating shaft within the magnetic field of a magnet. The commutator is the part that switches the contact/non-contact between the power source and the coil. The brush is responsible for bringing the commutator into contact with the power supply. When a DC current is applied to the coil, the Lorentz force acts according to the direction of the current and the coil begins to rotate.
However, when the coil rotates 180 degrees and the left and right sides are reversed, rotation stops and a commutator is required. The commutator suspends contact between the coil and the power supply when the coil has rotated 90 degrees. In this state, the coil continues to rotate by inertia, and the next time the commutator contacts the power supply, the Lorentz force again acts in the direction of coil rotation.
Classification of Motors
Motors are classified by drive power supply into two types: DC (direct current) and AC (alternating current). In addition, motors are classified by structure and principle as follows:
1. DC Motors
DC motors are capable of high-speed rotation of 30,000~40,000 rpm and have high torque.
- Brushed Motors
Brushed motors are the most common type of motor. The current is switched by sequentially bringing the brushes, which are electrodes on the stator side, into contact with the commutator on the armature side, thereby causing the motor to rotate.
- Brushless Motor
Brushless motors do not use brushes and commutators. The current is switched electrically using a switching function with a transistor, etc. (Application example: CD player).
- Stepping Motor
A stepping motor operates using pulsed electric power and are also called a pulse motor. They are characterized by its ability to easily perform accurate positioning operations. (Application example: Printer)
2. AC Motor
Also called induction motors, AC motors are motors that rotate on an AC power source. A coil that generates a magnetic field around an aluminum disk is prepared, and an alternating current is used to rotate the aluminum disk. An inverter is used to control the speed of the AC motor, allowing smooth acceleration from low speeds and speed control at will.
- Induction Motor
AC generates a rotating magnetic field in the stator and an induced current in the rotor. Rotation is caused by this action.
- Synchronous Motor
Rotation occurs when the rotor with magnetic poles is attracted and followed by the rotating magnetic field created by the alternating current. The speed of rotation is synchronized with the power supply frequency.