The structure and principle of DC motor
1. Basic structure of DC motor
1) Stator
The main function of the stator is to generate a magnetic field and serve as a mechanical support for the motor. It is composed of main magnetic poles, reversing magnetic poles, machine bases, end covers, and brush devices.
(1) Main pole
The main magnetic pole is used to generate the main magnetic field. Most of the main magnetic poles of DC motors do not use permanent magnets, but the field winding is fed with DC current to establish the magnetic field. The main magnetic pole is composed of an iron core and winding.
The rivet is riveted, and the enlarged part close to the air gap is called the pole shoe. The pole shoe supports the excitation winding so that the air gap magnetic flux has a better wave distribution. The excitation winding is wound with insulated copper wire and is insulated The lacquer is impregnated and then set on the pole core. The main magnetic poles N and S are alternately arranged, evenly distributed, and fixed on the inner ring of the machine base with screws.
(2) Commutation pole
The commutation pole is used to improve the commutation of the DC motor, also known as the additional pole, which is composed of an iron core and a commutation pole winding on the iron core. The commutation pole winding is connected in series with the armature winding, the number of poles of the commutation pole is generally the same as that of the main magnetic pole or halved, and the air gap between the commutation pole and the armature can be adjusted. In DC motors with very small power, commutation poles may not be installed.
(3) Base
The frame is both the shell of the motor and a part of the magnetic circuit of the motor. It is generally cast with low carbon steel or welded with steel plates. There are end covers at both ends of the frame. The front and rear end covers of small and medium-sized motors are equipped with bearings to support the rotating shaft. Large motors use seat type sliding bearings.
(4) Brush device
The function of the brush device is to connect the armature winding of the rotating part with the external circuit, and lead the electromotive force and current of the armature winding to the load or power supply of the external circuit. The brush device is composed of brushes, brush sockets, brush rod holders and bus bars. The brushes are generally made of graphite and copper powder pressed and roasted. The brushes are placed in the brush holder and pressed against the commutator by a spring. On the surface, the number of brush rods is generally equal to the number of main poles.
2) rotor
The rotor of a DC motor, also known as an armature, consists of iron cores, windings, commutators, and cooling fans.
(1) iron core
The armature core is used to form the magnetic circuit of the motor and to embed the armature winding. In order to reduce core loss, it is usually stacked with 0.35mm or 0.5mm thick silicon steel sheets coated with insulating paint. In order to enhance cooling, there are axial ventilation holes on the armature core of the small-capacity motor, and radial ventilation grooves on the large-capacity motor.
(2) winding
The role of the armature winding is to generate induced electromotive force and electromagnetic torque, thereby converting electrical energy into mechanical energy. The armature winding is made of insulated copper wire, and then embedded in the slot of the armature core. The lead wire ends of the winding are connected with the commutator segments according to certain rules, and the slots of the winding are pressed tightly with insulating slot wedges. tied with a glass ribbon.
(3) commutator
The commutator is the key component of the DC motor, which converts the AC electromotive force inside the armature winding into the DC electromotive force between the brushes. The commutation segments are made of hard electrolytic copper, and the pads between the commutation segments are insulated with 0.4~1.0mm thick mica. Mica insulation, the end of each piece of commutator has a protruding riser piece, which is used to connect with the winding lead end.
2. The basic principle of DC motor
The DC motor works according to the principle that the current-carrying conductor will be affected by the electromagnetic force in the magnetic field. The stator winding is fed with a DC excitation current to generate an excitation magnetic field; the main circuit introduces a DC power supply, which is transmitted to the commutator through the brush, and then the DC power is converted into an alternating current through the commutator and passed into the armature winding to generate an armature magnetic field , the armature magnetic field and the excitation magnetic field synthesize the air-gap magnetic field, and the armature winding cuts the synthesized air-gap magnetic field to generate electromagnetic torque to drive the rotor to rotate. This is the basic principle of a DC motor.
