Principle and structure of commutator

Update:23 Feb 2021

The commutator is a component of a DC permanent magnet series motor and a single-phase series motor in order to allow the motor to continue to rotate. See the following figure. When the coil passes the current, it is rotated by the attraction and repulsive force under the action of the magnetic field. When it is turned to balance with the magnet, the original coil that is connected to the commutator is separated from the brush, and the brush is separated. Connected to the contact pads corresponding to the set of coils that generate the driving force, so that the DC motor is turned up and down.

If there is no function of the commutator, the motor can only be stuck in less than half a turn and it can not achieve continuous operation.

Structurally, the commutator is a plurality of shaped contact pieces enclosing a circular ring, respectively connected to each of the contacts on the rotor winding element, and the outer side is in contact with the two brushes.

Most of the commutator uses a semi-plastic commutator consisting of a plastic housing, a copper commutator, mica interplate insulation and a metal bushing, as shown below. Because the insulation between the sheets is still mica, not all plastic, it is called semi-plastic commutator. A small commutator can have no metal bushings.

Most of the commutator segments are made of electrolytic copper. The computator with higher requirements on wear resistance and surface softening temperature can be silver copper or cadmium copper.

The side of the commutator piece is trapezoidal, so it must be formed by trapezoidal copper bar. The trapezoidal copper bar is mostly drawn from the bar material. By cold drawing, the size of the trapezoidal row is ensured, and the electrolytic copper is improved. hardness. The commutator segments shown in the figure below have a downwardly elongated dovetail structure to prevent the commutator from being pulled out by centrifugal force during high speed operation. In recent years, in order to save copper material, the dovetail portion of the commutator piece is omitted, the side of the commutator piece is concave and embossed, and the hook shape is formed at the upper portion. This structure has been used abroad. Many, can also withstand the role of the centrifugal force of the commutator at high speed. Since the structure of the connection between the commutator piece and the coil wire head is different, it can be divided into a groove type commutator and a hook type commutator. In the rising part of the commutator segment, the coil head is embedded in the groove, and then spot welding (hot press welding), the paint film of the enameled wire is melted and dissipated at the high temperature during spot welding, so that the wire end and the wire end and The wall of the commutator segment forms a good electrical connection.

When the hook-shaped commutator winds the rotor coil, the coil head is wound around the hook of the commutator piece, the coil is wound, the respective wire ends are wound around the corresponding commutator hooks, and then the hooks are pressed during spot welding. The wire head and the commutator form a good electrical connection, and the hook-shaped commutator is used to easily automate the process of connecting the coil wire head and the commutator, but at present, it is mostly used in the case of a small number of commutating segments and a small motor power, mainly considering large The wire diameter of the power motor coil is thick and difficult to entangle. When the number of commutator segments is large, the width of the hook is narrow, and the adjacent wire ends are easy to be short-circuited, so they are mostly used on small power motors.

The shell of the commutator is made of glass fiber reinforced thermosetting plastic or bakelite powder, which has high requirements on the heat resistance and mechanical strength of the plastic, and requires the thermal expansion system to be as close as possible to the commutator copper. The role of the metal bushing is to prevent the plastic from mechanical stress when the commutator is pressed onto the shaft.

Mica board or powder mica board is used for inter-chip insulation. Since mica wear resistance is stronger than copper, it is necessary to pull the groove so that the mica board between the sheets is lower than the commutator piece, and the wear-resistant mica board is prevented from protruding. The film affects the contact between the brush and the commutator, causing the commutation to deteriorate and the motor not to operate.

Contact us