1. Definition of a Commutator A commutator, also known as a rectifier, is a critical component on the armature of DC motors, DC generators, and AC rectifier motors. It plays a role in reversing the direction of current flow when the motor is rotating, enabling the motor to continue rotating continuously. A commutator consists of a set of copper plates fixed around the circumference of the rotating machine or rotor, and a set of spring brushes fixed to the machine's stationary frame. Two or more stationary brushes are connected to the external circuit, serving either as the motor's current source or as the generator's load.

II. Working Principle of the Commutator The commutator consists of a set of contact bars fixed to the motor's rotating shaft and connected to the armature windings. As the shaft rotates, the commutator reverses the current in the windings. For a single armature winding, when the shaft completes half a revolution, the winding is now connected so that current flows through it in the opposite direction to the initial direction. In an electric motor, the armature current generates a rotational force or torque on the fixed magnetic field, causing the windings to rotate. In a generator, the mechanical torque applied to the shaft maintains the movement of the armature windings through the fixed magnetic field, thereby inducing a current in the windings. In both electric motor and generator applications, the commutator periodically reverses the direction of current flowing through the windings, ensuring that the current in the motor's external circuit continues to flow in only one direction. That is, when current flows through the coil, it rotates under the influence of the permanent magnet through attractive and repulsive forces. When it rotates to a position balanced with the magnet, the original current-carrying coil corresponding to the commutator contact plate separates from the brush, while the brush connects to the contact plate corresponding to the coil group that generates the driving force. This process repeats continuously, causing the DC motor to rotate.

III. Commutator Classification

1. By winding configuration: a. Groove-type commutator; b. Slot-type commutator.  

2. By mechanical strength: a. Standard-type commutator; b. Reinforced-type commutator.  

3. By inner bore structure: a. Commutator with bushings; b. Commutator without bushings.  

4. By copper bar material: a. Pure copper; b. Cadmium-cobalt copper; c. Silver-copper.

4. Function of the commutator The commutator consists of multiple copper plates (commutator segments) arranged in a cylindrical or disc-shaped structure. The copper plates are insulated from each other by mica or other insulating materials. Each copper plate is connected to an armature winding element. When the motor's armature rotates, the copper plates sequentially come into contact with the stationary carbon brushes. In a DC generator, the commutator and brushes convert the alternating current (AC) in the armature windings into direct current (DC) between the brushes. When the commutator segments connected to both ends of each armature winding element pass through the carbon brushes, the process of changing the direction or magnitude of the current is called commutation. During commutation, if the carbon brushes make poor contact with the commutator surface, sparks may appear on the contact surfaces between the carbon brushes and commutator segments, or even cause ringing, leading to winding damage. In AC commutator motors, the commutator's function is to ensure that the frequency of the alternating current between the brushes meets operational requirements.

5. Application Scope of Commutators Commutators are applied in electric tools, home appliances, automotive, and motorcycle motors, as well as in automotive generators and gasoline generators. They are primarily used in DC machines, DC generators, various DC motors, and general-purpose motors. In motors, the commutator applies current to the windings. By reversing the direction of the current in the rotating windings every half-turn, a stable rotational force (torque) is generated. In generators, the commutator collects the current generated in the windings, reverses the current direction every half-turn, and acts as a mechanical rectifier, converting the alternating current (AC) from the windings into direct current (DC) for the external load circuit.
Commutators have relatively low efficiency and require regular maintenance, such as replacing brushes. Therefore, the use of commutator motors is decreasing, being replaced by AC motors and, in recent years, brushless DC motors using semiconductor switches.  

6. Commutator Faults  

1. When power is applied, the indicator light does not illuminate.  

Method: Inspect the machine and replace components.

2. Gas pressure cannot be adjusted in advance.  

Method: Check the wiring for correctness and replace if necessary.  

3. The main switch fuse is broken.  

Method: Inspect and replace as needed.