The commutator is an important part of the dc motor and AC commutator armature. The commutator applies power to the optimal position on the rotor and produces a stable rotational force (torque) by reversing the direction of current in the armature moving coil of the motor. In a motor, a device that converts the square wave signal measured by the measuring electrode into pulsating direct current by reversing the direction of current in the rotating winding every half turn by applying a current commutator to the winding.
A commutator is an arrangement of insulation and copper strips connected to a coil of a motor to provide a reverse current to the coil of the motor. Commutation is the reversal of the direction of current. According to the commutator of different styles and various internal lock design is divided into integral commutator and plane commutator, integral commutator for cylindrical, copper strip parallel to the hole, it is characterized by simple structure, high manufacturing efficiency. Integral commutators are available in three basic styles: copper and mica, cloud mother mold and molded housing. The planar commutator looks like a fan with a copper strip with a fan section perpendicular to the hole.
Three types of molded commutators
With the use of plastic inner hole and rotating shaft, the structure is simple, but the size of the plastic inner hole is not easy to grasp, must strictly control the size of the pressure die and plastic shrinkage rate, in order to ensure the tolerance of the shaft hole, should try to avoid good pressure on plastic processing, plastic machining performance is generally poor.
The copper sleeve is pressed together with the plastic, and the size of the shaft hole is easy to meet the requirements. In order to prevent the movement between the plastic and the sleeve, the outer circular surface of the sleeve is often furrowed or knurled. The sleeve material can be copper, steel or aluminum alloy. But it must be noted that the hardness of the material must match the hardness of the rotor shaft, slightly lower than the hardness of the rotor shaft.
The strengthening ring is added to the u-shaped groove of the commutator piece. It is commonly used to bear the centrifugal force of the electric field when the diameter of the commutator is subdivided and the height is increased. The insulation between the ring and the commutator piece must be ensured. With stiffening rings, the diameter of the commutator can be made up to 500.
In fact, it is also a molded commutator, and the copper surface in contact with the brush is a ring plane, in fact, called the plane commutator, this commutator has a special structure, is on the copper sheet and a layer of graphite, its role is to replace the friction of the commutator and carbon brush, prolong the life of the commutator.
Three kinds of commutator processing
Direct assembly of the commutator, the size of the commutator is small, generally insert the lower part of the commutator copper sheet into the commutator body, and then use a copper ring to press the copper sheet on the external circular surface of the commutator, because the geometric size of the component is very small, mechanical processing is difficult, the accuracy of the commutator is generally low.
The copper plate of the commutator has a hook at the top and two straight convex roots are inserted into the commutator body respectively, so that the copper plate is closely attached to the outer circular surface of the commutator, and then the copper plate is fixed with the lower two inverted buckles. This commutator in turning feed quantity is too large to produce defective flying copper sheet, in turning must control the feed quantity in a certain range. If necessary, several more lathe procedures can be used to obtain the desired results.
Mechanical connection commutator, this is a split commutator, after the assembly of five components, commonly known as "five in one", the top of the copper plate has an indented ring buckle, buckle on the convex commutator body, the lower part of the invert buckle into the commutator support body, there is a connection commutator body and support body. After peeling off the paint leather wire, the copper piece of the commutator is connected with the paint leather wire. This commutator will also produce defective flying copper pieces if the cutting quantity is too large when turning.
The commutator plate is connected to the coils of the armature. The number of coils depends on the speed and voltage of the motor. The copper brush is better suited for very low voltage and high current, while the high resistance of the carbon brush causes a larger voltage drop. Copper's high conductivity means components can be made smaller and kept closer together. Using a cast copper commutator can improve its efficiency, current will flow easily in copper, and the motor is usually 85 to 95 percent efficient in transferring energy to its load. Electronic commutation uses solid-state electronics instead of mechanical commutators and corresponding brushes, and the removal of brushes means less friction or wear on the system and more efficiency. These types of motors tend to be more costly and complex than simple brush systems because of the need for controllers and electronics.