The working principle of a DC motor is based on the interaction of the rotating armature magnetic field and the fixed stator magnetic field. When the positive pole of the armature is attracted to the negative pole of the stator (and vice versa), a force is generated on the armature to make it rotate. Commutation is the process of converting the magnetic field in the armature winding to produce a constant torque in one direction, and the commutator is a device connected to the armature, which can achieve the conversion of current. The lever arm that generates torque on the armature changes with the angle of the coil (cosα). When the coil is perpendicular to the stator magnetic field, no torque is generated. This is why DC motors have multiple coils. Therefore, even if a coil is perpendicular to the magnetic field, the armature mechanism will continue to be stressed.
The commutator opens and closes the coil to control which direction the electromagnetic field points
The basic purpose of commutation is to ensure that the torque acting on the armature is always in the same direction. The electromotive force generated in the armature is essentially AC, and the commutator converts it to DC. In short, the commutator opens and closes. Coils to control which direction the electromagnetic field points. On one side of the coil, the current should always “flow away”, and on the other side, the current should always “into” flow, which ensures that the torque is always generated in the same direction, otherwise the coil will rotate 180 degrees in one direction, Then switch directions.
The commutator itself is a split ring made of copper
The commutator itself is a split ring, and generally, each end of the ring is connected to each end of the armature coil. If the armature has multiple coils, the commutator will also have multiple segments, one for each end of each coil. Carbon brushes are installed on each side of the commutator, and when the commutator rotates, The contactor supplies voltage to the commutator section and the corresponding armature coil.
When the carbon brush passes through the gap of the commutator, the provided charge will switch the commutator segment, thereby switching the polarity of the armature coil. This conversion of the coil polarity keeps the armature rotating in one direction. The voltage between the brushes fluctuates between zero and maximum, but always maintains the same polarity.
Combination of commutator and carbon brush
The term "brushes" was coined in the early days of DC motors when they consisted of multiple strands of copper wire. These devices need to be replaced frequently and damage the commutator ring. Modern DC motors often use "brushes" made of carbon. These brushes wear more slowly and cause less damage to the commutator.
The above is a conventional brushed DC motor. These motors are commutated mechanically. Brushless DC motors also need to be commutated. However, for brushless designs, commutation is performed electronically through encoders or Hall-effect sensors. The sensor senses the position of the rotor to determine when and how to energize the coil.