Single Phase motors include brushed motors, voice coil motors, electro-magnets, magnetic bearings, and pure inductive loads. Brushed motors are the most common single phase motor. For the purposes of this article we will be discussing permanent magnet brushed DC servo motors.
Construction
The brushed DC motor is the simplest and most common type of motor. This motor has a stationary set of permanent magnets on the stator and an armature, or rotor, with insulated wire coiled around an iron core. The wires connect directly to a mechanical commutator, eliminating the need for both external commutation and feedback. How are the coils powered if they are attached to a moving rotor? Since the coils are constantly in motion power needs to be supplied to them externally, this is where brushes come in. Brushes bridge the gap between the external DC source and the rotor. Brushes are usually made of graphite or carbon. The brushes make contact with the rotating commutator to direct current into the correct coils at the correct time. Just like the brushless DC servo motor, rotation of the brushed DC servo motor is achieved by individually altering the magnitude and direction of current into each set of coils. As current flows through the commutator and armature windings the electromagnetic field that is produced either repels or attracts the stator’s permanent magnets, creating torque that drives the motor.
Brushed DC servo motors are favored for their high-power capabilities and ease of use. However, because of the constant mechanical friction between the brushes and commutator these motors require periodic maintenance. The carbon brushes can be easily replaced but over time the commutator is also likely to wear down to the point that the whole motor must be replaced.
Advantages
- Brushed servo motors tend to have a low initial cost
- They are easy to set up, and control of motor speed is simple and reliable
- Mature technology that has had lots of time to be refined and optimized
- Favored for simple applications that don’t require high precision
Disadvantages
- Entire motor must be replaced once commutators ware down
- Brushes need to be replaced and produce dust that needs to be routinely cleaned
- Poor heat dissipation
History
The brushed DC motor played a pivotal roll in the industrial revolution of the late 1800’s. The DC motor was the first electric motor, made possible by William Sturgeon’s invention of the electromagnet. Sturgeon’s DC motor was further developed by Thomas Davenport to add brushes and commutators, creating the first working brushed DC motor. Thomas Edison promoted the use of DC motors and popularized their use for industrial applications. With the brushed DC motor being the first electric motor with any significant power, many machines came to be powered by electric motors rather than steam or hydraulic pressure. The industrial process was forever changed. Equipment was able to be smaller and much safer, more jobs were created, and new processes were enabled that created new products and markets.
ADVANCED Motion Control's Capabilities
- All off-the-shelf servo drives from ADVANCED Motion Controls can operate with single phase motors
