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Innovative and Advanced Motor Design
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Another alternative design is shown in Figure 15.13, where the toroidal coil assembly acts as the rotor that is coupled with slip ring-brush assemblies, and the magnet assembly (including fine magnetic cylinders and four magnetic discs, firmly connected in a specific pattern and predefined magnetic pole arrangement) acts as the stator. Brushes are used to impart or collect electric current. This design greatly intensifies the magnetic field (i.e., magnetic flux density B or magnetic field strength H, where the two physical parameters are closely related to each other as B = μ0H). Although only one rotor and one stator are presented in the figure, any number of rotor or stator may be adopted depending on the application requirements.
DC Motors and Generators
Published in Muhammad H. Rashid, Ahmad Hemami, Electricity and Electronics for Renewable Energy Technology, 2017
A commutator is illustrated in Figure 7.13. It consists of a number of copper segments that are arranged around the periphery of a cylinder. Each opposite pair of these segments is connected to the two ends of one of the loops of the armature, and, therefore, a commutator has twice as many segments as the number of bundle loops in the armature. The concept of a commutator can be more clearly understood from Figure 7.14, which shows only two loops and four commutation segments. Copper segments in a commutator are connected to the power supply through brushes that can slide on the commutator when it rotates. Thus, the brushes are stationary and do not rotate. Brushes are made of carbon (or a similar manufactured electric conductive material, containing carbon) and are spring loaded (sufficiently pressed on the commutator by some springs) to have a good contact. Otherwise, they spark in operation. Normally, a brush can cover a few of the commutator segments. Therefore, more than one loop is connected to electricity at a time. These are the loops with maximum force and giving maximum torque to a motor shaft (see Figure 7.15). After a few degrees of rotation each loop disengages and another loop substitutes for it. Thus, during one revolution a motor always benefits from engaging the part of winding that gives the highest torque, while the rest of the loops carry no current.
Spindle Motor Control
Published in Abdullah Al Mamun, GuoXiao Guo, Chao Bi, Hard Disk Drive, 2017
Abdullah Al Mamun, GuoXiao Guo, Chao Bi
It is obvious from Figure 4.19 that, if there is no change in the current of the coil, the average torque of the coil over 360° is zero. That means the coil cannot sustain continuous rotation if the current is not changed in the coil. To make the coil rotate continuously, the direction of the current must be changed, or commutated, according to the position of the coil such that the average torque becomes positive in the direction of coil rotation. The commutation can be realized by the mechanical means, that is, using a commutator and brushes to change the current at the right positions as shown in Figure 4.20. The brush is made of conductive materials such as graphite. The commutation process for different rotor positions is illustrated in Figure 4.21.
Effect of Expanded Graphite on the Tribological Behavior of Tin–Bronze Fiber Brushes Sliding against Brass
Published in Tribology Transactions, 2020
Bo Luo, Chengshan Liu, Xinli Liu, Lei Zhang
Metal fiber brushes, composed of thousands of arranged fibers with a micrometer-scale diameter, slide end-on upon the surface of a commutator to transfer electricity or electrical signals between two surfaces in relative motion (Elger (1)). The fibers are assembled with a low packing fraction, typically below 20 vol%, to offer sufficient space for fibers to bend freely. Thus, a great number of fiber tips remain in contact with the rotor surface during sliding, and each fiber shares an extremely small part of the normal load and electrical current (Zhou, et al. (2); Bhushan (3)). As a result, metal fiber brushes possess the following characteristics: high current-carrying capacity, low electrical noise, long service life, high sliding speed, good contact reliability, etc. (Slade (4)), which can be applied to substitute for carbon brushes or metal–graphite composite brushes.