Disc motor
A disc rotor motor ( English pancake motor, disc motor, motor printed ) is an electric motor whose rotor (rotor) has the shape of a disk. The current-carrying windings are, for example, in the form of a disk and have no cores , which means in this context without an iron core . Disc rotors are characterized by the fact that the magnetic field runs parallel to the axis of rotation. The diameter of the motors is larger than their length. However, disk-shaped motors are not always disk rotors such as the bell-shaped armature motor, for example .
Disc motors with ironless rotor
The windings are implemented on a thin insulating layer in the form of conductor tracks on a circuit board or consist of more solid copper or aluminum conductors in the form of wires or stamped parts. The disc runs in a narrow gap between electric or permanent magnets that generate the stator field. The magnetic circuit is closed by a soft magnetic material outside the disc. The electric current is supplied via brushes ; In the simplest case, these touch the disk directly on the axis and on the outer circumference. This structure corresponds to the principle of a DC machine .
Aluminum has the advantage of a lower specific weight compared to copper, but has poorer electrical conductivity . With the same electrical resistance, the aluminum conductor requires a larger volume, but is lighter than a copper conductor with the same resistance. This means that the disc can be built very easily and has a low moment of inertia . Disc motors can accelerate and decelerate particularly quickly. In addition, magnetic forces only act on the rotor when current is flowing through the disk, there is no cogging torque, so the rotor of the switched-off motor has no preferred positions. Disc motors run very smoothly even at low speeds. In many cases it is possible to dispense with a gear reduction because the ratio between torque and speed is high due to the relatively large diameter.
Another advantage of pancake motors is the high power density made possible by the thin construction of the windings on the pulley. As a result, the windings are well cooled by the large surface area and can be operated with high electrical current densities . However, the heat capacity of the disc is low, so there is a greater risk of destruction due to the rise in temperature in the event of brief overload than in the case of electric motors with rod armature, where the iron in the rotor can absorb heat energy.
An arrangement in which the coils are in the form of a cylinder instead of a disk is known as a bell-type rotor motor or a bell- shaped armature motor . Apart from the field orientation, there is no fundamental difference between the two.
Ironless bell and disc runners are mostly made from enameled wire. This has two insulation layers with different thermal behavior, so the winding can be pressed into shape and thermally stabilized ("baked") without any insulation damage. Another variant is the manufacture of the coils or the rotor as a printed circuit board .
Iron-less bell and disc rotors have a higher degree of efficiency under certain conditions (high speed, low load) due to the lack of an iron core and the resulting reduced iron losses compared to machines that use windings with an iron core.
Brushless disc motors
The term pancake motor is also used to refer to motors in which the disk is a permanent magnet and fixed coils on one side (or both sides) of the disk create a magnetic field; compared to the disk rotors with ironless rotors discussed above, the rotor and stator have been swapped. The advantage of this arrangement is that no brushes are required for supplying power to the rotor and the motor is thus more reliable. The disadvantage is the higher mass of the permanent magnet and thus lower acceleration. Brushless pancake motors are synchronous motors , or stepper motors , and represent a type of brushless DC motor with electronic commutation .
Applications
Disc motors were used for dynamic control tasks, e.g. B. developed in servomotors . Disc rotors are also made for electric bicycles and electric cars . Small brushless pancake motors can be found in many devices, e.g. B. in video recorders and floppy disk drives . Disc motors are available for outputs from a few W to over 10 kW.
Disc rotors can also be used as generators (disc rotors generator).
literature
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
- Gerd Fehmel, Horst Flachmann, Otto Mai: The master's examination in electrical machines. 12th edition, Vogel Buchverlag, Oldenburg and Würzburg, 2000, ISBN 3-8023-1795-5
- Gregor D. Häberle, Heinz O. Häberle: Transformers and electrical machines in power engineering systems . 2nd edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 1990, ISBN 3-8085-5002-3