An example of the conventional flat brushless motor of the above described type will be discussed.
FIG. 4 illustrates the conventional flat brushless motor of rotary back-yoke type. Reference numeral 1 represents a flat annular magnet magnetized in a circumferential direction so as to have alternating N- and S-poles; reference numeral 2 represents a rotor frame made of a magnetizable body; reference numeral 3 represents a bracket made of a magnetizable body; reference numeral 3a represents a carrier made of insulating material for holding coils; reference numeral 4 represents a plurality of flat coils fixed to the carrier 3a in face-to-face relationship with the magnet 1; reference numeral 5 represents a back-yoke for enclosing a magnetic circuit of main magnetic fluxes produced by the magnet 1; and reference numeral 6 represents a weight formed into a generally rectangular shape for causing the motor to generate unbalanced vibrations. Reference numeral 7 represents a shaft of the motor; reference numeral 8 represents a metal bearing; and reference numeral 9 represents a rotor boss rigidly mounted on the shaft 7 and to which the rotor frame 2 and the back-yoke 5 are secured.
FIG. 5 illustrates the shape of the weight 6.
FIG. 6 is a perspective view of the conventional flat brushless motor of rotary back-yoke type.
With respect to the conventional flat brushless motor of rotary back-yoke type constructed as hereinabove described, the operation thereof will be described hereinafter.
Assuming that magnetic fluxes are generated from the magnet 1, the magnetic flux developing towards the bracket 3 is shielded by the rotor frame 2 and the bracket 3. Because of this, the main magnetic flux develops in a direction towards the coil 4. If an electric current is allowed to flow across the coils 4 under this condition, a magnetic field is developed by the current and a rotating force is produced by the relationship with the magnetic flux of the magnet 1. Also, a magnetic circuit is formed by the magnetic flux towards the back-yoke 5 to thereby increase the efficiency. The weight 6 is fixed to the shaft 7 with its center of gravity displaced from the shaft so that the weight 6 is in an unbalanced relationship with the shaft 7 to allow the motor to produce an unbalanced rotation when the weight 6 is driven to produce vibrations.
However, in the conventional construction, since a portion corresponding to the weight 6 increases the thickness of the motor, there are some problems in that flattening of the motor, is hampered and the number of manufacturing steps as well as the number of component parts is increased. Accordingly, the present invention has for its object to provide a flat brushless motor of a thin type capable of generating vibrations. Also, the present invention has for its object to provide a flat brushless motor capable of, reducing the number of component parts and the number of manufacturing steps.