Abstract:
Disclosed is a spherical wheel motor including: a spherical rotor having freedom of rotation along surrounding magnetized directions; a stator formed in a dome shape enclosing the rotor and configured to form magnetization at various angles through a plurality of coils distributed therein, and impart the freedom of rotation to the rotor; and a driving unit configured to identify a position of the rotor, supply current to each coil of the stator according to the position of the rotor, and drive the rotor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority from Korean Patent Application No. 10-2011-0116256, filed on Nov. 9, 2011, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a spherical wheel motor, and more particularly, to a spherical wheel motor including a bipolar spherical rotor and a stator having a radial coil structure. 
     BACKGROUND 
     As a device that relays electrical energy in the form of mechanical energy, a motor is used in many different forms in various machines, electric products, and electronic products. Because existing motors rotate about one axis and are restricted by that axis to rotating in only two directions, the motors are restricted in movement. Therefore, due to limits in how motors of the related art may be controlled in terms of rotating direction, applications of the motors were limited. 
     In order to solve this problem and realize greater freedom of movement for a motor, although a method of connecting multiple motors with one joint has been proposed, there is the drawback of requiring many links and a complicated converting device. To compensate for this drawback, a spherical motor having a 3-directional degree of freedom has been introduced, which is exemplified by the spherical motor disclosed in Korean registered patent 0954772 (registration date: Apr. 29, 2010). The spherical wheel motor having a freedom of rotational direction as disclosed in the above patent may be used for steering movement in automobiles and motorboats, for eye movement and arm, neck, and hip joint movement in robots. 
     Spherical wheel motors that can replace the wheels of transportation means such as automobiles needs to be capable of rotational movement without an axis, and require accurate positional control of the rotor and a simple structure. However, the rotors of related art spherical wheel motors are formed on the basis of a shaft, are structurally complicated due to the use of a plurality of permanent magnets, and are also limited in terms of freedom of rotation. 
     SUMMARY 
     The present disclosure has been made in an effort to provide a spherical wheel motor that is not limited in terms of rotating direction and has a comparatively simple shape. 
     The present disclosure has been made in an effort to also provide a spherical wheel motor in which the stator more easily controls the rotor, so as to facilitate the driving thereof. 
     An exemplary embodiment of the present disclosure provides a spherical wheel motor including: a spherical rotor having freedom of rotation along surrounding magnetized directions; a stator formed in a dome shape enclosing the rotor and configured to form magnetization at various angles through a plurality of coils distributed therein, and impart the freedom of rotation to the rotor; and a driving unit configured to identify a position of the rotor, supply current to each coil of the stator according to the position of the rotor, and drive the rotor. 
     According to the exemplary embodiment of the present disclosure, a spherical wheel motor is provided which is not limited in terms of the rotational direction thereof, so that the motor may be used for a wheel of transportation means such as an automobile, and may be applied as a propelling means for a motorboat and for the movement of a camera lens. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating the structure of a spherical wheel motor according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is a view illustrating the structure of a rotor according to an exemplary embodiment of the present disclosure. 
         FIG. 3A  and  FIG. 3B  is a view illustrating the structure of a stator according to an exemplary embodiment of the present disclosure. 
         FIG. 4  is a circuit diagram of a spherical wheel motor according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawing, which form a part hereof. The illustrative embodiments described in the detailed description, drawing, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
       FIG. 1  is a view illustrating the structure of a spherical wheel motor according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 1 , a spherical wheel motor according to the present disclosure includes a rotor cover  100 , a rotor  110 , a stator  120 , and a driving unit  130 . The spherical wheel motor may further include a gap or a bearing between the stator  120  and the rotor  110  so as to reduce friction. 
     The rotor  110  is formed in the shape of a sphere, and forms a magnetic field which is the starting point for the movement of the motor. To this end, the rotor  110  includes a permanent magnet, and the permanent magnet may be formed as a surface magnet or a buried magnet. The detailed structure of the rotor  110  according to the present disclosure will be described with reference to  FIG. 2 . 
     The stator  120  is formed in the shape of a dome to enclose the rotor  110 , and has a plurality of coils arranged radially about a central coil on the inner surface thereof to enclose the rotor  110 . Here, each coil forms a magnetic field that has a polarity opposite to that of a symmetrical coil with respect to the center of the rotor  110 . The detailed structure of the stator  120  according to the present disclosure will be described with reference to  FIG. 3A  and  FIG. 3B . 
     The driving unit  130  identifies the position of the rotor  110 , and drives the rotor  110  by supplying a current to each coil of the stator  120  according to the position of the rotor  110 . To this end, the driving unit  130  has a power device and a driving circuit mounted therein to drive the motor, and a detailed description thereof will be provided below with reference to  FIG. 4 . 
       FIG. 2  is a view illustrating the structure of a rotor according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 2 , the rotor  110  according to the present disclosure includes a permanent magnet  112  having one each of an N pole and an S pole. The permanent magnet  112 , as illustrated in the drawing, is inserted in the rotor  110  as a buried permanent magnet. Accordingly, the rotor  110  is rotated and directly actuated by receiving the force of a magnetic field formed by the coils of the stator  120  during the operation of the motor, and because the rotor  110  has a spherical shape, the rotating direction thereof may easily be changed. 
       FIG. 3A  and  FIG. 3B  is a view illustrating the structure of a stator according to another exemplary embodiment of the present disclosure. In particular,  FIG. 3A  is a side view illustrating the structure of the stator according to an exemplary embodiment of the present disclosure, and  FIG. 3B  is a plan view illustrating the structure of the stator according to an exemplary embodiment of the present disclosure. 
     The stator  120  according to the present disclosure includes a plurality of coils disposed radially with respect to a central coil disposed at the center of the top portion thereof. Accordingly, the precision in directional control of the stator  120  is determined by the number of coils formed diverging from the center of the top portion (θ=360°/2n, where θ is the angle between radial directions, and n is the number of radial directions), and the greater the number of radial directions, the angles may be more precisely controlled. However, as the number of radial directions increases, the number of coils (x=4n+1, where x is the number of coils, and n is the number of radial directions) increases, and the greater the number of coils, the number of power devices of the driving unit  130  also increases. 
     As illustrated in  FIG. 3A  and  FIG. 3B , a plurality of first coils (A 1 , A 2 , B 1 , B 2 , C 1 , and C 2 ) is disposed in three directions passing a central coil T disposed at the center of the top portion of the stator  120 , and when a circle is drawn centered around the top portion of the stator  120 , radial directions are set at 60 degree intervals (θ=360°/2n, where n is 3). A plurality of second coils (a 1 , a 2 , b 1 , b 2 , c 1 , and c 2 ) is disposed at 60 degree intervals from the aforementioned radial directions, respectively. By virtue of the dome structure of the stator  120 , the lowermost portion of the rotor  110  is excluded from coils. Therefore, the total number of coils (x=4n+1, where n is the number of radial directions) disposed in the stator  120  according to the present disclosure is 13. 
     With the exception of the central coil T, each of the coils is symmetrically formed with respect to the center of the spherical rotor  110 . Specifically, coil A 1  and coil a 1  are formed symmetrically to each other, and coil A 2  and coil a 2  are formed symmetrically to each other. Coil B 1  and coil b 1  are formed symmetrically to each other, and coil B 2  and coil b 2  are formed symmetrically to each other. Coil C 1  and coil c 1  are formed symmetrically to each other, and coil C 2  and coil c 2  are formed symmetrically to each other. 
     In order to drive the aforementioned plurality of coils (T, A 1 , A 2 , B 1 , B 2 , C 1 , C 2 , a 1 , a 2 , b 1 , b 2 , c 1 , and c 2 ), seven phases are required, where two coils per phase are serially connected, and each phase converges at an N node—that is, at the central coil T. Accordingly, when the motor is driven and current flows through the coils, while current that flows through two coils located in one phase is the same, because the two coils are symmetrical centered about the rotor  110 , the directions of current at positions in contact with the inner surface of the rotor  110  are different, and the two coils form opposed magnetic fields respectively centered about a circle, so that the stator  120  controls both poles of the rotor  110 . By virtue of this structure, the stator  120  according to the present disclosure may simultaneously control both poles of the rotor  110  when current is applied to the coils. 
     The spherical wheel motor according to the present disclosure may further include a position sensing unit for sensing the position of the rotor  110 . As an embodiment of a position sensing unit, a Hall sensor (not illustrated) may be installed in the stator  120  to sense magnetic force. If a Hall sensor (not illustrated) as a position sensing unit is to be applied, one Hall sensor is attached for each phase. Therefore, the Hall sensor (not illustrated) senses the magnetic force generated from the permanent magnet  112  of the rotor  110  and generates a signal corresponding to an N pole and an S pole. 
       FIG. 4  is a circuit diagram of a spherical wheel motor according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 4 , the driving unit  130  according to the present disclosure includes a position sensing unit  132 , a motor control unit  134 , and a power device driving unit  136 . 
     As a preprocessing unit for a driving signal, the position sensing unit  132  identifies the position of the rotor  110  and outputs a position signal. Here, the position sensing unit  132  receives a signal according to a magnetic field of the rotor  110  from a Hall sensor attached within the stator  120  to identify the position of the rotor  110 , or senses an output current signal and a voltage signal for each phase and calculates a counter-electromotive force so as to identify the position of the rotor  110 . The position sensing unit  132  in an exemplary embodiment of the present disclosure uses a Hall sensor to identify the position of the rotor  110 . 
     The motor control unit  134  is a component that performs the important function of driving the motor by outputting a driving signal according to the position signal received from the position sensing unit  132 , and may include a micro controller unit (MCU), a field-programmable gate array (FPGA), and an A/D mixed circuit module. That is, the motor control unit  134  receives a position signal for the rotor  110  from the position sensing unit  132 , and outputs a driving signal to the power device driving unit  136 . The driving algorithm of the motor control unit  134  may use a trapezoidal, sinusoidal, and vector method employed in an existing brushless DC (BLDC)/brushless AC (BLAC) motor. 
     The power device driving unit  136  performs a switching function for supplying current to each coil disposed in the stator  120  according to the driving signal received from the motor control unit  134 . Connected as a bundle including a power device and a coil, the power device driving unit  136  thus supplies current to a coil to generate magnetic force by means of the coil and drive the rotor  110 . 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.