Abstract:
A direct current (DC) motor including: a cylindrical frame, at least one end of which is open; a cylindrical end cover including an opening configured to block the at least one open end; a rotor including a rotor shaft supported by the frame and the end cover, and a rotor core installed on the rotor shaft; a commutator installed on the rotor shaft and arranged on one end of the rotor core; a cover unit installed on the rotor shaft, arranged between the rotor and the commutator, and including at least one location detection device; and a rotation detection unit installed in the end cover and configured to detect the at least one location detection device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2014-0047602, filed on Apr. 21, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present disclosure relate to a direct current (DC) motor, and more particularly, to a DC motor including a rotation detection unit. 
         [0004]    2. Description of the Related Art 
         [0005]    When a current is applied to a direct current (DC) motor, the resulting electromagnetic force generated by a magnetic circuit included in the DC motor causes a rotor to rotate. Terminals that contact brushes change in accordance with the rotation of the rotor, and the rotor continuously rotates because the current flowing in a rotor coil periodically changes direction. The rotation velocity of the rotor is proportional to the current flowing in the rotor coil. However, the rotation velocity may also change according to a rotation load. It is therefore difficult to control the velocity or position of the rotor accurately by using only the DC motor. In particular, in the case of a DC motor being applied to an autofocus (AF) lens or a zoom lens of a compact camera that requires accurate control, a rotation detection sensor unit for detecting the amount of rotation of the rotor shaft is necessary. 
         [0006]    Thus, a rotation velocity, amount of rotation, or angle of rotation of the DC motor may be detected by using a rotation detection unit, and based on the detected rotation velocity, amount of rotation, or angle of rotation of the DC motor, a location or velocity of a lens may be controlled. An optical encoder using a photo-interrupter (PI) type sensor or a photo-reflector (PR) type sensor, or a magnetic encoder using a Hall sensor or a magnetoresistive (MR) sensor may be generally used to determine a rotation velocity, amount of rotation, or angle of rotation of the DC motor. 
         [0007]    A torque generated by the motor may be transmitted to an object via a gear unit installed on an external surface of a main body of the motor, but a rotation detection unit for detecting a rotation amount of a rotor shaft may be necessary to control a rotation amount or velocity of the motor. When the rotation detection unit is installed in the gear unit, space in a lengthwise direction of the motor is required. However, this space may be hinder miniaturization of a product to which the DC motor is applied. 
       SUMMARY 
       [0008]    One or more embodiments include a miniaturized direct current (DC) motor including a rotation detection unit. 
         [0009]    Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
         [0010]    According to various embodiments, a DC motor includes: a cylindrical frame, at least one end of which is open; a cylindrical end cover including an opening configured to block the at least one open end; a rotor including a rotor shaft supported by the frame and the end cover, and a rotor core installed on the rotor shaft; a commutator installed on the rotor shaft and arranged on one end of the rotor core; a cover unit installed on the rotor shaft, arranged between the rotor and the commutator, and including at least one location detection device; and a rotation detection unit installed in the end cover and configured to detect the at least one location detection device. 
         [0011]    The DC motor may include a pair of brushes supported by the end cover, contacting the commutator, and spaced apart from each other along a circumferential direction of the rotor shaft. The rotation detection unit may be arranged between the pair of brushes along the circumferential direction of the rotor shaft. 
         [0012]    The DC motor may include: a commutator installed on the rotor shaft and arranged on one end of the rotor core; and a pair of brushes supported by the end cover, contacting the commutator, and spaced apart from each other along a circumferential direction of the rotor shaft. The rotation detection unit may be arranged between an external wall of the end cover and any one of the pair of brushes, along a diameter direction of the rotor shaft. 
         [0013]    The at least one location detection device may be arranged along a side portion of the cover unit, and the rotation detection unit may be inserted into an external wall of the end cover along a diameter direction of the rotor shaft. 
         [0014]    The DC motor may further include additional rotation detection units. 
         [0015]    The at least one location detection device may include one or more reflectors arranged at regular intervals along a circumferential direction of the cover unit, and the rotation detection unit may include a light source and a light reception unit. 
         [0016]    The at least one location detection device may include one or more slits arranged at regular intervals along a circumferential direction of the cover unit, and the rotation detection unit may include a light source and a light reception unit. 
         [0017]    The at least one location detection device may include permanent magnets that have an N pole and an S pole and are alternately arranged along a circumferential direction of the cover unit, and the rotation detection unit may include a magnetic flux sensor. 
         [0018]    The at least one location detection device may include permanent magnets that have an N pole and an S pole and are alternately arranged along a circumferential direction of the cover unit, and the rotation detection unit may include coils that are arranged along a circumferential direction of the rotor shaft. 
         [0019]    The DC motor may further include a flexible printed circuit board (FPCB) facing the cover unit and arranged on the end cover. The at least one location detection device may include one or more protrusions formed of conductors and arranged on a surface of the cover unit along a circumferential direction of the cover unit, and the rotation detection unit may include one or more metal members that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate a capacitance together with the one or more protrusions. 
         [0020]    The at least one location detection device may include one or more protrusions formed of conductors and arranged on a surface of the cover unit along a circumferential direction of the cover unit, and the rotation detection unit may include one or more coils that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate an inductance together with the one or more protrusions. 
         [0021]    The at least one location detection device may include materials having different permittivities and alternately arranged along a circumferential direction of the cover unit, and the rotation detection unit may include one or more metal members that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate a capacitance together with the materials having different permittivities. 
         [0022]    The at least one location detection device may include metallic and non-metallic materials alternately arranged along a circumferential direction of the cover unit, and the rotation detection unit may include one or more coils that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate an inductance together with the metallic and non-metallic materials. 
         [0023]    According to various other embodiments, a DC motor includes: a cylindrical frame, at least one end of which is open; a cylindrical end cover including an opening configured to block the at least one open end; a rotor including a rotor shaft supported by the frame and the end cover and a rotor core installed on the rotor shaft; a commutator installed on the rotor shaft and arranged on one end of the rotor core; a cover unit installed on the rotor shaft and arranged between the rotor and the commutator; and a rotation panel arranged between an end plate of the frame and the other end of the rotor core which is opposite to the one end of the rotor and including one or more location detection devices, wherein the commutator is arranged on the one end of the rotor core; and a rotation detection unit installed in the frame and configured to detect the one or more location detection devices. 
         [0024]    The one or more location detection devices may be arranged on a surface of the rotation panel, which faces the rotation detection unit, along a circumferential direction of the rotation panel, and the rotation detection unit may be inserted into the end plate of the frame. 
         [0025]    The one or more location detection devices may be arranged along a side portion of the rotation panel, and the rotation detection unit may be inserted into an external wall of the frame along a diameter direction of the rotor shaft. 
         [0026]    The DC motor may further include one or more rotation detection units. 
         [0027]    The one or more location detection devices may include one or more reflectors that are arranged at regular intervals along a circumferential direction of the rotation panel, and the rotation detection unit may include a light source and a light reception unit. 
         [0028]    The one or more location detection devices may include one or more slits or light absorption plates that are arranged at regular intervals along a circumferential direction of the rotation panel, and the rotation detection unit may include a light source and a light reception unit. 
         [0029]    The one or more location detection devices may include permanent magnets that have an N pole and an S pole and are alternately arranged along a circumferential direction of the rotation panel, and the rotation detection unit may include a magnetic flux sensor. 
         [0030]    The one or more location detection devices may include permanent magnets that have an N pole and an S pole and are alternately arranged along a circumferential direction of the rotation panel, and the rotation detection unit may include coils arranged along a circumferential direction of the rotor shaft. 
         [0031]    The DC motor may further include a FPCB facing the cover unit and arranged on the end cover. The one or more location detection devices may include one or more protrusions that are arranged on a surface of the rotation panel along a circumferential direction of the cover unit and formed of conductors, and the rotation detection unit may include one or more metal members that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate a capacitance together with the one or more protrusions. 
         [0032]    The one or more location detection devices may include one or more protrusions that are arranged on a surface of the rotation panel along a circumferential direction of the cover unit and formed of conductors, and the rotation detection unit may include one or more coils that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate an inductance together with the one or more protrusions. 
         [0033]    The one or more location detection devices may include one or more materials that have different permittivities and are arranged on a surface of the rotation panel along a circumferential direction of the cover unit, and the rotation detection unit may include one or more coils that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate a capacitance together with the materials having the different permittivities. 
         [0034]    The one or more location detection devices may include metallic and non-metallic materials that are arranged on a surface of the rotation panel along a circumferential direction of the cover unit, and the rotation detection unit may include one or more coils that are spaced apart from each other on the FPCB along a circumferential direction of the rotor shaft and generate an inductance together with the metallic and non-metallic materials. 
         [0035]    According various embodiments, when the rotation detection unit and the location detection device are installed in a main body of the DC motor, it is unnecessary to secure an additional space where the rotation detection unit and the location detection device are to be arranged, and thus, a size of a product may be reduced. Also, design of the product may be simplified due to the modularization of a motor driving unit, and also, a structure of a gear box unit configured to transmit power may be simplified by installing the rotation detection unit in the main body of the DC motor. Also, an amount of effort involved in assembly is reduced, and manufacturing costs may be decreased because motor manufacturers may assemble sensor units more easily. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
           [0037]      FIG. 1  is a perspective view of a DC motor according to an embodiment; 
           [0038]      FIGS. 2A to 2C  are cross-sectional views of a DC motor including a cover unit on which a location detection device is disposed, according to various embodiments; 
           [0039]      FIGS. 3A and 3B  are cross-sectional views of a DC motor including a rotation panel on which a location detection device is disposed, according to various embodiments; 
           [0040]      FIG. 4A  is a partial perspective view of an optical encoder for detecting rotation of a cover unit, according to an embodiment; 
           [0041]      FIGS. 4B and 4C  are front views of a cover unit on which a location detection device used for an optical encoder is formed as a reflector or a slit; 
           [0042]      FIG. 5  is a partial perspective view of a magnetic encoder including a magnetic flux sensor in order to detect rotation of a cover unit, according to an embodiment; 
           [0043]      FIG. 6  is a partial perspective view of a DC motor including coils instead of a magnetic flux sensor in order to detect rotation of a cover unit, according to an embodiment; 
           [0044]      FIGS. 7A and 8A  are partial perspective views of a DC motor including a FPCB in order to measure a rotation velocity of a cover unit including a plurality of protrusions, according to various embodiments; 
           [0045]      FIG. 7B  is a front view of a cover unit in which different dielectric substances are alternately arranged; and 
           [0046]      FIG. 8B  is a front view of a cover unit in which metallic and non-metallic materials are alternately arranged. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Hereinafter, various embodiments will be described with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
         [0048]      FIG. 1  is a perspective view of a DC motor  100  according to an embodiment. 
         [0049]    Referring to  FIG. 1 , the DC motor  100  includes a stator  101 , a frame  107 , a rotor  102 , and a pair of brushes  104   a  and  104   b . The stator  101  includes a plurality of fixed magnets, for example a pair of fixed magnets  101   a  and  101   b , which have opposite poles and may maintain a magnetic field. The fixed magnets  101   a  and  101   b  may be fixed on, for example, an inner surface of the frame  107 . The frame  107  may be a cylindrical shape, an end portion of which is open and includes an external wall  1072  and an end plate  155 , and the open end portion may be blocked by an end cover  105 . The rotor  102  includes a rotor shaft  103 , a rotor core  110  that is arranged between the fixed magnets  101   a  and  101   b , generates a magnetomotive force by receiving a current, and has coils wound around it, and a commutator  109  that contacts the brushes  104   a  and  104   b  and transmits a current to coils. The rotor shaft  103  may be rotated by the rotor core  110  and is supported by an end cover  105  and the frame  107 . The commutator  109  is arranged on the rotor shaft  103  and may rotate along with the rotor shaft  103 . The cover unit  106  is arranged between the rotor core  110  and the commutator  109 , may rotate along with the rotor shaft  103 , and may fix the coils wound around the rotor core  110 . The brushes  104   a  and  104   b  are respectively supported by brush holders  111   a  and  111   b , are arranged in the end cover  105 , and may transmit a current to the coils by contacting the commutator  109 . The DC motor  100  further includes one or more location detection devices, represented in  FIG. 1  by location detection devices  136 . 
         [0050]      FIG. 2A to 2C  are cross-sectional views of the DC motor  100  including the cover unit  106  on which the location detection devices  136  are disposed, according to various embodiments, and  FIGS. 3A and 3B  are cross-sectional views of the DC motor  100  including a rotation panel  207  on which the location detection devices  136  are disposed, according to various embodiments. 
         [0051]    As noted above, and as shown in  FIGS. 2A to 3B , the location detection devices  136  may be arranged on the cover unit  106  or the rotation panel  207 . The location detection devices  136  may transmit location signals to a rotation detection unit  108  to be described below, as the cover unit  106  or the rotation panel  207  rotates, and may be, for example, a reflector, a permanent magnet, or the like. 
         [0052]    The rotation detection unit  108  is configured to detect a rotation velocity of the cover unit  106  or the rotation panel  207  by using location signals transmitted by the location detection devices  136  that are arranged on the cover unit  106  or the rotation panel  207 , and a rotation velocity of the rotor shaft  103 , that is, a rotation velocity of the DC motor  100  may be detected by the rotation detection unit  108 . An output form of a detected rotation velocity may be a pulse or sine-wave form and may be determined by a circuit unit. Thus, a plurality of rotation detection units  108  may also be used to detect a rotation direction or improve the accuracy of detection (resolving power). The number of the rotation detection units  108  arranged in the DC motor  100  may be determined in accordance with manufacturing costs, accuracy, or the like. 
         [0053]    Referring to  FIGS. 1 and 2A , the rotation detection unit  108  may be arranged in an area formed between the first brush  104   a  and the second brush  104   b  along a circumferential direction of the rotor shaft  103 . In an embodiment, the location detection devices  136  are arranged on a surface of the cover unit  106 , which faces the rotation detection unit  108 , at regular intervals along the circumferential direction. The other surface of the cover unit  106 , on which the location detection devices  136  are not arranged, may be coupled to the coils wound around the rotor core  110  and may fix the same. Referring to  FIG. 2C , possible locations of the rotation detection unit  108  are not limited to an area formed between the first brush  104   a  and the second brush  104   b  along the circumferential direction of the rotor shaft  103 . For example, the rotation detection unit  108  may be arranged on an area formed between the first brush  104   a  and an external wall  1051  of the end cover  105  or an area formed between the second brush  104   b  and the external wall  1051  of the end cover  105 . Also, a plurality of rotation detection units  108  may be arranged on areas formed between the first brush  104   a  and the external wall  1051  of the end cover  105 , between the second brush  104   b  and the external wall  1051  of the end cover  105 , and between the first brush  104   a  and the second brush  104   b  along the circumferential direction of the rotor shaft  103  in order to detect a rotation direction or improve the accuracy of detection (resolving power). 
         [0054]    When the DC motor  100  operates according to an embodiment, the rotor shaft  103  is rotated by the rotor core  110 , and the cover unit  106  (arranged on the rotor shaft  103 ) also rotates. In this case, as the cover unit  106  rotates, the location detection devices  136  arranged on a surface of the cover unit  106  may also rotate. As the location detection devices  136  rotate, periodical signals may be transmitted to the rotation detection unit  108 , which is arranged to face the location detection devices  136 . A rotation direction or velocity of the DC motor  100  may be detected by detecting the rotation of the cover unit  106  by using the periodical signals transmitted to the rotation detection unit  108 . 
         [0055]    Referring to  FIG. 2B , according to an embodiment, the rotation detection unit  108  is inserted into the external wall  1051  of the end cover  105 , and the location detection devices  136  are arranged at regular intervals along a side portion  176  of the cover unit  106 . In this case, the rotation detection unit  108  may be arranged along a diameter direction of the rotor shaft  103 . For example, the rotation detection unit  108  may be arranged in an entire portion of the external wall  1051  of the end cover  105  that faces the location detection devices  136 . 
         [0056]    When the DC motor  100  operates according to an embodiment, the rotor shaft  103  is rotated by the rotor core  110 , and the cover unit  106  that is arranged on the rotor shaft  103  also rotates. In this case, as the cover unit  106  rotates, the periodical signals may be transmitted from the location detection devices  136  arranged on the side portion  176  of the cover unit  106  to the rotation detection unit  108  arranged to face the location detection devices  136 . As described above, the rotation of the DC motor  100  may be detected by using the periodical signals transmitted to the rotation detection unit  108 . 
         [0057]    As described above, the rotation detection unit  108  is arranged in the DC motor  100  and the location detection devices  136  are arranged on the cover unit  106 . Thus, it may be unnecessary to secure additional space for arranging a rotation plate on which the rotation detection unit  108  (which measures a rotation velocity of the DC motor  100 ) and the location detection devices  136  are arranged. This allows a product including the DC motor  100  to be reduced in size because, although the size of the DC motor  100  remains the same, the space needed to arrange the rotation detection unit  108 , etc. is reduced. Also, if the motor driving unit is modularized, design of the DC motor  100  may be simplified, and external components driven by the DC motor  100  (for example, a structure of a gear box) may be simplified. In addition, the amount of effort involved in assembly may be reduced, thus reducing manufacturing costs. 
         [0058]    Referring to  FIG. 3A , according to an embodiment, the rotation panel  207  is installed on the rotor shaft  103  and is additionally arranged on the other end of the rotor core  110  on which the commutator  109  is not arranged. The rotation detection unit  108  is inserted into the end plate  155 , and the location detection devices  136  are arranged on a surface of the rotation panel  207 , which faces the rotation detection unit  108 , at regular intervals along a circumferential direction. In this case, the rotation detection unit  108  may be inserted into an entire portion of the end plate  155  that faces the location detection devices  136 . 
         [0059]    A method of measuring a rotation velocity of the DC motor  100  by using the location detection devices  136  arranged on a surface of the rotation panel  207  and the rotation detection unit  108  is the same as the description provided with reference to  FIG. 2A , and thus, descriptions regarding the method will not be repeated here. 
         [0060]    Referring to  FIG. 3B , the rotation panel  207  is installed on the rotor shaft  103  and is arranged on the other end of the rotor core  110  on which the commutator  109  is not arranged. The rotation detection unit  108  is inserted into the external wall  1072  of the frame  107 , and the location detection devices  136  are arranged at regular intervals along the side portion  176  of the rotation panel  207  that faces the rotation detection unit  108 . In this case, the rotation detection unit  108  may be arranged along a diameter direction of the rotor shaft  103 . For example, the rotation detection unit  108  may be inserted into an entire portion of the external wall  1072  of the frame  107  that faces the location detection devices  136 . 
         [0061]    A method of measuring a rotation velocity of the DC motor  100  by using the location detection devices  136  arranged on the side portion  176  of the rotation panel  207  and the rotation detection unit  108  is the same as the description provided with reference to  FIG. 2B , and thus, descriptions regarding the method will not be repeated here. 
         [0062]    In comparison with the DC motor  100  of  FIG. 2A to 2C , the volume of the DC motor  100  of  FIGS. 3A and 3B  may be greater according to the thickness of the rotation panel  207  because the rotation panel  207  is additionally arranged on the other end of the rotor core  110 , that is, an opposite surface of the commutator  109 . However, the location detection devices  136  may be densely arranged along a circumferential direction of the rotation panel  207  as the rotation panel  207  is arranged on the other end of the rotor core  110 . Accordingly, the rotation of the DC motor  100  may be accurately detected as the resolving power of the rotation detection unit  108  is improved. 
         [0063]    Hereinafter, a method of detecting the rotation of the cover unit  106  and the rotation panel  207  by using the location detection devices  136  and the rotation detection unit  108  arranged in the DC motor  100  according to an embodiment will be described. Because the methods of detecting the rotation of the DC motor  100  of  FIGS. 2A to 3B  may be identical (except for the arrangement of the cover unit  106 , the rotation panel  207 , and the rotation detection unit  108 ), the method of detecting the rotation of the DC motor  100  will be described in detail on the basis of the DC motor  100  of  FIG. 2A . It is to be understood, however, that the method may also be used for the embodiments of  FIGS. 2B-3C . 
         [0064]      FIG. 4A  is a partial perspective view of an optical encoder  300  for detecting rotation of the cover unit  106 , according to an embodiment, and  FIGS. 4B and 4C  are front views of the cover unit  106  on which the location detection devices  136  used for the optical encoder  300  are formed as reflectors  236  or slits  237 . 
         [0065]    Referring to  FIG. 4A , the optical encoder  300  according to an embodiment includes a cover unit  106  and a rotation detection unit  108  including a light source  310  and a light reception unit  320 . One or more location detection devices  136  having the same width w may be arranged on a surface of the cover unit  106  at intervals of the same pitch p along the circumferential direction of the cover unit  106 . The light source  310  may be implemented as any of a variety of light-emitting devices such as light-emitting diodes (LEDs) and may emit light to the cover unit  106 . The light reception unit  320  may be, for example, a photo diode, a photo transistor, a photo resistor, or the like, and light reflected from the cover unit  106  may be incident on the light reception unit  320 . 
         [0066]    Referring to  FIGS. 4A and 4B , the location detection devices  136  according to an embodiment may be formed as reflectors  236  arranged along the circumferential direction of the cover unit  106 . As described above, the rotor shaft  130  rotates as the DC motor  100  operates, and thus, the cover unit  106  is also rotated by the rotor shaft  130 . In this case, the location detection devices  136  arranged on the surface, that is, the reflectors  236 , also rotate, and the light emitted by the light source  310  is reflected from the reflectors  236  and may be incident to the light reception unit  320 . As the light is incident on the light reception unit  320 , output signals are generated in a light reception area of the light reception unit  320 , and electrodes (not shown) connected to the light reception area transmit the output signals to the outside. Therefore, the rotation of the cover unit  106  may be detected. 
         [0067]    Referring to  FIGS. 4A and 4C , the location detection devices  136  according to an embodiment may be formed as slits  237  arranged along the circumferential direction of the cover unit  106 . In this case, the cover unit  106  may be formed of materials that have good reflectivity, and the light emitted by the light source  310  is reflected from areas except for the slits  237  and is incident on the light reception unit  320 . Thus, the output signals may be generated, and the rotation of the cover unit  106  may be detected. 
         [0068]      FIG. 5  is a partial perspective view of a magnetic encoder to detect rotation of the cover unit  106 , according to an embodiment. 
         [0069]    Referring to  FIG. 5 , the magnetic encoder according to an embodiment includes the cover unit  106  and a rotation detection unit  108  including a magnetic flux sensor  403 . Permanent magnets  401  and  402  having opposite poles are alternately disposed on the cover unit  106  along the circumferential direction of the cover unit  106 . In this case, the permanent magnets  401  and  402  may be integrally formed where half of the cover unit  106  is an N pole  401  and the other half of the cover unit  106  is an S pole  402 , or may be independent permanent magnets arranged at regular intervals along a circumference. The magnetic flux sensor  403  detects a magnetic flux interlinkage with respect to the permanent magnets  401  and  402 , wherein the magnetic flux interlinkage regularly changes in accordance with the rotation of the cover unit  106  while the DC motor  100  operates, and the magnetic flux sensor  403  may output the detected magnetic flux interlinkage as electrical signals. Then, output signals are transmitted to a predetermined signal processor (not shown), and the rotation of the DC motor  100  may be detected thereby. The magnetic flux sensor  403  according to an embodiment may be a Hall sensor or a magneto resistive (MR) sensor. 
         [0070]      FIG. 6  is a partial perspective view of a magnetic encoder including coils  501  instead of the magnetic flux sensor  403  in order to detect rotation of the cover unit  106 , according to an embodiment. 
         [0071]    Referring to  FIG. 6 , the magnetic encoder according to an embodiment includes the cover unit  106  to which the permanent magnets  401  and  402  are coupled, and the coils  501 . The permanent magnets  401  and  402  having opposite poles are alternately coupled to the cover unit  106  along the circumferential direction of the cover unit  106 . In this case, as described above, the permanent magnets  401  and  402  may be integrally formed or may be independent permanent magnets. The coils  501  are arranged between the brushes  104   a  and  104   b  and the external wall  1051  of the end cover  105  along a circumferential direction. As the cover unit  106  rotates while the DC motor  100  operates, a magnetic field formed by the permanent magnets  401  and  402  regularly changes, and thus, electrical signals generated by an induced current may be output to the coils  501 . The electrical signals are transmitted to the predetermined signal processor (not shown), and the rotation of the DC motor  100  may be detected thereby. 
         [0072]      FIGS. 7A and 8A  illustrate a flexible FPCB  600  in which a detection pattern  601  is formed instead of the rotation detection unit  108  in order to measure a rotation velocity of the cover unit  106 , according to various embodiments.  FIG. 7B  is a front view of a cover unit in which different dielectric substances are alternately arranged, and  FIG. 8B  is a front view of a cover unit in which metallic and non-metallic materials are alternately arranged. 
         [0073]    Referring to  FIGS. 7A and 8A , a plurality of protrusions  602  formed of conductors having conductivity are arranged at regular intervals along the circumferential direction of the cover unit  106 . The ring-shaped FPCB  600  is arranged between the brushes  104   a  and  104   b  and the external wall  1051  of the end cover  105 , and the detection pattern  601  is circularly arranged on the FPCB  600  to be opposite to the protrusions  602 . Signals having a frequency corresponding to half the number of protrusions  602  are generated whenever the FPCB  600  rotates through one complete revolution, and passive elements such as coils  652  of an inductance sensor, or metal members  651  of a capacitance sensor are arranged on the detection pattern  601 . As the detection pattern  601  faces the protrusions  602 , an inductance or capacitance having constant intensity may be generated. As the cover unit  106  rotates while the DC motor  100  operates, the protrusions  602  (formed of conductors having conductivity) may be arranged on the detection pattern  601 , and in this case, a capacitance generated between the protrusions  602  and the metal members  651  or an inductance generated between the protrusions  602  and the coils  652  may be regularly detected. A change of the capacitance or inductance is output as electrical signals, and thus, the rotation of the DC motor  100  may be detected. 
         [0074]    Referring to  FIG. 7B , first and second materials  701  and  702  having different permittivities are alternately arranged along the circumferential direction of the cover unit  106 . As described above, the metal members  651  of the capacitance sensor may be arranged on the detection pattern  601  of the FPCB  600 . As the cover unit  106  rotates while the DC motor  100  operates, the first and second materials  701  and  702  having different permittivities may be alternately arranged on the detection pattern  601 , and in this case, a difference between capacitances is detected in accordance with materials arranged on the detection pattern  601 . Thus, a difference between permittivities of the first material  701  and the second material  702  may be detected. The difference between the permittivities is output as electrical signals, and thus, the rotation of the DC motor  100  may be detected. 
         [0075]    Referring to  FIG. 8B , metallic and non-metallic materials  801  and  802  are alternately arranged along the circumferential direction of the cover unit  106 . As described above, the coils  652  of the inductance sensor may be arranged on the detection pattern  601  of the FPCB  600 . As the cover unit  106  rotates while the DC motor  100  operates, the metallic and non-metallic materials  801  and  802  may be alternately arranged on the detection pattern  601 , and in this case, a difference between inductances is detected in accordance with a difference between the first material  701  and the second material  702  which are arranged on the detection pattern  601 , and thus, a conductivity difference may be detected. The conductivity difference is output as electrical signals, and thus, the rotation of the DC motor  100  may be detected. 
         [0076]    It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
         [0077]    While various embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims. 
         [0078]    The use of the terms “a”, “an”, and “the” and similar referents in the context of describing the inventive concept (especially in the context of the following claims) are to be construed to cover both the singular and the plural. Furthermore, recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Also, the steps of all methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The inventive concept is not limited to the described order of the steps. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the disclosure unless otherwise claimed. Numerous modifications and adaptations will be readily apparent to one of ordinary skill in the art without departing from the spirit and scope of the disclosure.