Abstract:
Embodiments of the present invention provide an apparatus for convenient tightening and loosening of strings such as those found in shoelaces of footwear. The apparatus includes a rotating portion within a base portion. A cover portion, when operated in a first position, provides a ratchet movement that allows rotation in a tightening direction while preventing movement in a loosening direction. When the cover is moved to a second position, the ratchet mechanism disengages, and the strings can then be easily loosened.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present disclosure relates to a string winding and unwinding apparatus and, more particularly, to a string winding and unwinding apparatus having a simple configuration and facilitating maintenance and repair. 
         [0003]    2. Background of the Invention 
         [0004]    In general, shoes, bags (or sacks), backpacks, or clothes include a tightening/loosening unit using strings, or the like. For example, in shoes (footwear), strings are provided to be connected in a zigzag manner, and as the strings are pulled to be tightened, shoes may be tightly attached to the feet of users. 
         [0005]    However, it is very cumbersome to loosen or tighten strings each time a user puts on or takes off shoes, and thus, generally, when a user wears shoes, he or she does not fully pull and tighten strings so that the shoes may not be completely tightly attached to his or her feet. In this case, when the shoes are intended to be completely tightly attached to the user&#39;s feet for exercise, or the like, the user should pull to tighten the strings, and thereafter, the user may loosen the strings, involving user inconvenience. In addition, when the tightened strings are loosened while the user is walking or doing exercise, the user should tighten the strings again. 
       SUMMARY OF THE INVENTION 
       [0006]    Embodiments of the present invention provide an apparatus for convenient tightening and loosening of strings such as those found in shoelaces of footwear. The apparatus includes a rotating portion within a base portion. A cover portion, when operated in a first position, provides a ratchet movement that allows rotation in a tightening direction while preventing movement in a loosening direction. When the cover is moved to a second position, the ratchet mechanism disengages, and the shoelaces can then be easily loosened. In some embodiments, a restoring string or spring provides assistance in the loosening of shoelaces by assisting in moving the rotating portion in a loosening direction. 
         [0007]    In a first aspect, embodiments of the present invention provide a string winding apparatus, comprising a base unit, the base unit comprising a housing and having a lateral aperture in the housing, a middle unit coupled to the base unit, a rotating unit positioned within the base unit, wherein the rotating unit is configured and disposed to be rotatable with respect to the base unit, and wherein the rotating unit comprises a upper surface with a first engaging portion formed thereon and allowing a string to be wound around an outer circumferential surface thereof or unwound therefrom through rotation; and a cover unit coupled to the middle unit, wherein the cover unit is configured and disposed to be rotatable with respect to the middle unit, and wherein the cover unit comprises a second engaging portion configured and disposed to engage with the first engaging portion of the rotating unit. 
         [0008]    In a second aspect, embodiments of the present invention provide a string winding apparatus comprising: a base unit having a base plate and a lower housing positioned on an upper surface of the base plate and having a lateral aperture; a middle unit having a upper housing coupled to the lower housing, an upper stoppage portion positioned within the upper housing, and a lower stoppage portion positioned within the upper housing and disposed to be closer to the base plate than the upper stoppage portion; a rotating unit being at least partially positioned within the lower housing so as to be rotatable with respect to the base unit, and allowing a string to be wound around an outer circumferential surface thereof or unwound therefrom through rotation; and a cover unit coupled to the middle unit so as to be rotatable with respect to the middle unit, having a responsive stoppage portion protruding in a radial direction, varied in distance to the base unit according to a relative position of the responsive stoppage portion with respect to the upper stoppage portion and the lower stoppage portion so as to be engaged with the rotating unit or separated from the rotating unit, and rotated together with the rotating unit when engaged therewith. 
         [0009]    In a third aspect, embodiments of the present invention provide a string winding apparatus comprising: a base unit having a base plate and a lower housing positioned on an upper surface of the base plate; a rotating unit being at least partially positioned within the lower housing so as to be rotatable with respect to the base unit, and allowing a string to be wound around an outer circumferential surface thereof or unwound therefrom through rotation; a cover unit varied in distance to the base unit so as to be engaged with the rotating unit or separated from the rotating unit, and rotated together with the rotating unit when engaged therewith; and a restoring unit configured and disposed to move the rotating unit in an unwinding direction when the cover unit is separated from the rotating unit in a wound state. 
         [0010]    In a fourth aspect, embodiments of the present invention provide a string winding apparatus, comprising: a base unit, the base unit comprising a housing and having a lateral aperture in the housing; a middle unit coupled to the base unit, the middle unit comprising a partition with a plurality of responsive protrusions thereon; a rotating unit positioned within the base unit, wherein the rotating unit is configured and disposed to be rotatable with respect to the base unit, and wherein the rotating unit comprises a upper surface with a first engaging portion formed thereon and allowing a string to be wound around an outer circumferential surface thereof or unwound therefrom through rotation; a cover unit coupled to the middle unit, wherein the cover unit comprises a central shaft and is configured and disposed to be rotatable with respect to the middle unit, and wherein the rotating unit further comprises a first wing part and a second wing part, wherein a space is formed between the first wing part and the second wing part, wherein the space is configured and disposed to store the string; and wherein the cover unit comprises a second engaging portion on the central shaft that is configured and disposed to engage with the first engaging portion of the rotating unit; and wherein the string winding apparatus comprises a first stage defined by a height of the cover unit, and a second stage defined by a distance between the first wing part and the second wing part, and wherein a reverse rotation prevention portion is disposed in the first stage, a stoppage portion is disposed in the first stage, and a string winding portion is disposed in the second stage. 
         [0011]    In a fifth aspect, embodiments of the present invention provide a string winding apparatus, comprising: a middle-base composite unit, the base unit comprising a housing and having a lateral aperture in the housing; a rotating-coverrotating-cover composite unit positioned within the middle-base composite unit, the rotating-cover composite unit comprising a partition with a plurality of responsive protrusions thereon, and wherein the rotating-cover composite unit is configured and disposed to be rotatable with respect to the middle-base composite unit, wherein the rotating-cover composite unit further comprises a first wing part and a second wing part, wherein a space is formed between the first wing part and the second wing part, wherein the space is configured and disposed to store a string that is allowed to be wound around an outer circumferential surface thereof or unwound therefrom through rotation; and wherein the string winding apparatus comprises a single stage defined by a distance between a top surface of the cover unit and the first wing part of the rotating-cover composite unit, and wherein a reverse rotation prevention portion, a stoppage portion, and a string winding portion are disposed in the single stage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings, which are included to provide a further understanding of embodiments of the present invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of embodiments of the invention. 
           [0013]    In the drawings: 
           [0014]      FIG. 1  is an exploded perspective view schematically illustrating a string winding and unwinding apparatus according to an embodiment of the present disclosure. 
           [0015]      FIG. 2  is a cross-sectional view schematically illustrating a coupled state of the string winding and unwinding apparatus of  FIG. 1 . 
           [0016]      FIG. 3  is a perspective view schematically illustrating a base unit of  FIG. 1 . 
           [0017]      FIG. 4  is a perspective view schematically illustrating a middle unit of  FIG. 1 . 
           [0018]      FIG. 5  is a perspective view schematically illustrating a rotating unit of  FIG. 1 . 
           [0019]      FIG. 6  is a bottom perspective view schematically illustrating the rotating unit of  FIG. 5 . 
           [0020]      FIG. 7  is a bottom perspective view schematically illustrating a cover unit of  FIG. 1 . 
           [0021]      FIG. 8  is a cross-sectional view of a portion of the string winding and unwinding apparatus of  FIG. 1 . 
           [0022]      FIG. 9  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0023]      FIG. 10  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0024]      FIG. 11  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0025]      FIG. 12  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0026]      FIG. 13  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0027]      FIG. 14  is a perspective view schematically illustrating a middle unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0028]      FIG. 15  is a cross-sectional view of a portion of a cover unit that may be used together with the middle unit of  FIG. 14 . 
           [0029]      FIG. 16  is a perspective view illustrating a reverse rotation preventing portion according to another embodiment of the present disclosure. 
           [0030]      FIG. 17  is a perspective view illustrating a reverse rotation preventing portion according to another embodiment of the present disclosure. 
           [0031]      FIG. 18  is a perspective view illustrating an engaging portion according to another embodiment of the present disclosure. 
           [0032]      FIG. 19  is a perspective view illustrating an engaging portion according to another embodiment of the present disclosure. 
           [0033]      FIG. 20  is a cross-sectional view schematically illustrating a base unit, a rotating unit, and a restoring unit of the string winding and unwinding apparatus of  FIG. 1 . 
           [0034]      FIG. 21  is a perspective view schematically illustrating a base unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0035]      FIG. 22  is a cross-sectional view schematically illustrating a base unit and a rotating unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0036]      FIG. 23  is an exploded side view schematically illustrating a rotating unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0037]      FIG. 24  is a side view schematically illustrating a rotating unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0038]      FIG. 25  is a side view schematically illustrating a rotating unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0039]      FIG. 26  is a perspective view schematically illustrating a restoring unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0040]      FIG. 27  is a cross-sectional view illustrating that the embodiment of  FIG. 2  has a 3-stage configuration. 
           [0041]      FIG. 28  is a cross-sectional view illustrating a wound state of a first embodiment having a 2-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0042]      FIG. 29A  is a cross-sectional view taken along line A-A′ of  FIG. 28 . 
           [0043]      FIG. 29B  is an alternative embodiment of the portion shown in  FIG. 29A . 
           [0044]      FIG. 30  is a cross-sectional view illustrating a winding-released state of the first embodiment having the 2-stage configuration illustrated in  FIG. 28 . 
           [0045]      FIG. 31  is a cross-sectional view illustrating a wound state of a second embodiment having a 2-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0046]      FIG. 32  is a cross-sectional view illustrating a winding-released state of the second embodiment having the 2-stage configuration illustrated in  FIG. 31 . 
           [0047]      FIG. 33  is a cross-sectional view illustrating a wound state of a third embodiment having a 2-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0048]      FIG. 34  is a cross-sectional view illustrating a winding-released state of the third embodiment having the 2-stage configuration illustrated in  FIG. 33 . 
           [0049]      FIG. 35  is a cross-sectional view illustrating a wound state of a fourth embodiment having a 2-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0050]      FIG. 36  is a cross-sectional view illustrating a winding-released state of the fourth embodiment having the 2-stage configuration illustrated in  FIG. 35 . 
           [0051]      FIG. 37  is a cross-sectional view illustrating a wound state of a fifth embodiment having a 1-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0052]      FIG. 38  is a cross-sectional view illustrating a winding-released state of the fifth embodiment having the 1-stage configuration illustrated in  FIG. 37 . 
           [0053]      FIG. 39  is a cross-sectional view illustrating a wound state of a sixth embodiment having a 1-stage configuration to reduce an overall height of the apparatus according to the present disclosure. 
           [0054]      FIG. 40  is a cross-sectional view illustrating a winding-released state of the sixth embodiment having the 1-stage configuration illustrated in  FIG. 39 . 
           [0055]      FIG. 41  is a perspective view schematically illustrating footwear according to another embodiment of the present disclosure. 
           [0056]      FIG. 42  is a perspective view schematically illustrating a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0057]      FIG. 43  is a perspective view schematically illustrating a string winding and unwinding apparatus according to another embodiment of the present disclosure. 
           [0058]      FIG. 44  is a perspective view schematically illustrating a fastening clip that may be coupled to the string winding and unwinding apparatus of  FIG. 43 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0059]    The present invention will now be described fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Like numbers refer to like elements throughout. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Those of ordinary skill in the art will realize that the following embodiments of the present invention are only illustrative and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
         [0060]    Illustrative embodiments will now be described more fully herein with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0061]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms “a”, “an”, etc., do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
         [0062]    Reference throughout this specification to “one embodiment,” “an embodiment,” “embodiments,” “exemplary embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “in embodiments”, “in some embodiments”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. It will be understood that one skilled in the art may cross embodiments by “mixing and matching” one or more features of one embodiment with one or more features of another embodiment. 
         [0063]    The terms “overlying” or “atop”, “positioned on, “positioned atop”, or “disposed on”, “underlying”, “beneath” or “below” mean that a first element, such as a first structure (e.g., a first layer) is present on a second element, such as a second structure (e.g. a second layer) wherein intervening elements, such as an interface structure (e.g. interface layer) may be present between the first element and the second element. When various components such as layer, film, region, and plate are referred to as being “on” another component, the component may be directly formed on the other component or substrate or indirectly formed with an intervening component therebetween. 
         [0064]    In the embodiments described hereinafter, x axis, y axis and z axis may be construed in a broad sense, rather than being limited to a Cartesian coordinate system. For example, x axis, y axis and z axis may be perpendicular to each other or may designate other directions not perpendicular to each other. 
         [0065]      FIG. 1  is an exploded perspective view schematically illustrating a string winding and unwinding apparatus according to an embodiment of the present disclosure, and  FIG. 2  is a cross-sectional view schematically illustrating a coupled state of the string winding and unwinding apparatus of  FIG. 1 . 
         [0066]    As illustrated in  FIGS. 1 and 2 , the string winding and unwinding apparatus according to the present embodiment includes a base unit  100 , a middle unit  200  coupled to the base unit  100 , a rotating unit  300  positioned within the base unit  100  and/or the middle unit  200  so as to be rotatable with respect to the base unit  100 , and a cover unit  400  coupled to the middle unit  200  so as to be rotatable with respect to the middle unit  200 . 
         [0067]      FIG. 3  is a perspective view schematically illustrating the base unit  100  of  FIG. 1 . As illustrated in  FIG. 3 , the base unit  100  includes a base plate  110  having a plate shape such as a disc and a cylindrical lower housing  120 , for example. However, a shape of the base plate  110  is not limited to the disc shape and the base plate  110  may have various other plate shapes. Here, the cylindrical shape may be understood as a shape similar to a hollow cylinder. The lower housing  120  is positioned in an upper surface of the base plate  110  (+z direction). The base plate  110  and the lower housing  120  may be integrally formed by a resin, or the like. 
         [0068]    The lower housing  120  has a second lateral aperture  122 . A non-limiting example of an aperture is a hole or through-hole. In some embodiments, the lower housing  120  may have a first lateral aperture  121  as illustrated in  FIG. 3 . Here, the first lateral aperture  121  may be positioned to be closer to the base plate  110  than the second lateral aperture  122 . Thus, the second lateral aperture can be at a different elevation (z direction) than the first lateral aperture. It is illustrated that the lower housing  120  has two first lateral apertures  121  substantially facing each other and also may have two second lateral apertures  122 , but these are merely illustrative and at least one first lateral aperture  121  and at least one second lateral aperture  122  may exhibit functions thereof. In  FIG. 3 , it is illustrated that the first lateral apertures  121  are positioned to be aligned in the y axis direction and the second lateral apertures  122  are also positioned to be aligned in the y axis direction, but these are merely illustrative and the first lateral apertures  121  and the second lateral apertures  122  may exhibit functions thereof as long as they are positioned to be aligned substantially, regardless of direction. In  FIG. 3 , it is illustrated that the first lateral apertures  121  and the second lateral apertures  122  are positioned abreast up and down, but the present disclosure is not limited thereto. For example, the first lateral apertures  121  may be positioned to be aligned substantially in the y axis direction as illustrated in  FIG. 3 , while the second lateral apertures  122  may be positioned to be aligned substantially in the x axis direction unlike those illustrated in  FIG. 3 . 
         [0069]    Apertures  111  having a central axis in a z axis direction may be formed in an outer portion of the lower housing  120  of the base plate  110  of the base unit  100 . The apertures  111  serve to allow fasteners to pass therethrough to fix the base plate  110  to footwear, or the like, when the string winding and unwinding apparatus according to the present embodiment is installed in the footwear, for example. 
         [0070]    The base unit  100  may further have a rotation support portion  130  protruding from an inner surface of the lower housing  120  in a direction toward the center of the lower housing  120 . A rotation support protrusion portion  132  may be formed in an upper surface of the rotation support portion  130  and may protrude upwardly (+z direction). The rotation support portion  130  and the rotation support protrusion portion  132  may serve to support smooth rotation of the rotating unit  300  when the rotating unit  300  rotates with respect to the base unit  100 . This will be described hereinafter. 
         [0071]    As illustrated in  FIG. 4 , the middle unit  200  has a cylindrical upper housing  210 , an inwardly directed upper stoppage portion  221 , and an inwardly directed lower stoppage portion  222 . The upper stoppage portion  221  and/or the lower stoppage portion  222  may have slight elasticity or flexibility within a range in which an overall shape thereof is not changed. The cylindrical upper housing  210  understood as having a shape similar to a hollow cylinder may be coupled to the lower housing  120  of the base unit  100 . Both the upper stoppage portion  221  and the lower stoppage portion  222  may be positioned on an inner circumferential surface  210   a  of the upper housing  210  toward the center of the upper housing  210 . In particular, both the upper stoppage portion  221  and the lower stoppage portion  222  may be convex in a direction away from the inner circumferential surface  210   a  of the upper housing  210 . That is, the upper stoppage portion  221  and the lower stoppage portion  222  may have a convex shape protruding in a direction toward the center of the upper housing  210 . Here, the lower stoppage portion  222  is positioned to be closer to the base plate  110  (−z direction) than the upper stoppage portion  221 . 
         [0072]    The middle unit  200  may have a partition  240  as necessary. The partition  240  may be positioned to be closer to the base plate  110  than the lower stoppage portion  222  and protrudes inwardly from the upper housing  210 . A responsive protrusion  250  may be positioned on a surface of the partition  240  in a direction (+z direction) of the lower stoppage portion  222 . Functions of the partition  240  and/or the responsive protrusion  250  will be described hereinafter. 
         [0073]    The upper housing  210 , the upper stoppage portion  221 , the lower stoppage portion  222 , the partition  240 , and/or the responsive protrusion  250  may be formed of a resin, or the like, as one body. Alternatively, as described hereinafter, a portion of the components may be separately formed and coupled to the upper housing  210 , and in such a case, the portion of the components may be formed of various materials including a resin, a plastic, or a metal. 
         [0074]      FIG. 5  is a perspective view schematically illustrating the rotating unit  300  of  FIG. 1 , and  FIG. 6  is a bottom perspective view schematically illustrating the rotating unit  300  of  FIG. 5 . As illustrated in  FIGS. 5 and 6 , the rotating unit  300  is positioned within the lower housing  120  of the base unit  100  and disposed to be rotatable with respect to the base unit  100 . Here, when the rotating unit  300  is positioned within the lower housing  120 , it means that at least a portion of the rotating unit  300  is positioned within the lower housing  120 , and thus, here, various modifications may be implemented such that a portion of the rotating unit  300  is positioned within the upper housing  210  above the lower housing  120 , or the like. 
         [0075]    As illustrated in  FIG. 5 , the rotating unit  300  has a first engaging portion  310  in an upper surface  317  thereof (+z direction). In  FIG. 5 , it is illustrated that the first engaging portion  310  has a concave recess shape but the first engaging portion  310  may be modified to have a convex protrusion shape. When the first engaging portion  310  is engaged with a second engaging portion  450  (to be described hereinafter) of the cover unit  400 , the rotating unit  300  may be rotated together with the cover unit  400 . Here, in order to prevent slipping between the rotating unit  300  and the cover unit  400  while the first engaging portion  310  and the second engaging portion  450  are engaged with each other, the first engaging portion  310  and the second engaging portion  450  may have various shapes such as a polygonal shape, an oval shape, or an asymmetrically distorted circular shape in an x-y plane. Alternatively, the first engaging portion  310  and the second engaging portion  450  may be configured as one or more pairs of pins and pin apertures in the x-y plane such that the rotating unit  300  and the cover unit  400  may be engaged with each other as the one or more pairs of pins and pin apertures are engaged. 
         [0076]    As illustrated in  FIGS. 5 and 6 , the rotating unit  300  may have a first wing part  321  positioned in a upper portion thereof and protruding in a radial direction and a second wing part  322  positioned in a lower portion thereof (in the −z direction) so as to be closer to the base plate  110  than the first wing part  321  and protruding in the radial direction, like the first wing part  321 . In a space between the first wing part  321  and the second wing part  322 , a string may be wound around an outer circumferential surface of the rotating unit  300  according to a rotation direction of the rotating unit  300 . That is, the first wing part  321  and the second wing part  322  may serve to limit the space in which the string is to be positioned when wound according to the direction in which the rotating unit  300  rotates. 
         [0077]    If necessary, as illustrated in  FIG. 6 , the rotating unit  300  may additionally include a third wing part  323  positioned in a lower portion thereof so as to be even closer (in the −z direction) to the base plate  110  than the second wing part  322  and protruding in the radial direction, like the second wing part  322 . The third wing part  323  may have a flat lower surface, whereby the rotating unit  300  may stably rotate with respect to the base plate  110  of the base unit  100  in a state in which at least a portion of the lower surface of the third wing part  323  is in contact with an upper surface (+z direction) of the base plate  110  or in a state in which at least a portion of the lower surface of the third wing part  323  is in close proximity to the upper surface of the base plate  110  if not in contact therewith. 
         [0078]    As illustrated in  FIG. 6 , the rotating unit  300  may have a first aperture  331  positioned below the second wing part  322  (−z direction) and penetrating through the rotating unit  300  at an orientation perpendicular to the rotational shaft (z axis of the rotating unit). The first aperture  331  may correspond to the first lateral apertures  121  of the base unit  100 . Here, when the first aperture  331  corresponds to the first lateral apertures  121 , it means that a height of the first aperture  331  from the base plate  110  and a height of the first lateral apertures  121  from the base plate  110  are substantially equal. 
         [0079]    As illustrated in  FIG. 6 , the rotating unit  300  may have a second aperture  332  penetrating through the rotating unit  300  in a space between the first wing part  321  and the second wing part  332 . The second aperture  332  may correspond to the second lateral apertures  122  of the base unit  100 . Here, when the second aperture  332  corresponds to the second lateral apertures  122 , it means that a height of the second aperture  332  from the base plate  110  and a height of the second lateral apertures  122  from the base plate  110  are substantially equal. 
         [0080]    A string (not shown) of footwear, or the like, may pass through any one of the second lateral apertures  122  of the base unit  100 , penetrate through the second aperture  332  of the rotating unit  300 , and subsequently pass through the other of the second lateral apertures  122 . In another embodiment of the present disclosure, after the string passes through the second aperture  332  of the rotating unit  300 , the string may be fixed within the base unit  100 . Accordingly, when the rotating unit  300  in a state of being engaged with the cover unit  400  rotates in one direction, the string may be wound around the rotating unit  300 . In detail, the string is wound in the space between the first wing part  321  and the second wing part  322 . In this manner, the string may be wound in the footwear, or the like. Here, although a ratchet protrusion  460  (described further in  FIG. 7 ) and the responsive protrusion  250  meet each other, wedge shapes of the ratchet protrusion  460  and the responsive protrusion  250  allow the cover unit  400  to rotate in one direction, and when the rotation of the cover unit  400  in one direction is stopped, the wedge shapes of the ratchet protrusion  460  and the responsive protrusion  250  limit rotations of the cover unit  400  and the rotating unit  300  in the other direction, i.e., the opposite direction, in the stopped position. Thus, the ratchet protrusions are unidirectional ratchet protrusions, and enable rotational motion in one direction while preventing rotational motion in the opposite direction. In this state, when the rotating unit  300  is separated from the cover unit  400 , the ratchet protrusion  460  and the responsive protrusion  250  are also separated, releasing the wound state, and thus, the rotating unit  300  may rotate in the other direction, the opposite direction of the one direction, by virtue of elastic restoring force of the string itself, and accordingly, the string, which has been wound around the rotating unit  300 , may be unwound from an outer circumferential surface of the rotating unit  300 . 
         [0081]    However, the present disclosure is not limited thereto and the rotating unit  300  may not have the second aperture  332 . In this case, one end of the string of the footwear, or the like, may pass through any one of the second lateral apertures  122  of the base unit  100  so as to be fixed to the rotating unit  300  and the other end of the string of the footwear, or the like, may pass through the other of the second lateral aperture  122  of the base unit  100  so as to be fixed to the rotating unit  300 . In this case, in order to fix the one end and the other end of the string, the rotating unit  300  may have at least one fixing protrusion portion configured for string fixing. 
         [0082]    When rotating, the rotating unit  300  rotates relatively with respect to the base unit  100 , and thus, it is preferred to increase rotation stability of the rotating unit  300 . To this end, the rotation support portion  130  and the rotation support protrusion portion  132  of the base unit  100  may interact with the second wing part  322  of the rotating unit  300 . For example, the rotating unit  300  may have a rotation protrusion portion  322   a  (described further in  FIG. 20 ) protruding downwardly (−z direction) from an end of the second wing part  322  in the radial direction, and a portion of a lower surface (−z direction) of the second wing part  322  adjacent to the rotation protrusion portion  322   a  may be configured to be in close proximity to or may be in contact with the rotation support protrusion portion  132  of the base unit  100 , whereby when the rotating unit  300  rotates, a position of a rotational central axis of the rotating unit  300  may be uniform, rather than being moved relatively with respect to the base unit  100 . 
         [0083]    The rotating unit  300  may be formed of a resin and/or a metal. 
         [0084]      FIG. 7  is a bottom perspective view schematically illustrating the cover unit of  FIG. 1 . As illustrated in  FIG. 7 , the cover unit  400  may be coupled to the middle unit  200  such that it is rotatable with respect to the middle unit  200 . Also, as mentioned above, when the cover unit  400  is engaged with the rotating unit  300 , the cover unit  400  may rotate in one direction together with the rotating unit  300 . 
         [0085]    The cover unit  400  has a responsive stoppage portion  410  protruding in a radial direction. As the responsive stoppage portion  410  of the cover unit  400  performs a mutual grasping operation with the upper stoppage portion  221  and/or the lower stoppage portion  222  of the middle unit  200 , the cover unit  400  may be rotatably coupled to the middle unit  200 . In addition, according to a relative position of the responsive stoppage portion  410  with respect to the upper stoppage portion  221  and the lower stoppage portion  222 , the cover unit  400  may be varied in distance to the base unit  100  so as to be engaged with the rotating unit  300  or separated from the rotating unit  300 . 
         [0086]    In detail, as the responsive stoppage portion  410  is positioned in a first space between the lower stoppage portion  222  and the partition  240  or positioned in a second space between the upper stoppage portion  221  and the lower stoppage portion  222 , a distance of the cover unit  400  to the base unit  100  may be varied. When the responsive stoppage portion  410  is positioned in the first space, the cover unit  400  may be engaged with the rotating unit  300  and rotate together with the rotating unit  300  in one direction, and when the responsive stoppage portion  410  is positioned in the second space, the cover unit  400  may be separated from the rotating unit  300  and the ratchet protrusion  460  and the responsive protrusion  250  are separated accordingly, and thus, the rotating unit  300  may rotate in one direction or in the other direction, opposite to the one direction, regardless of movement of the cover unit  400 . 
         [0087]    As illustrated in  FIG. 7 , the cover unit  400  has the second engaging portion  450  formed on a lower surface thereof in a direction (−z direction) toward the rotating unit  300 . In  FIG. 7 , it is illustrated that the second engaging portion  450  has a concave protrusion shape. However, the second engaging portion  450  may have a concave recess shape. That is, the second engaging portion  450  may be modified according to shapes of the first engaging portion  310  of the rotating unit  300 . When the second engaging portion  450  is engaged with the first engaging portion  310  of the rotating unit  300  described above, the rotating unit  300  may be rotated together with the cover unit  400 . Here, in order to prevent slipping between the rotating unit  300  and the cover unit while the first engaging portion  310  and the second engaging portion  450  are engaged with each other, shapes of cross-sections of the first engaging portion  310  and the second engaging portion  450  in the x-y plane may have various shapes such as a polygonal shape, an oval shape, or an asymmetrically distorted circular shape, or may have a configuration of a pin and a pin aperture. Other modified examples of the engaging portions will be described in detail with reference to  FIGS. 18 and 19 . 
         [0088]    As illustrated in  FIG. 7 , the cover unit  400  may have a central shaft  430  and the responsive stoppage portion  410  may be understood as a disk-shaped end portion extending from the central shaft  430  in a radial direction. A cover plate  420  may be positioned above (+z direction) the central shaft  430 . A lateral plate  440  may be understood as a portion bent at substantially 90 degrees from the edge of the cover plate  420 . When the cover unit  400  is coupled to the middle unit  200 , the lateral plate  440  may cover at least a portion of an outer circumferential portion of the middle unit  200  as illustrated in  FIG. 2 . In  FIG. 2 , it is illustrated that the lateral plate  220  covers most of the outer circumferential surface of the upper housing  210  of the middle unit  200 . 
         [0089]    A variety of these components of the cover unit  400  may be formed of a resin, plastic, and/or a metal, as one body. Alternatively, a portion of the components of the cover unit  400  may be separately formed and coupled to the central shaft  430 , and in this case, such a portion of the components may be formed of a resin, plastic, or a metal. 
         [0090]    In the string winding and unwinding apparatus according to the present embodiment, as mentioned above, when the responsive stoppage portion  410  is positioned in the first space below the lower stoppage portion  222 , the cover unit  400  may be engaged with the rotating unit  300  and rotated together with the rotating unit  300  in one direction, and accordingly, the string may be wound on the outer circumferential surface of the rotating unit  300 . When the responsive stoppage portion  410  is positioned between the upper stoppage portion  221  and the lower stoppage portion  222 , the rotating unit  300  may be rotated in the other direction, opposite to the one direction, i.e., an unwinding direction, regardless of movement of the cover unit  400  as the cover unit  400  is separated from the rotating unit  300 , and accordingly, the string wound around the outer circumferential surface of the rotating unit  300  may be unwound. That is, the string may be easily wound and unwound according to relative positions of the responsive stoppage portion  410  of the cover unit  400  and the upper stoppage portion  221  and the lower stoppage portion  222  of the middle unit  200 . 
         [0091]    In order to select winding and unwinding of the string, the user may need to control relative positions of the responsive stoppage portion  410  of the cover unit  400  and the upper stoppage portion  221  and the lower stoppage portion  222  of the middle unit  200 . 
         [0092]    That is, the user needs to control the responsive stoppage portion  410  of the cover unit  400  positioned in the first space below the lower stoppage portion  222  to be moved so as to be positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222 , or control the responsive stoppage portion  410  of the cover unit  400  positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  to be moved so as to be positioned in the first space below the lower stoppage portion  222 . During the controlling process, an impact may be applied to the upper stoppage portion  221  and/or the lower stoppage portion  222  of the middle unit  200 , and a repeated use thereof may result in damage to the upper stoppage portion  221  and the lower stoppage portion  222 . 
         [0093]    However, in the string winding and unwinding apparatus according to the present embodiment, when the upper stoppage portion  221  and/or the lower stoppage portion  222  of the middle unit  200  are damaged, only the middle unit  200  may need to be replaced, while leaving the base unit  100 , the rotating unit  300 , and the cover unit  400  as is, and thus, maintenance and repair may be easily and rapidly performed. In addition, in the string winding and unwinding apparatus according to the present embodiment, since maintenance and repair is performed by simply replacing a screw-fit component or inserting a replacement unit without the necessity of a specialized skill or without having to use a specific tool, users may directly easily perform maintenance and repair. 
         [0094]    Meanwhile, in the string winding and unwinding apparatus according to the present embodiment, a smooth coating may be formed on surfaces of the upper stoppage portion  221  and/or the lower stoppage portion  222  and/or the responsive stoppage portion  410  or elasticity and/or flexibility may be provided thereto in order to reduce a possibility of damage due to frictional force during a usage process. 
         [0095]    During the aforementioned controlling process, an impact may be applied to the responsive stoppage portion  410  of the cover unit  400 , rather than to the upper stoppage portion  221  and/or the lower stoppage portion  222  of the middle unit  200 , and thus, the responsive stoppage portion  410  of the cover unit  400  may be damaged due to repeated use thereof. Such a problem may be solved by allowing the responsive stoppage portion  410  to have elasticity. 
         [0096]    However, in the case of the string winding and unwinding apparatus according to the present embodiment, when the responsive stoppage portion  410  of the cover unit  400  is damaged, only the cover unit  400  may be simply replaced, while leaving the base unit  100 , the middle unit  200 , and the rotating unit  300  as is, and thus, maintenance and repair may be easily and rapidly performed. 
         [0097]      FIG. 8  is a cross-sectional view of a portion of the string winding and unwinding apparatus of  FIG. 1 . Similarly,  FIG. 2 , a cross-sectional view of the string winding and unwinding apparatus of  FIG. 1 , illustrates a state in which the responsive stoppage portion  410  is positioned in the first space below the lower stoppage portion  222  so the cover unit  400  is engaged with the rotating unit  300 , and in this state, the string may be wound according to rotation of the cover unit  400  and the rotating unit  300  in one direction. In  FIG. 8 , the response stoppage portion  410  is positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  so the cover unit  400  is spaced apart from the rotating unit  300 , releasing winding of the string. In this state, the rotating unit  300  may be able to rotate in the other direction (an unwinding, or releasing direction), an opposite direction of the one direction (winding direction), regardless of the cover unit  400 , the string may be unwound. 
         [0098]    As illustrated in  FIG. 8 , a distance d 2  between a second portion  221   b  of the upper stoppage portion  221  away from the upper housing  210  and the base plate  110  may be shorter than a distance d 1  between a first portion  221   a  of the upper stoppage portion  221  adjacent to the upper housing  210  and the base plate  110 . 
         [0099]    As described above, in order to select winding and unwinding of the string, the user needs to control relative positions of the responsive stoppage portion  410  of the cover unit  400  and the upper stoppage portion  221  and the lower stoppage portion  222  of the middle unit  200 . In a state in which the responsive stoppage portion  410  is positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222 , the user may press the cover unit  400  in a direction toward the base unit  100  such that the responsive stoppage portion  410  is moved to be positioned in the first space below the lower stoppage portion  222 . Conversely, in a state in which the responsive stoppage portion  410  of the cover unit  400  is positioned in the first space below the lower stoppage portion  222 , the user may pull the cover unit  400  in a direction (+z direction) away from the base unit  100  such that the responsive stoppage portion  410  is moved to be positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222 . During this process, in order to prevent the cover unit  400  from being separated from the middle unit  200 , as illustrated in  FIG. 8 , the distance d 2  between the second portion (end portion in the direction toward the central shaft  430 ) of the upper stoppage portion  221  away from the upper housing  210  and the base plate  110  is shorter than the distance d 1  between the first portion of the upper stoppage portion  221  adjacent to the upper housing  210  and the base plate  110 . For example, the upper stoppage portion  221  may have a shape of drooping in a direction toward the base plate  110  so that the upper stoppage portion  221  is closer to the base plate  110  as it is away from the inner circumferential surface  210   a  of the upper housing  210 . However, the present disclosure is not limited thereto and the upper stoppage portion  221  may have a shape that does not droop toward the base plate  110 . 
         [0100]    Meanwhile, in order to control the response stoppage portion  410  positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  to move to be positioned in the first space below the lower stoppage portion  222 , the user may press the cover unit  400  in a direction toward the base unit  100 . According to circumstances, it may be necessary to prevent the cover unit  400  from excessively moving toward the base unit  100 . This may be implemented by using the partition  240  of the middle unit  200 . 
         [0101]    As described above, the partition  240  is positioned to be closer to the base plate  110  than the lower stoppage portion  222 , and may have a shape protruding in an inward direction (direction toward the central shaft  430 ) from the upper housing  210 . When the responsive stoppage portion  410  of the cover unit  400  is positioned in the space below the lower stoppage portion  222 , an excessive movement of the responsive stoppage portion  410  in the direction toward the base unit  100  may be effectively prevented by the partition  240 . 
         [0102]    When the responsive stoppage portion  410  is positioned in the first space below the lower stoppage portion  222 , the cover unit  400  is engaged with the rotating unit  300 , and in this case, the cover unit  400  and the rotating unit  300  may rotate only in one preset direction according to operations of the ratchet protrusion  460  and the responsive protrusion  250 . In detail, surfaces of the ratchet protrusion  460  and the responsive protrusion  250  that meet each other in the winding direction are surfaces that meet each other at a gentle sloped angle so as to mutually overstride, while surfaces of the ratchet protrusion  460  and the responsive protrusion  250  that meet each other in the opposite direction of the winding direction are vertical surfaces standing in the +z direction, and thus, rotation is not possible in the opposite direction, namely, in the winding releasing direction. This is because, if the rotating unit  300  rotates in the other direction, regardless of a user&#39;s intention, the string wound on the rotating unit  300  may be unwound irrespective of the user intention. 
         [0103]    As described above, the responsive protrusion  250  may be positioned on a surface of the partition  240  in a direction (+z direction) of the lower stoppage portion  222 . Here, when the cover unit  400  may have the ratchet protrusion  460  (please refer to  FIG. 7 ) in one direction, and when the responsive stoppage portion  410  is positioned in the first space below the lower stoppage portion  222 , the responsive protrusion  250  may be engaged with the ratchet protrusion  460 . When the responsive protrusion  250  is engaged with the ratchet protrusion  460 , the cover unit  400  may rotate only in one preset direction with respect to the middle unit  200 , and thus, the rotating unit  300  engaged with the cover unit  400  may also rotate only in one preset direction. 
         [0104]    In the case of the responsive protrusion  250  having such a shape as that illustrated in  FIG. 4  and the ratchet protrusion  460  having such a shape as that illustrated in  FIG. 7 , in a state in which the responsive stoppage portion  410  is positioned in the first space below the lower stoppage portion  222 , the cover unit  400  may rotate only in a clockwise direction (i.e., the winding direction) when the user views the cover unit  400  in the −z direction. Here, as illustrated in  FIG. 8 , when the response stoppage portion  410  is positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222 , the responsive protrusion  250  may be separated from the ratchet protrusion  460 . 
         [0105]      FIG. 9  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. As illustrated in  FIG. 9 , the string winding and unwinding apparatus according to the present embodiment, the middle unit  200  may have a stoppage support portion  230 . 
         [0106]    The stoppage support portion  230  may have a shape extending from the upper housing  210  inwardly (direction toward the central shaft  430 ) and bent such that a space is present between the stoppage support portion  230  and the inner circumferential surface  210   a  of the upper housing  210 . In detail, the stoppage support portion  230  may have a first portion  231  extending inwardly from the upper housing  210 , a second portion  233  extending in a direction (−z direction) intersecting the first portion  231 , and a bent portion  232  between the first portion  231  and the second portion  233 . Thus, a space may be present between the second portion  233  of the stoppage support portion  230  and the inner circumferential surface  210   a  of the upper housing  210 . The stoppage support portion  230  may be integrated with the upper housing  210  as illustrated in  FIG. 9 . The upper stoppage portion  221  and the lower stoppage portion  222  may be positioned on a surface of the stoppage support portion  230  in a direction (direction toward the central shaft  430 ) away from the upper housing  210 . The upper stoppage portion  221  and the lower stoppage portion  222  may be integrated with the stoppage support portion  230  as illustrated in  FIG. 9  or may be installed as separate components. 
         [0107]    When the user presses the cover unit  400  in a direction toward the base unit  100  or when the user pulls the cover unit  400  away from the base unit  100 , the responsive stoppage portion  410  positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  may move to the first space below the lower stoppage portion  222 . Here, since the space is present between the stoppage support portion  230  and the inner circumferential surface  210   a  of the upper housing  210  as described above, when the responsive stoppage portion  410  moves, the stoppage support portion  230  may be slightly bent to move in a direction toward the inner circumferential surface  210   a  of the upper housing  210 , and thereafter, when the movement of the responsive stoppage portion  410  is completed, the stoppage support portion  230  may return to its original position. Accordingly, damage to the responsive stoppage portion  410 , the upper stoppage portion  221  and/or the lower stoppage portion  222  due to the movement of the responsive stoppage portion  410  may be effectively prevented, and in addition, ease of manipulation of the cover unit  400  by the user may be further enhanced. 
         [0108]    In addition to the upper stoppage portion  221  and the lower stoppage portion  222 , as illustrated in  FIG. 9 , a third (additional) stoppage portion  223  may be positioned on the stoppage support portion  230  such that the additional stoppage portion  223  is closer to the base plate  110  than the lower stoppage portion  222 . Like the upper stoppage portion  221  and the lower stoppage portion  222 , the additional stoppage portion  223  may be positioned on a surface of the stoppage support portion  230  in a direction (direction toward the central shaft  430 ) away from the upper housing  210 . The additional stoppage portion  223  may serve to limit the first space below the lower stoppage portion  222  together with the lower stoppage portion  222 . The additional stoppage portion  223  may limit a movement of the responsive stoppage portion  410  in a direction toward the base plate  110 , thus serving to prevent the cover unit  400  from excessively moving in the direction toward the base unit  100 . However, without the additional stoppage portion  223 , the space between the lower stoppage portion  222  and the partition  240  may serve to limit the first space. This is no different in the embodiments or modified examples thereof described above and/or described hereinafter. 
         [0109]      FIG. 10  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. In the string winding and unwinding apparatus according to the present embodiment, the stoppage support portion  230  has a shape extending inwardly (direction toward the central shaft  430 ) from the upper housing  210 . The stoppage support portion  230  extends inwardly from the upper housing  210  such that a space is present between the stoppage support portion  230  and the inner circumferential surface  210   a  of the upper housing  210 , and has a shape of being bent a plurality of times. In detail, the stoppage support portion  230  is bent a plurality of times such that at least two portions thereof are convex in a direction (direction toward the central shaft  430 ) away from the upper housing  210 . The upper stoppage portion  221  and the lower stoppage portion  222  may be understood as the convex portions of the stoppage support portion  230 . As illustrated in  FIG. 10 , the stoppage support portion  230  may be integrated with the upper housing  210 . 
         [0110]    When the user presses the cover unit  400  in a direction toward the base unit  100  or when the user pulls the cover unit  400  away from the base unit  100 , the responsive stoppage portion  410  positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  may move to the first space below the lower stoppage portion  222 . Here, since the space is present between the stoppage support portion  230  and the inner circumferential surface  210   a  of the upper housing  210  as described above, when the responsive stoppage portion  410  moves, the stoppage support portion  230  may be slightly bent to move in a direction toward the inner circumferential surface  210   a  of the upper housing  210 , and thereafter, when the movement of the responsive stoppage portion  410  is completed, the stoppage support portion  230  may return to its original position. Accordingly, damage to the responsive stoppage portion  410 , the upper stoppage portion  221  and/or the lower stoppage portion  222  due to the movement of the responsive stoppage portion  410  may be effectively prevented, and in addition, ease of manipulation of the cover unit  400  by the user may be further enhanced. 
         [0111]    As illustrated in  FIG. 10 , in the stoppage support portion  230  having a shape of being bent a plurality of times, an end portion thereof in a direction toward the base plate  110  may have a shape of being oriented in a direction (direction toward the central shaft  430 ) away from the inner circumferential surface  210   a  of the upper housing  210 . The end portion may be understood as the additional stoppage portion  223  as described above with reference to  FIG. 9 . That is, the end portion may serve to limit the first space below the lower stoppage portion  222  together with the lower stoppage portion  222 . The additional stoppage portion  223  may limit a movement of the responsive stoppage portion  410  in a direction toward the base plate  110 , thus serving to prevent the cover unit  400  from excessively moving in the direction toward the base unit  100 . 
         [0112]    In  FIG. 10 , the stoppage support portion  230  having a shape which is bent a plurality of times, which extends in an inward direction from the upper housing  210 , is integrated with the upper housing  210 , but the present disclosure is not limited thereto. For example, as illustrated in  FIG. 11 , a cross-sectional view of a portion of the string winding and unwinding apparatus according to another embodiment of the present disclosure, the middle unit  200  of the string winding and unwinding apparatus according to the present embodiment may have a flexure  230 ′ as a separate component. The flexure  230 ′ may be installed in a aperture penetrating through the upper housing  210  or a recess. In  FIG. 11 , it is illustrated that the flexure  230 ′ is fixed to the upper housing  210  as a portion thereof is inserted into a aperture penetrating through the upper housing  210 . Most of the flexure  230 ′ is positioned at an inner side of the upper housing  210 . That is, when the flexure  230 ′ is fixed to the upper housing  210 , most of the flexure  230 ′ is positioned at the inner side of the upper housing  210  except for a portion thereof used to be fixed to the upper housing  210 . 
         [0113]    The flexure  230 ′ may have a shape similar to that of the stoppage support portion  230  having a shape of being bent a plurality of times described above with reference to  FIG. 10 . That is, the flexure  230 ′ may have a bent shape such that a space is present between the flexure  230 ′ and the inner circumferential surface  210   a  of the upper housing  210 . In detail, the flexure  230 ′ may be bent a plurality of times such that at least two convex portions are present in a direction (direction toward the central shaft  430 ) away from the upper housing  210 . The upper stoppage portion  221  and the lower stoppage portion  222  may be understood as the convex portions of the flexure  230 ′. The flexure  230 ′ may be formed using a resin, plastic, or a metal plate, and preferably, the flexure  230 ′ has elasticity. 
         [0114]    When the user presses the cover unit  400  in a direction toward the base unit  100  or when the user pulls the cover unit  400  away from the base unit  100 , the responsive stoppage portion  410  positioned in the second space between the upper stoppage portion  221  and the lower stoppage portion  222  may move to the first space below the lower stoppage portion  222 . Here, since the space is present between the flexure  230 ′ and the inner circumferential surface  210   a  of the upper housing  210  as described above, when the responsive stoppage portion  410  moves, the flexure  230 ′ may be slightly moved in a direction toward the inner circumferential surface  210   a  of the upper housing  210 , and thereafter, when the movement of the responsive stoppage portion  410  is completed, the flexure  230 ′ may return to its original position. Accordingly, damage to the responsive stoppage portion  410 , the upper stoppage portion  221  and/or the lower stoppage portion  222  due to the movement of the responsive stoppage portion  410  may be effectively prevented, and in addition, ease of manipulation of the cover unit  400  by the user may be further enhanced. In addition, when the flexure  230 ′ is damaged due to repeated use thereof by the user, only the flexure  230 ′ may be replaced, remarkably enhancing ease of maintenance and repair of the string winding and unwinding apparatus. 
         [0115]    As illustrated in  FIG. 11 , the flexure  230 ′ having the shape of being bent a plurality of times, an end portion thereof in a direction toward the base plate  110  may have a shape of being oriented in a direction (direction toward the central shaft  430 ) away from the inner circumferential surface  210   a  of the upper housing  210 . The end portion may be understood as the additional stoppage portion  223  as described above with reference to  FIG. 9 . That is, the end portion may serve to limit the first space below the lower stoppage portion  222 . The additional stoppage portion  223  may limit a movement of the responsive stoppage portion  410  in a direction toward the base plate  110 , thus serving to prevent the cover unit  400  from excessively moving in the direction toward the base unit  100 . 
         [0116]    Also, in the embodiments of  FIGS. 8 through 10 , the upper stoppage portion and the lower stoppage portion may be configured using separate components, like the embodiment of  FIG. 11 . 
         [0117]      FIG. 12  is a cross-sectional view of a portion of a string winding and unwinding apparatus according to another embodiment of the present disclosure. As illustrated in  FIG. 12 , in the string winding and unwinding apparatus according to the present embodiment, the upper stoppage portion  221  and the lower stoppage portion  222  may have a shape of being concavely recessed from the surface of the upper housing  210 . That is, the upper stoppage portion  221  and the lower stoppage portion  222  may be understood as concave portions formed on the inner circumferential surface  210   a  of the upper housing  210 . In this case, when at least a portion of the responsive stoppage portion  410  is positioned within the lower stoppage portion  222 , the cover unit  400  is engaged with the rotating unit  300 , and when at least a portion of the responsive stoppage portion  410  is positioned within the upper stoppage portion  221 , the cover unit  400  may be separated from the rotating unit  300 . 
         [0118]    In the string winding and unwinding apparatus according to the present embodiment, when the responsive stoppage portion  410  positioned within the upper stoppage portion  221  moves to be positioned within the lower stoppage portion  222  or when the responsive stoppage portion  410  positioned within the lower stoppage portion  222  moves to be positioned within the upper stoppage portion  221 , the movement of the responsive stoppage portion  410  needs to be facilitated. To this end, at least a portion of the responsive stoppage portion  410  may be flexible. Specifically, at least an end portion of the responsive stoppage portion  410  (in the direction toward the upper housing  210 ) may be flexible. For example, the end portion of the responsive stoppage portion  410  may include rubber or a leaf spring so as to be flexible. The configuration in which at least a portion of the responsive stoppage portion  410  is flexible may also be applied to all of the embodiments described above with reference to the drawings, embodiments to be described hereinafter, or modified examples thereof, as well as to the case of the present embodiment. 
         [0119]    Alternatively, as illustrated in  FIG. 13 , a cross-sectional view of a portion of the string winding and unwinding apparatus according to another embodiment, a recess  430   a  may be formed on an outer surface of the central shaft  430  of the cover unit  400 , and the responsive stoppage portion  410  may be press-fit to the recess  430   a . Also, in this case, at least a portion of the responsive stoppage portion  410  may be formed to be flexible. Specifically, an end portion (in the direction toward the upper housing  210 ) of the responsive stoppage portion  410  may be formed to be flexible. For example, the responsive stoppage portion  410  or the end portion of the responsive stoppage portion  410  may include rubber or a leaf spring so as to be flexible. The configuration in which the recess  430   a  is formed on an outer surface of the central shaft  430  of the cover unit  400  and the responsive stoppage portion  410  is press-fit to the recess  430   a  may also be applied to all of the embodiments described above with reference to the drawings, embodiments to be described hereinafter, or modified examples thereof, as well as to the case of the present embodiment. Here, for reference, the configuration in which the recess  430   a  is formed on an outer surface of the central shaft  430  may be understood as including a configuration in which a aperture penetrating through the central shaft  430  is formed. This is because, a portion of the aperture may be construed as a recess of the outer surface of the central shaft  430 . 
         [0120]    As described above, when the cover unit  400  is engaged with the rotating unit  300 , the ratchet protrusion  460  and the responsive protrusion  250  are engaged with each other, and when the cover unit  400  is separated from the rotating unit  300 , the ratchet protrusion  460  and the responsive protrusion  250  are separated from each other. 
         [0121]    In  FIGS. 1 through 13  referred to which describe the embodiments so far, it is illustrated that the ratchet protrusion  460  is positioned on a lower surface of the cover unit  400  in the direction (−z direction) toward the base plate  110  and the responsive protrusion  250  is formed in the middle unit  200  and protrudes in the +z direction toward the cover unit  400 . In detail, in  FIGS. 1 through 13 , it is illustrated that the ratchet protrusion  460  is positioned on a lower surface of the central shaft  430  in the direction (−z direction) toward the base plate  110  or on a lower surface of the responsive stoppage portion  410  in the direction (−z direction) of the base plate  110  and the responsive protrusion  250  is positioned on an upper surface of the partition  240  in the direction (+z direction) of the cover unit  400 . However, the present disclosure is not limited thereto. 
         [0122]    For example, as illustrated in  FIG. 14 , a perspective view schematically illustrating the middle unit  200  of the string winding and unwinding apparatus according to another embodiment of the present disclosure, the responsive protrusion  250  may be positioned on an inner surface of the partition  240  in a direction toward the center of the upper housing  210 . In this case, as illustrated in  FIG. 15 , a cross-sectional view of a portion of the cover unit  400  that may be used together with the middle unit  200  of  FIG. 14 , the ratchet protrusion  460  may also be positioned on a side surface of the central shaft  430  of the cover unit  400 , namely, on an outer side surface of the central shaft  430  of the cover unit  400  in a direction toward the upper housing  210 , so that the ratchet protrusion  460  may be engaged with the responsive protrusion  250  or may be separated therefrom. To this end, as illustrated in  FIG. 15 , the central shaft  430  of the cover unit  400  may extend further than the position of the responsive stoppage portion  410  in a downward direction (−z direction). 
         [0123]    In the embodiments described so far, the examples in which both the ratchet protrusion  460  and the responsive protrusion  250  protrude convexly have been described, but any one of the ratchet protrusion  460  and the responsive protrusion  250  may have a concavely recessed shape. That is, any configuration may belong to the technical concept of the present invention as long as a ratchet protrusion and a response protrusion are fit to each other, surfaces thereof that meet in a winding direction meet at a gentle sloped angle so as to mutually overstride, and surfaces thereof that meet in a winding releasing direction meet at an angle similar to that of at least a vertical wall so movement thereof is limited. 
         [0124]    According to another embodiment of the present disclosure illustrated in  FIG. 16 , an elastic bar  465 , instead of the ratchet protrusion  460 , is installed in the cover unit  400 . Meanwhile, the responsive protrusion  250  of the middle unit  200  is formed to protrude toward the cover unit  400  from the partition  240  of the middle unit  200 . A plurality of responsive protrusions  250  are continuously formed along the partition  240  formed to have a circular shape, a gentle sloped surface is formed on one surface thereof to allow the elastic bar  465  of the cover unit  400  to overstride thereon so as to be rotated in a direction in which the string is wound, and a vertical surface or a sloped surface more tilted in the winding direction is formed on the other surface thereof such that the string cannot rotate reversely in an unwinding direction. The use of the configuration of the elastic bar  465 , instead of the ratchet protrusion  460 , may prevent reverse rotation of the cover unit  400  through only one or some elastic bars  465 , reduce frictional wear due to the elastic deformation of the elastic bar  465 , and thus may be used many times before wearing out. 
         [0125]    According to another embodiment of the present disclosure illustrated in  FIG. 17 , an elastic bar  255 , instead of the responsive protrusion  250 , is installed in the middle unit  200 . Here, the ratchet protrusion  460  of the cover unit  400  is formed on the lower surface of the cover unit  400  in a direction (−z direction) toward the base plate  110  in the same manner as those described above with reference to  FIGS. 1 through 13 . The ratchet protrusion  460  of the cover unit  400  has a gentle sloped surface formed on one surface thereof so as to rotate in a direction in which the string is wound and a vertical surface, or a sloped surface more tilted in the winding direction, formed on the other surface thereof so as not to reversely rotate in a direction in which the string is unwound. The use of the configuration of the elastic bar  255 , instead of the responsive protrusion  250 , as in the present embodiment allows the ratchet protrusion  460  to smoothly overstride on the elastic bar  255  due to elastic deformation of the elastic bar  255 , ensuring a smooth operation and enhancing durability. 
         [0126]      FIGS. 18 and 19  are views illustrating modified examples of the first engaging portion  310  of the rotating unit  300  and the second engaging portion  450  of the cover unit  400  illustrated in  FIGS. 1 through 13 . 
         [0127]    According to another embodiment of the present disclosure illustrated in  FIG. 18 , a first engaging portion  315  of the rotating unit  300  and a second engaging portion  455  of the cover unit  400  are configured as ratchet protrusions having a sloped surface and a vertical surface in mutually opposite directions. According to this configuration, in the direction in which the string is wound, the vertical surfaces of the second engaging portion  455  of the cover unit  400  and the first engaging portion  315  of the rotating unit  300  are tightly attached, and thus, the mutual vertical surfaces cannot overstride on each other, and in the direction in which the string is unwound, the gentle sloped surfaces thereof are tightly attached, and thus, the gentle sloped surfaces overstride on each other so as to rotate. In other words, the engaging portions are configured in a direction opposite to the directions of the sloped surface and vertical surface of the reverse rotation preventing portion described above with reference to  FIGS. 16 and 17 . The reason for the configuration of the engaging portions is because the cover unit  400  and the rotating unit  300  should be engaged with each other to rotate together when the engaging portions are rotated in the direction in which the string is wound. According to another embodiment of the present disclosure, in the embodiment of  FIG. 18 , any one of the first engaging portion  455  of the cover unit  400  and the first engaging portion  315  of the rotating unit  300  may be configured as an elastic bar as illustrated in  FIGS. 16 and 17 . Also, in the embodiment of  FIG. 18 , any one of the first engaging portion  455  of the cover unit  400  and the first engaging portion  315  of the rotating unit  300  may be configured as a protrusion and the other may be configured as a recess to which the protrusion may be press-fit. 
         [0128]    According to another embodiment of the present disclosure illustrated in  FIG. 19 , the first engaging portion  315  has a recess shape having a serrated sloped surface formed along an inner circumferential surface, and the second engaging portion  456  of the cover unit  400  has a bar shape having a serrated sloped surface formed along an outer circumferential surface. According to the configuration of the first engaging portion  310  having a hexagonal recess and the second engaging portion  450  having a hexagonal bar shape, when the cover unit  400  is pressed (in the −z direction), if the hexagonal corners of the first engaging portion  310  and the second engaging portion  450  do not fit to each other, angles should be repeatedly adjusted to align them. In contrast, according to the present embodiment illustrated in  FIG. 19 , when the cover unit  400  is pressed (in the −z direction), since a probability that adjacent sawteeth are engaged is high, compared with the hexagonal shape, aligning may be easily performed. In addition, the uppermost end of the sloped surface of the recess having the serrated shape forming the first engaging portion  315  of the rotating unit  300  may be cut away in a chamfered manner and the lowermost end of the sloped surface of the bar having the serrated shape forming the second engaging portion  455  of the cover unit  400  may be cut away in a chamfered manner, and in this state, when the cover unit  400  is pressed (in the −z direction), the first engaging portion  316  and the second engaging portion  455  may be smoothly engaged with each other, eliminating the necessity of aligning. 
         [0129]    Although not shown in  FIGS. 18 and 19 , according to another embodiment of the present disclosure, the engaging portions between the cover unit  400  and the rotating unit  300  may be configured as a unidirectional clutch bearing. 
         [0130]      FIG. 20  is a cross-sectional view schematically illustrating the base unit  100 , the rotating unit  300 , and a restoring unit of the string winding and unwinding apparatus according to an embodiment of the present disclosure. As illustrated in  FIG. 20 , the string winding and unwinding apparatus according to the present embodiment may include an elastic member. Such an elastic member may be a restoring string (RS) including a material such as resin, plastic, and/or a metal and having elasticity including rubber and/or a spring. In addition to the restoring string RS, any object may also be used as the elastic member as long as the object has elasticity. For example, a spring such as a tension spring may also be used as the restoring string. Hereinafter, for the purposes of description, a case in which the restoring unit has the restoring string RS will be described. The restoring string RS may sequentially pass through one of the first lateral apertures  121 , the first aperture  331 , and the other of the first lateral apertures  121 . That is, the restoring string RS may pass through the first aperture  331  of the rotating unit  300 , and in addition, both ends of the restoring string RS may pass through the first lateral apertures  121  so as to be fixed to the base unit  100 . For example, one end of the restoring string RS may pass through the first lateral aperture  121  and may subsequently be knotted on the outer side of the lower housing  120 , and the other end thereof may also pass through the first lateral aperture  121  and may subsequently be knotted on the outer side of the lower housing  120 . Alternatively, both ends of the restoring string RS may meet on an outer side of the base unit  100  so as to be knotted. One end and the other end of the restoring string RS may be fixed to the base unit  100 , or one end thereof may be fixed to the base unit  100  and the other end thereof may be fixed to the rotating unit  300 . 
         [0131]    In this manner, the restoring string RS may pass through the first aperture  331  of the rotating unit  300  and may be fixed to the base unit  100  through various methods. Accordingly, when the rotating unit  300  is engaged with the cover unit  400  and rotated in one direction so the string of footwear, or the like, is wound around the outer circumferential surface of the rotating unit  300 , the restoring string RS having elasticity may also extend in length and may be wound around the rotating unit  300 . In this state, when the rotating unit  300  is separated from the cover unit  400 , the rotating unit  300  is automatically rotated in the unwinding direction by the elasticity of the restoring string RS. The restoring string RS provides a restoring force which serves to help unwind the strings (e.g. shoelaces). Thus, the user may not need to directly turn the rotating unit  300  in the other direction in order to loosen the string of the footwear, or the like, and thus, user convenience may remarkably be enhanced. 
         [0132]    For reference,  FIGS. 1 through 3  illustrate that the base unit  100  has the first lateral apertures  121 , but the present disclosure is not limited thereto. For example, the base unit  100  may have a recess or a protrusion portion at an inner side thereof, without the first lateral apertures  121 , and both ends of the restoring string RS may be fixed to the recess or the protrusion portion within the base unit  100 . At least one end of the restoring string RS may be fixed to the base unit  100  and the other end thereof may be fixed to the rotating unit  300  or may be fixed to the opposite side of the base unit  100  across the rotating unit  300 . 
         [0133]    As illustrated in  FIG. 6 , the rotating unit  300  may have the second aperture  332  penetrating through the rotating unit  300  in a space between the first wing part  321  and the second wing part  322 . As illustrated in  FIG. 6 , the second aperture  332  may be positioned to be farther from the base plate  110  than the first aperture  331  in the z+ direction. The second aperture  332  may correspond to the second lateral apertures  122  of the base unit  100 . Here, when the second aperture  332  corresponds to the second lateral apertures  122 , it means that a height of the second aperture  332  from the base plate  110  and a height of the second lateral apertures  122  from the base plate  110  are substantially equal. 
         [0134]    A string (not shown) of footwear, or the like, may pass through any one of the second lateral apertures  122  of the base unit  100 , penetrate through the second aperture  332  of the rotating unit  300 , and subsequently pass through the other of the second lateral apertures  122 . Accordingly, when the rotating unit  300  in a state of being engaged with the cover unit  400  rotates in one direction, the string may be wound around the rotating unit  300 . In detail, the string is wound in the space between the first wing part  321  and the second wing part  322 . In this manner, the string may be wound in the footwear, or the like. Here, although a ratchet protrusion  460  and the responsive protrusion  250  meet each other, wedge shapes of the ratchet protrusion  460  and the responsive protrusion  250  allow the cover unit  400  to rotate in one direction, and when the rotation of the cover unit  400  in one direction is stopped, the wedge shapes of the ratchet protrusion  460  and the responsive protrusion  250  limit rotations of the cover unit  400  and the rotating unit  300  in the other direction, i.e., the opposite direction, in the stopped position. In this state, when the rotating unit  300  is separated from the cover unit  400 , the ratchet protrusion  460  and the responsive protrusion  250  are also separated, releasing the wound state, and thus, the rotating unit  300  may rotate in the other direction (the loosening/unwinding direction) by virtue of restoring force of the restoring string RS, and accordingly, the string, which has been wound around the rotating unit  300 , may be unwound from an outer circumferential surface of the rotating unit  300 . 
         [0135]    However, the present disclosure is not limited thereto and the rotating unit  300  may not have the second aperture  332 . In this case, one end of the string of the footwear, or the like, may pass through any one of the second lateral apertures  122  of the base unit  100  so as to be fixed to the rotating unit  300  and the other end of the string of the footwear, or the like, may pass through the other of the second lateral aperture  122  of the base unit  100  so as to be fixed to the rotating unit  300 . In this case, in order to fix the one end and the other end of the string, the rotating unit  300  may have at least one fixing protrusion portion (not shown) or a fixing recess portion (not shown) configured for string fixing. 
         [0136]    When rotating, the rotating unit  300  rotates relatively with respect to the base unit  100 , and thus, it is preferred to increase rotation stability of the rotating unit  300 . To this end, the rotation support portion  130  and the rotation support protrusion portion  132  of the base unit  100  may interact with the second wing part  322  of the rotating unit  300 . For example, the rotating unit  300  may have a rotation protrusion portion  322   a  protruding downwardly (−z direction) from an end of the second wing part  322  in the radial direction, and a portion of a lower surface (−z direction) of the second wing part  322  adjacent to the rotation protrusion portion  322   a  may be configured to be in close proximity to or may be in contact with the rotation support protrusion portion  132  of the base unit  100 , whereby when the rotating unit  300  rotates, a position of a rotational central axis of the rotating unit  300  may be uniform, rather than being moved relatively with respect to the base unit  100 . 
         [0137]    The rotating unit  300  may be formed of a resin, plastic, and/or a metal. 
         [0138]      FIG. 21  is a cross-sectional view schematically illustrating the base unit  100  of a string winding and unwinding apparatus according to another embodiment of the present disclosure. As described above, the restoring string RS may sequentially pass through one of the first lateral apertures  121  of the base unit  100 , the first aperture  331  of the rotating unit  300 , and the other of the first lateral apertures  121 . Here, the restoring string RS may have a closed loop shape in which opposing ends are tied or engaged. In this case, residual portions of the restoring string RS (the portions outside of the base unit), excluding the portion thereof sequentially passing through any one of the first lateral apertures  121 , the first aperture  331 , and the other of the first lateral apertures  121 , may be exposed to the outside of the base unit  100 . In this case, the restoring string RS may be damaged by an external impact, which, thus, may need to be protected. 
         [0139]    To avoid the damage, in the string winding and unwinding apparatus according to the present embodiment, the base unit  100  has a shielding unit  125 . Thus, a tunnel formed within the shielding unit  125  shields at least a portion of the residual portions of the restoring string RS, serving to prevent damage to the restoring string RS. 
         [0140]    In  FIG. 21 , it is illustrated that the shielding unit  125  is positioned in a portion in which the base plate  110  of the base unit  100  and the lower housing  120  meet and a space defined by an inner surface of the shielding unit  125 , an outer surface of the lower housing  120 , and an outer surface of the base plate  110  is a tunnel. However, the present disclosure is not limited thereto and the tunnel may be defined by the inner surface of the shielding unit  125  in contact with at least any one of the outer surface of the lower housing  120  and the outer surface of the base plate  110 . Alternatively, the tunnel may be formed within the lower housing  120  or within the base plate  110 . Also, if necessary, the tunnel may be formed as an open trench with an open upper portion. 
         [0141]      FIG. 22  is a cross-sectional view schematically illustrating the base unit  100  and the rotating unit  300  of a string winding and unwinding apparatus according to another embodiment of the present disclosure. The string winding and unwinding apparatus according to the present embodiment is different from the string winding and unwinding apparatus according to the previous embodiment described above with reference to  FIG. 2 , in that the second lateral apertures  122  are positioned to be closer to the base plate  110  than the first lateral apertures  121  in the base unit  100  and that the second aperture  332  is positioned to be closer to the base plate  110  than the first aperture  331  in the rotating unit  300 . In this case, a string of footwear, or the like, may sequentially pass through any one of the second lateral apertures  122  positioned in the lower portion, the second aperture  332 , and the other of the second lateral apertures  122  positioned in the lower portion, so as to be wound around an outer circumferential surface of the rotating unit  300  in the space between the second wing part  322  and the third wing part  323 , or may be unwound therefrom. The restoring string RS of the restoring unit may sequentially pass through any one of the first lateral apertures  121  positioned in the upper portion, the first aperture  331 , and the other of the first lateral apertures  121  positioned in the upper portion. 
         [0142]    In the string winding and unwinding apparatus according to the present embodiment, the string of footwear, or the like, passes through the lowermost end portion of the string winding and unwinding apparatus. Thus, the string of footwear, or the like, is effectively prevented from being separated in a direction away from the surface of footwear, or the like, or a degree to which the string is separated from the surface of footwear, or the like, may be minimized. If the string of footwear, or the like, is separated significantly from the surface of footwear, or the like, the string of footwear, or the like, may be caught by an external object or damaged when used. However, the string winding and unwinding apparatus according to the present embodiment may prevent or minimize generation of such a problem. 
         [0143]    That is, according to the technical concept of the present invention, as in the embodiment described above with reference to  FIG. 2 , the string may be wound around in the space between the first wing part  321  and the second wing part  322  and the restoring string may be wound in the space between the second wing part  322  and the third wing part  323 , and also, as in the embodiment described above with reference to  FIG. 22 , the restoring string may be wound in the space between the first wing part  321  and the second wing part  322  and the string to be wound may be wound around in the space between the second wing part  322  and the third wing part  323 . 
         [0144]      FIG. 23  is an exploded side view schematically illustrating the rotating unit  300  of a string winding and unwinding apparatus according to another embodiment of the present disclosure. The rotating unit  300  of the string winding and unwinding apparatus according to the present embodiment has a first rotating portion  301  and a second rotating portion  302  that may be detachably coupled. The first rotating part  301  may have a second wing part  322  and a third wing part  323 , and the second rotating part  302  may have a first wing part  321 . The first rotating part  301  and the second rotating part  302  may be fastened to each other as a coupling concave portion  322   b  of an upper surface of the second wing part  322  of the first rotating part  301  and a coupling protrusion portion  321   a  of a lower surface of the first wing part  321  of the second rotating part  302  are engaged with each other. 
         [0145]    The first rotating part  301  has a first aperture  331  allowing the restoring string RS to pass therethrough. When the first rotating part  301  and the second rotating part  302  are coupled, a second aperture  332  is formed therebetween. The second aperture  332  formed thusly corresponds to the second lateral apertures  122  of the lower housing  120  of the base unit  100 . A string of footwear, or the like, may sequentially pass through one of the second lateral apertures  122 , the second aperture  332  formed as the first rotating part  301  and the second rotating part  302  are coupled, and the other of the second lateral apertures  122 . The string may be wound around an outer circumferential surface of the rotating unit  300  or unwound therefrom according to rotation of the rotating unit  300 . 
         [0146]    The string winding and unwinding apparatus according to the present embodiment may be easily connected to an external string and very easy in maintenance and repair. For example, when the string winding and unwinding apparatus according to the present embodiment is intended to be installed in footwear, or the like, the base unit  100  in which the first rotating part  301  is positioned may be installed in the footwear, or the like, an upper portion of the first rotating part  301  may be positioned to allow a string to pass therethrough, and the second rotating part  302  may subsequently be coupled to the first rotating part  301 , whereby the string of the footwear, or the like, may be connected to the rotating unit  300 . When the string of the footwear, or the like, is damaged while in use, so it is required to be replaced, the second rotating part  302  may be separated from the first rotating part  301 , the string of the footwear, or the like, may be replaced, and the second rotating part  302  may subsequently be coupled to the first rotating part  301 , and thus, maintenance and repair may also be easily performed. In addition, in the case of the string winding and unwinding apparatus according to the present embodiment, a specialized skill or a specific tool is not required for maintenance and repair. That is, a component installed between the middle unit  200  and the base unit  100  may be easily disassembled and replaced through simple screw fitting, bolt-nut coupling, or clip coupling. Also, for example, since maintenance and repair is performed by simply inserting a replacement unit like the second rotating part  302 , users may directly perform maintenance and repair easily for use. 
         [0147]    In  FIG. 23 , it is illustrated that the second rotating part  302  is positioned above the first rotating part  301 , but the present disclosure is not limited thereto. For example, the first rotating part  301  may have the first wing part  321  and the second wing part  322  and have the first aperture  331  formed between the first wing part  321  and the second wing part  322  and allowing the restoring string RS of the restoring unit to pass therethrough. The second rotating part  302  may be positioned below (−z direction) the first rotating part  301 . In addition, when the upper first rotating part  301  and the lower second rotating part  302  are coupled to each other, the second aperture  332  may be formed therebetween. That is, in the rotating unit  300  having the configuration such as described above with reference to  FIG. 10 , a portion including the third wing part  323  may be detachably coupled to the portion including the first wing part  321  and the second wing part  322 . 
         [0148]      FIG. 24  is a side view schematically illustrating the rotating unit  300  of a string winding and unwinding apparatus according to another embodiment of the present disclosure. The rotating unit  300  according to the present embodiment has a trench  331 ′ formed in a surface thereof in the direction (−z direction) toward the base plate  110 . The restoring string RS included in the restoring unit may pass through the trench  331 ′ so as to be fixed to the base unit  100  in both ends thereof. Also, in this case, the lower housing  120  may have the first lateral apertures  121 , and the restoring string RS of the restoring unit may sequentially pass through one of the first lateral apertures  121 , the trench  331 ′, and the other of the first lateral apertures  121 . 
         [0149]    In the case of the string winding and unwinding apparatus according to the present embodiment, in order to couple the restoring string RS included in the restoring unit and the rotating unit  300 , the restoring string RS may be fixed to the base unit  100  and, in this state, the rotating unit  300  may be simply moved in a direction toward the base plate  110 , and thus, ease of manufacturing or maintenance and repair of the string winding and unwinding apparatus may be significantly enhanced. 
         [0150]    Even when the rotating unit  300  has the trench  331 ′ as in the present embodiment, a tunnel may protect the restoring string RS as in the embodiments and the modified examples thereof described above with reference to  FIG. 21 . The rotating unit  300  may have a second aperture  332  extending in a direction intersecting a rotation axis (z axis) of the rotating unit  300 , so the string that sequentially passes through any one of the second lateral apertures  122  of the lower housing  120 , the second aperture  332 , and the other of the second lateral apertures  122  may be wound around the outer circumferential surface of the rotating unit  300  or may be unwound therefrom. 
         [0151]    The string winding and unwinding apparatus according to the present embodiment may also have the configuration in which the rotating unit  300  is divided into the first rotating part and the second rotating part as illustrated in  FIG. 23 . That is, in the rotating unit  300  having the configuration such as described above with reference to  FIG. 23 , the first rotating part  301  positioned in the lower portion may have the trench  331 ′ such as illustrated in  FIG. 24 , instead of the first aperture  331 . In this case, the rotating unit  330  may have the first rotating part  301  having the trench  331 ′ and the second rotating part  302  positioned above the first rotating part  301 , detachably coupled to the first rotating part  301 , and forming the second aperture  332  with the first rotating part  301  when coupled to the first rotating part  301 . 
         [0152]      FIG. 25  is a side view schematically illustrating the rotating unit  300  of a string winding and unwinding apparatus according to another embodiment of the present disclosure. The string winding and unwinding apparatus according to the present embodiment is different from the string winding and unwinding apparatus according to the previous embodiment described above with reference to  FIG. 24 , in that the aperture formed between the first wing part  321  and the second wing part  322  is the first aperture through which the restoring string RS passes and the trench  332 ′ formed on the surface of the rotating unit  300  in the direction (−z direction) toward the base plate  110  is used for the purpose of allowing the string of footwear, or the like, passing through the second lateral apertures  122  to pass therethrough. Here, the restoring string RS may be fixed to the base unit  100  in both ends thereof, while passing through the first aperture  331 , or may pass through the first lateral apertures  121  of the base unit  100 . 
         [0153]    The string winding and unwinding apparatus according to the present embodiment may have such a configuration in which the rotating unit  300  is modified to include the first rotating part  301  and the second rotating part  302  as that of the string winding and unwinding apparatus according to the previous embodiment described above with reference to  FIG. 23 . That is, the rotating unit  300  may have the first rotating part having the trench  332 ′ and the second rotating part positioned above (+z direction) of the first rotating part, detachably coupled to the first rotating part, and forming the first aperture  331  with the first rotating part when coupled to the first rotating part. 
         [0154]      FIG. 26  is a perspective view schematically illustrating a restoring unit of a string winding and unwinding apparatus according to another embodiment of the present disclosure. So far, the case in which the restoring unit is the restoring string RS having elasticity has been described, but the present disclosure is not limited thereto and any unit may be used as the restoring unit as long as it includes an elastic member. Such an elastic member may include a spiral spring TS, a tension spring, or a rubber band. For example, as illustrated in  FIG. 26 , the restoring unit may have a spiral spring TS. The spiral spring TS may be fixed to a first fixing portion such as a recess or a protrusion portion of the base unit  100  in one end TS 1  thereof and fixed to a second fixing portion such as a recess or a protrusion portion of the rotating unit  300  in the other end TS 2  thereof. Thus, in a state in which the rotating unit  300  is engaged with the cover unit  400  and rotated in one direction (for example, clockwise direction centered on the −z direction) so the string is wound around the outer circumferential surface of the rotating unit  300 , when the cover unit  400  is separated from the rotating unit  300 , the spiral spring TS may restore the rotating unit  300  to be rotated in the other direction (counterclockwise direction centered on −z direction), the opposite direction of the one direction). 
         [0155]    In the embodiments illustrated in  FIGS. 1 through 13 , the user presses the cover unit  400  (−z direction) in order to wind a string. Here, the stoppage portion elements  410 ,  221 , and  222  and the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200 , the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300 , and the string winding portion elements  321  and  322  of the rotating unit  300  operate together to allow the string to be wound or unwound. Various embodiments may be implemented depending on how these four components are disposed. Here, in particular, an embodiment for lowering an overall height of the apparatus will be mainly described. An overall height of an apparatus is a very critical factor in increasing utilization of products. For example, when the product is installed in bags or backpacks, a height of the product may not be significant, but in order to be installed in footwear, girdles, or other garments, or the like, it is preferred for the product to be produced with a height as low as possible. 
         [0156]      FIG. 27  is a cross-sectional view illustrating that the embodiment of  FIG. 2  has a 3-stage configuration, which corresponds to a case in which the apparatus is the tallest. In detail, the engaging portion elements  410 ,  221 , and  222  between the cover unit  400  and the middle unit  200  are included in a first stage (I), the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200  and the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300  are included in a second stage (II), and the string winding portion elements  321  and  322  of the rotating unit  300  are included in a third stage (III). That is, since four components form the configuration of 3 stages present in different areas with respect to the z-axis direction, the overall height of the apparatus increases. 
         [0157]    In another embodiment of the present disclosure illustrated in  FIGS. 28 through 30 , the overall apparatus has a 2-stage configuration, and thus, a height thereof may be lowered. In detail, the stoppage portion elements  410  and  270  and the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200 , and the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300  are all included in a first stage (I), and the string winding portion elements  321  and  322  of the rotating unit  300  are included in a second stage (II). As a result, the height of the apparatus may be lowered, relative to the 3-stage configuration of  FIG. 27 . 
         [0158]    Hereinafter, the elements will be described in even further detail. First, in the reverse rotation preventing portion elements  460  and  250 , the responsive protrusion  250  of the middle unit  200  is formed on the upper housing  210  extending upwardly from the partition  240 . This is differentiated from the configuration in which the responsive protrusion  250  is formed on the lower partition  240  (+z direction) of the middle unit  200  in  FIG. 2 . In this manner, in the present embodiment, since the responsive protrusion  250  is positioned on the upper housing  210 , the response protrusion  250  is present in the first stage (I), the same area in which the engaging portion elements  410  and  270  are included. 
         [0159]    As for the engaging portion elements  410  and  270 , the cover unit  400  has the central shaft  430 , and the responsive stoppage portion  410  has a disk shape extending from the central shaft  430  in a radial direction. As the responsive stoppage portion  410  and the elastic stoppage portion  270  of the middle unit  200  mutually perform a grasping operation, the cover unit  400  may be rotatably coupled to the middle unit  200 . The elastic stoppage portion  270  of the middle unit  200  is configured as a wire-formed line spring (or spring clip) or an elastic flexure. The wire-formed line spring or the elastic flexure may be used to form the upper stoppage portion and the lower stoppage portion included in all of the embodiments described above. 
         [0160]      FIG. 29A  is a cross-sectional view taken along line A-A′ of  FIG. 28 , in which embodiments of the elastic stoppage portion  270  are illustrated. As illustrated in  FIG. 29A  and the alternative embodiment of  29 B, elastic stoppage portions  270   a  may be fixedly installed to be spaced apart by a predetermined interval in two rows when viewed from the x-y plane in an installation protrusion  260  formed separately within the middle unit  200  ( FIG. 29A ), or may be fixedly installed in a triangular shape ( FIG. 29B ). In another embodiment of the present invention, the elastic stoppage portion  270  may be installed only at one side in  FIG. 29A , and may be fixedly installed to have various other shapes such as a polygonal shape or a curved or bent line shape, as well as the triangular shape in the alternative embodiment shown in  FIG. 29B . In this manner, the use of the elastic stoppage portion  270  formed of a line spring or an elastic flexure allows the stopping and releasing operation to be performed more smoothly and enhances durability. 
         [0161]    Also, in this embodiment, the stoppage portion elements  410 ,  221 , and  222  having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0162]    Also, an upper elastic stoppage portion  270   a  and a lower elastic stoppage portion  270   b  of the elastic stoppage portion  270  are disposed to be spaced apart from one another in the z direction. According to relative positions of the responsive stoppage portion  410  with respect to the upper elastic stoppage portion  270   a  and the lower elastic stoppage portion  270   b , a distance of the cover unit  400  to the base unit  100  may be varied such that the cover unit  400  is engaged with the rotating unit  300  or engagement of the cover unit  400  with the rotating unit  300  is released. 
         [0163]    That is, as illustrated in  FIG. 28 , when the responsive stoppage portion  410  is positioned between the upper elastic stoppage portion  270   a  and the lower elastic stoppage portion  270   b , the engaging portions  450  and  310  are engaged with each other and the reverse rotation preventing portions  460  and  250  are also coupled to each other. As a result, when the user rotates the cover unit  400 , the rotating unit  300  engaged with the cover unit  400  is rotated to wind the string. Here, the cover unit  400  is prevented from being rotated reversely by the reverse rotation preventing portions  460  and  250 , whereby the string wound by a predetermined length may not be unwound. 
         [0164]    As illustrated in  FIG. 30 , when the cover unit  400  is pulled upwardly so the responsive stoppage portion  410  is positioned above the upper elastic stoppage portion  270   a , the engaging portions  450  and  310  are disengaged from each other and coupling of the reverse rotation preventing portions  460  and  250  is also released. Here, in order to prevent the responsive stoppage portion  410  from being completely separated, a step  280  is formed in an upper end of the installation protrusion  260 . In this manner, when the coupling of the cover unit  400  and the rotating unit  300  is released, the string wound around the rotating unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0165]    According to another embodiment (second embodiment having a 2-stage configuration) of the present disclosure illustrated in  FIGS. 31 and 32 , like the embodiment of  FIGS. 28 through 30 , the stoppage portion elements  410  and  270  and the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200 , and the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300  are all included in a first stage (I), and the string winding portion elements  321  and  322  of the rotating unit  300  are included in a second stage (II). As a result, the height of the apparatus may be lowered, relative to the 3-stage configuration of  FIG. 27 . 
         [0166]    Hereinafter, the elements will be described in even further detail. First, in the reverse rotation preventing portion elements  460  and  250 , the responsive protrusion  250  of the middle unit  200  is formed on the partition  240  (in the +z direction). Here, compared with the partition  240  of the middle unit  200  formed relatively at a lower side in  FIG. 2 , the partition  240  of the present embodiment is formed at an upper side. As a result, the responsive protrusion  250  formed on the partition  240  is present within the first stage (I), the same area in which the stoppage portions elements  410  and  270  are included. 
         [0167]    The stoppage portion elements  410  and  270  are differentiated in that the responsive stoppage portion  410  of the cover unit  400  is formed on a side surface of a separate protrusion protruding from the cover unit  400  toward the base unit  100 , rather than being formed on the central shaft  430 . The responsive stoppage portion  410  performs a mutual grasping operation with the elastic stoppage portion  270  formed on the upper housing  210  of the middle unit  200 , whereby the cover unit  400  may be rotatably coupled to the middle unit  200 . The elastic stoppage portion  270  of the middle unit  200  is formed as a wire-formed line spring or an elastic flexure and fixedly installed in two rows or in a triangular shape when viewed from the x-y plane as mentioned above with reference to  FIG. 29A . 
         [0168]    Also, in the present embodiment, the stoppage portion elements  410 ,  221 , and  222  having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0169]    Also, an upper elastic stoppage portion  270   a  and a lower elastic stoppage portion  270   b  of the elastic stoppage portion  270  are disposed to be spaced apart from one another in the z direction, and here, according to relative positions of the responsive stoppage portion  410  with respect to the upper elastic stoppage portion  270   a  and the lower elastic stoppage portion  270   b , a distance of the cover unit  400  to the base unit  100  may be varied such that the cover unit  400  is engaged with the rotating unit  300  or engagement of the cover unit  400  with the rotating unit  300  is released. 
         [0170]    That is, as illustrated in  FIG. 31 , when the responsive stoppage portion  410  is positioned below the lower elastic stoppage portion  270   b , the engaging portions  450  and  310  are engaged with each other and the reverse rotation preventing portions  460  and  250  are also coupled to each other. As a result, when the user rotates the cover unit  400 , the rotating unit  300  engaged with the cover unit  400  is rotated to wind the string. Here, the cover unit  400  is prevented from being rotated reversely by the reverse rotation preventing portions  460  and  250 , whereby the string wound by a predetermined length may not be unwound. 
         [0171]    As illustrated in  FIG. 32 , when the cover unit  400  is pulled upwardly so the responsive stoppage portion  410  is positioned between the upper elastic stoppage portion  270   a  and the lower elastic stoppage portion  270   b , the engaging portions  450  and  310  (see  FIG. 5  and  FIG. 7 ) are disengaged from each other and coupling of the reverse rotation preventing portions  460  and  250  is also released. In this manner, when the coupling of the cover unit  400  and the rotating unit  300  is released, the string wound around the rotating unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0172]    According to another embodiment (third embodiment having a 2-stage configuration) of the present disclosure illustrated in  FIGS. 33 and 34 , like the embodiment of  FIGS. 28 through 30 , the stoppage portion elements  410  and  270  and the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200 , and the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300  are all included in a first stage (I), and the string winding portion elements  321  and  322  of the rotating unit  300  are included in a second stage (II). As a result, the height of the apparatus may be lowered, relative to the 3-stage configuration of  FIG. 27 . 
         [0173]    Compared with the embodiments described above, the present embodiment has the following differences. First, among the stoppage portion elements  470  and  215 , the elastic stoppage portion  470  is formed in the cover unit  400 , rather than in the middle unit  200 , and the responsive protrusion portion  215  is formed in the middle unit  200 , rather than in the cover unit  400 . Also, the single elastic stoppage portion  470  is installed in a vertical direction, compared with the two elastic stoppage portions  270   a  and  270   b  always installed in the vertical direction according to the other embodiments described above. Whether to install a single elastic stoppage portion or whether to install two elastic stoppage portions up and down may be selectively applied according to specific configurations of an application, and the technical concept of the present invention may include all of the modifications. 
         [0174]    Here, in order to prevent the responsive stoppage portion  410  from being completely separated, a step  480  is formed in a lower end of a lateral plate  440  of the cover unit  400 . 
         [0175]    The responsive stoppage portion  215  performs a mutual grasping operation with the elastic stoppage portion  470  formed on an inner circumferential surface of the cover unit  400 , whereby the cover unit  400  may be rotatably coupled to the middle unit  200 . The elastic stoppage portion  270  of the middle unit  200  is formed as a line spring or an elastic flexure and fixedly installed in two rows or in a triangular shape when viewed from the x-y plane as mentioned above with reference to  FIG. 29A . 
         [0176]    Also, in the present embodiment, the stoppage portion elements  410 ,  221 , and  222  having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0177]    In the case of the reverse rotation preventing portion elements  460  and  250 , like the embodiment of  FIG. 31 , the responsive protrusion  250  of the middle unit  200  is formed on the partition  240  (in the +z direction). 
         [0178]    As illustrated in  FIG. 33 , when the responsive stoppage portion  215  is positioned above the elastic stoppage portion  270 , the engaging portions  450  and  310  are engaged with each other and the reverse rotation preventing portions  460  and  250  are also coupled to each other. As a result, when the user rotates the cover unit  400 , the rotating unit  300  engaged with the cover unit  400  is rotated to wind the string. Here, the cover unit  400  is prevented from being rotated reversely by the reverse rotation preventing portions  460  and  250 , whereby the string wound by a predetermined length may not be unwound. 
         [0179]    As illustrated in  FIG. 34 , when the cover unit  400  is pulled upwardly so the responsive stoppage portion  215  is positioned below the elastic stoppage portion  270 , the engaging portions  450  and  310  are disengaged from each other and coupling of the reverse rotation preventing portions  460  and  250  is also released. In this manner, when the coupling of the cover unit  400  and the rotating unit  300  is released, the string wound around the rotating unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0180]    According to another embodiment (fourth embodiment having a 2-stage configuration) of the present disclosure illustrated in  FIGS. 35 and 36 , like the embodiment of  FIGS. 28 through 30 , the stoppage portion elements  410  and  270  and the reverse rotation preventing portion elements  460  and  250  between the cover unit  400  and the middle unit  200 , and the engaging portion elements  450  and  310  between the cover unit  400  and the rotating unit  300  are all included in a first stage (I), and the string winding portion elements  321  and  322  of the rotating unit  300  are included in a second stage (II). As a result, the height of the apparatus may be lowered, relative to the 3-stage configuration of  FIG. 27 . 
         [0181]    In the present embodiment, like the embodiment of  FIG. 33  described above, among the stoppage portion elements  470  and  215 , the elastic stoppage portion  470  is formed in the cover unit  400 , rather than in the middle unit  200 , and the responsive protrusion portion  215  is formed in the middle unit  200 , rather than in the cover unit  400 . Here, two elastic stoppage portions  470   a  and  470   b  are installed in a vertical direction, compared with the embodiment of  FIG. 33 . Whether to install a single elastic stoppage portion or whether to install two elastic stoppage portions up and down may be selectively determined, and both may be included in the technical concept of the present invention. Thus, in all the embodiments of the present disclosure, the number of the elastic stoppage portions may be one or two. 
         [0182]    Also, among the reverse rotation preventing portion elements  460  and  250 , the ratchet protrusion  460  of the cover unit  400  is formed in a lower end of the lateral plate  440  serving as a handle of the cover unit  400 , and the responsive protrusion  250  of the middle unit  200  is formed to face the ratchet protrusion  460  on the upper housing  210 . In this manner, when the reverse rotation preventing portion elements  460  and  250  are positioned in the outermost portion of the cover unit  400 , there is no need to install a separate partition within the middle unit  200 , unlike the previous embodiments, further reducing the overall height of the apparatus. 
         [0183]    According to the present embodiment configured as described above, the responsive stoppage portion  215  performs a mutual grasping operation with the elastic stoppage portion  470  formed on an inner circumferential surface of the cover unit  400 , whereby the cover unit  400  may be rotatably coupled to the middle unit  200 . The elastic stoppage portion  270  of the middle unit  200  is formed as a line spring or an elastic flexure and fixedly installed in two rows or in a triangular shape when viewed from the x-y plane as mentioned above with reference to  FIG. 29A  or  FIG. 29B . 
         [0184]    Also, in the present embodiment, the stoppage portion elements  410 ,  221 , and  222  (see  FIG. 4  and  FIG. 7 ) having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0185]    As illustrated in  FIG. 35 , when the responsive stoppage portion  215  is positioned above the elastic stoppage portion  470   a , the engaging portions  450  and  310  are engaged with each other and the reverse rotation preventing portions  460  and  250  are also coupled to each other. As a result, when the user rotates the cover unit  400 , the rotating unit  300  engaged with the cover unit  400  is rotated to wind the string. Here, the cover unit  400  is prevented from being rotated reversely by the reverse rotation preventing portions  460  and  250 , whereby the string wound by a predetermined length may not be unwound. 
         [0186]    As illustrated in  FIG. 36 , when the cover unit  400  is pulled upwardly so the responsive stoppage portion  215  is positioned between the upper elastic stoppage portion  470   a  and the lower elastic stoppage portion  470   b , the engaging portions  450  and  310  are disengaged from each other and coupling of the reverse rotation preventing portions  460  and  250  is also released. In this manner, when the coupling of the cover unit  400  and the rotating unit  300  is released, the string wound around the rotating unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0187]    According to another embodiment (fifth embodiment having a 1-stage configuration) of the present disclosure illustrated in  FIGS. 37 and 38 , all of the stoppage portion elements, the reverse rotation preventing portion elements, and the string winding portion elements described above are included in the first stage (I). As a result, a height of the apparatus may be significantly lowered, compared with those of the embodiments described above. 
         [0188]    Significant differences of the present embodiment to the other embodiment lie in that a middle unit and a base unit are combined to be used as a single middle-base composite unit  100  and a rotating unit and a cover unit are combined to be used as a single rotating-cover composite unit  300 . As a result, the engaging portion elements between the existing cover unit and rotating unit are omitted. Also, according to the present embodiment, reverse rotation preventing portions  150  and  360  are formed between the first wing part  321  of the rotating-cover composite unit  300  and an upper inner side surface of the middle-base composite unit  100 . In this manner, in the present embodiment, the string winding portion elements  321  and  322 , the stoppage portion elements  160  and  370 , and the reverse rotation preventing portion elements  150  and  360  are integrally installed on the rotating-cover composite unit  300 , thereby significantly lowering a height of the apparatus. 
         [0189]    Hereinafter, the components will be described in even further detail. The responsive stoppage portion  160  of the middle-base composite unit  100  performs a mutual grasping operation with the elastic stoppage portion  370  formed on an inner circumferential surface of an upper lateral plate  380  of the rotating-cover composite unit  300 , whereby the rotating-cover composite unit  300  may be rotatably coupled to the middle-base composite unit  100 . In order to prevent the responsive stoppage portion  160  from being completely released, a step  390  is formed in a lower end of the lateral plate  380  of the rotating-cover composite unit  300 . Meanwhile, according to another embodiment of the present disclosure, conversely from the case of  FIG. 37 , the responsive stoppage portion may be formed in the rotating-cover composite unit  300  and the elastic stoppage portion may be formed in the middle-base composite unit  100 . 
         [0190]    The elastic stoppage portion  370  of the rotating-cover composite unit  300  is formed as a wire-formed line spring or an elastic flexure and fixedly installed in two rows or in a triangular shape when viewed from the x-y plane as mentioned above with reference to  FIG. 29A . 
         [0191]    Also, in the present embodiment, the stoppage portion elements  410 ,  221 , and  222  having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0192]    As illustrated in  FIG. 37 , when the responsive stoppage portion  160  is positioned above the elastic stoppage portion  370 , the reverse rotation preventing portions  150  and  360  are also coupled to each other. As a result, when the user rotates the rotating-cover composite unit  300 , a string is wound. Here, the rotating-cover composite unit  300  is prevented from being rotated reversely by the reverse rotation preventing portions  150  and  360 , whereby the string wound by a predetermined length may not be unwound. 
         [0193]    As illustrated in  FIG. 38 , when the rotating-cover composite unit  300  is pulled upwardly so the responsive stoppage portion  160  is positioned below the elastic stoppage portion  370 , coupling of the reverse rotation preventing portions  150  and  360  is released. In this manner, when the coupling of the rotating-cover composite unit  300  and the middle-base composite unit  100  is released, the string wound around the rotating-cover composite unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0194]    According to another embodiment (sixth embodiment having a 1-stage configuration) of the present disclosure illustrated in  FIGS. 39 and 40 , all of the stoppage portion elements, the reverse rotation preventing portion elements, and the string winding portion elements described above are included in the first stage (I). As a result, a height of the apparatus may be significantly lowered, compared with those of the embodiments described above. 
         [0195]    The present embodiment is the same as the embodiment described above with reference to  FIGS. 37 and 38 , in that a middle unit and a base unit are combined to be used as a single middle-base composite unit  100 , and a rotating unit and a cover unit are combined to be used as a single rotating-cover composite unit  300 . As a result, the engaging portion elements between the existing cover unit and rotating unit are omitted. 
         [0196]    The present embodiment is different from the embodiment described above with reference to  FIGS. 37 and 38 , in that all of the reverse rotation preventing portion elements  150  and  360  and the stoppage portion elements  170  and  315  are installed in the first wing part  321  and the second wing part  322  of the rotating-cover composite unit  300 . In  FIGS. 39 and 40 , it is illustrated that the stoppage portion elements  170  and  315  are formed in the first wing part  321  of the rotating-cover composite unit  300  and the reverse rotation preventing portion elements  150  and  360  are installed in the second wing part  322 . However, the technical concept of the present invention is not limited thereto, and conversely, the reverse rotation preventing portion elements may be formed in the first wing part  321  of the rotating-cover composite unit  300  and the stoppage portion elements may be installed in the second wing part  322  of the rotating-cover composite unit  300 . 
         [0197]    In the present embodiment, the string winding portion elements  321  and  322 , the stoppage portion elements  170  and  315 , and the reverse rotation preventing portion elements  150  and  360  are integrally installed between the first wing part  321  and the second wing part  322  of the rotating-cover composite unit  300 , whereby a height of the apparatus may be lowest. 
         [0198]    Hereinafter, the components will be described in even further detail. The responsive stoppage portion  315  formed in the first wing part  321  of the rotating-cover composite unit  300  performs a mutual grasping operation with the elastic stoppage portion  170  of the of the middle-base composite unit  100 , whereby the rotating-cover composite unit  300  may be rotatably coupled to the middle-base composite unit  100 . In order to prevent the responsive stoppage portion  315  from being completely released, a step  180  is formed in an upper end of a side surface of the middle-base composite unit  100 . 
         [0199]    Meanwhile, according to another embodiment of the present disclosure, conversely from the case of  FIG. 39 , the responsive stoppage portion may be formed in the rotating-cover composite unit  300  and the elastic stoppage portion may be formed in the middle-base composite unit  100 . 
         [0200]    The elastic stoppage portion  170  of the middle-base composite unit  100  is formed as a wire-formed line spring or an elastic flexure and fixedly installed in two rows or in a triangular shape when viewed from the x-y plane as mentioned above with reference to  FIG. 29A . 
         [0201]    Also, in the present embodiment, the stoppage portion elements  410 ,  221 , and  222  (see  FIG. 4  and  FIG. 7 ) having various shapes described above with reference to  FIGS. 8 through 13  may be employed. 
         [0202]    As illustrated in  FIG. 39 , when the responsive stoppage portion  315  is positioned below the elastic stoppage portion  170 , the reverse rotation preventing portions  150  and  360  are also coupled to each other. As a result, when the user rotates the rotating-cover composite unit  300 , a string is wound. Here, the rotating-cover composite unit  300  is prevented from being rotated reversely by the reverse rotation preventing portions  150  and  360 , whereby the string wound by a predetermined length may not be unwound. 
         [0203]    As illustrated in  FIG. 40 , when the rotating-cover composite unit  300  is pulled upwardly so the responsive stoppage portion  315  is positioned above the elastic stoppage portion  170 , coupling of the reverse rotation preventing portions  150  and  360  is released. In this manner, when the coupling of the rotating-cover composite unit  300  and the middle-base composite unit  100  is released, the string wound around the rotating-cover composite unit  300  is naturally unwound by virtue of restoring force of the string. 
         [0204]      FIG. 41  is a perspective view schematically illustrating footwear according to another embodiment of the present disclosure. As illustrated in  FIG. 41 , the footwear according to the present embodiment has a string winding and unwinding apparatus  1  according to any one of the embodiments described above or modified examples thereof. For example, the string winding and unwinding apparatus  1  may be attached to a tongue T of the footwear to allow a string S to be connected to the string winding and unwinding apparatus  1 . The string winding and unwinding apparatus  1  may also be attached to other portion such as a side surface or a portion of a heel of a rear surface of the footwear. That is, the string S of the footwear may pass through any one of the second lateral apertures  122  of the base unit  100 , penetrate through the second aperture  332  of the rotating unit  300 , and pass through the other of the second lateral apertures  122 . Accordingly, when the rotating unit  300  is engaged with the cover unit  400  and rotated in one direction, the string is wound around the rotating unit  300 . As the string S is wound in this manner, the footwear may be tightly attached to the foot of the user. In this state, when the rotating unit  300  is separated from the cover unit  400 , the rotating unit  300  may be rotated in the other direction (the loosening direction) and accordingly, the string S wound around the rotating unit  300  may be unwound from an outer circumferential surface of the rotating unit  300 . 
         [0205]    In  FIG. 41 , the footwear is illustrated, but the string winding and unwinding apparatus according to the embodiments described above and the modified examples thereof may be installed to be used in a variety of articles requiring locking by a string, such as hats, belts, watches, bags, and clothes, and various articles in which the string winding and unwinding apparatus according to the embodiments described above and the modified examples thereof should also be within the scope of the present invention. 
         [0206]      FIG. 42  is a perspective view schematically illustrating a string winding and unwinding apparatus according to another embodiment of the present disclosure. Referring to  FIG. 42 , the base unit  100  of the string winding and unwinding apparatus according to the present embodiment further includes a clip unit  140 . The clip unit  140  corresponds to the base plate  110  and extends from the base plate  110  such that a space is present between the clip unit  140  and the base plate  110 . To this end, as illustrated in  FIG. 42 , the clip unit  140  may extend from the base plate  110  and may be bent to have a portion substantially parallel to the base plate  110 . The clip unit  140  may be integrated with the base plate  110  (one body), or may be formed as a separate component and fixed to the base plate  110 . The clip unit  140  may include, for example, a resin, plastic, or a metal plate to have flexibility. 
         [0207]    The a string winding and unwinding apparatus according to the present embodiment may be easily attached to or detached from an article in which the string winding and unwinding apparatus is desired to be used, by using the space between the base plate  110  and the clip unit  140 . For example, in the case of the footwear illustrated in  FIG. 41 , the space between the base plate  110  and the clip unit  140  may be inserted into a heel tap HT or the tongue T (see  FIG. 41 ), a portion adjacent to the ankle, or the rear portion of the footwear, whereby the string winding and unwinding apparatus may be easily detachably attached to the footwear. 
         [0208]      FIG. 43  is a perspective view schematically illustrating a string winding and unwinding apparatus according to another embodiment of the present disclosure. Unlike the embodiment described above with reference to  FIG. 42 , the base unit  100  according to the present embodiment may further include a rail  144  positioned on a lower surface of the base plate  110  (−z direction) and extending in one direction (y-axis direction). A connection portion  142  connecting the rail  144  to the base plate  110  and having a width narrower than that of the rail  144  (in the x-axis direction) may be provided to allow a space to be present between the rail  144  and the base plate  110 . 
         [0209]    The string winding and unwinding apparatus according to the present embodiment may be used together with a fastening clip  500  illustrated in  FIG. 44 . The fastening clip  500  may have a shape bent or curved one or more times as illustrated in  FIG. 44 . In  FIG. 44 , it is illustrated that the fastening clip  500  is bent twice, mutually adjacent first portion  510  and second portion  520  are substantially parallel to each other and allow a space to be present therebetween, and a third portion  530  is adjacent to the second portion  520 , is positioned on the opposite side of the first portion  510 , and is substantially parallel to the second portion  520  to allow a space to be present therebetween. Here, the third portion  530  has a first guide rail  531  and a second guide rail  532  positioned to be coplanar, spaced apart from one another, and parallel to each other. 
         [0210]    The fastening clip  500  may enable the string winding and unwinding apparatus according to the present embodiment to be easily detachably attached to a variety of articles. For example, in the case of the footwear illustrated in  FIG. 41 , the space between the first portion  510  and the second portion  520  of the fastening clip  500  illustrated in  FIG. 44  may be inserted into a heel tap HT or the tongue T, a portion adjacent to the ankle, or the rear portion of the footwear, whereby the string winding and unwinding apparatus may be installed in the footwear such that the third portion  530  is positioned outside of the footwear. Thereafter, the rail  144  of the string winding and unwinding apparatus according to the present embodiment illustrated in  FIG. 43  may be inserted into the space between the first guide rail  531  and the second guide rail  532  of the fastening clip  500  and the second portion  520 , whereby the rail  144  may be easily installed in the fastening clip  500 . 
         [0211]    Meanwhile, the connection portion  142  may extend in one direction (y-axis direction) like the rail  144 . A shape of the connection portion  142  corresponds to a shape of the space between the first guide rail  531  and the second guide rail  532  of the fastening clip  500 , and the connection portion  142  allows a relative position of the string winding and unwinding apparatus with respect to the fastening clip  500  to be fixed, rather than being changed, while the string winding and unwinding apparatus is in use such that the user rotates the cover unit  400 , or the like. The shape of the connection portion  142  may be varied in various manners, without being limited thereto. 
         [0212]    According to the embodiments of the present disclosure described above, the string winding and unwinding apparatus may be implemented to have a simple configuration and facilitate maintenance and repair. However, the scope of the present invention is not limited thereto. 
         [0000]    While the invention has been particularly shown and described in conjunction with exemplary embodiments, it will be appreciated that variations and modifications will occur to those skilled in the art. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.) the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the invention.