Patent Publication Number: US-2021186160-A1

Title: Fastening device

Description:
RELATED APPLICATIONS 
     This application is a continuation of International application No. PCT/CN2019/095132, filed Jul. 8, 2019, which claims the benefits of priority of CN application No. 201811275429.6 filed on Oct. 30, 2018, the content of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a fastening device. More particularly, the present disclosure relates to a fastening device for securing an article through loosening or tightening a lace. 
     Description of Related Art 
     In daily life, cords, such as a lace or a thread, are usually used to tighten articles. The most common tightening method is to use the cord to reciprocately pass through holes on the article, such as eyelets of a shoe, and then tie a knot to secure the article. But in this kind of tightening method, the knot is loosened easily because of an external force. Not only does the knot need to be tied again, but also lots of inconveniences come owing to the insecurity of the articles. 
     In order to solve such problems, some practitioners developed a simple fastening mechanism including a case, a driving unit and a spring. The case includes holes configured for the lace to pass therethrough. Through the reaction force between the spring and the driving unit, the lace can be clamped between the driving unit and the case so as to be fastened. The length of the lace can be changed by pressing the spring to change the position of the driving unit. However, in such fastening mechanism, the restoring force of the spring is served as the securing force; thus, the lace is easily to be released owing to vibrations or an external force. In addition, the fastening mechanism has no space to receive the lace, and the exposure of the lace may bring danger. 
     Therefore, some practitioners developed another kind of buckle which can be rotated to tighten the lace, and the lace can be received inside the buckle. Through the interference between components inside the buckle, the length of the lace as well as the tightness can be adjusted. However, the structure of the buckles is complex; as a result, the manufacturing cost is increased, and the buckle has assembly and repair difficulty. 
     Hence, the inner structure of the buckle is continuously improved by the practitioners, with a hope that the structure can be simplified while the securing capability thereof is remained, and the structure reliability thereof is increased to prevent shortness of the life time. 
     Based on the aforementioned problems, how to simplify the structure of the fastening device, reduce the manufacturing cost and maintain the securing capability becomes a pursuit target for practitioners. 
     SUMMARY 
     The present disclosure provides a fastening device, through the configuration of a spool and a connecting unit, the structure reliability thereof is increased. 
     According to one embodiment of the present disclosure, a fastening device is provided, which includes a case unit, a spool, a driving unit, a knob and a connecting unit. The case unit has a radial direction and an axial direction and includes an annular wall. The annular wall surrounds an inner space. The spool is within the inner space and includes an axial space. The axial space includes a large-diameter segment and a small-diameter segment, and the small-diameter segment is connected to the large-diameter segment along the axial direction. The driving unit is disposed above the spool along the axial direction, and the driving unit selectively prohibits the spool from rotating in a loosening direction. The knob is disposed above the driving unit along the axial direction, and the knob is coupled to the driving unit. The connecting unit includes a first part set and a second part set. The first part set is connected to the knob. The second part set inserts in the axial space to connect to the first part set, and the second part set is limited within the large-diameter segment. 
     Therefore, since the axial space of the spool includes the large-diameter segment and the small-diameter segment, the connecting unit can be limited within the large-diameter segment, and separation of the case unit, the spool, the driving unit and the knob during rotation can be avoided, thereby increasing the structure reliability. 
     According to examples of the aforementioned fastening device, the first part set can include a screw bar. The second part set can include a connecting barrel, and the connecting barrel includes a top portion and a barrel body portion. The barrel body portion is connected to the top portion. The barrel body portion passes through the small-diameter segment and is configured for the screw bar to screw therewith, and the top portion is limited within the large-diameter segment. Or the knob can include a boss protruding toward the inner space, and the barrel body portion is engaged with the boss, thereby allowing the connecting barrel to move simultaneously with the knob. 
     According to examples of the aforementioned fastening device, the first part set can include a fastening barrel. The second part set can include a stop ring and a screw bar. The stop ring is limited within the large-diameter segment, and the screw bar passes through the stop ring and the small-diameter segment to screw with the fastening barrel. Or the fastening barrel can include a lower engaging portion, and the stop ring can include an inner engaging groove configured for engaging with the lower engaging portion. Or the knob can include a boss protruding toward the inner space. The fastening barrel can include an upper engaging portion connected to the lower engaging portion, and the upper engaging portion is engaged with the boss. Or the fastening barrel can include a lower end surface, and after the screw bar is fastened with the fastening barrel, the stop ring abuts against the lower end surface. 
     According to examples of the aforementioned fastening device, the first part set can include a fastening barrel. The second part set can include a screw bar, and the screw bar includes a head portion and a bar portion. The bar portion is connected to the head portion. The bar portion inserts in the axial space to screw with the fastening barrel, and the head portion is limited within the large-diameter segment. 
     According to examples of the aforementioned fastening device, the case unit can further include an inner annular groove, which is disposed at a lower end of the annular wall. Or the case unit can further include a stop portion, which is located at the annular wall and protrudes toward the inner space along the radial direction, and the spool is located below the stop portion. 
     According to another embodiment of the present disclosure, a fastening device is provided, which includes a case unit, a spool, a driving unit, a knob and a connecting unit. The case unit has a radial direction and an axial direction and includes an annular wall. The annular wall surrounds an inner space. The spool is within the inner space and includes an axial space. The axial space includes a large-diameter segment and a small-diameter segment, and the small-diameter segment is connected to the large-diameter segment along the axial direction. The driving unit is disposed above the spool along the axial direction, and the driving unit selectively prohibits the spool from rotating in a loosening direction. The knob is disposed above the driving unit along the axial direction, and the knob is coupled to the driving unit. Operation of the knob causes the spool to release a lace. The connecting unit is connected to the knob, and the connecting unit is disposed within the axial space and limited within the large-diameter segment. 
     According to examples of the aforementioned fastening device, the connecting unit can include a first part set and a second part set. The first part set is connected to the knob. The second part set is disposed within the axial space to connect to the first part set, and the second part set is limited within the larger-segment. Or the first part set can include a screw bar. The second part set can include a connecting barrel, and the connecting barrel includes a top portion and a barrel body portion. The barrel body portion is connected to the top portion. The barrel body portion passes through the small-diameter segment and is configured for the screw bar to screw therewith, and the top portion is limited within the large-diameter segment. Or the knob can include a boss protruding toward the inner space, and the barrel body portion is engaged with the boss, thereby allowing the connecting barrel to move simultaneously with the knob. 
     According to examples of the aforementioned fastening device, the first part set can include a fastening barrel. The second part set can include a stop ring and a screw bar. The stop ring is limited within the large-diameter segment, and the screw bar passes through the stop ring and the small-diameter segment to screw with the fastening barrel. Or the fastening barrel can include a lower engaging portion, and the stop ring can include an inner engaging groove configured for engaging with the lower engaging portion. Or the knob can include a boss protruding toward the inner space. The fastening barrel can include an upper engaging portion connected to the lower engaging portion, and the upper engaging portion is engaged with the boss. Or the fastening barrel can include a lower end surface, and after the screw bar is fastened with the fastening barrel, the stop ring abuts against the lower end surface. 
     According to examples of the aforementioned fastening device, the first part set can include a fastening barrel. The second part set can include a screw bar, and the screw bar includes a head portion and a bar portion. The bar portion is connected to the head portion. The bar portion inserts in the axial space to screw with the fastening barrel, and the head portion is limited within the large-diameter segment. Or the case unit can further include a stop portion, which is located at the annular wall and protrudes toward the inner space along the radial direction. The spool is located below the stop portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a three-dimensional schematic view of a fastening device according to a first embodiment of the present disclosure; 
         FIG. 2  shows one exploded view of the fastening device of  FIG. 1 ; 
         FIG. 3  shows another exploded view of the fastening device of  FIG. 1 ; 
         FIG. 4  shows one cross-sectional view of the fastening device of  FIG. 1 ; 
         FIG. 5  shows another cross-sectional view of the fastening device of  FIG. 1 ; 
         FIG. 6  shows a three-dimensional exploded view of a fastening device according to a second embodiment of the present disclosure; 
         FIG. 7  shows a cross-sectional view of the fastening device of  FIG. 6 ; 
         FIG. 8  shows a three-dimensional exploded view of a fastening device according to a third embodiment of the present disclosure; 
         FIG. 9  shows a cross-sectional view of the fastening device of  FIG. 8 ; 
         FIG. 10  shows a three-dimensional exploded view of a fastening device according to a fourth embodiment of the present disclosure; and 
         FIG. 11  shows a cross-sectional view of the fastening device of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiment will be described with the drawings. For clarity, some practical details will be described below. However, it should be noted that the present disclosure should not be limited by the practical details. That is, in some embodiment, the practical details are unnecessary. In addition, for simplifying the drawings, some conventional structures and elements will be simply illustrated, and repeated elements may be represented by the same labels. 
     In addition, it will be understood that when an element (or mechanism or module) is referred to as being “disposed on”, “connected to” or “coupled to” another element, it can be directly disposed on, connected or coupled to the other elements, or it can be indirectly disposed on, connected or coupled to the other elements, that is, intervening elements may be present. In contrast, when an element is referred to as being “directly disposed on”, “directly connected to” or “directly coupled to” another element, there is no intervening element present. The terms first, second, third, etc. are used herein to describe various elements or components, these elements or components should not be limited by these terms. Consequently, a first element or component discussed below could be termed a second element or component. 
     Please refer to  FIGS. 1, 2, 3, 4, and 5 .  FIG. 1  shows a three-dimensional schematic view of a fastening device  100  according to a first embodiment of the present disclosure.  FIG. 2  shows one exploded view of the fastening device  100  of  FIG. 1 .  FIG. 3  shows another exploded view of the fastening device  100  of  FIG. 1 .  FIG. 4  shows one cross-sectional view of the fastening device  100  of  FIG. 1 .  FIG. 5  shows another cross-sectional view of the fastening device  100  of  FIG. 1 . The fastening device  100  includes a case unit  200 , a spool  300 , a driving unit  400 , a knob  500  and a connecting unit  600 . 
     The case unit  200  has a radial direction (not shown) and an axial direction  11  and includes an annular wall  220 . The annular wall  220  surrounds an inner space  240 . The spool  300  is within the inner space  240  and includes an axial space  340 . The axial space  340  includes a large-diameter segment  342  and a small-diameter segment  341 , and the small-diameter segment  341  is connected to the large-diameter segment  342  along the axial direction  11 . The driving unit  400  is disposed above the spool  300  along the axial direction  11 , and the driving unit  400  selectively prohibits the spool  300  from rotating in a loosening direction A 1 . The knob  500  is disposed above the driving unit  400  along the axial direction  11 , and the knob  500  is coupled to the driving unit  400 . The connecting unit  600  is connected to the knob  500 , and the connecting unit  600  is disposed within the axial space  340  and limited within the large-diameter segment  342 . 
     Therefore, since the axial space  340  of the spool  300  includes the large-diameter segment  342  and the small-diameter segment  341 , the connecting unit  600  can be limited within the large-diameter segment  342 , and separation of the case unit  200 , the spool  300 , the driving unit  400  and the knob  500  during rotation can be avoided, thereby increasing the structure reliability. The detail of the fastening device  100  will be described hereafter. 
     The case unit  200  can further include a stop portion  250 , and the stop portion  250  is located at the annular wall  220  and protrudes toward the inner space  240  along the radial direction. The spool  300  is located below the stop portion  250 . The case unit  200  can further include a base  210 , a plurality of mounting teeth  230  and an inner annular groove  260 . The base  210  is configured for the annular wall  220  to be disposed thereon, and the annular wall  220  can be assembled with the base  210  through engagements. The mounting teeth  230  are disposed at the annular wall  220  and face toward the inner space  240 , and the inner annular groove  260  is located at a lower end of the annular wall  220 . The mounting teeth  230  are located on an upper end of the annular wall  220 . The stop portion  250  has a convex ring structure and is adjacent to the mounting teeth  230 . In other words, the inner annular groove  260  and the stop portion  250  can be formed by the variation of the inner-diameter of the annular wall  220 . 
     The spool  300  includes a hollow shaft  380 , an upper annular portion  360  and a lower annular portion  370 . The upper annular portion  360  and the lower annular portion  370  protrude outwardly from the hollow shaft  380  along the radial direction, respectively, and the upper annular portion  360  is located above the lower annular portion  370  along the axial direction  11 , thereby allowing an annular track  310  to be formed between the upper annular portion  360  and the lower annular portion  370 . The annular track  310  can be configured for a lace (not shown) to be wound thereabout. The spool  300  can include a plurality of engaging teeth  320  located above the upper annular portion  360  along the axial direction  11 , and an inner surface  350  of the hollow shaft  380  is closed to form the axial space  340 . The large-diameter segment  342  and the lower-diameter segment  341  connected thereto can be formed by the variation of the inner-diameter of the hollow shaft  380 , and the large-diameter segment  342  is located below the small-diameter segment  341 . The inner surface  350  of the hollow shaft  380  can include an expanding region  351  and a perpendicular region  352 , and both of the expanding region  351  and a perpendicular region  352  are located at the large-diameter segment  342 . The spool  300  can further include a lower opening  330  connected to the axial space  340 . 
     The driving unit  400  can include a ring body portion  440 , a first retaining portion  410 , a second retaining portion  420 , three guiding portions  430 , three pawl arms  450 , three restricting portions  460 , a plurality of meshing teeth  470 , a central hole  480  and two protrusions  491  and  492 . The central hole  480  is located at a center of the ring body portion  440 , and each of the guiding portions  430  has a helical tooth structure protruding outwardly from the ring body portion  440  and is configured to couple to the knob  500 . The first retaining portion  410  and the second retaining portion  420  include a free end  411  and a free end  421 , respectively. The free ends  411  and  421  can be displaced radially by a force, and can be restored after removing the force. The protrusions  491  and  492  protrude inwardly from the ring body portion  440 , and the two protrusions  491  and  492  are spaced apart from the two free ends  411  and  421 . Each of the pawl arms  450  includes a distal end  452  and a proximal end  451 . The proximal ends  451  are configured to connect to an outside of the ring body portion  440 , and the distal ends  452  are configured to selectively engage with the mounting teeth  230 . The three restricting portions  460  are located above three pawl arms  450 , respectively. The meshing teeth  470  are located at a lower side of the ring body portion  440 , which can be selectively engaged with the engaging teeth  320  of the spool  300 . 
     The knob  500  can include a guiding track  510 , a boss  520 , a through hole  530  and two positioning blocks  540 . The guiding track  510  is located at an inner wall of the knob  500 , and the boss  520  protrudes into the inner space  240  along the axial direction  11 . The through hole  530  passes through the boss  520 . The two positioning blocks  540  are disposed at an outside of the boss  520  along the radial direction. Please be noted that, only one position block  540  is shown in  FIG. 3  owing to the view angle thereof, and it can be understood by a reader that, on the other side which cannot be seen, the other positioning block  540  is located. 
     The connecting unit  600  includes a first part set (not labeled) and a second part set (not labeled). The first part set is connected to the knob  500 . The second part set is disposed within the axial space  340  to connect to the first part set, and the second part set is limited within the large-diameter segment  342 . In the first embodiment, the first part set of the connecting unit  600  can include a screw bar  610 . The second part set can include a connecting barrel  620 , and the connecting barrel  620  includes a top portion  622  and a barrel body portion  621 . The barrel body portion  621  is connected to the top portion  622 . The barrel body portion  621  passes through the small-diameter segment  341  and is configured for the screw bar  610  to screw therewith, and the top portion  622  is limited within the large-diameter segment  342 . 
     Precisely, when the spool  300  is put into the inner space  240  from the bottom of the annular wall  220 , as shown in  FIG. 4 , the upper annular portion  360  and the lower annular portion  370  can be limited by the stop portion  250  and the inner annular groove  260 , respectively, thereby avoiding the spool  300  from leaving from the upper side of the annular wall  220 . The guiding portions  430  (shown in  FIG. 3 ) are coupled to the guiding track  510  to connect the driving unit  400  to the knob  500 . The boss  520  of the knob  500  protrudes into the central hole  480  (shown in  FIG. 2 ) of the driving unit  400 . 
     The connecting barrel  620  can be put from the lower opening  330  (shown in  FIG. 3 ) into the axial space  340 , and through the diameter relationship of the small-diameter segment  341 , the large-diameter segment  342 , the top portion  622  and the barrel body portion  621 , the barrel body portion  621  can pass through the small-diameter segment  341  while the top portion  622  is limited within the large-diameter segment  342 . Then, the screw bar  610  is fastened into the barrel body portion  621 , and combination of the knob  500 , the driving unit  400  and the spool  300  is completed. Because of the stop portion  250 , after the screw bar  610  is fastened with the barrel body portion  621 , the knob  500 , the driving unit  400 , the spool  300  and the annular wall  220  cannot separate from each other, thereby completing assembly. In other embodiments, the stop portion can be omitted; instead, the mounting teeth can protrude into the inner space to prevent the spool from leaving from the upper side of the annular wall. Moreover, only one of the stop portion and the inner annular groove is required to be disposed on the annular wall, and the present disclosure is not limited thereto. 
     Furthermore, the barrel body portion  621  can be engaged with the boss  520 , thereby allowing the connecting barrel  620  and the knob  500  to move simultaneously. A shape of the outer wall of the barrel body portion  621  can coordinate with the inner wall of the through hole  530 , which results in engagement between the barre body portion  621  and the boss  520 . Moreover, the outer wall of the barrel body portion  621  and the inner wall of the through hole  530  are non-circular. When pulling the lace to rotate the spool  300  in a loosening direction A 1 , the spool  300  may rub against the second part set, and if the barrel body portion  621  of the second part set is engaged with the boss  520 , rotation of the second part set caused by the friction from the spool  300  can be avoided, thereby avoiding it from separating from the first part set. 
     As shown in  FIG. 4 , the driving unit  400  is in the first position, and the engaging teeth  320  of the spool  300  are engaged with the meshing teeth  470  of the driving unit  400 . The distal ends  452  (shown in  FIG. 2 ) of each of the pawl arms  450  are engaged with the mounting teeth  230  in the loosening direction A 1  (shown in  FIG. 2 ) while disengaged from the mounting teeth  230  in a fastening direction A 2  (shown in  FIG. 2 ). The restricting portion  460  is not engaged with the mounting teeth  230  owing to that the location of the restricting portion  460  is lower than the mounting teeth  230 . Hence, rotating the knob  500  in the fastening direction A 2  can drive the driving unit  400  to allow the spool  300  to draw back the lace. When the knob  500  is immobile, the distal end  452  of each of the pawl arms  450  is abutted against the mounting teeth  230  to prevent rotation of the spool  300  in the loosening direction A 1 , thereby avoiding release of the lace. 
     On the contrary, rotating the knob  500  in a loosening direction A 1  drives the driving unit  400  to move upward along the axial direction  11 , such that the driving unit  400  is separated from the spool  300 . To be more specific, when the driving unit  400  is in the first position, the guiding portions  430  are engaged with the guiding track  510  of the knob  500 . One of the position blocks  540  is located between the free end  411  of the first retaining portion  410  and the protrusion  491 , and the other one of the position blocks  540  is located between the free end  421  of the second retaining portion  420  and the protrusion  492 . When the knob  500  is rotated in the loosening direction A 1 , the driving unit  400  cannot rotate simultaneously owing to the engagement between the pawl arms  450  and the mounting teeth  230 , and therefore the two positioning blocks  540  press the two free ends  411  and  421 , respectively, which allows the two free ends  411  and  421  to be displaced along the radial direction such that the knob  500  can rotate relative to the driving unit  400 . The guiding portions  430  will be guided by the guiding track  510  to move upward relative to the guiding track  510  along the axial direction  11 , allowing the driving unit  400  to switch to the second position. Hence, the aforementioned one of the positioning blocks  540  switches to a position between the free end  411  of the first retaining portion  410  and the protrusion  492 , and the aforementioned the other one of the positioning blocks  540  switches to a position between the free end  421  of the second retaining portion  420  and the protrusion  491 . 
     Hence, as shown in  FIG. 5 , when the driving unit  400  is in the second position, the meshing teeth  470  of the driving unit  400  will disengage from the engaging teeth  320  of the spool  300 , and the spool  300  is not affected by the driving unit  400  and rotation in the loosening direction A 1  is allowed; as a result, the lace can be released by pulling the lace itself. 
     Please refer to  FIG. 6  and  FIG. 7 .  FIG. 6  shows a three-dimensional exploded view of a fastening device  100   a  according to a second embodiment of the present disclosure.  FIG. 7  shows a cross-sectional view of the fastening device  100   a  of  FIG. 6 . The fastening device  100   a  includes a case unit (not labeled), a spool  300   a , a driving unit  400   a , a knob  500   a  and a connecting unit  600   a . The structure and relation of the case unit, the spool  300   a , the driving unit  400   a  and the knob  500   a  are similar to that of the case unit  200 , the spool  300 , the driving unit  400  and the knob  500  in the first embodiment, but the structure of the connecting unit  600   a  is different from the connecting unit  600  of the first embodiment. 
     The connecting unit  600   a  includes a first part set and a second part set  620   a . The first part set includes a fastening barrel  610   a . The second part set  620   a  includes a stop ring  621   a  and a screw bar  622   a . The stop ring  621   a  is limited within the large-diameter segment (not labeled), and the screw bar  622   a  passes through the stop ring  621   a  and the small-diameter segment (not labeled) to screw with the fastening barrel  610   a . The fastening barrel  610   a  can include a lower engaging portion  611   a . The stop ring  621   a  includes an inner engaging groove  6211   a , and the inner engaging groove  6211   a  is configured to engage with the lower engaging portion  611   a . The knob  500   a  can include a boss (not labeled) protruding toward the inner space (not labeled) along the axial direction. The fastening barrel  610   a  can further include an upper engaging portion  612   a  connected to the lower engaging portion  611   a , and the upper engaging portion  612   a  is engaged with the boss. 
     To be more specific, the stop ring  621   a  further includes a bottom portion  6213   a  and a body portion  6212   a . The body portion  6212   a  is connected to the bottom portion  6213   a , and the inner engaging groove  6211   a  is located at the body portion  6212   a . The shape of the upper engaging portion  612   a  of the fastening barrel  610   a  fits the through hole (not labeled) of the boss, and the shape of the lower engaging portion  611   a  fits the inner engaging groove  6211   a . Hence, when the fastening barrel  610   a  passes through the through hole, the upper engaging portion  612   a  is engaged with the boss, and the lower engaging portion  611   a  exposes from the boss to protrude toward the small-diameter segment. 
     In addition, as shown in  FIG. 7 , the body portion  6212   a  of the stop ring  621   a  passes through the small-diameter segment, and the inner engaging groove  6211   a  is engaged with the lower engaging portion  611   a . The bottom portion  6213   a  is remained in the large-diameter segment to be limited within the larger segment, and the screw bar  622   a  can fasten into the fastening barrel  610   a  upward from a bottom side thereof along the axial direction, thereby completing combination of the knob  500   a , the driving unit  400   a , the spool  300   a  and the annular wall  220   a . As pulling the lace to rotate the spool  300   a  in the loosening direction, the spool  300   a  may rub against the second part set  620   a , and because the stop ring  621   a  of the second part set  620   a  is engaged with the boss through the fastening barrel  610   a , rotation of the second part set  620   a  caused by the friction can be avoided, which also avoids separation between the first part set and the second part set  620   a.    
     Please refer to  FIG. 8  and  FIG. 9 .  FIG. 8  shows a three-dimensional exploded view of a fastening device  100   b  according to a third embodiment of the present disclosure.  FIG. 9  shows a cross-sectional view of the fastening device  100   b  of  FIG. 8 . The fastening device  100   b  includes a case unit (not shown), a spool  300   b , a driving unit  400   b , a knob  500   b  and a connecting unit  600   b . The structure and relation of the case unit, the spool  300   b , the driving unit  400   b  and the knob  500   b  are similar to that of the case unit, the spool  300   a , the driving unit  400   a  and the knob  500   a  in the second embodiment, but the structure of the connecting unit  600   b  is different from the connecting unit  600   a  of the second embodiment. 
     Precisely, the first part set of the connecting unit  600   b  includes a fastening barrel  610   b , and the second part set  620   b  includes a stop ring  621   b  and a screw bar  622   b . The structure of the fastening barrel  610   b  is identical to the fastening barrel  610   a  of the second embodiment, but the lower engaging portion is omitted while the length of the upper engaging portion along the axial direction is elongated to protrude into the small-diameter segment. The present disclosure includes the above but is not limited thereto. In the third embodiment, the stop ring  621   b  has a ring structure, and the fastening barrel  610   b  includes a lower end surface  611   b . After the screw bar  622   b  is fastened into the fastening barrel  610   b , the stop ring  621   b  is abutted against the lower end surface  611   b , such that combination of the knob  500   b , the driving unit  400   b , the spool  300   b  and the annular wall  220   b  are completed. As pulling the lace to rotate the spool  300   b  in the loosening direction, the spool  300   b  may rub against the second part set  620   b , and because the stop ring  621   b  is forced by the screw bar  622   b  to abut against the lower end surface  611   b , the friction between the stop ring  621   b , the screw bar  622   b  and the lower end surface  611   b  is larger than that between the spool  300   b  and the stop ring  621   b ; therefore, rotation of the second part set  620   b  caused by the friction can be avoided, which also avoids separation between the first part set and the second part set  620   b.    
     Please refer to  FIG. 10  and  FIG. 11 .  FIG. 10  shows a three-dimensional exploded view of a fastening device  100   c  according to a fourth embodiment of the present disclosure.  FIG. 11  shows a cross-sectional view of the fastening device  100   c  of  FIG. 10 . 
     The fastening device  100   c  includes a case unit (not shown), a spool  300   c , a driving unit  400   c , a knob  500   c  and a connecting unit  600   c . The structure and relation of the case unit, the spool  300   c , the driving unit  400   c  and the knob  500   c  are similar to that of the case unit, the spool  300   b , the driving unit  400   b  and the knob  500   b  in the third embodiment, but the structure of the connecting unit  600   c  is different from the connecting unit  600   b  of the third embodiment. 
     Precisely, the first part set of the connecting unit  600   c  includes a fastening barrel  610   c , and the second part set includes a screw bar  620   c . The screw bar  620   c  includes a head portion  622   c  and a bar portion  621   c , and the bar portion  621   c  is connected to the head portion  622   c . The bar portion  621   c  inserts in the axial space to fasten the fastening barrel  610   c , and the head portion  622   c  is limited within the large-diameter segment. In configuration, the diameter of the head portion  622   c  can be larger than the diameter of the small-diameter segment, and the diameter of the screw bar  620   c  is smaller than the large-diameter segment, such that the screw bar  620   c  can be limited within the large-diameter segment, thereby completing combination of the knob  500   c , the driving unit  400   c , the spool  300   c  and the annular wall  220   c . As pulling the lace to rotate the spool  300   c  in the loosening direction, the spool  300   c  may rub against the second part set, and therefore the fastening force between the screw bar  620   c  and the fastening barrel  610   c  can be enlarged when fastening the screw bar  620   c . For example, the teeth pitch thereof can be widened, or a glue can be dispended thereon, which avoids rotation of the second part set caused by friction and separation between the first part set and the second part set. 
     In other embodiments, the connecting unit can have a boss structure, which can be integrally connected to the knob and can protrude into the axial space, or it can be secured on the knob by adhesion of glue. The connecting unit can include a lower flange, and with the upper end connected to the knob and the lower flanged limited within the large-diameter segment, the combination of the knob, the driving unit, the spool and the annular wall can be completed. 
     Although the invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the invention covers modifications and variations of this disclosure provided they fall within the scope of the following claims.