Patent Publication Number: US-6712723-B2

Title: Tennis racket stringing machine

Description:
TECHNICAL FIELDS 
     The present invention relates to a portable tennis racket stringing machine, and more particularly, the present invention relates to a tennis racket stringing machine which enables a user to easily adjust the tension of strings installed through a head frame of a tennis racket. 
     BACKGROUND ART 
     Generally, a tennis racket essentially consists of a racket handle, a throat, a head frame and strings. A string which is also called a gut, serves as an energy center of the tennis racket. In other words, a string bed which is formed inside the head frame by installation of the strings through the head frame, is directly brought into contact with a tennis ball to hit the tennis ball. At this time, stroke energy which is generated by a tennis player, is transferred to the tennis ball via the strings. 
     A natural gut string and a synthetic string are mainly used in a tennis racket. In order to allow a tennis racket to be used under the best condition, the tension force on the strings must be adjusted to be suited to a particular player. Research has shown that four weeks after a string is installed through a head frame an elasticity loss reaches at the maximum 15% in the case of the natural gut string and 20% in the case of the synthetic string. After eight hours an elasticity loss reaches at the maximum 5% in the case of the natural gut string and 15% in the case of the synthetic string. Therefore, even though a string did not break, the string must be changed with a new one every three months, or every six months at the latest. 
     Also, in a tennis racket, it is, necessary to finely adjust the tension force of strings depending upon a situation. That is to say, by finely adjusting the tension force of strings relying upon a factor such as a season, a temperature, a court surface condition, or the like, it is possible to vary striking power of a string bed for a tennis ball. 
     Apart from the fact that, although strings of a tennis racket did not break, the strings must be changed with new ones every predetermined period of time, particularly, in the case of a professional tennis player, breakage of strings frequently occurs. When the strings are made of natural gut strings, the breaking of the strings occurs more frequently. Thus, in order to adjust the tension force of tennis racket strings so that the tension force is suited to a particular player, or in order to change a broken string, a tennis racket stringing machine is needed. 
     Referring to FIG. 1, there is shown a schematic perspective view illustrating a conventional tennis racket stringing machine. Since the conventional tennis racket stringing machine  100  must be constructed in such a way as to create high tension forces, it is usually a large-sized structure. Due to this, it is the norm that the tennis racket stringing machine  100  is located in a tennis shop. Hence, a problem is caused in that a tennis player must travel to the tennis shop so as to change a string or adjust the tension of the strings. 
     While the tension force of strings must be frequently and finely adjusted relying upon factors such as temperature, humidity, court surface condition, or the like, so as to produce optimum playing efficiency, it is inconvenient that a tennis racket user must leave a tennis court and visit a location which is equipped with a tennis racket stringing machine. This is time-consuming and causes annoyance to the tennis racket user. 
     Moreover, due to the fact that different tennis racket stringing machines are located in tennis shops, and are respectively configured in such a way as to apply different levels of tension force to the string, a stringing operation must be repeatedly performed through a multitude of times to adjust the tension force to that optimally suited to the user. 
     DISCLOSURE OF THE INVENTION 
     Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a tennis racket stringing machine in which respective component elements are fabricated in such a way as to be capable of being assembled one with another to allow the machine to be carried around and conveniently used irrespective of time and place, and which provides a simple configuration with a reduced manufacturing cost. 
     Another object of the present invention is to provide a tennis racket stringing machine which enables the tension force of the strings to be adjusted and whereby the tennis racket to be used under optimum tension force suitable for each tennis player. 
     In order to achieve the above objects, according to one aspect of the present invention, there is provided a tennis racket stringing machine comprising: racket fastening means including a lower supporting plate on which a head frame of a tennis racket is seated and which has a larger length than the head frame so that the head frame of the tennis racket can be securely maintained on the lower supporting plate in a lengthwise direction of the lower supporting plate, a fixed projecting section which is disposed adjacent to one end of the lower supporting plate and functions to fasten one end of the head frame of the tennis racket, a movable section which is disposed adjacent to the other end of the lower supporting plate in such a way as to be capable of being moved along the lengthwise direction of the lower supporting plate and functions to fasten the other end of the head frame of the tennis racket, and a clamp which is located below the lower supporting plate in such a way as to rotatably support a center portion of the lower supporting plate; and tension force adjusting means brought into close contact with the head frame of the tennis racket and wherein it is separated from the racket fastening means, for adjusting the tension force of strings installed through the head frame, so that the strings can be held under optimum tension force. 
     According to another aspect of the present invention, the fixed section comprises a fixed shaft which has one end secured to the lower supporting plate and the other end projecting upward, a first upper auxiliary plate which is fitted around the fixed shaft, and a first butterfly nut which is threadedly locked to the other end of the fixed shaft. 
     According to another aspect of the present invention, the movable section comprises a pair of bent pieces which are formed by a pair of portions of the lower supporting plate which are partially cut and bent downward, a rotating bolt which is rotatably fitted through the pair of bent pieces in such a way as to be supported by the pair of bent pieces and to a circumferential outer surface to which a manipulating wheel is secured at a predetermined position, a movable body which is threadedly coupled with the rotating bolt so that the movable body can be moved along the lengthwise direction of the lower supporting, plate by rotation of the rotating bolt, a movable shaft which has one end secured to an upper surface of the movable body and the other end projecting upward, a second upper auxiliary plate which is fitted around the other end of the movable shaft, and a second butterfly nut which is threadedly locked to the other end of the movable shaft. 
     According to another aspect of the present invention, the movable section comprises a pair of guide rails which are formed at the other end of the lower supporting plate, a wheel receiving groove which is defined in the lower supporting plate adjacent to the pair of guide rails, a movable block which is assembled with the pair of guide rails so that it can be slid along the pair of guide rails in the lengthwise direction of the lower supporting plate, a movable bolt which has one end secured to the movable block and the other end extending in the lengthwise direction of the lower supporting plate in such a way as to be capable of being moved inward of the lower supporting plate, a manipulating wheel which is received in the wheel receiving groove and is threadedly coupled with the movable bolt so that the movable bolt can be moved along the lengthwise direction of the lower supporting plate by rotation of the manipulating wheel, a movable shaft which has one end secured to an upper surface of the movable block and the other end projecting upward, a second upper auxiliary plate which is fitted around the other end of the movable shaft, and a second butterfly nut which is threadedly locked to the other end of the movable shaft. 
     According to still another aspect of the present invention, the lower supporting plate is composed of a pair of lower supporting plate halves, a socket portion is defined in a first lower supporting plate half, and a plug portion which is fitted into the socket portion, is formed on a second lower supporting plate half. 
     According to yet still another aspect of the present invention, the tension force adjusting means comprises a string drawing section, a tension force adjusting section and a motor stopping section; the string drawing section including a squeezing plate which is brought into close contact with the head frame of the tennis racket, a squeezing rod which is coupled to the squeezing plate so that it is aligned with a string installed through the head frame, a string reel which winds up the string connected to the squeezing plate, and a motor for rotatably driving the string reel; the tension force adjusting section including a seesaw plate which has one end coupled to the squeezing rod so that the seesaw plate can be rotated about a center shaft, a coil spring which has one end secured to the other end of the seesaw plate, and a tension force—adjusting dial which is connected to the other end of the coil spring; and the motor stopping section including a projection which is formed on a circumferential outer surface of the squeezing rod at a preselected position, and a limit sensor which is arranged on a moving path of the projection and functions to stop the motor when the projection comes into contact with the limit sensor. 
     In accordance with the features of the present invention, not only the tension force of tennis racket strings can be finely adjusted to a level which is desired by a user, but the entire structure of the tennis racket stringing machine is simplified, whereby the machine can be easily carried around and conveniently used irrespective of time and place, and it is possible to manufacture the tennis racket stringing machine at reduced cost. Portability of the tennis racket stringing machine according to the present invention is further improved by the fact that a lower supporting plate is composed of a pair of lower supporting plate halves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which: 
     FIG. 1 is a schematic perspective view illustrating a conventional tennis racket stringing machine; 
     FIG. 2 is an exploded perspective view illustrating an entire structure of a tennis racket stringing machine in accordance with an embodiment of the present invention; 
     FIG. 3 is a perspective view illustrating the tennis racket stringing machine of FIG. 2 in use; 
     FIG. 4 is a cross-sectional view illustrating the tennis racket stringing machine of FIG. 2 in use; 
     FIG. 5 is a perspective view illustrating the structure of the tension force adjusting means of the tennis racket stringing machine according to the present invention; 
     FIG. 6 is an exploded perspective view illustrating the structure of a tennis racket stringing machine in accordance with another embodiment of the present invention; and 
     FIG. 7 is a cross-sectional view illustrating the tennis racket stringing machine of FIG. 6 in use. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
     FIG. 2 is an exploded perspective view illustrating an entire structure of a tennis racket stringing machine in accordance with the present invention; FIG. 3 is a perspective view illustrating the tennis racket stringing machine of FIG. 2 in use; and FIG. 4 is a cross-sectional view illustrating the tennis racket stringing machine of FIG. 2 in use. 
     As shown in the drawings, a tennis racket stringing machine according to a first embodiment of the present invention, which is designated by the drawing reference numeral  10 , includes racket fastening means  20  for fastening a head frame  51  of a tennis racket  50  along a lengthwise direction thereof, and tension force adjusting means  60  separately disposed from the racket fastening means  20 , for holding strings  53  (which are installed through the head frame  51 ), under predetermined tension. 
     As shown in FIGS. 2 through 4, the racket fastening means  20  includes a lower support plate  21 , a fixed section, a movable section and a clamp  27 . 
     The head frame  51  of the tennis racket  50  is seated on the lower support plate  21 . The lower support plate  21  has a larger length than the head frame  51  so that the lower support frame  21  can fasten the head frame  51  of the tennis racket  50  in a lengthwise direction of the lower support plate  21 . 
     The fixed section includes a fixed shaft  23 . The fixed shaft  23  has one end which is fastened to an upper surface of the lower support plate  21  adjacent to one end of the lower support plate  21  and the other end which projects upwardly. A threaded portion is formed on a circumferential outer surface of the fixed shaft  23 . A first upper auxiliary plate  25  receives the other end of the fixed shaft  23 , and a first butterfly nut  22  is threadedly locked to the other end of the fixed shaft  23 . In use, the fixed shaft  23  is brought into close contact with one end of the head frame  51  of the tennis racket  50 , and by tightening the first butterfly nut  22 , the first upper auxiliary plate  25  is pressed against the one end of the head frame  51 . Accordingly, the one end of the head frame  51  is maintained in a securely fastened status. When the fixed shaft  23  is brought into close contact with the one end of the head frame  51  of the tennis racket  50 , in order to prevent the head frame  51  from being damaged by the threaded fixed shaft  23 , a first protective ring  23 a is fitted around the fixed shaft  23 . 
     The movable section is disposed adjacent to the other end of the lower supporting plate  21  in such a way as to be capable of being moved along the lengthwise direction of the lower supporting plate  21  and functions to fasten the other end of the head frame  51  of the tennis racket  50 . The movable section includes a pair of bent pieces  37 . The pair of bent pieces  37  are formed by a pair of portions of the lower supporting plate  21  which are partially cut and bent downward. As shown in FIGS. 2 and 4, a rotating bolt  34  is rotatably fitted through the pair of bent pieces  37  in such a way as to be supported by the pair of bent pieces  37 . A manipulating wheel  35  is secured at a predetermined position to a circumferential outer surface of the rotating bolt  34 . A movable body  36  is threadedly coupled with the rotating bolt  34 . If the rotating bolt  34  is rotated by the rotation of the manipulating wheel  35 , the movable body  36  can be moved along the lengthwise direction of the lower supporting plate  21 . One end of a movable shaft  33  is secured to an upper surface of the movable body  36 , and the other end of the movable shaft  33  projects upwardly. A threaded portion is formed on a circumferential outer surface of the movable shaft  33 . A second upper auxiliary plate  25  receives the other end of the movable shaft  33  therethrough, and a second butterfly nut  22  is threadedly locked to the other end of the movable shaft  33 . In use, the movable shaft  33  is brought into close contact with the other end of the head frame  51  of the tennis racket  50 , and, by tightening the second butterfly nut  22 , the second upper auxiliary plate  25  is pressed against the other end of the head frame  51 . Accordingly, the other end of the head frame  51  is thereby maintained in a securely fastened status. When the movable shaft  33  is brought into close contact with the other end of the head frame  51  of the tennis racket  50 , in order to prevent the head frame  51  from being damaged by the threaded movable shaft  33 , a second protective ring  33   a  is fitted around the movable shaft  33 . 
     The clamp  27  is located below the lower support plate  21  and functions to rotatably support a center portion of the lower support plate  21 . The clamp  27  includes a rotatable knob  26  which is provided at a lower end thereof. A jaw is formed on an upper end of the knob  26 . By rotating the knob  26  and thereby moving the jaw upward, the clamp  27  can be firmly affixed to a desired supporting member such as a desk. A pipe into which a height regulating rod  28  is threadedly fitted, is integrally secured to an upper end of the clamp  27 . A nut  29  is threadedly coupled to a circumferential outer surface of the height regulating rod  28 . Hence, by rotating the nut  29 , it is possible to regulate the height of the height regulating rod  28 . An upper end of the height regulating rod  28  is fitted into a hole  24  which is defined at the center of the lower support plate  21 . Accordingly, the lower support plate  21  can be freely rotated on the height regulating rod  28 . 
     The tension force adjusting means  60  is also brought into close contact with the head frame  51  of the tennis racket  50  to a position wherein it is separated from the racket fastening means  20 . The means  60  functions to adjust the tension in the strings  53  which are installed through the head frame  51 , so that the strings  53  can be held under optimum tension. The tension force adjusting means  60  includes a string drawing section, a tension force adjusting section and a motor stopping section (see FIG.  5 ). The string drawing section functions to draw the strings  53  through the head frame  51  of the tennis racket  50 . The string drawing section includes a squeezing plate  61  which is brought into close contact with the head frame  51  of the tennis racket  50 , a squeezing rod  62  which is coupled to the squeezing plate  61  so that it is aligned with a string  53  installed through the head frame  51 , a string reel  63  which winds up the string  53  connected to the squeezing plate  61 , and a motor  64  for rotatably driving the string reel  63 . 
     The tension force adjusting section includes a seesaw plate  65  which has one end coupled to the squeezing rod  62  so that the seesaw plate  65  can be rotated about a center shaft  70 , a coil spring  66  which has one end secured to the other end of the seesaw plate  65 , and a tension force adjusting dial  67  which is connected to the other end of the coil spring  66 . An indicating pin  67   a  is provided on the tension force adjusting dial  67 , and functions to indicate current tension on a scale portion  72  having approximate markings on an outer surface of the tension force adjusting means  60 . In order to allow force to be accurately transferred to respective surfaces of the squeezing rod  62  and the coil spring  66  ball members (not shown) are properly arranged on the surfaces, respectively. 
     The motor stopping section functions to stop the motor  64  when the strings  53  are held under desired tension. The motor stopping section includes a projection  68  which is formed on a circumferential outer surface of the squeezing rod  62  at a preselected position, and a limit sensor  69  which is arranged in the path of movement of the projection  68  and functions to stop the motor  64  when the projection  68  comes into contact with the limit sensor  69 . Here, it is preferred that the motor stopping section includes a reset button  71 . In this regard, the reset button  71  can rotate the motor  64  by one revolution in a reverse direction so that the string  53  which is wound on the string reel  63 , can be smoothly unwound therefrom. The drawing reference number  57  represents a string clamp. 
     Operation of the tennis racket stringing machine  10  in accordance with the first embodiment of the present invention, constructed as mentioned above, will be described in detail with reference to FIGS. 3 and 4. 
     When it is necessary to change the string  53  of the tennis racket  50  or adjust the tension of the string  53 , a user first affixes the clamp  27  to a desired supporting member such as a desk. At this time, the racket installation height may be adjusted by rotating the nut  29  of the clamp  27  and thereby causing movement of the height regulating rod  28  in upward and downward directions. 
     Thereafter, the head frame  51  of the tennis racket  50  is fastened to the lower supporting plate  21 . In other words, the first and second protective rings  23   a  and  33   a  are respectively fitted around the fixed shaft  23  and the movable shaft  33  so as to prevent the head frame  51  from being damaged by the threaded fixed shaft  23  and the threaded movable shaft  33  when the fixed shaft  23  and the movable shaft  33  are brought into contact with the head frame  51 . One end and the other end of the head frame  51  are positioned on the fixed section and the movable section of the racket fastening means  20 , respectively. At this time, position alignment between the other end of the head frame  51  and the movable section of the racket fastening means  20  is effected by the rotation of the manipulating wheel  35  and the rotating bolt  34  to axially shift the movable shaft  33  thereby. Thereafter, by tightening the first and second butterfly nuts  22 , the first and second upper auxiliary plates  25  press the head frame  51  against the lower support plate  21 , and thereby maintain head frame  51  in securely fastened position. By this, the head frame  51  of the tennis racket  50  is supported in a manner such that the strings  53  can be installed therethrough. 
     A string changing method is commonly applied to all tennis rackets, and therefore, main strings and cross strings must be knotted separately. That is to say, four knots must be formed, and the main string and the cross string should be knotted while they are drawn one by one by the string reel  63 . As a consequence, the user can wind the main string and the cross string in regular sequence on the string reel  63  which draws the strings  53  with the predetermined force, and then, can knot the main string and the cross string with each other while clamping first wound string  53  using the string clamp  57  in such a way as not to allow the first wound string  53  to be unwound from the string reel  63 . Since the lower support plate  21  is configured in a manner such that it can be rotated on the clamp  27 , the main strings and the cross strings can be wound on the string reel  63  while, being rotated. 
     To obtain a desired tension, the dial  67  is rotated until the desired tension force is indicated on scale  72 . This causes the coil spring to exert a force against the plate  65  to rotate it about shaft  70  and push plate  61  outwardly through the rod  62 . The plate  61  is placed in contact with head  50  and the string attached to reel  63 . As the reel  63  rotates the tension in the string increases and the head  50  moves the plate  61  rearwardly causing the plate  65  to rotate about shaft  70  against the force of coil spring  66 . When the projection  68  engages the limit sensor, the motor  64  stops. Hence, the tension force of the string will be equal to the preset force indicated by the scale  72 . 
     FIG. 6 is an exploded perspective view illustrating an entire structure of a tennis racket stringing machine in accordance with another embodiment of the present invention; and FIG. 7 is a cross-sectional view illustrating the tennis racket stringing machine of FIG. 6 in use. 
     In a tennis racket stringing machine in accordance with this second embodiment of the present invention, only the differences in the racket fastening means with respect to the first embodiment of the present invention is shown. Thus, only the differences existing therebetween will be described hereinbelow. 
     In this embodiment of the present invention, a lower support plate  11  is composed of a pair of lower support plate halves  73  and  74 . A socket portion  75  is defined in a first lower support plate half  73 , and a plug portion  76 , which is fitted into the socket portion  75 , is formed on a second lower support plate half  74 . 
     A pair of guide rails  12  are formed at one end of the second lower support plate half  74 . A wheel receiving groove  13  is defined through the second lower supporting plate half  74  adjacent to the pair of guide rails  12 . An accommodating slot  11   a  is defined through the second lower supporting plate half  74  adjacent to the wheel receiving groove  13 . The movable section of the racket fastening means according to this embodiment of the present invention includes a movable block  14 . The movable block  14  is assembled with the pair of guide rails  12  so that it can be slid along the pair of guide rails  12  in the lengthwise direction of the lower supporting plate  11 . Both sides of the movable block  14  are respectively defined with a pair of guide grooves so that the pair of guide rails  12  can be engaged into the pair of guide grooves, respectively. A movable bolt  17  is secured at one end of the movable block  14 . The other end of the movable bolt  17  movably projects into the accommodating slot  11   a  through the wheel receiving groove  13 , which is defined through the second lower supporting plate half  74 . A manipulating wheel  16  is received in the wheel receiving groove  13 . The manipulating wheel  16  is threadedly coupled with the movable bolt  17  so that the movable bolt  17  can be moved along the lengthwise direction of the lower supporting plate  11  by rotation of the manipulating wheel  16 . One end of a shaft  15  is secured to an upper surface of the movable block  14 . The other end of the shaft  15  projects upwardly. A threaded portion is formed on a circumferential outer surface of the movable shaft  15 . A second upper auxiliary plate  18  receives the other end of the movable shaft  15 , and then, a second butterfly nut  22  is threadedly locked to the other end of the shaft  15 . Hence, when the shaft  15  is brought into close contact with an end of the head frame  51  of the tennis racket  50 , tightening the second butterfly nut  22  causes the second upper auxiliary plate  18  to be pressed against the end of the head frame  51 , and thereby, the end of the head frame  51  can be maintained in a securely fastened status. In order to prevent the head frame  51  from being damaged by the threaded shaft  15 , a second protective ring  15   a  is fitted around the movable shaft  15 . 
     Instead of having one end of the movable shaft  15  secured to the upper surface of the movable block  14  as shown in FIG. 6, the shaft  15  can be integrally secured to the second butterfly nut  22  as shown in FIG.  7 . Of course, in this case, it is to be readily understood that a threaded hole into which the shaft can be threadedly fitted, must be defined in the movable block  14 . 
     Consequently, as a user rotates the manipulating wheel  16  and thereby causes the movable block  14  to be moved along the lengthwise direction of the lower supporting plate  11 , the head frame  51  of the tennis racket  50  can be easily fastened to the lower supporting plate  11 . 
     Industrial Applicability 
     As a result, the tennis racket stringing machine according to the present invention provides advantages in that, since tensioning force of a tennis racket can be finely adjusted to a level which is desired by a user, and the entire structure of the tennis racket stringing machine is simplified, the machine can be easily carried around and conveniently used irrespective of time and place. Moreover, it is possible to manufacture the tennis racket stringing machine with a reduced cost. Portability of the tennis racket stringing machine according to the present invention is further improved by the fact that a lower supporting plate is composed of a pair of lower supporting plate halves. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.