Patent Publication Number: US-2023149790-A1

Title: Structure for tennis practice frame

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of PCT International Application No. PCT/KR2021/010757, titled “STRUCTURE OF TENNIS PRACTICE FRAME” filed Aug. 12, 2021, which claims the benefit of priority to: Korea Patent Application No. 20-2020-0003046, titled “TENNIS TRAINING DEVICE,” filed Aug. 19, 2020, which is now Korea Patent No. 20-0495480; and Korea Patent Application No. 20-2020-0003154, titled “TENNIS TRAINING DEVICE,” filed Aug. 26, 2020; each of which above applications are herein, incorporated by reference in entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a structure of/for a tennis practice frame, stand, or device, which is installed much higher than the height of a person, and particularizes on configuration or installation structure of ball cord connection(s). 
     Background Art 
     Riding on the popularity of tennis, tennis practice device or training equipment(s) that allow trainees to practice alone have been developed in various forms, and non-motorized tennis practice devices include: 
     A. Tennis Practice Device (Date of Publication 1980.08.05.)
         Hit is a ball hung at a center of 2 poles; the height of the ball is adjusted with vertical adjustment of the poles.       

     B. Multiple Sports Train Machine (Date of Patent 2001.01.31.)
         Hit is a ball suspended from a connecting cord or string at an end portion of horizontal pole formed in an inverse “L” shape with a vertical pole; a shield net is installed behind the ball to return the ball to the hitting origin after hitting the ball, and on the vertical pole is installed, a rotating reel capable of pulling or loosening another one end of the connecting cord, mainly for the purpose of adjusting the height of the ball. The structure according to the present invention may appear to be similar but in outer appearance to this structure with the shield excluded.       

     C. Apparatus for Stoke Training of Tennis (Date of Patent 2001.11.29.)
         Hit is a ball bound to an upper portion of an elastic pole or to a center of a vertical, top-to-bottom cord connection. There is no height control.       

     D. Portable Tennis Training Apparatus (Date of Patent 2012.03.16.)
         Hit is a ball connected to a weight via an elastic connecting cord, which returns due to elastic force of the connecting cord; the speed of the ball is controlled via the length of the connecting cord.       

     E. Ping-Pong and Tee Ball Sporting Equipment by Oneself (Date of Publication 2015.06.16.)
         Hit is a ball hanging from a connecting cord, connected to an end portion of a horizontal pole, which with a vertical pole, is formed in an inverse “L” shape, with elastic character; the height of the ball is adjusted by controlling the height of the vertical pole. While this technology is limited to table tennis and tee ball, there is similarity only in outer appearance with that in the present invention.       

     F. Hitting Device for a Game (Date of Publication 2015.10.22.)
         Hit is a ball connected to a connecting cord temporarily to an end portion a vertical pole and a horizontal pole, which are formed in an inverse “L” shape; the height of the ball is adjusted by controlling the height of vertical pole or the horizontal angle of the horizontal pole and the ball is thereby hit. However, this technology has similarity with that of the present invention only in outer appearance.       

     These conventional technologies have been developed and demonstrated, and each of these technologies has contributed to the development of tennis skills, each with unique advantages. 
     Among the 6 listed prior arts, which may be used for non-motorized tennis training apparatuses, 
     “A. Tennis Practice Device (Date of Publication 1980.08.05.)” 
     “C. Apparatus for Stoke Training of Tennis (Date of Patent 2001.11.29.)” 
     “D. Portable Tennis Training Apparatus (Date of Patent 2012.03.16.)” 
     these 3 are almost non-analogous in terms of structure or layout, and are excluded from discussion for now. 
     In the remaining 3 technologies, which are not excluded, 
     “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.)” without the shield net has similarity with the training device of the present invention in outer appearance. However, there are significant differences with the training device of the present invention, not only in terms of structure or layout but functions, and the key differences/points are as follows: 
     First, the ball connection cords are entirely different. As described later, the ball connection string or cord, according to an embodiment in the present invention, is divided into a front-end connection cord ( 200 ) and a rear-end connection cord ( 210 ), and has become a very important issue with respect to its specification and material. In particular, for the rear-end connection cord ( 210 ), the material and performance are considered the most sensitive and important in the practice device, in terms of practicing or training ball-hitting (strokes) or sense thereof by repeatedly hitting a ball ( 220 ) that flies in the air in front(ward) of the trainee in a trajectory ( 230 ) of a certain distance due to a hit (stroke) and then flies back toward front(ward) of the trainee. 
     To feel and get the real sense of hit (stroke, impact) as to the ball as in an actual game, the flight trajectory ( 230 ) of the ball should be as large as possible so that a horizontal angle of the ball flying in front of the trainee is small as possible. Since a/the ground height of the practice device&#39;s horizontal pole ( 130 ) should be as high as possible to do so, the rear-end connection cord ( 210 ) should also be lengthened accordingly. As described later, the rear-end connection cord ( 210 ) should first be light-weight and must have flexibility and tensile strength at equivalent levels. 
     On the other hand, in that the front-end connection cord ( 200 ) has have performance and material, etc. that requires more tensile force and durability than lightness, there are professional concerns that are difficult to find in the ball connection cord as applied in “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.).” 
     Also, while not in “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.),”, there are big differences in structure as compared to the present invention, such as that a weight ( 300 ), which plays an important role, is formed or installed on the front-end connection cord ( 200 ) just below a guide ring ( 131 ) at the end of the horizontal pole, as mentioned above. The workings (function, configuration) of the weight ( 300 ) are detailed later. 
     Next, in operational aspects, there is a fundamental difference in operation in that “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.)” provides a technique of continuously hitting a ball in a stationary state with a certain time difference, whereas the practice device according to the present invention, above all, provides a technique for hitting a flying ball, flying toward the trainee, each time with a different flight trajectory and a different flight distance at a different speeds (since the highest reaching point is different at every time, due to a hit). 
     That is, to lively practice as in an actual game, hitting (stroke) techniques, such as whether to hit the ball as a forehand drive or a backhand slice while quickly obtaining/securing a hitting position according to a direction of the flying ball as in the present invention, there are many deficiencies in “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.).” 
     Moreover, “E. Ping-Pong and Tee Ball Sporting Equipment by Oneself (Date of Publication 2015.06.16.)” or “F. Hitting Device for a Game (Date of Publication 2015.10.22.)” has overall appearance similar to that of the practice device of the present invention in that each has a vertical pole, horizontal pole, and structure for hitting a ball hanging at an end of the horizontal pole; however, as explained above in the same context as with “B. Multiple Sports Train Machine (Date of Patent 2001.01.31.),” there are significant differences in the function/operation and structure of the practice device of the present invention. Detailed description thereof is omitted. 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the tennis practice device, the ball should be a ball that travels a distance that actually has a certain trajectory to a trainee rather than a stationary ball, and for each ball, the trainee should be able to alternately (take different turns to) hit various hitting techniques in realistic sense. Further, every time the trainee hits the balls accurately, not only should the strokes be fun/enjoyable but there should also be functional aspects so that the trainee can practice tennis strokes without much effort on the practice device installed in the house yard or a vacant lot near the house, even if the trainee does not go to the tennis court. 
     In the tennis practice device, it should also semi-permanently maintain stability even in the worst weather conditions such as typhoons, and characteristics (e.g., shot, flight path, control) of the ball to be hit should not be twisted, distorted or overly difficult, and whenever trainee wants to practice, s/he should do so without being burdened with installing or dismantling the practice device. The trainee should be able to practice easily and safely, and the structural aspects of the practice device should/must be carefully considered. 
     Solution to Problem 
     Described in the present invention are: a basic/foundation frame ( 100 ) of a tennis practice device, which is a pipe-type/shaped metallic structure, wherein a vertical pole or support ( 120 ), and a horizontal/cross pole ( 130 ) extending horizontally from near an upper end portion of the central or vertical support, form an “L” or inverse “L” shape as a whole; or a basic/foundation frame ( 100 ) of a tennis practice device, wherein a bracket (or brackets) ( 101 ) is installed at a certain height on a wall surface ( 400 ) of a house or building structure, and the horizontal pole ( 130 ) is installed in a horizontal direction with the ground on the bracket, to create or construct the tennis practice device; 
     so as to provide a structure for a tennis practice device in which a person practices tennis by hitting a ball ( 220 ) suspended on a string or cord downward from an end of the horizontal pole of the frame. Described embodiments of the present invention particularizes on configuration or installation structure of a/the ball cord-connection. 
     In the basic frame ( 100 ) of the tennis practice device, the vertical support ( 120 ), which is a pipe-type metallic structure in which a lower, foundational base ( 121 ) is firmly fixed to the ground or ground concrete structure ( 500 ), extends from the lower base ( 121 ) to form a central support shaft disposed and extending in the skyward direction, and the horizontal pole ( 130 ) extending horizontally from a certain point at an upper end of the vertical support is mounted (and the basic frame ( 100 ) so configured), 
     or, the bracket ( 101 ) is affixed at a certain height to a vertical wall of a house or building structure, and then the horizontal pole ( 130 ) extending horizontally with the ground is mounted on the bracket; and the basic frame is configured and should initially be provided. 
     To solve above and other problems, a structure for the tennis practice device may comprise, as the configuration or installation structure of the ball cord-connection built or installed on the basic frame: a ball connection cord extending from a roller ( 140 ), which is ordinarily installed at the height of a person&#39;s chest in the vertical support, or house or building structure, to the weight ( 300 ) just below the guide ring ( 131 ) at the end of the horizontal pole, comprising the front-end connection cord ( 200 ) made of a material with greater durability and tensile force than the rear-end connection cord ( 210 ); a ball connection cord formed or attached to the weight ( 300 ), which in turn is formed or attached to the front-end connection cord ( 200 ), and is joined to and hangs the ball ( 220 ) below the weight, comprising the rear-end connection cord ( 210 ) made of material of lighter weight and more flexibility than the front-end connection cord ( 200 ); a tennis ball ( 220 ) hanging from the rear-end connection cord; the weight ( 300 ) formed or attached to an end of the front-end connection cord ( 200 ), the weight having multi-purposes, such as functions of providing a load to the front-end connection cord to enable the front-end connection cord ( 200 ) to free fall or fall naturally, preventing tangling of the connection cord ( 200 ) inside or outside of the frame or at the roller ( 140 ) when the front-end connection cord ( 200 ) is in descent (lowered) and lift (raised) operations, and acting as a stopper for the front-end connection cord ( 200 ) when the front-end connection cord ( 200 ) is in the lift (raised) operation. 
     Advantageous Effects of Invention 
     In the tennis practice device according to embodiments of the present invention, when the trainee hits the ball with a racket (racquet) from/under the horizontal pole, the ball flies along a circumferential orbit/trajectory with weight ( 300 ), which is at an end of the horizontal pole, as a center point—that is the ball flies in the skyward direction in front (forward region) of the trainee and then returns to the same circumferential orbit/curve due to gravity, and the trainee practices tennis by repeatedly hitting the ball that falls in front of the trainee. 
     With only one setup for the present practice device, the trainee need not be burdened with tasks of assembling and disassembling the device when s/he wants to practice strokes. Further, the trainee need not work on gathering the balls when finished with the practice, and there is great advantage in that tennis-strokes practice may continue to be enjoyed semi-permanently whenever time permits. 
     Also, it is obvious, only natural that young children who have never played tennis will feel considerable interest if they try to hit the ball hanging on the present practice device with a racket. It is difficult to hit the ball bound at/to the tennis court, but the ball of the present practice device is not so difficult, and thus it is easy to become familiar with various ball-hitting(s) or strokes through the practice device, and it can bring about the effect of developing motor nerves (system) from childhood. 
     Also to a tennis novice or mid-level trainee, the present practice device has a great effect on honing the practical skill of determining in an instant, from which position and to which direction to hit and with what posture and hitting (stroke) techniques, and where to hit the ball accurately, in order to effectively hit the ball that repeatedly comes flying in a reasonable trajectory toward the trainee&#39;s own body. 
     Of course, although the speed, flight trajectory, and rotation angle of the ball in actual use/game and of the ball flying toward front of the trainee in practice are very different, steadily honing the stroke techniques through the practice device according to the present invention and developing abilities to apply, implement the techniques, the trainee will be able to more than adequately perform her/his skills even with the ball of any (e.g., shot, flight, control) characteristics, as changed or modified during actual games/settings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an overall concept diagram of the tennis practice device as an inverse “L” shaped metallic structure, according an embodiment of the present invention. 
         FIG.  2    is an overall concept diagram of the tennis practice device configured as the bracket ( 101 ) fixed to the wall of a house or building structure and the horizontal pole ( 130 ) mounted on the bracket ( 101 ), according an embodiment of the present invention. 
         FIG.  3    is an overall concept diagram of a ball connection cord configuration of the tennis practice for a sports park, according an embodiment of the present invention. 
         FIG.  4    is a cross-sectional diagram of the tennis ball ( 220 ) according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Hereinafter, various embodiments of the present invention are shown and described. Particular embodiments are exemplified herein and are used to describe and convey to a person skilled in the art, particular structural, configurational and/or functional, operational aspects of the invention. The present invention may be altered/modified and embodied in various other forms, and thus, is not limited to any of the embodiments set forth. 
     The present invention should be interpreted to include all alterations/modifications, substitutes, and equivalents that are within the spirit and technical scope of the present invention. 
     Terms such as “first,” “second,” “third,” etc. herein may be used to describe various elements and/or parts but the elements and/or parts should not be limited by these terms. These terms are used only to distinguish one element and/or part from another. For instance, a first element may be termed a second element and vice versa, without departing from the spirit and scope of the present invention. 
     When one element is described as being “joined” or “connected” etc. to another element, the one element may be interpreted as “joined” or “connected” to that another element directly or indirectly via a third element, unless the language clearly specifies. Likewise, such language as “between,” “immediately between,” “neighboring,” “directly neighboring” etc. should be interpreted as such. 
     Terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the present invention. As used herein, singular forms (e.g., “a,” “an”) include the plural forms as well, unless the context clearly indicates otherwise. The language “comprises,” “comprising,” “including,” “having,” etc. are intended to indicate the presence of described features, numbers, steps, operations, elements, and/or components, and should not be interpreted as precluding the presence or addition of one or more of other features, numbers, steps, operations, elements, and/or components, and/or grouping thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have same meaning as those commonly understood by a person with ordinary skill in the art to which this invention pertains. Terms, such as those defined in commonly used dictionaries, should be interpreted as having meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereafter, various embodiments of the present invention are described in more detail with reference to the accompanying drawings. Same reference numerals are used for the same elements in the drawings, and duplicate descriptions are omitted for the same elements or features. 
       FIG.  1    is an overall concept diagram of the tennis practice device as an inverse “L” shaped metallic structure, according an embodiment of the present invention. 
     Referencing  FIG.  1   , shown are: the lower base ( 121 ) of the practice device fixed to a metal, reinforced concrete structure of the ground ( 500 ); the vertical support ( 120 ) extending from/to the lower base ( 121 ) and disposed and extending in the skyward direction; the horizontal pole ( 130 ) formed as curved in a horizontal direction from an upper end of the vertical support; the roller ( 140 ) formed or installed on the vertical support, the ball connection cords ( 200 ,  210 ) and the weight ( 300 ); and the ball ( 220 ) and the ball trajectory ( 230 ). A basic frame ( 100 ) may be formed in an inverse “L” shape, may comprise the lower base ( 121 ), the vertical support ( 120 ), and the horizontal pole ( 130 ). 
     The metal, pipe-type vertical support ( 120 ) has an extruded circular or polygonal shape, with a maximum inner diameter of 8.2 and an outer diameter of 10 (cm), and may be gradually narrowed from a middle portion to an upper portion within a range that is not unreasonable in supporting the horizontal pole ( 130 ). For transportation to the installation site or for overseas delivery, it is possible to divide the upper and lower portions into about 4 upper and lower segments with means to enable disassembling and assembling/combining, and on the vertical support ( 120 ) is formed or attached to/at the height of a person&#39;s chest, the roller ( 140 ) is installed to adjust the front-end connection cord. 
     The vertical support ( 120 ) is disposed and extends at/from the lower base ( 121 ), which is made of the ground or metal, reinforced concrete, etc., in the skyward direction, and when the trainee hits the ball, the horizontal pole ( 130 ) should withstand the tension without much shaking to enable the ball to fly or traverse smoothly without being distorted while practicing the hits (strokes). 
       FIG.  2    is an overall concept diagram of the tennis practice device configured as is the bracket ( 101 ) fixed to the wall of a house or building structure and the horizontal pole ( 130 ) mounted on the bracket ( 101 ), according an embodiment of the present invention. 
     Referencing  FIG.  2   , shown are: a vertical support unit ( 410 ) affixed to the wall ( 400 ), on which the bracket ( 101 ) for mounting the horizontal pole is installed at a certain height on the wall ( 400 ); a horizontal support unit ( 420 ) configured for mounting the horizontal pole; and a reinforcing support unit ( 430 ) configured for reinforcing bearing capacity of the horizontal support unit by attaching and binding the horizontal support unit and the wall ( 400 ) in a diagonal direction of the horizontal support unit and the wall ( 400 ). A basic frame ( 101 ) may be formed by a combination of the three (the vertical support unit ( 410 ), the horizontal support unit ( 420 ), and the reinforcing support unit ( 430 )), wherein a rear-end portion of the horizontal pole ( 130 ) is attached to the horizontal support unit ( 420 ) and the horizontal pole ( 130 ) is disposed in a horizontal direction with the ground. 
     When the basic frame of the tennis practice device is configured as an inverse “L” shaped metallic structure, the vertical support ( 120 ) is first provided. For overall-sturdy, strong metal, pipe-type support or pole structure, stainless steel or aluminum alloy material may be used. 
     When configuring and forming the basic frame of the tennis practice device by using the wall ( 400 ) of a house or building structure as the vertical support to mount or install the horizontal pole ( 130 ), first, the bracket ( 101 ) should be installed at a certain height on the surface, which is significantly higher than a person&#39;s height. The bracket ( 101 ) should be at a level that can sufficiently secure a support force (i.e., vertical support force, horizontal support force, and reinforcement support force) that can withstand strong tension caused by the hitting/string of the ball, by fixing the bracket and the horizontal pole to the wall, 
     The bracket ( 101 ) may be of metallic material, but types, forms and shapes may be diverse. However, when the trainee hits the ball, the horizontal pole ( 130 ) should be firmly fixed to the wall ( 400 ) so that there is not any swaying. The brackets and the horizontal pole may not sway for the ball to fly smoothly without being distorted while practicing the hits (strokes). 
     Meanwhile, a guide ring ( 411 ), through which the front-end connection cord passes through or penetrates, should be built or installed at a certain point below the bracket, so that the front-end connection cord ( 200 ) (described later) may be connected from the end of the horizontal pole toward the bracket and to the roller ( 140 ) below; and the roller ( 140 ) is for adjusting the front-end connection cord is built or installed at the height of a person&#39;s chest, below the bracket. 
     Next, the horizontal pole ( 130 ) is built or installed on the upper end of the vertical support ( 120 ), or the bracket ( 101 ). The horizontal pole is made in a length of about 2 m so that there is no hindrance to the trainee wielding the racket and practicing strokes there under. and is formed to be gradually narrowed from the upper end of the vertical support ( 120 ) to the guide ring ( 131 ) at the end of the horizontal pole. This way, beauty of the form of the training device is emphasized, and effects of the load and wind on upper part of the training device is minimized, within the range of maintaining safety and stability of the training device. 
     At the end of the horizontal pole, the guide ring ( 131 ) with an inner diameter of 1.5 and an outer diameter of 3 (cm) is built or installed, through which the front-end connection cord ( 200 ) may pass but the weight ( 300 ) may not pass. A height of the horizontal pole may be set to 7˜8 m. The reason that the horizontal pole of the practice device is configured and installed so high is that the flight trajectory ( 230 ) of the ball is maximized to certain extent to minimize the horizontal angle of the ball at a/the ball-hitting point, so that the flight trajectory of the ball is analogous to that in an/the actual tennis court, and thus, enable the trainee to realistically (with the sense of a live game) practice hitting balls (strokes). The height (from the ground) may be more than 10 m; however, since wind effects with respect to the connection cord ( 210 ) may respectively be high, higher height may cause hindrance to the practice in many cases, and lower height may reduce an/the actual feel for strokes. 
     Then, the roller ( 140 ), which is built or installed on the vertical support ( 120 ) or the vertical wall surface ( 400 ) of a house, etc. at the height of a person&#39;s chest may be available in all versions, electrical or fully manual types. Also, the roller may be operated using application (digital signals) installed in the trainee&#39;s smartphone. 
     Next, the ball connection cords ( 200 ,  210 ) are installed on the practice device. 
     The front-end connection cord ( 200 ), which is formed or attached to the roller ( 140 ), passes through the inside, inner space of the vertical support ( 120 ) and the horizontal pole ( 130 ), or traverse and climb up the wall ( 400 ) of a house to reach the bracket guide ring ( 411 ); then after passing through the guide ring ( 131 ) at the end of the horizontal pole, the front-end connection cord ( 200 ) is formed or attached to the weight ( 300 ). 
     The front-end connection cord ( 200 ) may be configured as/comprises a stainless steel wire with an outer diameter of 2.5 mm and a length of 20 m, which is as strong as possible and to certain extent, flexible as it does not directly affect the flight of the ball; and the weight ( 300 ) may be built or installed as one 150 g iron-bead coated with a silicon coating for impact prevention and surface fluorescence, with such functions, purposes as: providing a load to the front-end connection cord so that the front-end connection cord ( 200 ) may fall/drop naturally toward the ground by the (load of the) weight while the roller ( 140 ) is in a release state, and operating as a stopper so that the weight does not pass through the guide ring ( 131 ) at the end of the horizontal pole while the roller ( 140 ) is a wound state. 
     Next, the rear-end connection cord ( 210 ) is formed or attached below the weight ( 300 ). The ball ( 220 ) is formed or attached to the end of the rear-end connection cord. The weight ( 300 ) becomes a dividing point and a connection point between the front-end connection cord ( 200 ) and the rear-end connection cord ( 210 ), and when the weight comes into close contact with the guide ring ( 131 ) at the end of the horizontal pole by winding the roller, the front-end connection cord ( 200 ) is kept taut (in a “tight” state) by the weight ( 300 ) and a/the load of the ball ( 220 ), and the rear-end connection cord ( 210 ), kept taut by the load of the ball ( 220 ). 
     Material and specification of the connection cords ( 200  and  210 ) are further described. The front-end connection cord ( 200 ) and the rear-end connection cord ( 210 ) have different materials and specifications. The material and specifications of the connection cords are as sensitive and important matter as the safety of the entire tennis practice device, and they are related to the purpose of weight installation. 
     For instance, if the material of the rear-end connection cord ( 210 ) is stiff and inflexible even by little, or if not, if the cord is somewhat thick, somewhat heavy, or elastic like a rubber band, when hitting the ball with a/the racket, the ball ( 220 ) will not fly in a normal circumferential trajectory. In other words, the ball does not traverse far, or the ball is twisted or distorted in the air, or fluctuates up and down. That is, the practice device will become useless. 
     Accordingly, the rear-end connection cord ( 210 ) should be thin and light-weight above all else, and should not be easily broken without stretching even under strong tension. That is, in the ball ( 220 ) having a flexible and stable flight, only when the ball ( 220 ) has the material and specification for performance to prevent the ball from dropping or falling away with minimum resistance, the ball hit will excitingly fly (travel) in a desired direction in air space forward (of the trainee) and then flexibly follow or come back (in) the trajectory according to hitting style or ball characteristics—thus, making repeated hitting practice possible. 
     One of the materials suitable for the above conditions is cotton braided lines or cords (cotton thread, about 2.5 mmT). Cotton braids are light, flexible, and resistant to UV rays, and are relatively satisfactory, although they have a disadvantage of receiving some air resistance. However, chemical braids such as PE and Silicon braids, and cotton yarns/threads and tough/durable plied yarns/threads of chemical yarns/threads, may be inappropriate, because they lack flexibility or are elastic like rubber bands. The problems mentioned above or the problems caused by solar rays would occur. 
     However, the problem is that it is difficult to obtain the rear-end connection cord ( 210 ) made of a material that is thin, light, flexible, and does not break even when exposed to ultraviolet rays for a very long time and does not interfere with the ball-hitting practice. That is, the above connection cord made of cotton braids is a consumable type that may be used normally for only a certain period of time, and sometimes conditions of the rear-end connection cord ( 210 ) may need to be checked and replaced with a new connection cord. During the ball-hitting practice, there may also be cases where the rear-end connection cord ( 210 ) is suddenly/unintentionally cut just below the weight, where it is out of reach. 
     As such, when the front-end connection cord ( 200 ), which is out of reach due to the cutting of the rear-end connecting cord ( 210 ) during the ball-hitting practice, must be lowered, it is difficult to lower the front-end connection cord ( 200 ) below the guide ring ( 131 ) to the chest level (height) of the trainee only by operating the roller ( 140 ), if the front-end connection cord ( 200 ), which is located directly below the guide ring ( 131 ) at the end of the horizontal pole, is not provided with the weight ( 300 ). 
     Meanwhile, where the practice device of the inverse “L” shaped metal structure according to embodiments of the present invention is used as/in of a multi-use/public facility (e.g., as a sports park installation/equipment) that anyone can use free of charge, the rear-end connection cord ( 210 ) and the ball ( 220 ) hanging thereon should preferably be brought/supplied by the trainee using the practice device. This is because, in the present embodiment, the  101  weight ( 300 ) is needed below the front-end connection cord ( 200 ) to connect the ball ( 220 ) with the rear-end connection cord ( 210 ) brought by the trainee. 
     That is, when the practice device is not in use, the front-end connecting cord ( 200 ) or the weight ( 300 ) should be kept in close contact with the guide ring ( 131 ) so that neither sways or swings in the air, and when the trainee begins the ball-hitting practice, the roller ( 140 ) may be operated to lower the weight ( 300 ) to the level of the trainee&#39;s chest, so that the trainee may practice hitting balls by hanging the connection cord ( 210 ) and the ball ( 220 ) brought by the trainee on the weight ( 300 ). 
     Here, if the weight ( 300 ) is not built or attached to the end of the front-end connection cord ( 200 ), when the front-end connection cord ( 200 ) is lowered or raised, not only could it be difficult to identify and distinguish where the end (of the front-end connection cord) is being lowered, it could also be difficult to catch it because it may be blown away by the wind; these may be in addition to the problem of tangling within the pipe(s) of the practice device or the roller ( 140 ). At least for these reasons, it may be necessary to install the weight ( 300 ). 
     And after completing the practice, the trainee may need to separate and recover the rear-end connection cord ( 210 ) and the ball ( 220 ) from the weight ( 300 ), and then, manually or semi-automatically return the weight ( 300 ) to its original position below/under the guide ring ( 131 ); or after 1 to 2 minutes after a/the point of lowering of the weight ( 300 ), the weight ( 300 ) may need to be automated so that it automatically rises and returns (in its position). 
     Also the weight ( 300 ) may be configured as a plurality of light weights, or of another material, different types or forms. For example, the weight may comprise an iron-chain of a certain length, and not a/the one iron-bead. This is for safety, to prevent an accident by the weight ( 300 ). 
     Additionally, the biggest reason for the practice with the weight ( 300 ) stopped in close contact, just below the horizontal pole guide ring ( 131 ) is to not to affect a/the radius of rotation of the ball, as (was discussed) in the reason for high installing of the horizontal pole ( 130 ) of the practice device. 
     However, on another aspect, it may be proposed that the front-end connection cord ( 200 ) be comprised (entirely) of chain(s). In such case, it may not be difficult to prevent the chain from getting tangled when the roller ( 140 ) is placed at or near the guide ring ( 131 ) at the end of the horizontal pole ( 130 ) and the chain is wound or unwound with the roller ( 140 ). Also, since the end (of the horizontal pole) is not lightly blown away by the wind, the trainee will not have any difficulty identifying it. 
     That is, the connection cord comprising the chain simultaneously performs the original roles, functions of the front-end connection cord ( 200 ) and of the weight ( 300 ), and here, the weight ( 300 ) will be an end-most portion of the chain. 
     In the case of the front-end connection cord ( 200 ) of such chain, the trainee may practice normal strokes after the trainee lowers the chain connection cord ( 200 ) to the height of her/his chest and adjoining/hanging the rear-end connection cord ( 210 ) with the ball hanging thereon to a hook/ring at an end-most portion of the chain. When the practice is over, the chain connection cord ( 200 ) may be automatically raised to the roller ( 140 ), manually or semi-automatically, or 1 to 2 minutes after the chain is lowered. Drawing(s) of the front-end connection cord ( 200 ) made of the chain is omitted. 
       FIG.  3    is an overall concept diagram of a ball connection cord configuration of the tennis practice device (e.g., for a sports park), according another embodiment of the present invention. 
     Referencing  FIG.  3   , the tennis practice device may (further) comprise the front-end connection cord ( 200 ) (or alternatively termed, an upper front-end connection cord ( 200 ) in the present embodiment of  FIG.  3   ), a lower front-end connection cord ( 201 ), an auxiliary cord ( 202 ), and additionally, comprise the roller ( 140 ) for operating the upper front-end connection cord, a roller ( 142 ) for operating the auxiliary cord, and a roller ( 141 ) for operating the lower front-end connection. Here, each of the rollers may be a manual or motorized, machine-based operator/controller type, and may be installed at the height of a person (i.e., user, trainee) for greater ease-of-use, safety and reliability, particularly when installing, replacing, or adjusting/controlling heights, etc., of the front- and/or rear-end and other connection cords described herein. 
     In the present embodiment, first, the upper front-end connection cord ( 200 ) is installed. The roller ( 140 ) for operating the upper front-end connection cord is built or installed on the vertical pole or support ( 120 ) at the height of a person&#39;s chest, and the upper front-end connection cord is attached to the roller ( 140 ), passes through along the inside (e.g., the inner tube/space of the pipe-type pole/support) of the vertical pole ( 120 ) and the horizontal pole ( 130 ) from the roller ( 140 ), and exits the guide ring ( 131 ) at the end of the horizontal pole. Then, the upper front-end connection cord ( 200 ) is installed/attached to an upper side of a stopper ( 301 ), which may serve as an alternate to the weight ( 300 ). The upper front-end connection cord ( 200 ) may be a stainless steel wire of 2.5 mm in outer diameter and 20 m in length, and the stopper ( 301 ) may be configured as round ring-type stainless steel material of 6 cm in outer diameter and 3.5 cm in inner diameter, 
     Next, the lower front-end connection cord ( 201 ) is installed. The roller ( 141 ) for operating the lower front-end connection cord is built or installed on the vertical pole or support ( 120 ) at the height of a person&#39;s chest, and the lower front-end connection cord ( 201 ) is attached to the roller ( 141 ) and installed (extending) from the roller ( 141 ) to lower left side of the stopper ( 301 ) below the horizontal pole ( 130 ). The lower front-end connection cord ( 201 ) may be configured as stainless steel wire of 2.0 mm in outer diameter and 15 m in length. 
     Next, the auxiliary cord ( 202 ) is installed. The roller ( 142 ) for operating the auxiliary connection cord is built or installed on the vertical pole or support ( 120 ) at the height of a person&#39;s chest, and the auxiliary cord is attached to the roller ( 142 ) and (as shown in  FIG.  3   ) (extending) from the roller ( 142 ), passes through a guide ring ( 111 ) attached to an outer circumference of a curved point of the vertical pole and the horizontal pole, and then is formed or attached to a certain, set point ( 205 ) of the lower front-end connection cord ( 201 ). The set point ( 205 ) is a point where the lower front-end connection cord ( 201 ) starts from the stopper ( 301 ) and reaches the guide ring ( 111 ) attached to the curved point of the vertical and horizontal poles. The auxiliary cord may be configured as a stainless steel wire of 1.0 mm in outer diameter and 15 m in length. 
     Next, the rear-end connection cord ( 210 ) is installed, which is formed or attached to the lower right side of the stopper ( 301 ) in close contact with the end of the horizontal pole, so that the tennis ball ( 220 ) hangs there below. The rear-end connection cord may be a cotton braid with an outer diameter of 2.5 mm, and a length appropriate to make the ball reach the height of a person&#39;s knee; the length may be slightly shorter or longer depending on the type of hitting (stroke) technique used to practice tennis. 
     Hence forth, operational aspects of the above embodiment are described. First, in order to attach and bind the rear-end connection cord ( 210 ), which may be brought by the trainee, to the stopper ( 301 ), or to bind a new/replacement rear-end connection cord to the stopper ( 301 ), the stopper ( 301 ) may be lowered by winding the lower front-end connection cord roller ( 141 ) while the upper front-end connection cord ( 200 ) and the auxiliary cord roller ( 142 ) are in a state of being loosened or released. 
     Next, after binding the rear-end connecting cord ( 210 ) to the stopper ( 301 ), in order to raise the stopper ( 301 ), whereon the lower front-end connection cord ( 201 ) and the rear-end connection cord ( 210 ) are formed or attached, to the guide ring ( 131 ) at the end of the horizontal pole, the stopper ( 301 ) may be raised by winding the upper front-end cord roller ( 140 ) after loosening or releasing the lower front-end connection cord roller ( 141 ) and the auxiliary cord roller ( 142 ). Here, the rear-end connection cord ( 210 ) may hang or suspend from the guide ring ( 131 ) at the end of the horizontal pole due to a/the load of the ball, and the lower front-end connection cord ( 201 ) may lay or be disposed to form a diagonal line extending from and joining the guide ring ( 131 ) and the lower front-end connection cord roller ( 141 ). 
     In the above described configuration of the ball connection cords, there may be a difficulty in practicing tennis strokes with a racket, for instance, because in the course of (the) reciprocating/swinging motions of the ball ( 220 ) (due to the strokes) with respect to the stopper ( 301 ) as the center point, such factors as wind or trainee mistakes may cause the ball to be caught on the lower front-end connection cord ( 201 ). That is, the rear-end connection cord ( 210 ) (which the ball hangs from) and the lower front-end connection cord ( 201 ) may get tangled together. 
     To address this difficulty and resolve other problems, the auxiliary cord ( 202 ) may play a role. That is, in one embodiment, after loosening or releasing the roller ( 141 ) for operating the lower front-end connection cord ( 201 ), the roller ( 140 ) for operating the upper front-end connection cord is wound so that the stopper ( 301 ) is in close contact with the guide ring ( 131 ) at the end of the horizontal pole. Meanwhile, the roller ( 142 ) for operating the auxiliary cord is wound, and the upper part of the lower front-end connection cord is pulled somewhat tightly to the curved point of the vertical and horizontal poles (near the guide ring ( 111 )) of the practice device, and then by forming the lower front-end connection cord ( 201 ) in the inverse “L” shape as a whole, it may be possible to solve problems such as tangling of the connection cords as described above. 
     The stopper ( 301 ) may or may not be analogous to the weight ( 300 ) describe above, in form and functions. For example, unlike the weight ( 300 ), the stopper ( 301 ) may have lighter or negligible load (e.g., mass in kg/lb) so that in an unfortunate accident of the stopper ( 301 ) dropping toward the ground (especially while the tennis practice device is in use), damage or injury may be preventable or reduced. Moreover, while the weight ( 300 ) may be configured with vertically disposed connectors for receiving and/or attaching the front-end connection cord ( 200 ) on a vertically upper portion of the weight ( 300 ) and for rear-end connection cord ( 210 ) on a vertically lower portion of the weight ( 300 ). The stopper ( 301 ) may be further distinguishable in that, for example, the stopper ( 301 ) may be configured with horizontally disposed connectors for the lower front-end connection cord ( 201 ) on a horizontally left side of the stopper ( 301 ) and for the rear-end connection cord ( 210 ) on a horizontally right side of the stopper ( 301 ). 
     Next, the ball ( 220 ) is described in detail. Ordinarily, a tennis ball used for competition has a felt on the outer circumference, a core made of natural rubber on the inside of the felt, and compressed air inside the core. Compressed air is included to improve elasticity on the ground, but since the ball according to embodiments of the present invention is not a ball bound to the ground, compressed air is not required. The elasticity of the rubber and the elasticity of the racket are sufficient for realistic stroke practice. 
       FIG.  4    is a cross-sectional diagram of the tennis ball ( 220 ) according to an embodiment of the present invention. 
     Referencing  FIG.  4   , shown are: an outer peripheral surface ( 221 ) of the ball (made) of fibrous felt; a core ( 222 ) made of natural rubber on an inside of the felt; the ball&#39;s inner space ( 223 ) interior of the core, when the ball is in a state in which compressed air has escaped; and a small hole ( 226 ) passing through or penetrating the inside (inner space,  223 ) from one point on the outer peripheral surface of the ball; a hook cord or loop string ( 225 ); and a locking/snag bar or rod ( 224 ). 
     For the ball ( 220 ) according to an embodiment of the present invention, the locking bar ( 224 ), having a length of about 3 to 4 cm and of which a mid-point is tied or bound on to one end-portion of the hook cord ( 225 ), is inserted into the ball&#39;s inner space ( 223 ) through the small hole ( 226 ), having a diameter of less than 2 mm and made from the ball&#39;s outer peripheral surface ( 221 ) to inner space ( 223 ). Then, when another end-portion the hook cord ( 225 ), remaining outside the ball&#39;s small hole ( 226 ), is pulled, the locking bar ( 224 ) is caught on an inner circumferential surface of the core ( 222 ) inside the ball, thereby making it impossible for the ball ( 220 ) to be separated from the hook cord ( 225 ). 
     The locking bar ( 224 ) may be any material that is not easily bent or broken, such as wood, metal, or plastic, and thickness may vary depending on the material, but in the case of wood, a cylindrical shape of about 5 mm is acceptable. By connecting one end-portion of the hook cord, which is outside the hole, to an end of the rear-end connection cord ( 210 ), the tennis practice device according to an embodiment of the present invention is completed. 
     Description as to ground, concrete base for the practice device is omitted. 
     Embodiments of the structure for tennis practice or training frame, stand, or device have been described. However, the present invention is not limited to tennis, but may be applied to other sports including table tennis and badminton. Further, the present invention is not limited to the materials or dimensions (length, height, etc.) described above. As an example, the practice device may be installed in plurality or the horizontal support may be formed or installed in plurality to one of the vertical support (the one as a main support) (e.g., resembling the assembly of an umbrella frame or a camera tripod). 
     Exemplary embodiments have been described in detail with references to the accompanying drawings, for illustrative purposes (and) to solve technical problems. Although the description above contains much specificity, these should not be construed as limiting the scope of the exemplary embodiments. The exemplary embodiments may be modified and implemented in various forms and should not be interpreted as thus limited. A person skilled in the art will understand that various modifications and alterations may be made without departing from the spirit and scope of the description and that such modifications and alterations are within the scope of the accompanying claims.