STRING PRE-STRETCHING APPARATUS AND METHOD FOR RACKET-STRINGING MACHINE

Abstract: A racket-stringing machine having a racket head holding fixture and a carriage (6) and string clamp (7) mounted for reciprocation toward and away from the fixture for engaging a string (8) drawn through a racket head mounted on the fixture for tensioning of the string upon movement of the carriage (6) away from the fixture; a brake (9) for locking the position of the carriage (6) relative to the fixture for maintaining the string (8) at a predetermined tension, the carriage (6) and brake (9) being constructed to permit additional tension to and pre-stretching of the string (8); and means (11) functioning on decrease of string tension to the desired predetermined tension to apply the brake (9).

Description: STRING PRE-STRETCHING APPARATUS AND METHOD FOR RACKET-STRINGING MACHINE TECHNICAL FIELD The invention relates to machines used for stringing of tennis rackets and the like and particularly to those machines which incorporate structure designed to assist in the obtaining of the desired objective of a uni¬ form tensioning of the strings. BACKGROUND ART United States Patent. 3,441,275 discloses a machine in which the string is tensioned by manual rotation of a crank, causing displacement of a carriage and string clamp away from a fixture holding the racket head, and in which the carriage is automatically locked against dis¬ placement relative to the head when the string reaches a predetermined tension. United States Patent 2,154,870 in¬ corporates a friction clutch in the string-tensioning structure so that only a predetermined degree of tension can be imparted to the string. Due, however, to the many fac¬ tors involved, such as varying friction between the engaged strings and racket head, subsequent stress relieving of the strings, and other factors, a variable, uncertain and ran¬ dom loss of string tension will result. Nor is the loss consistent, but will vary from string to string and between the longitudinal main strings and the cross strings. The amount of stress release cannot be precisely determined and will vary with size, quality and length of string used and OMPI °' and the variable, random friction between contacting strings. Moreover, stress release will occur over a perio of time so that the playing characteristics of a racket will change (deteriorate) with use. Accordingly, expert players have come to accept a required break-in period for newly strung racket. However, even accepting a break-in period, the player cannot know in advance what the ultimat tension and playing characteristics of the racket will be. The above-noted inconsistency may vary anywhere from about 4.5 to 8.1 kilograms from string to string, even after the break-in period. DISCLOSURE OF INVENTION I have found that the above-noted disadvantages may be overcome by pre-stretching of the racket string over and above the amount which occurs on drawing the string to its desired predetermined tension and then retur ing the string to its predetermined tension. Pre-stretchi minimizes the characteristics that allow the strings to settle or relieve stresses and " lose tension with use and time. Use of the apparatus of the present invention has virtually eliminated the need for a break-in period for newly strung rackets. The racket is ready for use as it comes off of the stringing machine. Moreover, the rate of string tension loss due to playing stress and time is sub¬ stantially reduced, thereby maintaining good string tensio over a much longer period of time and use. Another object of the present invention is to provide the racket-stringing machine of the character des- cribed which will produce a significantly more uniform ten sion string to string, provide an improved overall evennes of resilience and improved accuracy of ball action and con trol. A further object " of the present invention is to provide a racket-stringing machine of the character above which will afford a heretofore unobtainable repeatability, O Λ. WI enabling a repeated stringing of a racket to a much more precise string tension, assuring the player in advance of what the final string tension will be. Still another object of the present invention is to provide a structure of the character described which may be readily added to existing racket-stringing machines. The invention possesses other objects and features of advantage, some of.which of the foregoing will be set forth in the following description of the preferred form of the invention which is illustrated in the drawings accompanying and forming part of this specification. It is to be understood, however, that variations in the showing made by the said drawings and description may be adopted within the scope of the invention as set forth in the claims. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side elevation, of a racket pre- stretching apparatus for racket-stringing machines con¬ structed in accordance with the present invention. FIGURE 2 is a side elevation similar to FIGURE 1, but showing the parts in a different position, FIGURE 3 is a side elevation similar to FIGURES 1 and 2, but showing the parts in a third position. BEST MODE OF CARRYING OUT THE ' INVENTION The apparatus of the present invention is de¬ signed as an improvement to the racket-stringing machine illustrated and described in United States Patent 3,441,275 and the structure illustrated in the accompanying drawings is directed to that part of the machine which is subject to the present invention. Briefly, the racket-stringing ma¬ chine comprises a racket head holding fixture, see Patent 3,441,275, and a carriage 6 mounted for reciprocation toward and away from the head fixture and a string clamp 7 mounted on the carriage for engaging a string 8 drawn through a racket head mounted on the fixture for tensioning the string O PI ^2&ϊϊτio*$ upon movement of the carriage away from the fixture, e.g., to the right as seen in the drawings; a brake 9 for lockin the position of the carriage relative to the fixture for maintaining the string in a predetermined tension and mean 11 functioning on decrease of string tension to a predeter mined tension to apply the brake. Machines constructed generally in accordance with United States Patent 3,441,27 are sold under the trademark EKTELON, manufactured by EKTELON in San Diego, California, and reference is made to the aforementioned patent and the EKTELON machine for fur¬ ther details of the carriage, string clamp and brake con¬ struction. As here illustrated, the carriage is mounted f reciprocation on an arm 12 extending laterally from the racket head holding fixture and which carries a rack 13 which is engaged by a pinion 14 on the carriage which, on rotation, causes the carriage to move on arm 12. Also mounted on carriage 6 concentrically with pinion 14 is a brake disc 16 to which a handle 17 is attached for manual rotation of the disc and pinion to cause reciprocation of the carriage, rotation of handle 17 in a clockwise direc¬ tion, as viewed in the drawings, causing the carriage to move away from the head fixture, " to the right, as seen in the drawings, to tension string 8; and movement of the han dle in a counterclockwise direction causes the carriage to move toward the fixture, thus reducing the tension of string 8. Of importance, insofar as the present invention is concerned, is the fact that brake 9 is operated by a brake arm 18 which is biased by spring 19 to move from a generally upright brake-releasing position to a clockwise displaced brake-setting position, as seen in phantom line in FIGURE 3. Retention of brake arm 18 in its generally up¬ right brake-releasing position is effected by a detent 21 mounted on clamp 7 and engaging the upper end 22 of arm 18.- Clamp 7 is itself pivotally mounted to carriage 6 by pivot pin 23 and is resiliently supported by spring 24 so that, as the carriage is moved away from the head fixture to - ϊ1-E O P --n WIP tension string 8, clamp 7 will rock in a counterclockwise direction, as indicated by arrow 26, to lift detent 21 from the upper end 22 of arm 18, thus releasing the arm to swing under the urge of spring 19 to brake-setting position. This action occurs in the standard EKTELON machine when the string is drawn to a predetermined tension, and adjustment of this tension may be effected by a manually engageable knob 28 controlling the tension of spring 24, and the set¬ ting is shown on an indicator 29. As will be observed from the drawing, detent 21 is pivoted for rotation in housing 25 about a pivot pin 27; and housing 25 is itself fastened by a bolt 30 to one side of clamp 7, permitting arcuate adjustment of the housing and detent 21. Accordingly, and in accordance with the present invention, bolt 30 is loos- ened to permit a small clockwise displacement of housing 25 and then tightened to fix the position of detent 21 to cause release of arm 18 only after the carriage has been moved to attain not only the amount of desired string tension, as shown by indicator 29, but also a predetermined designated pre-stretching of string 8 beyond such predetermined ten¬ sion. For example, I have found that such super-added pre- stretching of the string represented by an additional ten- sioning in the order of about 6.8 kilograms pull is highly satisfactory. Accordingly, if indicator 29 is adjusted by knob to show a tensioning of say 18.14 kilograms pull, detent 21 will release arm 18 as the pull on string 8 in¬ creases to 24.95 kilograms. The term "tension," as used herein, is defined and expressed as kilograms pull on the string. As the limit of pre-stretching is reached, detent 21 will release arm 18 for movement automatically under the urge of spring 19 toward brake-setting position. However, in accordance with the present invention, means 11, here in the form of a second detent,- is mounted on clamp 7 in position to intercept arm 18 " -when released by detent 21, thus retaining the arm in brake-releasing position; and the structure and mounting of detent 11 is such that it is responsive on decreasing string tension, see FIGURE 3, on OJ^PI Λ, IFO . — o— return movement of the -carriage toward the head fixture to release arm 18 as the desired predetermined final string tension is reached, thus permitting biased movement of ar 18 to brake-setting position, as shown in phantom line in FIGURE 3. As a feature of the present invention, arm 18, when released by detent 21, will impact detent 11 with an audible snap, see phantom line, FIGURE 2, thus advising th operator that the desired pre--stretching of the string has been accomplished and the operator is to initiate the retu movement of the carriage. On return movement of the carriage to- decrease string tension, arm 18 will be releas by detent 11 at the desired predetermined string tension, e.g., 18.14 kilograms, as herein explained. The foregoing operation is accomplished by causin release of arm 18 by detent 21 upon movement of clamp 7 in a counterclockwise direction, see arrow 26 in FIGURE 1, on increasing string tension, and by releasing arm 18 from detent 11 upon subsequent movement of the clamp in a clock wise direction, as indicated by arrow 31 in FIGURE 3. As will be observed from the drawings, a laterally extending bracket or keeper 33 is mounted on arm 18 adjacent its up¬ per end 22 in position for engagement by detent 11 when ar 18 is released by detent 21, see phantom line in FIGURE 2, it being noted that while detent 21 engages over the upper end of arm 18, detent 11 extends below keeper 33 and engag es the leading upright side 34 of the keeper. Accordingly the upper end 22 of arm 18 is released upon counterclock¬ wise direction of clamp 7 while keeper 33 is released by detent 11 upon clockwise direction of the clamp. Conversion of the standard EKTELON machine to a machine of the present invention requires only the additio of two parts, detent 11 which may be mounted on bolt 30 an keeper 33 which is mounted on arm 18. As will be noted, detent 11 is formed at one end of an arm 41 having its opposite end mounted on bolt 30, the length of arm 41 bein such as to position detent 11 beyond detent 21 so as to intercept the arm as it is released by detent 21. The length of the detent face 42 engaged with keeper 33 will determine the point of release of the keeper upon clockwise movement of the detent on releasing string tension. Operation With the racket head mounted in the head holding fixture (not shown) arid string 8 drawn through the string openings in the racket head and engaged in clamp 7, handle 17 is engaged and rotated in a clockwise direction as indi- cated by arrow 36 in FIGURE 1, causing carriage 6 to move to the righ , away from the fixture, on the rack and pinion connection 13 and 14, to tension string 8. Tensioning of string 8 is accompanied by a counterclockwise rocking of clamp 7, as indicated by arrow 26, and as a desired pre- determined tension plus pre-stretch is reached, see phantom position of handle 17, detent 21 will lift off from the upper end of brake arm 18, releasing the latter to swing in a clockwise direction • under the urge of spring 19 until keeper 33 strikes and is held by detent 11, see phantom position of arm 18, in FIGURE.2. This release and action of arm 18 provides a visual and audible indication to the operator that the full pre-stretching step has been com- ' pleted. The interruption of movement of brake arm 18 re- tains the brake in its released position, thus enabling the operator to start a return movement of the carriage. This action is best seen in FIGURE 3 where handle 17 is shown in full lines displaced to its advanced position and its return movement is indicated in phantom line. Upon completion of the pre-stretching step, as depicted in FIGURE 3, handle 17 is swung in a return, counterclockwise direction, see arrows 38 in FIGURE 3, thus - decreasing the tension on string 8 and causing clamp 7 to rock in a clockwise direction, as indicated by arrow 31. As the predetermined final string tension is attained in the tension-decreasing mode, detent 11 will move downwardly, as indicated in phantom line in FIGURE 3, to release keeper 33, thus permitting brake arm 18 to abrupt swing clockwise, as indicated by arrow 39, to brake- setting position. A string clamp is then placed at the racket head to hold the string tension in the head, strin 8 released from clamp 7 and re-threaded through the racke head, the racket head " fixture swung about to permit re- engagement of string 8 'in clamp 7 for tensioning the next string in the racket head, all in accordance with standar racket-stringing practice. O ?I ft. WIIPPOO

Claims: WHAT IS CLAIMED IS: 1. In a racket-stringing machine having a racket head holding fixture and a carriage mounted for reciproca¬ tion toward and away from said fixture and a string clamp carried by said carriage for engaging a string drawn through a racket head mounted on said fixture for tension- ing said string upon movement of said carriage away from said fixture; a brake for locking the position of said carriage relative to said fixture for maintaining said string at a predetermined tension; and means functioning on decrease of string tension to said predetermined tension to apply said brake. 2. The structure of claim 1 and means indicating the attainment of a predetermined amount of pre-stretching of said string beyond said predetermined tension. 3. The structure of claim 2, said brake having a brake arm mounted on said carriage and movable between brake-setting and brake-releasing positions and being biased to brake-setting position; said second-named means comprising a first detent mounted on said carriage and holding said arm in brake-releasing position and being responsive to said predetermined string tension and said predetermined pre-stretching of said string to release said arm ? said first-named means comprising a second detent mounted on said carriage in position to intercept said arm on release thereof by said first-named detent and retain said arm in brake-releasing position; and said second detent being responsive to decreas¬ ing string tension on return movement of said carriage toward said fixture to release said arm at said predetermined tension for biased movement of said arm to brake-setting position. 4. The structure of claim 3, said string clamp being pivotally mounted on said carriage for arcuate dis¬ placement in a first direction on increasing said string tension and in an opposite, second, direction upon decreas¬ ing string tension; said first detent being mounted on said clamp and having a connection to said arm releasing said arm upon displacement of said clamp in said first direction; and said second detent being mounted on said clamp and having a connection to said arm releasing said arm upon displacement of said clamp in said second direction. 5. The method of setting to a predetermined tension a racket string mounted on a racket head across the interior opening thereof comprising, drawing said string 'across said racket head opening to an elevated tension greater than said pre¬ determined tension to effect a pre-stretching of said string to a length beyond its length at said predetermined tension; decreasing the string tension to permit contrac¬ tion of said string to said predetermined tension; and locking said string at said predetermined ten¬ sion. OMP / ____ WIPO

Inventors: BALABAN J
Applicants: BALABAN J
Application year: 1980
Main classification: A63B51
IPC codes: A63B51