Title:
Racket stringing apparatus
United States Patent 3913912


Abstract:
Apparatus for stringing rackets having a vertical column, a work head assembly rotatably mounted on the column on which the racket is clamped, a tensioning assembly mounted on the column for releasably grasping and tensioning a string threaded through a pair of apertures in the racket frame, and a string clamping assembly carried by the work head assembly below the racket frame to releasably maintain the string under tension when the tensioning assembly is released. The string clamping assembly includes an electromagnet mounted for sliding vertical movement with respect to the base of the string clamping assembly. When downward pressure is exerted on the electromagnet, a breaker point assembly is actuated to energize the electromagnet and thereby lock the base to the work head assembly. A manually actuated switch is provided for deenergizing the electromagnet and a spring thereupon returns the electromagnet to its upper inactive position.



Inventors:
SMITH MELVIN WILLIAM
Application Number:
05/464246
Publication Date:
10/21/1975
Filing Date:
04/25/1974
Assignee:
The Garcia Corporation (Teaneck, NJ)
Primary Class:
Other Classes:
73/862.43, 81/126, 269/95, 335/290
International Classes:
A63B51/14; (IPC1-7): A63B51/14
Field of Search:
273/73A 73
View Patent Images:
US Patent References:
2993395Magnetically lockable universal vise1961-07-25Bohn
2309849Racket stringing device1943-02-02Kausal et al.
2100948Apparatus for stringing rackets1937-11-30Doll



Primary Examiner:
Oechsle, Anton O.
Attorney, Agent or Firm:
Fitzpatrick, Cella, Harper & Scinto
Claims:
What is claimed and desired to be secured by letters patent is

1. In a racket stringing apparatus for stringing rackets having a frame provided with pairs of apertures for the passage of a string which forms strands between the apertures, said apparatus having a substantially vertically disposed column, a work head assembly rotatably mounted on said column about a substantially vertical axis and on which the frame of the racket to be strung is clamped, the combination comprising a string clamping assembly positionable on said work head assembly below said racket frame to releasably act on said string threaded through said pair of apertures adjacent said frame to releasably maintain said string under tension, said string clamping assembly comprising a base, electromagnetic means for releasably locking said base to said work head assembly in a selected position on said work head assembly,

2. A string clamping assembly according to claim 1 wherein said means for actuating said magnet comprise a magnet breaker point assembly closable when said downward pressure is exerted, and wherein said means for releasing the magnetic force and returning the magnet to its upper inactive position includes means for reversing the polarity of said magnet and spring means for holding open the breaker point assembly and urging the magnet to its upper inactive position.

3. Racket stringing apparatus for stringing rackets having a frame provided with pairs of apertures for the passage of a string which forms strands between the apertures, said apparatus in combination comprising a substantially vertically disposed column, a work head assembly rotatably mounted on said column about a substantially vertical axis and on which the frame of the racket to be strung is clamped, a tensioning assembly mounted on said column for releasably grasping and tensioning a string threaded through a pair of said apertures in the racket frame, said tensioning assembly acting on the portion of said string exterior to said racket frame, said tensioning assembly comprising a reciprocating bar, an air cylinder and piston assembly, a connecting member interconnecting said air cylinder and piston assembly with said reciprocating bar, means for actuating said air cylinder and piston assembly, means mounted on one end of said reciprocating bar for releasably grasping and tensioning said string; a string clamping assembly carried by said work head assembly below said racket frame to releasably act on said string threaded through said pair of apertures adjacent said frame to maintain said string under tension when said tensioning assembly is released, said string clamping assembly comprising a sliding base, means mounted on said base for releasably grasping said string, a magnet body housing surmounted over said base, an electromagnet fixedly mounted within said housing having an inside surface adopted for sliding movement with respect to said base, a spring member interposed between said base and said housing for urging said housing upwardly with respect to the base, means for limiting the upward travel of said housing, an electrical pin jack, a magnet breaker point assembly having one lead connected to said electromagnet and having a second lead connected to said jack, a polarity reversing switch means for receiving power from a DC power source, said jack being connected to said switch means, whereby said string clamping assembly is movable into its desired position on the work head assembly by sliding the base on the upper surface of the work head assembly and when in its desired position downward pressure exerted on said magnetic body housing moves said electromagnet into engagement with said surface of said work head assembly and closes the contacts in the breaker point assembly to activate the magnet so that the magnet holds the string clamping assembly in said position on the work head assembly and whereby actuation of said switching means reverses the polarity from the DC power source to momentarily repel the magnet and open the contacts in the breaker point assembly so that the spring member holds the breaker point assembly open and returns the magnet and the housing to their upper inactive positions.

Description:
This invention relates to machines used for the stringing of rackets, such as tennis rackets or the like, for example. Machines of this type usually include a counterweight mechanism adapted to tension a string which has just been passed through a pair of corresponding apertures in the racket frame in order to form one of the strand elements. Generally, the longitudinal strands are strung first followed by the transverse strands. A clamping device is provided which clamps the string after the tensioning thereof, within the racket frame close to the outlet aperture. Once the strand under tension of the tensioning device is clamped, the tensioning device is released and the free end portion of the string is passed through the next pair of apertures in the frame. The racket is turned 180° so that the outlet aperture is adjacent the counterweight mechanism and the new strand is tensioned thereby. This process is continually repeated for each strand until the stringing operation is completed.

Related patents in this art include: U.S. Pat. No. 2,309,849 issued Feb. 2, 1943; U.S. Pat. No. 3,511,502 issued May 12, 1970; U.S. Pat. No. 3,635,080 issued Jan. 18, 1972; U.S. Pat. No. 2,114,216 issued Apr. 12, 1938; U.S. Pat. No. 2,188,250 issued Jan. 23, 1940; U.S. Pat. No. 2,154,870 issued Apr. 18, 1939; U.S. Pat. No. 2,262,110 issued Nov. 11, 1941; U.S. Pat. No. 1,969,826 issued Aug. 14, 1934; U.S. Pat. No. 3,441,275 issued Apr. 29, 1969; and U.S. Pat. NO. 2,000,948 issued Nov. 30, 1937.

The present invention involves a new combination of elements combined in such a way as to provide a new and improved racket stringing machine which speeds up production, which is less fatiquing to the operator, which provides uniformity of tension, which is a self-contained unit and which requires minimum operator skill.

In one form thereof the present invention contemplates the provision of a new and improved machine for stringing rackets having a frame provided with pairs of apertures for the passage of a string which forms strands between the apertures. The apparatus comprises, in combination, a vertically disposed column, a work head assembly rotatably mounted on the column, a tensioning assembly also mounted on the column for releasably grasping and tensioning a string threaded through a pair of the apertures in the racket frame, acting exteriorly of the frame, and a string clamping assembly carried by the work head assembly below the racket frame to releasably maintain the string under tension when the tensioning assembly is released.

According to one aspect of my invention the tensioning assembly is characterized by a reciprocating bar, an air cylinder and piston assembly, a connecting member interconnecting the air cylinder and piston assembly with the reciprocating bar, compressor means for actuating the air cylinder and piston assembly, an upright post fixedly mounted on one end of said reciprocating bar having an inclined upper end portion, a rod pivotally mounted on the post and having an upper rounded serrated portion, and means for resiliently urging the serrated portion and the inclined upper end portion to releasably grasp the string therebetween.

According to another aspect of my invention, the string clamping assembly is characterized by a base and electromagnetic means for releasably locking the base to the work head assembly in a selected position on the work head assembly.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be disclosed more fully hereinafter. Those skilled in the art will appreciate that the conception on which this disclosure is based may readily be utilized as the basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that this disclosure be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

One embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a perspective view of a racket stringing machine constructed in accordance with the concepts of my invention;

FIG. 2 is a longitudinal sectional view of the racket stringing machine of FIG. 1 showing the initial step of passing a string through a pair of corresponding apertures in a racket frame;

FIG. 3 is a view similar to FIG. 2, but showing the tensioning of the string so passed;

FIG. 4 is a view similar to FIG. 3, but showing the step of clamping the so tensioned string and thence releasing the tensioning device;

FIG. 5 is a view similar to FIG. 4, but showing the racket frame after it has been rotated 180° with respect to the string tensioning means;

FIG. 6 is a view similar to FIG. 5, but showing the next strand being tensioned;

FIG. 7 is a plan view drawn on a reduced scale showing the step illustrated in FIG. 2;

FIG. 8 is a plan view drawn on a reduced scale showing the step illustrated in FIG. 3;

FIG. 9 is a plan view drawn on a reduced scale showing the step illustrated in FIG. 4;

FIG. 10 is a plan view drawn on a reduced scale showing another aspect of the step illustrated in FIG. 4;

FIG. 11 is a plan view drawn on a reduced scale showing the step illustrated in FIG. 5;

FIG. 12 is a plan view drawn on a reduced scale showing the step illustrated in FIG. 6;

FIG. 13 is an enlarged, longitudinal, medial, sectional view of a base assembly of a clamping device constructed in accordance with the concept of this invention;

FIG. 14 is a view similar to the view of FIG. 13, but showing the base assembly in its clamping position and also showing the portion of the device which clamps the strings;

FIG. 15 is a fragmentary view of the portion of the device which clamps the strings in its clamping position; and

FIG. 16 is a sectional view taken along the line indicated at 16--16 of FIG. 15.

Referring to the drawings in detail, and initially to FIG. 1, there is shown a racket stringing machine comprising a base 10 with a column 12 mounted thereon. A tray assembly 14 extends partially around the column and a rotatable work head assembly 16 is mounted on a spindle 18 at the top thereof. Clamp supports 20 are fixedly mounted on the work head assembly and carry clamp members 22 which, by means of bolt and wing nut assemblies 23, cooperate to releasably hold a racket frame 24 during the stringing operation. Mounted inside the column 12 is a compressor assembly, indicated generally at 26, for actuating a tensioning assembly, indicated generally at 28, as will be described more fully hereinafter.

After the racket frame 24 has been secured by the clamps 22, the stringing operation commences. As best seen in FIGS. 2 and 7, a string 30 is knotted, as at 32, and threaded through oppositely disposed apertures 34 and 36 in the racket frame. The work head assembly 16, carrying the clamp members 22 and racket frame 24, is rotated on the spindle 18 until the string 30 in the frame is substantially parallel to the axis of translation of reciprocating bar 38. The reciprocating bar 38 is mounted on rollers 40 inside the column 12 with the ends thereof passing outwardly through openings 42 and 44. An air cylinder 46 is fixedly mounted within the column 12, as at 48, and carries a piston rod 50, which is connected to the reciprocating bar 38 by a connecting member 52, provided for the purpose. Controlled air pressure is supplied to the cylinder 46 from the compressor assembly 26 through a conventional value and piping arrangement, not shown.

Still referring to FIG. 2, the tensioning assembly 28 further includes an upright post 54 fixedly mounted on the end of the reciprocating rod 38, as at 56, and a pivotable rod 58 pivotally mounted on the post by means of a spring loaded pin 60 so that the rod 58 resiliently engages the post 54 in a clamp-like manner. As best seen in FIG. 1, the pivotable rod 58 is provided with a serrated surface 59, and the post 54 has an angularly inclined end portion 55 in order to effect a good gripping action of the string therebetween.

In operation, after the string 30 is threaded through the apertures 34 and 36, it is looped around the pivotable rod 58 and clamped between the rod 58 and the post 54, as shown in FIG. 2. Air is then supplied to the air cylinder 46 in order to move the reciprocating rod 38 from its position as shown in FIGS. 2 and 7 to its position as shown in FIGS. 3 and 8. The air pressure is selected, as indicated by gauge 62, FIG. 1, so that the proper tension is maintained on the string 30. The next step in the stringing operation is to move string clamping assembly, indicated generally at 64, to a position adjacent the aperture 36 in the racket frame 14, and the clamp (described more fully hereinafter) is moved to its clamping position to grip the string, as shown in FIG. 9. Then, the rod 38 is returned to its initial position, and the string is released from the tensioning assembly 28, as shown in FIGS. 4 and 10. The work head assembly 16 and the racket frame 24 are then rotated 180° from their positions as shown in FIGS. 4 and 10 to their positions as shown in FIGS. 5 and 11, and the string 30 is passed through the next pair of oppositely disposed apertures 66 and 68, as shown in FIGS. 6 and 12. The string is again passed around the pivotable rod 58 and clamped between the rod 58 and the post 54, and the reciprocating rod 38 is moved outwardly to again tension the string, as seen in FIGS. 6 and 12. Thence, the string clamping assembly 64 is released as shown in FIG. 12. The foregoing steps are then repeated until the stringing operation is completed. For stringing the transverse strands in the racket, the same steps are employed except that initially the work head assembly 16 is only rotated 90°. It will be appreciated that by controlling the air flow and pressure to the air cylinder 46 the speed of the tensioning and the stringing pressure may be selected as desired for each racket, and constant string tension is maintained for all strands in the racket.

As best seen in FIGS. 13 to 16, the string clamping assembly 64 includes a sliding base 70 which, preferably, is fabricated from a material such as nylon, for example. Fixedly mounted on the base is an upwardly projecting vertical slide tube 72. Mounted over the base 70 is a cup-shaped magnet body housing 74 fabricated from aluminum or the like material. An electromagnet 76 is fixedly mounted within the magnet body housing 74, and the inside diameter thereof is adapted for sliding movement as at 78 with respect to the base 70. Thus, the magnet 76 and the housing 74 are arranged for limited vertical movement with respect to the base 70. A spring member 80 is interposed between the base 70 and the housing 74, which urges the housing 74 upwardly with respect to the base 70, and a O-ring 82, mounted on the vertical slide tube 72, serves to limit the upward travel of the housing 74 and the electromagnet 76 and thereby locks the assembly together. As best seen in FIG. 13, a magnet breaker point assembly 84 has one lead 86 connected to the electromagnet 76 and a second lead 88 connected to an electrical pin jack 90, which receives power from a suitable power source, not shown, such as a 12 volt DC power source, for example, through a switch 92 that reverses the polarity of the power source when actuated. A set screw 85 serves to adjust the setting of contacts 87 and 89 of the breaker point assembly 84.

In operation, the string clamping assembly 64 is moved into its desired position on the work head assembly 16, FIG. 1, by sliding the base 70 on the upper surface of the work head assembly. When the assembly is in its desired location, downward pressure is exerted on the magnetic body housing 74 to move the housing 74 and the electromagnet 76 from their upper positions as seen in FIG. 13 to their lower positions as seen in FIG. 14. This motion closes the contacts in the breaker point assembly 84 and activates the electromagnet 76 so that the magnet firmly locks the string clamping assembly in position on the work head assembly 16. When it is desired to release the clamping assembly 64, the switch 92, which may be located in any convenient accessible location such as on the column 12, for example, is actuated to reverse the polarity from the DC power source, thereby momentarily repelling the magnet 76 and opening the contacts in the breaker point assembly 84. The spring 80 will now hold the breaker point assembly 84 open and return the body 74 and the magnet 76 to their upper inactive positions, as seen in FIG. 13. The clamping assembly is then ready to slide freely on the work head assembly 16 to its next position.

The string clamping assembly 64 further comprises a clamp body 94, which is mounted in the vertical slide tube 72, FIG. 14. As seen in FIGS. 14 and 16, the upper end of the body 94 is in the form of an upwardly opening fork. A flat member 96 is secured to the inner side of one of the branches of this fork, and a plurality of hooked or bent fingers 98 extend from the upper edge thereof to form the fixed jaw of a clamping device. A mating movable jaw of vertical teeth 100 is adapted to engage the fingers 98, respectively. The teeth 100 are formed along the upper edge of a plate 102 adapted to slide against the flat member 96. The plate 102 has a lower, integral rod-like guiding tail 104, which is axially slidable in the body 94, and a transverse pin 106 is also carried by this plate. An actuating lever 108 is hinged on the pin 106 and has one end pivotally attached to one end of a link 110, as at 112. The other end of the link 110 is hinged on a pin 114, which is eccentrically carried by a gudgeon 116 that is lockable in a selected angular position in the body 94, such as by a set-screw not shown.

In operation, when it is desired to clamp the string 20 in the string clamping assembly 65, the string is placed between the fingers 98 and the teeth 100 and the actuating lever is swung downwardly from its position as seen in FIG. 14 to its position as seen in FIG. 15. Thus, the lever 108 is swung about the pin 106 and the plate 102 is displaced vertically on the member 96, the latter being formed with a vertical guiding groove for this purpose in which the pin 106 slides, to thereby bring the teeth 100 up into the bent portion of the fingers 98 to clamp the string. When the axis of the pins 106, 112, and 114 are substantially in alignment, as seen in FIG. 15, the fingers 98 and the teeth 100 remain in their clamped positions, the force of the clamping action being adjustable by the angular position of the gudgeon 116. In order to release the string, the actuating lever 108 is returned from its position as seen in FIG. 15 to its position as seen in FIG. 14, to move the teeth 100 away from the fingers 98 and thereby release the string.

It will thus be seen that the present invention does indeed provide an improved racket stringing apparatus which is superior in operability, reliability and efficiency as compared to prior art such devices.

Although a particular embodiment of the invention is herein disclosed for purposes of explanation, various modifications thereof, after study of this specification will be apparent to those skilled in the art to which the invention pertains.