Abstract:
A stringed racquet includes a built-in, user-adjustable mechanism for changing the tension of the strings. The user-adjustable mechanism is disposed in a cavity within the handle of the racquet, and includes a mandrel over which at least some of the vertical strands of string are looped. A wishbone bracket secured to the mandrel is axially adjustable within the handle to raise or lower the tension in the vertical strands looped over the mandrel, after which the tension becomes evenly distributed over the entire string.

Description:
TECHNICAL FIELD 
   The present invention relates to stringed racquets for use in sports such as tennis, racquetball, and the like, and more particularly to a racquet that having a built-in, user-adjustable mechanism for changing the tension of the strings. 
   BACKGROUND OF THE INVENTION 
   With currently available racquets, the string tension is set at the factory, and is not adjustable by the user. If the user desires to change the string tension, the original string must be removed and replaced with a new string, using special fixtures and tensioning weights. Since installing a new string can be a difficult and time consuming process, most users would benefit from a racquet having easily adjustable string tension. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved stringed racquet including a built-in, user-adjustable mechanism for changing the tension of the strings. The user-adjustable mechanism is disposed in a cavity within the handle of the racquet, and includes a mandrel over which at least some of the vertical strands of string are looped. A wishbone bracket secured to the mandrel is axially adjustable within the handle to raise or lower the tension in the vertical strands looped over the mandrel, after which the tension becomes evenly distributed over the entire string. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to  FIG. 1 , which depicts a racquetball racquet equipped with a user-adjustable mechanism according to this invention for changing the racquet string tension; 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , the present invention is described herein primarily in the context of a racquetball racquet  10 . However, it will be understood that the invention is also applicable to other types of stringed racquets such as tennis racquets, squash racquets, and so forth. The frame  12  of racquet  10  is manufactured as a single piece, and includes a basket portion  14  and a handle  16 . A rubber or plastic grip  18  is fitted to the exterior periphery of handle  16 , and a lanyard  19  is tied to an end-cap  20  of handle  16 . The basket portion  14  of frame  12  has a number of drilled openings about its periphery, and the string is laced through the openings in a standard way to define a number of vertical strands  24  that extend more or less parallel to a longitudinal axis of handle  12 , and a number of horizontal strands  26  that extend perpendicular to the handle axis. 
   Racquets of the above-described type are available from several sources, including EF Composite Technologies, L.P., San Diego, Calif.; see for example, the U.S. Pat. No. 5,919,104 to Mortvedt et al., issued on Jul. 6, 1999. As illustrated in the aforementioned patent, at least some of the vertical strands  24  can be looped around a mandrel secured to the frame  12  within the handle  16  instead of being laced through openings in the basket portion  14  in order to increase the effective length of such strands. In the racquet  10  of the present invention, at least some of the vertical strands (i.e., those designated by the reference numeral  24 ′ in  FIG. 1 ) are also looped around a string support element such as mandrel  28 , only in this case, the mandrel  28  is adjustably supported within the handle  16  instead of being rigidly fastened to the handle  16 . Referring to  FIG. 1 , the mandrel  28  rides on an axle  30 , and the ends of axle  30  are secured in the opposing arms  32   a ,  32   b  of a wishbone bracket  32 . The wishbone bracket  32 , which may be formed of aluminum for example, extends into the handle  16  and includes a threaded opening for receiving a threaded adjustment element such as a bolt  34 . The bolt  34  passes through an opening  36   a  in an anchor block  36 , and the anchor block  36  is fastened to the handle  16  of frame  12  by the pins  38   a ,  38   b . The head  34   a  of bolt  34  seats against the outboard face  36   b  of anchor block  36  and is accessible by a user-manipulated nut driver tool for the purpose of rotating the bolt  34 . When the bolt  34  has the customary right-hand thread configuration, rotating the bolt head  34   a  clockwise acts to draw the wishbone bracket  32  axially deeper into the handle  16  to increase the string tension of racquet  10 ; rotating the bolt head  34   a  counter-clockwise of course produces the opposite effect. 
   Due to friction, rotating the bolt head  34   a  has a tendency to produce similar rotation of the wishbone bracket  32  and mandrel  28 . In the illustration of  FIG. 1 , for example, the wishbone bracket  32  and mandrel  28  are rotated approximately 90° in the clockwise direction (relative to the minimum tension orientation) due to clockwise rotation of the bolt head  34   a . However, the string tension produces a restoring torque that tends to rotate the bracket  32  and mandrel  28  back to the minimum tension orientation as soon as the racquet is put into use. 
   Although the vertical strands  24 ′ are looped over the mandrel  28 , their effective length remains similar to that of a racquet constructed according to the aforementioned U.S. Pat. No. 5,919,104 since the wishbone bracket  32  is allowed to pivot about the head  34   a  of bolt  34 . This pivoting actually improves the feel of the racquet  10  by absorbing shock and amplifying the rebound speed of a ball from the string face of the racquet. 
   When installing a new string on the racquet  10 , the bolt  34  is rotated counter-clockwise so that the mandrel  28  extends into the basket portion  14  of frame  12 , and the central vertical strands  24 ′ are looped over the mandrel as shown instead of being routed through the drilled frame openings. The string can be loosely tensioned during this process, and then properly tensioned by clockwise rotation of the bolt  34  once the string is fully routed and tied off. Although the tension produced by the clockwise rotation of the bolt  34  is initially concentrated in the central strands  24 ′, using the racquet or jarring the racquet frame  12  causes the strands to shift in a way that evenly distributes the tension. 
   In summary, the racquet of the present invention affords a user the ability to easily and quickly adjust the string tension to suit his or her preference. And should a string break during usage of the racquet, the racquet may be restrung and re-tensioned without requiring any special equipment, weights or fixtures. Alternately, the racquet may be temporarily patched by loosening the adjustment mechanism, knotting the broken string or adding in a short additional strand of string to fortify a weak area, and re-tensioning the strings as described above. 
   While the invention has been described in reference to the illustrated embodiment, it should be understood that various modifications in addition to those mentioned above will occur to persons skilled in the art. For example, the mandrel  28  can be provided with a hook or T-bar over which the strings are looped, more than one mandrel may be mounted on the wishbone bracket  32 , the handle  16  may include a shaped cavity for limiting rotation of the wishbone bracket  32 , more or fewer vertical strands  24 ′ may be looped over the mandrel  28 , and so on. Accordingly, it will be understood that racquets incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.