Ball Racket

Abstract

A ball racket includes a head frame for racket stringing, a shaft unit including first and second tubes non-rotatably fitted to each other to be moved relative to each other along an axis, an actuator disposed within the first tube and having an actuating end and a shank body, an expandable shell disposed between the actuating end and the first tube, and a force transmitting mechanism disposed between the expandable shell and the first tube. Counterclockwise rotation of the actuating end causes the expandable shell and thus the first tube to expand radially so as to generate increased friction between the first and second tubes to thereby guard against relative axial movement between the first and second tubes. Clockwise rotation of the actuating end permits the first tube to axially move relative to the second tube so as to adjust the length of the shaft unit.

1 . A ball racket comprising:
 a head frame adapted for racket stringing;   a shaft unit including
 a first tube which has a first front end securely connected to said head frame, and a first tubular segment extending from said first front end along an axis to terminate at a first rear end, said first tubular segment having inner and outer surrounding surfaces radially opposite to each other, and 
 a second tube having a second front end and a second tubular segment which extends from said second front end along the axis to terminate at a second rear end, said second tubular segment having an inner tubular surface which is configured to engage said outer surrounding surface with a frictional force and to be movable relative to said outer surrounding surface along the axis, and an outer tubular surface which is radially opposite to said inner tubular surface, and which is configured to be gripped by a player; 
   an actuator unit having an actuating end which is disposed within said first tube and which is radially spaced apart from said inner surrounding surface by a surrounding gap, and a shank body which extends from said actuating end along the axis to terminate at an operated end that extends outwardly of said first rear end such that said operated end is operable manually to rotate said actuating end about the axis;   an expandable shell which is inserted into said surrounding gap, and which has outer and inner shell surfaces that are radially opposite to each other, and that respectively confront said inner surrounding surface and said actuating end; and   a force transmitting mechanism disposed between said inner shell surface and said actuating end such that, as a result of counterclockwise rotation of said actuating end about the axis, said expandable shell is forced to expand radially to an expanded position, where said outer surrounding surface is urged against said inner tubular surface by an urging force to result in an increased frictional force therebetween, thereby guarding against movement of said second tube relative to said first tube along the axis, and such that, as a result of clockwise rotation of said actuating end about the axis, said expandable shell is displaced to a contracted position, where said inner tubular surface is relieved of the urging force so as to be movable relative to said outer surrounding surface along the axis.   
     
     
         2 . The ball racket according to  claim 1 , wherein said force transmitting mechanism includes internally and externally threaded portions which are respectively disposed on said inner shell surface and said actuating end, which are threadedly engaged with each other, and which are configured such that the counterclockwise and clockwise rotation of said actuating end result in threaded movement of said internally threaded portion relative to said externally threaded portion to permit displacement of said expandable shell to the expanded and contracted positions, respectively. 
     
     
         3 . The ball racket according to  claim 2 , wherein said externally threaded portion has an outer diameter which is gradually increased toward said shank body such that the threaded movement of said internally threaded portion toward said shank body as a result of the counterclockwise rotation of said actuating end results in radial expansion of said expandable shell so as to permit displacement of said expandable shell to the expanded position. 
     
     
         4 . The ball racket according to  claim 3 , wherein said expandable shell includes two shell halves which respectively have inner surface regions cooperatively serving as said inner shell surface, and outer surface regions cooperatively serving as said outer shell surface, and a spring O-ring which is fitted on said outer surface regions so as to bias said inner surface regions toward said actuating end such that, as a result of the counterclockwise rotation of said actuating end, said internally and externally threaded portions are fully engaged with each other and said outer surface regions are displaced radially and outwardly against a biasing action of said spring O-ring so as to increase the frictional force, and such that, as a result of the clockwise rotation of said actuating end, said internally and externally threaded portions are partially engaged with each other and said outer surface regions are displaced radially and inwardly by the biasing action of said spring O-ring so as to decrease the frictional force. 
     
     
         5 . The ball racket according to  claim 4 , wherein said shell halves respectively have groove segments respectively disposed in said outer surface regions and extending in an axial direction parallel to the axis to cooperatively define a guiding groove, said first tubular segment being punched radially and inwardly to form a guard rail region on said inner surrounding surface, and a corresponding keyway region in said outer surrounding surface, said guard rail region being configured to be fitted in said guiding groove in spline engagement such that rotation of said actuating end results in axial movement of said expandable shell relative to said actuating end between the expanded and contracted positions. 
     
     
         6 . The ball racket according to  claim 5 , wherein said second tubular segment has a key extending radially and inwardly from said inner tubular surface and engaging slidably said keyway region so as to guide movement of said first tubular segment relative to said second tubular segment along the axis. 
     
     
         7 . The ball racket according to  claim 4 , wherein said inner surrounding surface includes a first larger-diameter region and a first smaller-diameter region which are disposed adjacent to said first front end and said first rear end, respectively, said first larger-diameter region having a cross-section configured to mate with a combined cross-section of said outer surface regions of said shell halves for facilitating axial movement of said shell halves within said first tube, said first smaller-diameter region being dimensioned to permit movement of said shank body along the axis. 
     
     
         8 . The ball racket according to  claim 7 , wherein said actuator unit has front and rear stoppers which are respectively disposed forwardly and rearwardly of said externally threaded portion and which are dimensioned to limit the threaded movement of said internally threaded portion relative to said externally threaded portion, said rear stopper being further dimensioned to be prevented from moving outwardly of said first smaller-diameter region. 
     
     
         9 . The ball racket according to  claim 7 , wherein said inner tubular surface includes a second larger-diameter region and a second smaller-diameter region which are disposed adjacent to said second front end and said second rear end, respectively, said second larger-diameter region having a cross-section configured to mate with said outer surrounding surface for facilitating movement of said second tube relative to said first tube, said second smaller-diameter region being dimensioned to permit extension of said operated end therethrough. 
     
     
         10 . The ball racket according to  claim 9 , further comprising a twistable knob which is disposed rearwardly of said second rear end and which is coupled with said operated end so as to be operable manually to rotate said actuating end.