# US 4,177,990 A · Racket frame > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,177,990 A - Document ID: US4177990A - Status: Granted - Kind: A - Application number: 05/837,541 - Filed: 1977-09-28 - Granted: 1979-12-11 - Earliest claimed: 1976-10-04 - Assignees: Nippon Gakki Seizo Kabushiki Kaisha - Inventors: Takao Kajiwara - Web page: https://patentgrep.com/patent/US4177990A ## CPC - A63B 49/10: made of non-metallic materials, other than wood - A63B 60/00: Details or accessories of golf clubs, bats, rackets or the like - A63B 60/54: with means for damping vibrations - A63B 2049/0211: {with variable thickness of the head in a direction perpendicular to the string plane} - A63B 2049/0217: {with variable thickness of the head in the string plane} - A63B 2209/023: Long, oriented fibres, e.g. wound filaments, woven fabrics, mats - A63B: APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT (apparatus for passive exercising, massage A61H) ## Abstract A fiber reinforced racket frame advantageously usable for tennis rackets includes a discontinuous foamed resin core made up of a plurality of core pieces longitudinally aligned in end-to-end relationship which preferably vary in the transverse cross-sectional characteristic and/or density from piece to piece. Longitudinal discontinuity and, preferably, change in at least one of the transverse cross-sectional characteristics and density effectively hinder direct and smooth transmission to players' hands of the impact imposed on the playing face of the racket. The manufacturing process is greatly simplified so as to fit automatization and mass-production. ## Claims ### Claim 1 An improved racket frame comprising a discontinuous core extending continuously around said racket frame and made up of a plurality of foamed resin core pieces longitudinally aligned in end-to-end abutting relationship, and a fiber reinforced plastic envelope, with numerous fibers embedded therein, wholly covering said discontinuous core. ### Claim 2 (depends on 1) The improved racket frame as claimed in claim 1 in which the transverse cross-sectional characteristics of said discontinuous core change from one said piece to the abutting said piece. ### Claim 3 (depends on 2) The improved racket frame as claimed in claim 2 in which the transverse cross-sectional surface area of said discontinuous core changes from one said piece to the abutting said piece. ### Claim 4 (depends on 2) The improved racket frame as claimed in claim 2 in which the transverse cross-sectional profile of said discontinuous core changes from one said piece to the abutting said piece. ### Claim 5 (depends on 2) The improved racket frame as claimed in claim 2 in which said racket frame has a head portion and other portions away from said head portion, at least one said core piece in said head portion, said core piece in said head portion of said racket frame being relatively narrower in the width dimension of said racket frame and relatively thinner in the thickness dimension of said racket frame than the said core pieces in the portions of said racket frame other than said head portion. ### Claim 6 (depends on 2) The improved racket frame as claimed in claim 2 in which said racket frame has a head portion, a support shaft portion and intermediate portions between said head portion and said shaft portion, at least one said core piece in said head portion and at least another said core piece in said intermediate portions, said core pieces in said intermediate portions of said racket frame being relatively broader in the width dimension of said racket frame and relatively thicker in the thickness dimension of said racket frame than the said core piece in said head portion of said racket frame. ### Claim 7 (depends on 2) The improved racket frame as claimed in claim 2 in which said racket frame has a head portion and has a throat portion away from said head portion, at least one said core piece in said head portion, at least another said core piece in said throat portion, said core pieces in said throat portion of said racket frame being relatively broader in the thickness dimension of said racket frame for providing flexibility to said racket frame. ### Claim 8 (depends on 2) The improved racket frame as claimed in claim 2 in which said racket frame has a head portion and has a shaft portion away from said head portion, a grip portion at the end of said shaft portion away from said head portion, at least one said core piece being in said head portion, at least one said core piece being in said shaft portion, said core pieces in said shaft portion of said tennis racket gradually increase in their thickness dimension towards said grip portion of said tennis racket. ### Claim 9 (depends on 1) The improved racket frame as claimed in claim 1 in which the density of the resin of said discontinuous core changes from said piece to said piece. ### Claim 10 (depends on 1) The improved racket frame as claimed in claim 1 in which said racket frame includes a head portion, a throat portion, an intermediate portion between said head portion and said throat portion and a shaft portion extending away from said throat portion; said core pieces being shaped and placed so that there are abutting end portions of said core pieces located at least in said throat portion of said racket frame. ### Claim 11 (depends on 10) The improved racket frame as claimed in claim 10 in which said racket frame further includes a grip portion at said shaft portion, said discontinuous core comprises three said core pieces, one said core piece extending majorly in said head and intermediate portions and the other two said core pieces extending majorly in said throat, shaft and grip portions of said racket frame, respectively. ### Claim 12 (depends on 10) The improved racket frame as claimed in claim 10 in which said racket frame further includes a grip portion at said shaft portion, said discontinuous core comprises five said core pieces, one said core piece extending in said head portion, two other said core pieces extending majorly in said intermediate portions of said frame and the last two said core pieces extending majorly in said throat, shaft and grip portions of said racket frame, respectively. ### Claim 13 (depends on 1) The improved racket frame as claimed in claim 1 in which said discontinuous core is made of urethane foam. ### Claim 14 (depends on 1) The improved racket frame as claimed in claim 1 in which said fiber reinforced plastic envelope contains fibers of at least one selected from the group consisting of glass fibers, boron fibers, graphite fibers and carbon fibers and said envelope is impregnated by thermosetting resin.