Through-hole frame sports racket

Abstract

 The frame of a sports racket (50) is made by extrusion or molding method where the outer wall (22) and the inner wall (23) are parallel to each other, perpendicular to the plane (21) of the string network and supported by a system of parallel plate-like panels (24, 31) connected to each other and with the two walls (22, 23). There are large openings (25) formed between the panels (24, 31) and between the panels (24, 31) and the walls (22, 23), perpendicular to the plane (21) of the string network, such openings (25) are through holes, extending from one end of the frame's thickness to the other end without obstructions. The shape of such frames is ideal for the extrusion process and the extrusion may be cut at a thickness equal to the frame's thickness, and a single extrusion may produce a large number of raw frames, each may become a racket after finishing work is done.

Description

INVENTION BACKGROUND

[0001] In sports racket frame, the design goal is to have the highest in strength to weight ratio, and the lowest in cost. Materials have been changed from wood, metal to fiber reinforced thermoplastics. It contributes significantly to better rackets. But the cost of production remains high. The frame of a fiber reinforced racket is usually of a tubular, thin-walled cross section with a large number of fiber/thermoplastic layers piled one over the other at different fiber orientation angles for optimum strength. Cutting of the multi-layered cloth, laying Epoxy, folding over thermo-expandable core or air tube, laid into the mold, heated, polished and cosmetics, are all very time-consuming and labor intensive processes, hence the high production cost.

[0002] The main difficulty in racket frame design technology is the extreme high ratio of the strength to weight required. This explains why people in the trade stick to existing designs, shapes and fabrication practices and discouraged changes. Take the tennis racket frame as an example. The weight allocated to form the portion of the frame which supports the string networks is about 1 2 gm per centimeter along the axis of the frame. If the material is graphite-fiber/epoxy, which has a specific gravity of 1.35, the volume of the frame per cm long is about 0.885 cubic cm. If this volume of material is used to form a circular tubed frame with an inner radius of 16.0 mm, which is an average of tennis frame circumference, its wall thickness is 1.62 mm, or even less when the weight of the core is included. This thin walled tube composed of up to 5 or more layers of graphite cloth, rolled into a tube, formed in a forming mold, baked and cured to make a tennis racket. This hollow frame is characterized by having no surface openings except string holes in the plane of the string network. There has no relevant prior art suggesting functional large openings in the surface not in the plane of string network, especially surface openings perpendicular to the plane of the string network, because it weakens the frame at the most critical region. One prior art is a Soong patent, EPO No.104,930 which will be discussed later.

INVENTION

[0003] The invention suggests that, the frame of a sports racket is designed to be produced by extrusion, or injection molded, or by other suitable methods, by forcing suitable materials out of the extrusion die or injection mold to form the necessary outer wall and the inner wall of the frame which are rigidly connected to each other by a system of parallel, thin-walled panels characterized in that each panel is approximately perpendicular to the plane of the string network, with large special void, called openings, between the panels, which extend from one end to the other through the height of the frame without obstruction, along the direction perpendicular to the plane of the string network. It is called a through-hole frame. Panels link to each other as well as with the walls. Said unobstructed openings made among panels and the walls may be in the shape of polygons, or other geometrical shapes, as looked in a view perpendicular to the plane of the string network. This is a very inexpensive manufacturing technique, the frame is designed just for extrusion or injection molding, or other molding methods, taking advantage of the unprecedented large, end-to-end openings for reduction of weight and of air resistance. Due to the mutually supportive plate-like panel members, the frame is strong and light in weight. Materials may be short fiber-reinforced thermoplastics or high strength plastics. The racket of such a frame looks different and innovative. Details are described in later sections.

DRAWINGS

[0004] 

Fig. 1 shows a tennis racket.

Fig. 2 shows an embodiment of the invention design.

Fig. 3 shows another embodiment of the invention design.

Fig. 4 shows a piece cut out from an extruded stock of the racket frame.

Fig. 5 shows yet another embodiment of the invention design.

Fig. 6 shows details of the grommet strip attached to the inner wall.

DESCRIPTION

[0005] Fig. 1 shows a tennis racket 10. The frame 2 is the main structure from the handle 3 all the way to the head region 4. Lateral region 5 connects the head region 4 to the throat region 6. The string network 7 is supported by the head region 4, the lateral region 5 and the throat region 6. The shank region 8, flaring outwardly from the handle 3 towards the string network approximately the same as 7, connects the handle 3 to the throat region 6. There is a bumper guard 9 protects the frame at the head region and some part of the lateral region from scratch when the racket hits the ground.

[0006] Fig. 2 shows a typical portion of a desired frame conforming to the intent of the invention. The frame section 20 is symmetric to the midplane 21 of the frame which is the same plane of the string network. Outer wall 22 forms the outboard boundary of the frame, inner wall 23 forms the inboard boundary of the frame, all with respect to the center of the network. Multiple parallel panels 24 which connect the two walls are all parallel to each other, and perpendicular to the midplane 21, having large spatial voids 25 among them, called openings. The inner wall height 26 is the nominal frame height. The outer wall 22 with height 27 may have the same height 26 as the inner wall 23, or may be different. The height of the parallel panels 24 may vary from the outboard side to the inboard side, or they may be less than the heights of the two walls. Shape of openings 25 between the parallel panels and the walls may be triangular, polygon or of other geometrical shapes as looked in a view perpendicular to the midplane 21 Thickness of the wall of the panels may vary from each other or vary for the same panel from one end to the other end. But the openings 25 are through holes from one end to the other end. String holes 28 may be made in outer and inner walls as the case may be, in the plane of the string network or at a distance from the plane. Holes may also be inside panel's interior to pass strings through the frame. Openings at the inner wall for the string may be larger than the diameter of the string or the grommet that is used to guide the string. There may be an advantage having the string not contacting the inner wall. Distance 29 between the two walls may be varied along the length of the axis of the frame.

[0007] Figure 3 shows a length of a frame 30 which is the same frame as 20 except the parallel panels 31 are approximately at the right angle with the outer and the inner walls and the panels are not interconnected to each other. String holes 28 may be passed through the interior of the panel and are not exposed. This will reduce air resistance. For the same material volume, the Fig. 2 configuration is stiffer than the Fig 3 configuration in the bending in the plane of the string network, and is comparable to bending in the perpendicular direction and in torsion, but the thickness of the walls and panels would have to be less. Compared to the conventional tubular frame with the same weight per unit length, their rigidity are comparable.

[0008] Fig. 4 shows an innovative frame design 50 in which the entire frame from the head to the handle is cut from a length of extrusion. Each cut from the long extrusion with the proper wall height 51, along the axis of the extrusion 58, becomes one racket frame. Walls 52, panels 53, throat 54 and the handle 55 made from the extrusion will be all exactly parallel and perpendicular to the plane of the network. After polishing, paint and cosmetics, one needs only to put on a bumper guard, grommet strips, string, and a handle sleeve with grip, to complete the racket. It would be very inexpensive, need very little hand work after the piece is cut from the extrusion. It will be a good tennis racket because the frame has excellent longitudinal flexibility to bounce the ball, better than average in-plane frame stiffness to resist string tension, very good torsional rigidity for ball control, and has very little air resistance. Plane shape and size of the head can be made in any manner.

[0009] A sleeve is needed to finish the incompleted handle if the frame is extruded the sleeve may be made in different grip size to be installed onto the same handle core. The cross section A-A in Fig. 4 shows the cut out section from the extrusion of the handle 55. The sleeve consists of a tube 56 which has a foamed grip 57 as shown. The tube should fit the incomplete handle snugly before installation. There need to have only one tube size . The foamed grip 57 will have different grip sizes as the conventional grips do. Adhesive will be applied on the exterior surfaces of the incomplete handle 55 when the sleeve is fitted over the handle, at the time of installation or before. Shops will need only to store the raw frames and have different grip sized sleeves for players of different grips.

[0010] It is to be noted that Figures 2 and 3 show embodiments wherein outer wall and inner wall have the same height. If the height of the outer wall is desired to be less than the height of the inner wall, machining of the piece cut out from the stock would be a simple thing to do.

[0011] If injection molding is used, wall thickness and some other sectional details may be varied. Fig. 5 frame 60 may be produced either by extrusion then followed by machining, or by injection molding. Inner wall 61 and outer wall 62 have different height. Parallel panels 63 may be of varying thickness along its length from one end to the other end and from the out board to the inboard side, subjected to the constraints of the molding process. Openings 64 may be of a triangular shape, rectangular or other shapes. String holes 65 may be through the interior of the panel or not.

[0012] Strings may go through the outer wall and the inner wall to the interior of the network in the conventional way. However, to take advantage of the through-hole design in which access of the interior of the frame is easy, strings may be attached to the inner wall only. Fig. 6 shows a preferred embodiment of a new way of stringing. 71 is a portion of the frame where 72 is the inner wall, 73 is the outer wall and 74 panels. The grommet strip 75 consists of the strip 76 and grommets 77. String is not shown. Strings pass the inner wall only, the outer wall is not contacted. To accommodate the grommet strip 75, there is a longitudinal opening 78 running through all panels to let the string to pass through internally. This longitudinal opening 78 may be created during molding process. A Nylon tube or other suitable material which is flexible and can sustain molding temperature may be embedded between the upper and lower mold in the plane of the string network which is the parting plane of the mold. It will be held in place by the mold and fills the space intended for said longitudinal opening. The tube is flexible and can be pulled out after the frame cools off String holes in the inner wall may be made during molding or separately afterwards. The grommet strip is flexible and can be inserted into the space between the walls 72 and 73. Section B-B shows a cut through the two walls and a grommet. Section C-C shows the cut which includes a panel too.

[0013] There has been very little relevant prior art for sports racket frames with openings to the surface of a frame far from the midplane of the string network. Only Soong, EPO Patent No. 104,930 has similarly large surface openings. Its difference with the present application will be discussed. Soong, who is the present applicant, revealed a frame structure of a truss type, symmetric to the plane of the string network, with struts or bar-like members extending from the outer wall to the inner wall, across an empty space which is hollow and unobstructed in the axial direction of the frame. From the view perpendicular to the plane of the network, there are unobstructed openings in the frame so constructed. However, Soong does not disclose or make obvious panel or plate members extending through the thickness of the frame and which are perpendicular to the midplane of the frame or the string network required clearly by the present application. In Soong's teaching, no panel or plate members defining the so-called truss assembly are arranged perpendicular to the plane of the string network or the midplane of the frame, nor do they extend from one side to the other side across the midplane of the frame..

Claims

1. In a sports racket having a hand grip 1 joined to a frame 2 supporting a string network 7 extending throughout a ball-hitting region 7 spaced from the grip, the frame having an outwardly flaring throat region 6 and surrounding the ball-hitting region spanned by the string network, a major portion of the frame which is symmetric to its midplane 21 which coincides with the plane of the string network, is composed of an outer wall 22 approximately perpendicular to the midplane and an inner wall 23, closer to the string network, approximately parallel to the outer wall, which are separated but connected with each other by a multiple parallel panel system 24, 31 characterized by that the parallel panels are plate-like structural members, approximately parallel to each other and approximately perpendicular to the midplane, having large open spaces 25 among them which are through holes extending from one end to the other end of the height 26, 27 of the frame without obstruction.

2. The sports racket of claim 1 wherein said frame with multiple parallel panels extends towards regions 3,8, outside the ball hitting region 7.

3. The sports racket of claim 1 wherein said frame is made of an extrusion process and a frame is made by cutting a piece 51 off from said extrusion perpendicular to the direction of the axis 58 of said extrusion.

4. The sports racket of claim 1 wherein said open space 25 between the parallel panels and between parallel panels and the walls of said frame are of triangular shape or rectangular shape.

5. The sports racket of claim 1 wherein the majority of strings pass through the space between the outer wall and the inner wall of said frame are through the interior of said parallel panels.

6. The sports racket of claim 1 wherein the majority of strings enter into the frame from the string network through holes in the inner wall, turn around inside the space between the inner wall and the outer wall and exit to the string network through holes in the inner wall again without contacting the outer wall.

7. The sports racket of claim 6 wherein the majority of strings passing through the inner wall are supported by grommets 77 or grommet strips 75 accessible from said large open spaces 25 between the inner wall and the outer wall of the frame.

8. The sports racket of claim 6 wherein the majority of said string holes are made at a distance from the plane of the string network 21 and are not at the said plane.

9. The sports racket of claim 1 wherein an outer sleeve 56, 57 of suitable hand grip shape is fitted over and fastened to the incomplete handle 55 of said frame to make a grip for the finished handle.

10. The sports racket of claim 9 wherein said sleeve 56, 57 with suitable grip is a pre-fabricated handle assembly, a stand-alone equipment, ready to be fitted over a frame to make the racket complete and ready to be played.

Drawing