FIELD OF INVENTION

This invention relates to a bat having an unstressed perforated striking head, for use in playing ball games such as paddle tennis ball games, tethered tennis-type ball games, beach tennis games, streamer ball games, or the like.

BACKGROUND OF THE INVENTION

Bats having unstressed perforated ball-striking heads are known. Such bats are typically made from plastics material and are considered a cheaper and more robust alternative to conventional strung racquets or solid face bats. The present invention is not concerned with bats having solid striking heads which may or may not be partially perforated such as solid wooden bats, nor is it concerned with bats having stressed striking surfaces such as strung squash or tennis racquets. Bats having unstressed perforated ball-striking heads need to be appropriately weighted for the balls they are to be used with and if possible, to offer low air resistance. Such bats should also be of such a weight which is easy and practical for players to use and wield for any particular type of game. For a good ball striking feel, such bats need to be relatively rigid and offer minimal uncomfortable impact vibrations upon impact with a ball. The rigidity of the ball-striking head is derived from both its thickness and the stiffness of its material but it is an important design consideration that this is not achieved at the expense of increased mass of the bat. Thicker striking heads also tend to dampen and reduce impact vibration. It can therefore be advantageous for the ball-striking head to have a thickness which reduces vibration and renders it sufficiently rigid, without making the bat excessively heavy.

It has previously been proposed to provide a bat which includes a handle and a ball- striking head wherein the ball-striking head includes an unstressed monolithic perforated semi-hollow structure and has a pair of spaced apart lattice structures, the outer surfaces of which constitute the ball-striking surfaces, with the inner surfaces of the lattice structures being joined together by a plurality of discrete transverse struts. The provision of spaced apart lattices with a largely hollow core offers a relatively light structure and a way of increasing thickness and rigidity while also damping and reducing any tendency of vibration. The present invention is concerned with bats of this type.

In this specification the term "lattice" is intended to refer to lattice or grid structures which are thin in relation to their lengths and breadths and which are perforated by a series of openings of a variety of shapes. Such a prior art lattice bat is disclosed in US Patent 4,41 1 ,427 (Baumgartner) which discloses a bat including a head having a monolithic unstressed perforated structure characterized by having a pair of spaced apart lattices each comprised of a plurality of intersecting laths, the inner surfaces of the lattices being interconnected by a plurality of discrete transverse struts spanning corresponding intersections of the laths comprising the lattices. Another prior art lattice bat is disclosed in US Patent 5,961 ,404 to the Applicant. The bat disclosed in this patent incorporates a monolithic unstressed ball-striking head having a pair of spaced apart outer lattices which constitute the ball-striking surfaces of the head, with the two outer lattices being joined by a third internal lightweight "core lattice" which is covered and protected by the two outer lattices. In the prior art patents referred to hereinbefore which relate to bats of the "double lattice" type, the lattices of the ball-striking surfaces are of plastics material and are perforated by a series of openings in a variety of shapes and patterns.

A further characteristic of such double lattice bats is that the outer lattices are usually formed so as to include a connected network of nodal areas which are each covered by a layer or web of material and which alternate with neighbouring relatively larger unobstructed openings.

It has become standard practice to completely cover and fill the nodal areas which each comprise a web of material having a continuous flat outer surface. The webbing of the nodal areas has been discovered to be important in strengthening and stiffening of the lattice structures and also acts as a convenient point for the location of the ends of ejector pins on one side of a mould which eject the bat from the mould by pushing against inner surfaces of the nodal areas at the end of an injection moulding cycle.

By covering and thus reinforcing the nodal areas with webs of the material from which the bat is made, an identified problem of earlier lattice bat designs wherein balls deforming upon impact and bulging down into the relatively large openings and damaging the sides of the nodal areas surrounding such relatively large openings, is obviated because the webs help strengthen and reinforce the nodal areas which form part of the side of neighbouring relatively large openings.

The nodal areas are spread across the outer surfaces of both lattices to form a distributed and connected network of reinforced nodal areas which strengthens the overall lattice structures and reduces the risk of lattice damage to bats of this kind from impact with a ball.

The characteristics of double lattice bats of this kind in which the outer lattice structures include areas where the relatively large openings alternate with nodal areas is dictated by the requirements of the relatively complex design of the plastic mould which is required to produce bats of this type. This arises from the requirement of the mould design which dictates that the mould includes intermeshing discrete metal "fingers" extending inwardly from each mould half into a mould cavity wherein the bat is moulded. The fingers have tapered configurations wherein each finger tapers from a base region thereof towards an outer tip thereof in order to facilitate frictionless intermeshing and withdrawal of the fingers when the mould is opened for removal of a moulded bat. When the mould closes the fingers of both mould halves pass through an area where the large openings of the lattices to be moulded, will be formed and closely mesh with or lightly contact side surfaces of adjoining fingers of the other mould half. The presence of the fingers produces the hollow interior of these double lattice bats as no plastic moulding material can enter these areas.

The Applicant has found that the use of smooth-surfaced rubber balls offer an attractive alternative to the use of standard, cloth-covered tennis balls. More specifically, such smooth surfaced rubber balls have a reduced weight advantage compared to cloth-covered tennis balls enabling the use of lighter bats and furthermore have a cost advantage over cloth-covered tennis balls by eliminating the relatively expensive cloth covering used for all regulation tennis balls.

In experiments conducted by the Applicant using double lattice bats of the above described type (having flat, webbed nodal areas alternating with larger unobstructed openings) with rubber balls having a relatively smooth outer surface, it became apparent that the use of such lattice bats is not entirely satisfactory due to an unpleasant high pitched sound which is often generated upon impact between such bare rubber balls and the ball-striking surface of lattice bats of this type. The unpleasant high pitched sound discourages further play. On further scientific investigation and detailed acoustic analysis of the impact noise, it was established that the unpleasant high pitched sound was far greater in terms of pitch and volume when smooth surfaced rubber balls are used with double lattice bats of this type compared to the pitch and volume of sound recorded at impact with cloth covered tennis balls using the same type of lattice bat. From the experiments conducted by the Applicant, it became apparent that the standard cloth covering of a regulation tennis ball provides a sound muffling effect which the smooth surface of a bare rubber ball does not provide. Further investigation revealed that the interaction of a smooth-surfaced ball with the flat webbed nodal areas of the lattice bats described hereinabove, at impact, was the apparent cause of the unpleasant high pitched noise.

It is an object of the present invention to provide a lattice bat which is lightweight, yet rigid and which has low air resistance, and wherein the unpleasant noise generated when a smooth-surfaced bare rubber ball is struck by the striking head of such a lattice bat, is reduced.

SUMMARY OF INVENTION

According to the invention there is provided a bat including a handle and a ball- striking head for striking resilient balls having smooth outer surfaces, the ball-striking head comprising a pair of spaced apart outer lattices which define rigid, unstressed ball-striking surfaces of the bat, each lattice including a distributed and connected network of alternating nodal areas and relatively larger unobstructed openings, wherein the lattices are interconnected by a plurality of discrete internal struts spanning the lattices, the bat being characterised in that each nodal area comprises a web having an irregular outer surface.

In this specification, any reference to an "irregular outer surface" of a web must be interpreted to mean a reference to a non-uniform surface which is not continuously flat and which includes an irregularity in the form of at least one of a perforation, a raised protuberance and a depression.

In a first embodiment of the invention, the web of each nodal area may have an irregular outer surface provided by at least one perforation in the web. More particularly, the surface area of the perforation may comprise between 10% and 60% of the total surface area of the web when viewed in plan view. Yet more particularly, the web of each nodal area may include two or more equi-shaped perforations arranged in a symmetrical pattern.

In a second embodiment of the invention, the web of each nodal area may have an irregular outer surface including at least one raised protuberance.

In a third embodiment of the invention, the web of each nodal area may have an irregular outer surface including at least one depression. More particularly, the depression may have a surface area comprising between 1 0% and 60% of the total surface area of the web when viewed in plan view.

BRIEF DESCRIPTION OF THE DRAWINGS Further features of the invention are described hereinafter by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a fragmentary three-dimensional view of an external side of a lattice of a prior art bat;

Figure 1 A shows an enlarged fragmentary three-dimensional view of one of the nodal areas of the lattice of Figure 1 ; Figure 2 shows a sectional view of a mould illustrating the manner in which a prior art bat having outer lattices of the type shown in Figures 1 and 1 A, is moulded;

Figure 3 shows a fragmentary sectional side view of a ball as it deforms upon impact with a prior art bat having outer lattices of the type shown in Figures 1 and 1 A;

Figure 4 shows a further fragmentary sectional side view of a ball as it deforms further upon impact with the prior art bat of Figure 3; Figure 5 shows a three-dimensional view of a bat for playing ball games, in accordance with the invention;

Figure 6 shows a plan view of the bat of Figure 5;

Figure 6A shows an enlarged plan view of detail A of Figure 6;

Figure 6B shows an enlarged fragmentary three-dimensional view of a single nodal area of the bat of Figure 5;

Figure 7 shows a sectional side view of the bat of Figure 5, sectioned along section line VII-VII of Figure 6;

Figure 8 shows a sectional end view of the bat of Figure 5, sectioned along section line VIM-VIM of Figure 6;

Figure 8A shows an enlarged sectional side view of detail C of Figure 8;

Figure 9 shows an enlarged nodal area of a lattice of another embodiment of a bat in accordance with the invention; and

Figure 1 0 shows a three-dimensional view of part of a lattice of yet another embodiment of a bat in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 to 3 of the drawings, a lattice 1 of a prior art double lattice bat, is shown. The prior art double lattice bat is of the type illustrated in Figure 1 of US Patent 4,41 1 ,427 (Baumgarter) wherein the bat includes a head having a monolithic plastics unstressed perforated structure comprising a pair of spaced-apart lattices which are interconnected by a plurality of transverse struts. Each lattice comprises a plurality of intersecting laths with the struts spanning corresponding intersections of the laths. Outer sides of the lattices provide ball-striking surfaces. The lattices are formed so as to include a distributed and connected network of nodal areas 1 .1 which are each covered by a web of material which alternates with neighbouring relatively larger unobstructed openings 1 .2. The webs completely cover the nodal areas and more specifically, have a continuous flat outer surface.

The distributed and connected network of covered nodal areas alternating with larger openings, is dictated by the manner in which the bats are moulded.

With reference to Figure 2, a mould 2 for producing bats of the above described type, is shown. The mould includes two metal mould halves 3.1 and 3.2 which include discrete fingers 4.1 and 4.2, respectively, which mesh with one another when the mould halves are closed onto one another as is illustrated in Figure 2. The fingers 4.1 , 4.2 have tapered configurations wherein the fingers taper from base regions thereof towards outer tips 5.1 , 5.2 in order to facilitate frictionless intermeshing of the fingers when the mould halves are closed and withdrawal of the fingers when the mould is opened for removal of a moulded bat from the mould cavity. In Figure 2, a particular section of the mould is shown wherein there is a gap between the fingers 4.1 and 4.2 to permit the formation of discrete internal struts 26. It will be appreciated that another sectional view of the mould where there are no internal discrete struts, would show the fingers touching each other.

The layout or design of the lattices in the nodal areas is produced by leaving appropriate grooves or indentations around the tips of the fingers leaving a gap between sides of the tips of the fingers of one mould half and adjoining bases of neighbouring fingers of the other mould half through which the plastic material can flow while hot which forms a peripheral rim of the nodal areas. The web of each nodal area is produced by ensuring that gaps are defined between the tips of the "fingers' of one mould half and opposite faces of the other mould half defined between the finger bases. In the moulding process, the gaps are filled with plastic to form the webs of the nodal areas of the lattices. The internal transverse struts connecting the outer lattices which run between the corners of the nodal areas of the lattices are formed by gaps defined between the sides of the "fingers" when meshed together in the closed position of the mould halves. These gaps fill with plastic during the moulding process to form the internal cross struts which connect inner surfaces of the outer lattices. Ends of the internal struts where the struts terminate at the outer surface of the lattices, serve to connect the nodal areas to each other to form the distributed and connected network of nodal areas to make up the overall lattice structure of both lattices. The mould cavity designated by the reference numeral 6, in which the bat is moulded is thus defined by the above described gaps.

The mould half 3.2 includes ejector pins 7 which extend along passages defined therefor in the fingers 4.2. The webbing of the nodal areas is acted upon by the ends of the ejector pins in order to eject the bat from the mould at the end of an injection moulding cycle.

Because there is a need for the sets of metal fingers to taper from the bases to the outer tips thereof so that the two opposing sets of fingers can easily slide together and then mesh with each other, the tips of the fingers have a smaller cross-sectional area than the bases thereof. The nodal areas of the lattices which are formed around the tips of the fingers are therefore smaller than the neighbouring larger openings which are formed around the bases of the fingers.

Thus, all prior art double lattice bats produced in a mould of the above described type, have outer lattices having relatively larger unobstructed openings alternating with relatively smaller nodal areas, the nodal areas having webs formed by the smaller tapered tips of the fingers of the mould.

Figures 3 and 4 illustrate modes of deformation of a hollow rubber ball 8 having a bare smooth outer surface, when it is struck by the ball-striking head of a prior art double lattice bat as described hereinabove. In Figures 3 and 4, the bat includes the lattices 1 described hereinabove, outer surfaces of which constitute the ball-striking surfaces. With reference to Figure 3, the Applicant has observed that upon impact by the bat, the ball momentarily bulges outwardly into an opening 1 .2 defined between the nodal areas 1 .1 , exerting sideways pressure on parts of the lattice surrounding the opening. In Figures 3 and 4, the direction of deformation of the ball is illustrated by the arrows in the drawings.

With reference to Figure 4, the Applicant has observed that after bulging outwardly as illustrated in Figure 3, the ball flexes inwardly causing an area of the ball surrounding the inwardly flexed region to form an air-tight seal with the adjacent webbed nodal areas which the Applicant believes causes an irregular build up of air pressure which upon release of the seal causes an unpleasant high-pitched noise.

With reference to Figures 5 to 9 of the drawings, a bat for playing ball games, in accordance with the invention, is designated generally by the reference numeral 10. The bat 10 comprises, broadly, an integrally moulded handle 1 2 and a ball-striking head 14.

The ball-striking head is specifically adapted for striking resiliently deformable rubber balls having bare smooth outer surfaces.

The ball-striking head 14 is of a monolithic structure comprising a pair of spaced- apart outer lattices 1 6 which define rigid, unstressed ball-striking surfaces 1 8 and 20. The bat has a unitary structure and is integrally moulded from polymeric material. Each lattice comprises alternating nodal areas 22 and openings 24 in a grid pattern, the nodal areas of one lattice being staggered with respect to those on the other lattice as can be seen clearly in Figure 2.

The outer lattices are interconnected to one another by the ends of a plurality of discrete internal struts 26 which are integrally moulded with the lattices. The struts are radiused inwardly where they join the outer lattices so as to enhance the strength of the structure. The ball-striking head further includes a peripheral frame 28 which is integrally moulded with the outer lattices and the handle 12 which results in a lightweight monolithic structure. Each of the nodal areas 22 of the outer lattices comprises a web 23 having an irregular outer surface. More specifically, the web of each nodal area includes four irregularities in the form of discrete perforations 30 which are each triangularly shaped when viewed in plan view. The perforations of each nodal area are arranged in a symmetrical pattern. The Applicant has found in experiments conducted by the Applicant, that the perforations assist significantly in reducing the unpleasant noise generated when a smooth-surfaced bare rubber ball is struck by the bat 1 0 in accordance with the invention, compared to when the same ball is struck by a prior art lattice bat (hereinafter referred to as a "test bat") having the lattices 1 as described hereinabove, wherein the nodal areas have webs which completely cover the nodal areas and which have continuous flat outer surfaces.

It is believed that the high-pitched components of the unpleasant noise generated at impact, emanate from escaping air which is initially trapped at impact between the flat outer surface of a web of a nodal area and the ball and which is forced to escape laterally at high speed and pressure following escape pathways along constricted passages between sides of the voids and parts of the inwardly flexing or outwardly bulging ball. It was found that by perforating the nodal areas of the test bat, air exit vents are created which provide escape routes for the air located between the ball and the ball- striking surface of the bat in a direction directly towards the interior of the bat rather than sideways and out through the adjoining larger openings. This was found in investigations conducted by the Applicant to alleviate the problem.

The configuration of the perforations 30 in the webs 23 of the smaller nodal areas 22, is an important design consideration. The perforations of each nodal area need to be large enough to allow for trapped air to readily escape at impact of the ball-striking surface with a ball, while the nodal area must still retain sufficient material between the perforations to form a robust structure for the smaller nodal areas. This is vital to strengthen the area around the perforations and also to provide a sufficiently strong abutment surface against which the ends of ejector pins of a mould tooling can push in order to eject the bat moulding from the mould. The perforations also have an additional important advantage in that the perforations allow air to pass therethrough thereby reducing air resistance of the striking head as it passes through air during the playing of strokes.

The Applicant has found that the best noise attenuation results are achieved when the total surface area of the perforations 30 comprises between 1 0% and 60% of the total surface area of the web when viewed in plan view.

Alternative ways to alleviate the ball impact noise problem includes the provision of irregular outer surfaces for the webs of the smaller nodal areas. With reference to Figure 9, in one alternative embodiment, the web of each nodal area includes at least one irregularity in the form of a raised protuberance. Figure 9 shows an alternative web 123 of a nodal area 1 22 which has a cross-shaped raised protuberance 130.

With reference to Figure 10, in another alternative embodiment, the web of each nodal area includes an irregularity in the form of a raised protuberance having a different shape. Figure 1 0 shows part of a lattice 216 having smaller nodal areas 222 comprising webs 223 which each have a centrally located dome-shaped raised protuberance 230. The irregular outer surfaces of the smaller nodal areas 22, 122 and 222 thus provide an effective solution to the impact noise problem described hereinabove. The Applicant believes that the design imperatives of a lightweight construction offering low air resistance and a substantially improved impact sound while retaining reliable structural integrity of the ball-striking surfaces, have been met by the bat in accordance with the invention.