WO2005018757A1

WO2005018757A1 - An improved bat

Info

Publication number: WO2005018757A1
Application number: PCT/GB2004/003614
Authority: WO
Inventors: Roy Jones; Sean Robert Mitchell; Ashley Walter Symes
Original assignee: Loughborough University Enterprises Limited
Priority date: 2003-08-23
Filing date: 2004-08-23
Publication date: 2005-03-03
Also published as: GB0319921D0

Abstract

A bat for use in ball games such as cricket, baseball, golf or other similar games where the ball impacts directly onto the bat comprises a hollow bat having a blade of laminated construction. A method of construction of the bat is also disclosed.

Description

AN IMPROVED BAT

Field of the Invention

The present invention relates to bats.

Background of the Invention

The term bat is to be interpreted throughout this specification as a bat for use in ball games such as cricket, baseball, golf or other similar games where the ball impacts directly onto the bat rather than against a web of strings.

The term laminate construction is to be interpreted broadly but is not intended to include a shell construction of the kind with a single relatively high strength peripheral layer covering a relatively soft filler.

Excelling at sport is no longer just a matter of being physically fit and having a natural ability at your chosen discipline. Scientific investigation into understanding how the physical properties of essential equipment such as, for example, tennis rackets and golf clubs, effect playing performance is now a fundamental part of the process. Today's successful sportsmen combine their own abilities with equipment that has been designed to highlight or downplay these abilities resulting in improved performance overall.

Such design is now borne out of scientific research into materials, impact testing and modelling, and player perception of performance characteristics.

In an attempt to improve bat performance, hollow metal bat structures have been developed. One example of which can be found in GB2067078 filed in 1980 which is concerned with a cricket bat having a blade formed from extruded metal. In this patent document, there is also disclosed the use of filler material to be inserted into the hollow portion of these cricket bat in order to dampen the impact noise. It is also suggested that longitudinal strengthening ribs are employed stretching across the hollow portion, presumably to strengthen the bat in compression on impact.

Laminate bat structures using several plies bonded together are also known and have been employed for example in table tennis bats for many years. Apart from the plies section of the bat, these bats also include a foam cushion on the outside covered by high friction pad, the plies section, the foam cushion and the high friction pad being tightly bonded without any hollow portion between the layers.

Summary of the Invention

According to the broadest independent aspect of the invention there is provided a hollow bat whose blade is of laminated construction.

Since the conventional laminated table tennis rackets and hollow extruded bats have been in the market place for well-over twenty years, the above combination of features is not only new but also non-obvious.

Such a combination of features is advantageous as the mass of the bat is distributed towards the outer surface, increasing the 'twisting' moment of inertia. Greater resistance to twist from off-centre shots results in greater control over the direction of the ball from impacts that are not positioned centrally on the bat face. The bat is perceived as more 'forgiving'.

By re-distributing the mass towards the outer surface, the moment of inertia about the bat's centre of gravity increases. This is known to increase perceived size of the 'sweet spot'.

In this configuration, the mass of the blade may be re-distributed to reduce x and y 'swinging' moments of inertia about the handle. With a lower moment of inertia, the bat will 'feel' lighter and be more manoeuvrable.

Another advantage of this configuration is that a hollow design allows for the bat face to deflect inwards during impact with the ball. The majority of energy transfer occurs in the deflection of the face, rather than through deformation of the ball. Face deflection is more energy efficient and results in greater ball rebound velocity (often referred to as the 'trampoline' effect).

According to a subsidiary aspect of the present invention, there is provided a hollow bat in which the blade is of bonded laminated construction.

Having a bonded laminated construction increases the toughness and strength of the bat. The bond may also act as an additional barrier to the propagation of cracks through the bat.

According to a subsidiary aspect of the present invention, there is provided a bat comprising a first portion of layers having grain boundaries oriented in a first direction and a second portion of layers having grain boundaries oriented in a second direction substantially 90 degrees from said first direction.

Such a feature is advantageous because it reduced the likelihood of cracks propagating through the entire bat. The life expectancy of the bat is thus dramatically increased.

According to a further subsidiary aspect of the invention there is provided a bat wherein at least a portion of the bat's edges is made of a wood of higher durability than the wood employed in the inner portion of the bat.

This configuration is particularly advantageous because it enables specific areas of the blade to have different characteristics from other areas of the blade. For example, the areas prone to fracture can be strengthened by utilising a higher grade wood, whilst the cost of wood of the areas less likely to fracture may be reduced by choosing exclusively for those a lower grade wood. This approach will therefore minimise the overall production costs.

In a further subsidiary aspect, there is provided a method of construction of a bat of the kind defined in claim 1 , comprising the following steps: ^a generating an outer profile template of a bat; ^■ generating an inner profile template of a bat; ■ forming laminate layers and cutting-out a portion from said layers according to the inner profile template; ■ assembling said laminate layers to form a stack with a hollow portion; and ■ machining the outside of the stack according to said outer profile template.

This method is particularly advantageous because it allows the hollow portion to be more accurately generated than would have been the case had the layers first been assembled then hollowed out.

Brief Description of the Invention

A preferred embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings in which:

Figures 1 a and 1 b show an external and internal cut-away perspective view of a computer generated cricket bat in accordance with the invention;

Figures 2a, 2b and 2c show the 'twisting' moment of inertia, the 'swinging' moments of inertia about the handle and the 'sweet spot' of a cricket bat in accordance with the invention;

Figure 3 shows a perspective view of a computer generated model of a cricket bat in accordance with the invention;

Figure 4 shows a computer generated block in accordance with the invention;

Figure 5 shows an internal view of the computer generated block of Figure 2 having a hollow feature in accordance with the invention;

Figure 6 shows a computer generated layer of the hollowed block in accordance with the invention;

Figure 7 shows sheets of wood produced from the computer generated model in accordance with the invention;

Figure 8 shows a block formed from sheets of wood of Figure 7;

Figure 9 shows a perspective view of the finished outer surface of a cricket bat in accordance with the invention;

Figure 10 shows a perspective view of a cricket bat in accordance with the invention.

Detailed Description of the Invention

Figure 1 shows a representation of a Slazenger V800 (a trademark) cricket bat which was computer modelled. Figure 1b illustrates the internal geometry created. In this case, a simple cavity with a 10mm wall thickness on the face of the bat and 8mm wall thickness on the back face.

More complex geometry with varying wall thicknesses or internal structure such as honeycomb or cross-bracing can be generated, if additional strength is required.

A hollow is created through the re-distribution of mass. Table 1 illustrates how the current design compares to the traditional solid willow cricket bat with regard to mass distribution. Birch ply laminate was chosen as the material for the first prototypes. It is twice the density of English willow, the blade is therefore half the volume. The shape of the hollow has been designed so that the centre of mass remains at the same distance from the handle top as would be found in the traditional equivalent. Because of this, the present bat feels very similar to a traditional bat in terms of 'weight' and 'pick-up'. The hollow design would however exhibit improvement to impact performance, due to its hollow structure.

Table 1. Comparison between hollow and solid bat constructions.

Figure 2a shows that the mass of the bat is distributed towards the outer surface, increasing the 'twisting' moment of inertia. Greater resistance to twist from off- centre shots results in greater control over the direction of the ball from impacts that are not positioned centrally on the bat face. The bat is perceived as more 'forgiving'.

Figure 2b shows that the design allows the re-distribution of mass to reduce x and y 'swinging' moments of inertia about the handle. With a lower moment of inertia the bat will 'feel' lighter and be more manoeuvrable.

Figure 2c shows that by re-distributing the mass towards the outer surface the moment of inertia about the bat's centre of gravity increases. This is known to increase perceived size of the 'sweet spot'. Many sporting implements currently employ hollow design for this reason.

A method of building the bat up in a series of thin layers was chosen for the manufacture of the hollow bats, as it provided a number of significant advantages which are described below:

Design Flexibility

Each layer used describes the internal and external geometry through a section of the cricket bat. It is possible for each layer to describe complex patterns, such as cross bracing or honeycomb structures, which when added together create a complex 3 dimensional geometry. Therefore, the design is not constrained by the conventional machining of a block. For example, if a boring process was used to create the hollow out of a solid block, then the shape of the hollow would be limited to its bore diameter and length. The internal geometry would not follow the external geometry, to create a uniform wall thickness and true shell like structure, as observed in golf club driver heads and aluminium baseball bats.

Layer orientation

Wood is an isotropic, in that its strength is dependent upon grain orientation. As a traditional blade is made from one piece of willow, the grain orientation is in one direction and cracks that appear in the face of the bat through repeated impacts, are free to travel the length and also can travel into the depth of the bat. Willow is a resilient wood with long interwoven fibres, but there is no real mechanism to ensure cracks are arrested.

In laminate construction, neighbouring layers can be oriented at right angles to each other, so that the orientation of grain is in two directions, this guards against cracks running through the depth of the bat and also provides similar bending strength characteristics in two directions.

In addition, laminate construction provides the means to orient the major fibre axis along the inbound line of impact i.e. normal to the face of the blade instead of the conventional, longitudinal orientation of the fibre axis. Wood fibres are strongest in tension and compression along this axis, and it may prove beneficial to orient the wood fibres in this manner. Distribution of wood characteristics

Wood is an entirely natural composite material. In a 'cleft' of wood, used to manufacture the blade of a cricket bat, its structure will not be entirely regular. Subtle changes in climate, soil content, age and the onset of disease can all effect the resulting structure of the wood observed on a macroscopic level. Two clefts, even from the same tree, will never look identical as each has its unique structure. At present bat manufacturers grade the quality of the cleft on aesthetics terms. A cleft with an obvious irregularity such as a 'knot', 'fleck' or with a proportion of 'heart' wood will be graded down. This method of grading has no bearing upon playing performance. In addition to looking different, it is widely accepted that two bats manufactured identically from the same tree, will rarely 'feel' and perform identically again due to the inherent irregularity observed in the structure of wood.

Laminated bat manufacture adheres many thin layers of wood to form the body of the cricket bat. The process combines many different layers, from different trees of the same species in different orientations. Any irregularities that may have existed in the original tree, have been cut into thin layers and spread over a wide surface area of sheet material. Within a laminated bat, irregular wood structure has been more evenly distributed within and also between each product. This results in a bat which has a more regular construction, and also playing properties will be more consistent between different bats.

Material grading

The laminated bat is built from many thin layers adhered together. It is therefore possible for the design to employ layers of different wood species in order to get different characteristics in areas of the bat where those layers reside. For instance, if the cricket bat requires very tough edges to increase durability further, then layers of a more durable wood can be arranged to exist along the edges of the bat. Whilst a wood with more performance orientated characteristics can remain within the central region of the bat. In terms of reducing cost, it would be possible to arrange the layers so that a cheaper wood was used to build the non striking portion of the bat, whilst the more expensive, higher performance material was used to build the front face.

Addition of resin

All layers within the bat are adhered to each other. A urea-formaldehyde based resin has been used, for its 'stronger than wood' bond properties. One method by which an adhesive bonds is through mechanical interlock formed by the resin entering the voids present on, and just below, the bonding surface. Wood as a hollow composite naturally provides many sites for this bond to take place. The strength of the wood matrix improves as its voids are filled with resin.

Method of laminated bat manufacture

A computer generated model of a cricket bat is generated (Figure 3). The handle is subtracted from the model and a hollow feature is designed within the blade portion.

A block is generated (Figure 4), the hollow feature is subtracted from inside the block (Figure 5) and it is then 'sliced' to produce thin layers (Figure 6). The internal hollow is now defined in cross-section through each layer. Cutter paths defining the hollow boundary are generated for each layer.

Sheets of birch ply of the same thickness as the computer generated model are cut to the shape of the block. The hollow is cut from each layer with a CO2 laser cutting machine using the generated cutter paths.

Layers are 'layed up' in the correct order to make a physical block with the hollow geometry inside (Figure 7), resin is applied to each layer and the block is cured within a press to ensure complete surface contact between layers (Figure 8).

The outside shape of the hollow cricket bat is machined out of the block using a CNC 3 axis vertical milling machine with the tools paths generated from the external geometry of the bat computer model. The resulting bat blade is shown in Figure 9.

The handle is added to the blade, using traditional bat manufacturing technology to result in a finished bat such as that presented in Figure 10.

The scope of the present invention is defined in the claims that now follow.

Claims

1. A hollow bat whose blade is of laminated construction.

2. A hollow bat according to claim 1 in which the blade is of bonded laminated construction.

3. A bat according to either preceding claim, comprising a first portion of layers having grain boundaries oriented in a first direction and a second portion of layers having grain boundaries oriented in a second direction substantially 90 degrees from said first direction.

4. A bat according to any preceding claim, wherein at least a portion of the bat's edges is made of a wood of higher durability than the wood employed in the inner portion of the bat.

5. A bat substantially as described with reference to and as illustrated in any appropriate combination of the accompanying text and drawings.

6. A method of construction of a bat of the kind defined in claim 1 comprising the following steps:

■ generating an outer profile template of a bat; ^■ generating an inner profile template of a bat; ^■ forming laminate layers and cutting-out a portion from said layers according to the inner profile template; ■ assembling said laminate layers to form a stack with a hollow portion; and ■ machining the outside of the stack according to said outer profile template.