Characterization of a ball game racket string pattern

Abstract

The present invention relates to a method for characterizing a string pattern of a ball game racket frame as well as to the representation of a string pattern image of a strung ball game racket frame.

Claims

1. A method for characterizing a string pattern of a ball game racket frame strung in a string bed plane, wherein the intersecting strings of the string pattern form closed cells, said method comprising the steps of (a) creating an image of the string pattern with a viewing axis perpendicular to the string bed plane; (b) automatically determining closed cells in at least one area of the string pattern from the image; (c) automatically determining the respective size of the determined closed cells; (d) classifying the closed cells according to their size; (e) representing the string pattern image along with an indication of the class of the closed cells.

2. The method according to claim 1, wherein the classification is graphically visualized in the representation, preferably by assigning one or more of the following graphical parameters to predetermined classes of the classification: color value, tonal value, hatching.

3. The method according to claim 1, wherein the classification is based on one or more of the following size properties of the cells: area of a cell, length of one or more lateral edges of a cell, length ratio of two lateral edges of a cell.

4. The method according to claim 1, wherein step (b) comprises: (b1) converting the image of the string pattern into a binary pixel image, wherein the threshold value is selected such that a first value is assigned to each of the pixels of the closed cells, and preferably also to each of the pixels of the frame, and a second value is assigned to each of the pixels of the strings; and (b2) identifying the closed cells as those contiguous areas of the binary image which comprise pixels of the first value and are enclosed by pixels of the second value.

5. The method according to claim 4, wherein step (c) comprises: (c1) determining the number of pixels of each area identified as a closed cell; and (c2) converting each determined number of pixels to the size of the respective closed cell.

6. The method according to claim 5, wherein step (c2) is performed on the basis of a previously taken image of a scale with identical image settings.

7. The method according to claim 4, wherein step (c) comprises: (c1) for each area identified as a closed cell, determining a rectangle that best approximates that area; and (c2) determining one or more of the following size properties of the rectangle: area of the rectangle, length of one or more lateral edges of the rectangle, length ratio of two lateral edges of the rectangle.

8. The method according to claim 7, wherein step (c2) is performed on the basis of a previously taken image of a scale with identical image settings.

9. The method according to claim 1, comprising the additional step of (f) determining the playing properties of the ball game racket frame on the basis of the representation of the string pattern image according to steps (d) and/or (e).

10. The method according to claim 1, comprising the additional step of (g) determining at least one alternative string pattern that approximates the playing characteristics of the represented string pattern image according to steps (d) and/or (e).

11. The method according to claim 1, comprising the additional steps of (h) repeating the method for at least one further ball game racket frame; (i) comparing the determined string pattern images according to steps (d) and/or (e) and optionally the playing properties according to step (f).

Description

(1) In the following, the present invention is explained in more detail by means of some exemplary string patterns shown in the Figures, in which:

(2) FIG. 1A shows a string pattern image according to a first example;

(3) FIG. 1B shows a representation of the string pattern image according to FIG. 1A including the classification according to the invention;

(4) FIG. 2A shows a string pattern image according to a second example;

(5) FIG. 2B shows a representation of the string pattern image according to FIG. 2A including a classification according to the invention;

(6) FIG. 3A shows a string pattern image according to a third example;

(7) FIG. 3B shows a representation of the string pattern image according to FIG. 3A including a classification according to the invention;

(8) FIG. 4A shows a string pattern image according to a fourth example;

(9) FIG. 4B shows a representation of the string pattern image according to FIG. 4A including a classification according to the invention;

(10) FIG. 5A shows a string pattern image according to a fifth example;

(11) FIG. 5B shows a representation of the string pattern image according to FIG. 5A including a classification according to the invention;

(12) FIG. 6A shows a string pattern image according to a sixth example; and

(13) FIG. 6B shows a representation of the string pattern image according to FIG. 6A including a classification according to the invention.

(14) FIGS. 1A to 6A respectively show, by way of example, six different string patterns which differ significantly from one another in terms of their playing properties. However, as revealed by a comparison of FIGS. 1A to 6A, it is extremely difficult to recognize these differences with the naked eye, let alone to quantitatively compare the string patterns.

(15) FIGS. 1B to 6B respectively show the same string patterns as FIGS. 1A to 6A as well as the classifications according to the invention, wherein in these examples the individual meshes of the string pattern (i.e., the closed cells) have been colored with different shades of gray according to their respective area content. The scale ranges from 7.0 mm.sup.2 (white) to 18.0 mm.sup.2 and larger (black).

(16) As revealed by FIGS. 1B to 6B, the six string patterns can be clearly distinguished from one another by means of the representation of the classification. For example, in the case of FIGS. 1, 2 and 5, the area with the smallest meshes is relatively narrow in width but extends much further in the longitudinal direction than in the case of FIGS. 3, 4 and 6. In FIGS. 3 and 4, these areas with the smallest meshes have a similar, relatively wide shape which, however, is mirror-inverted and in FIG. 3 is oriented more in the direction of the racket heart, whereas in FIG. 4 this area is clearly shifted in the direction of the head end.

(17) FIGS. 4 and 6 show qualitatively similar patterns, but the variation from light to dark is much more pronounced in the case of FIG. 6, suggesting that this string pattern varies much more between very small and very large meshes.

(18) In fact, these different representations also allow conclusions to be drawn about the respective playing properties of the ball game racket. The more open a string pattern is, the softer it behaves in contact with the ball and the lower the energy dissipation is due to flattening of the ball during contact with the ball. Therefore, an open string pattern, such as the example according to FIG. 5, has a higher acceleration capacity than a denser one, such as the example according to FIG. 6. As Brody points out (cf. Dr. H. Brody, Unforced Errors and Error Reduction in Tennis, in Professional Tennis Registry), more ball acceleration, however, often means less directional control in play, because as the ball acceleration of the racket increases, the player will reduce or slow down his/her swing, and thus the speed of the struck ball will be determined more by the angle of incidence and angle of exit and less by his/her own swing direction.

(19) However, conclusions about the playing behavior can also be drawn from the dynamics of the string pattern along the longitudinal and/or transverse axis. For example, a string pattern that is relatively uniformly open in width, such as the example according to FIG. 1, has a very high acceleration capacity in the case of hits on the longitudinal axis of the racket, which, however, significantly decreases in the case of hits outside the longitudinal axis of the racket. This is due to the fact that, in the case of hits outside the longitudinal axis of the racket, the racket undergoes rigid-body movements such as rotation about the longitudinal axis and deformations such as torsion, whereby energy is taken away from the struck ball. However, since the string pattern outside this longitudinal axis of the racket is approximately as dense and thus as stiff as on the longitudinal axis of the racket, this leads to a loss of ball acceleration.

(20) In contrast, in the case of a string pattern that is configured dynamically along the width, as in the example according to FIG. 2, the ball can be better accelerated there via the string pattern due to the more open design of the string net outside the longitudinal axis and thus compensate for the above effects such as rigid body movement and torsion. Hence, such a string pattern has less acceleration capacity than a string pattern according to FIG. 1 in the case of hits on the longitudinal axis of racket, but a higher acceleration capacity in the case of hits outside the longitudinal axis of the racket. It is therefore more forgiving, so to speak, with regard to hitting-point deviations along the width of the racket.

(21) Since there are quite different hitting points for the maximum acceleration capacity depending on the kinematics of the swing (volley: mainly translational movement, groundstroke: strongly rotational component), it also makes sense to vary the string pattern along the longitudinal axis in different ways. For example, in the version according to FIG. 3, the densest point is positioned in the lower half of the racket and therefore the racket actually is well suited for volleys, since they should be hit primarily in this area. In contrast, in the version according to FIG. 4, the densest point is located in the upper half of the racket and the racket is therefore primarily suitable for groundstrokes comprising a strong rotational movement component, which should be hit above the center of the racket (half the length of the racket head).