Tennis Racquet String Bed with Fewer Cross Strings

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Solution Overview

Problem

Existing tennis racquets face challenges in imparting sufficient spin to a ball while maintaining a large sweet spot and maneuverability, often resulting in premature string breakage and increased moment of inertia due to conventional designs that prioritize cross strings over main strings.

Innovation Solution

A tennis racquet design featuring a string bed with fewer cross string segments than main string segments, optimized spacing, and a non-circular head shape to enhance spin and sweet spot performance without increasing the racquet's polar moment of inertia, using a frame with a hoop size between 93 and 120 square inches and string segments made of polyester monofilament material.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the number of cross string segments is increased to enhance structural stability, then the racquet frame support is improved, but the spin rate and main string deflection are reduced

Engineering Contradiction:

Improvestructural stabilityVSAvoidspin rate

Core Design Contradiction:

Stability of the object's compositionVSSpeed

Solution Approach 1:

The patent inverts the conventional string bed configuration by having fewer cross string segments than main string segments. This reversal allows the main strings to have greater freedom of movement and deflection, thereby increasing spin rate while the remaining cross strings provide sufficient structural support to maintain frame stability.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the numerical parameters of the string bed configuration by reducing the number of cross string segments relative to main string segments. This parameter change creates larger spacing between cross strings, allowing increased main string deflection and snapback velocity, which directly improves spin rate without compromising overall structural integrity.

Inventive Principle:

Principle #35Parameter changes

2Area of stationary object

If the head size is increased to enlarge the sweet spot, then the sweet spot area is improved, but the polar moment of inertia increases reducing maneuverability

Engineering Contradiction:

Improvesweet spot areaVSAvoidpolar moment of inertia

Core Design Contradiction:

Area of stationary objectVSForce

Solution Approach 1:

The patent employs an asymmetric head shape where the longitudinal dimension is significantly greater than the transverse dimension (ratio of at least 6.5:1). This asymmetric configuration enlarges the sweet spot area along the longitudinal axis while minimizing the increase in polar moment of inertia, thereby improving both sweet spot size and maneuverability compared to conventional symmetric head shapes.

Inventive Principle:

Principle #4Asymmetry

3Power

If the tension of the racquet strings is increased to improve power and responsiveness, then the coefficient of restitution is improved, but the string breakage risk increases

Engineering Contradiction:

Improvecoefficient of restitutionVSAvoidstring durability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies local quality by creating zones of varying string density and tension characteristics. The larger spacing between cross strings creates localized areas with different mechanical properties, allowing the string bed to provide high power and responsiveness in impact zones while reducing overall string stress and breakage risk through the distributed, lower-density configuration.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9339699B2Racquet configured with fewer cross strings than main strings

Publication Date: 2016.05.17 WILSON SPORTING GOODS CO(US)

AI summary

A racquet includes polyester, monofilament racquet string and a frame extending along a longitudinal axis and including a head portion coupled to a handle portion. The head portion includes a hoop having inner and outer peripheral walls. The hoop defines a head size having maximum longitudinal and transverse dimensions, a, and, b, respectively. The dimension a is at least 1.2 times the dimension b. The inner peripheral wall includes string holes. The string has a diameter within the range of 1.10 to 1.55 millimeters. The string forms a string bed of interlaced main and cross string segments. Each of the cross segments transversely extends from one of the string holes to another, and each of the main segments longitudinally extends from one of the string holes to another. The string bed has at least one more main segment than cross segment. At least one of the main segments contacting the tennis ball exhibits a snap back velocity of at least 1 meter per second.