Racket String Grommet Opening Geometry for Higher Spin
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Solution Overview
Problem
Conventional grommets, such as those described in Japanese Patent No. 5992471, fail to adequately facilitate the movement of main strings in a direction orthogonal to the main strings' initial contact point, resulting in insufficient spin when hitting a spin shot with a racket.
Innovation Solution
A grommet design featuring a tubular portion with a through hole that has an X-shaped opening edge, where the slope of the tangent of the opening edge increases and decreases in specific angles and positions, maximizing the distance between the opening edge and the center of the through hole to enhance main string movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the opening edge of the through hole is designed with a conventional elliptical shape, then the grommet structure is simple, but the main string movement in the second direction is insufficient resulting in reduced spin
Solution Approach 1:
The opening edge of the through hole is designed with an asymmetric shape where the distance from the center to the opening edge varies along the circumference. Specifically, the distance in the second direction (orthogonal to main string direction) is greater than the distance in the first direction (parallel to main string direction), creating an asymmetric configuration that facilitates enhanced main string movement in the second direction while maintaining structural simplicity
2Productivity
If the opening edge shape is modified to enhance spin, then the spin amount increases, but the manufacturing precision requirements increase
Solution Approach 1:
The opening edge shape is defined by specific geometric parameters including the distance from center to opening edge in different directions, and the angles formed by tangents at specific positions. By optimizing these parameters (distance ratio between directions, angle ranges), the design achieves enhanced spin capability while maintaining manufacturability through clearly defined geometric constraints
Data Source
AI summary
A grommet (20) includes a tubular portion (21). The tubular portion extends along a first direction (DR1), and has a tip end (21a) and a base end (21b) located opposite to the tip end in the first direction. The tubular portion is provided with a through hole (21c) extending in the first direction and opening at the tip end and the base end of the tubular portion. When the tubular portion is viewed from the tip end along the first direction, a first opening edge (21d) has a first portion (21da), the first opening edge being an opening edge of the through hole at the tip end of the tubular portion. The first portion has a first end and a second end, the first end being an intersection point of a first line (L1) and the first opening edge, the first line passing through a center (C) of the through hole and along a second direction (DR2) orthogonal to the first direction, the second end being an intersection point of a second line (L2) and the first opening edge, the second line passing through the center of the through hole and along a third direction (DR3) orthogonal to the first direction and the second direction.