Apparatus and methods for the understructure of a chair base
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Solution Overview
Problem
Existing chair base designs face challenges in evenly distributing rotational and vertical forces, leading to inefficiencies in material usage and structural strength, particularly at the arm-hub connection.
Innovation Solution
The design incorporates a central hub connected to evenly spaced arms with a hoop structure featuring ribs and cores that concentrate strength at the outer hub, reducing material usage and enhancing torsional and vertical strength by distributing forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If structural strengthening elements are placed centrally to the arms, then the chair base achieves balanced support, but material usage increases and cooling efficiency decreases
Solution Approach 1:
The patent applies local quality by placing hoop ribs specifically between the arms rather than uniformly distributing structural elements. The hoop ribs are positioned at locations where force concentration experiments showed maximum stress occurs, creating non-uniform local reinforcement that matches the actual stress distribution pattern. This allows strengthening where needed while reducing material in less critical areas.
Solution Approach 2:
The patent employs asymmetry by positioning the hoop ribs offset from the central axis, specifically between the arms rather than centered. This asymmetric placement corresponds to the experimentally determined force concentration pattern, which shows that rotational forces create maximum stress in the regions between arms rather than at arm centers or hub center. The asymmetric rib placement optimizes strength-to-material ratio.
2Strength
If wall thickness is increased to enhance structural strength, then the chair base becomes stronger, but cooling efficiency during injection molding decreases and production costs increase
Solution Approach 1:
The patent applies local quality by varying wall thickness non-uniformly throughout the chair base structure. Thicker walls are positioned specifically at the hoop rib locations between the arms where force concentration experiments showed maximum stress occurs. Other areas maintain thinner wall thickness, optimizing the strength-to-weight ratio and enabling faster cooling during injection molding while maintaining required structural strength.
3Quantity of substance
If material usage is reduced to lower production costs, then manufacturing expenses decrease, but structural strength may be compromised
Solution Approach 1:
The patent applies local quality by concentrating material specifically where stress analysis shows maximum force concentration occurs - namely at the hoop rib positions between the arms. Rather than uniformly reducing wall thickness throughout the entire structure, the design maintains thicker walls only in these critical load-bearing regions while using thinner walls elsewhere, achieving cost reduction through material savings without compromising overall structural strength.
Solution Approach 2:
The patent applies partial action by providing reinforcement only in the specific regions where it is most needed - the hoop ribs between the arms - rather than uniformly strengthening the entire chair base. This partial reinforcement strategy achieves the required strength level with minimal material usage, as the hoop ribs at force concentration points provide sufficient structural support without needing to over-strengthen all areas.
4Stability of the object's composition
If hoop ribs are positioned centrally to the arms, then structural symmetry is maintained, but force concentration is not optimized
Solution Approach 1:
The patent employs asymmetry by positioning the hoop ribs offset from the central axis, specifically in the regions between the arms rather than centered. This asymmetric placement directly corresponds to the experimentally determined force concentration pattern, which shows that rotational forces create maximum stress in the regions between arms rather than at arm centers or hub center. The asymmetric rib placement optimizes strength-to-material ratio.
Solution Approach 2:
The patent applies local quality by positioning hoop ribs specifically between the arms rather than uniformly distributing structural elements. The hoop ribs are positioned at locations where force concentration experiments showed maximum stress occurs, creating non-uniform local reinforcement that matches the actual stress distribution pattern. This allows strengthening where needed while reducing material in less critical areas.
Data Source
AI summary
The embodiments relate to a geometric under structure, central and outer hub for a GFN plastic chair base. The geometric shape and dimensions are critical components to the overall strength of the chair base hub and arms when either vertical or rotational forces are applied at the central hub. The central hub is of sufficient thickness to maintain dimensional stability when the forces are applied. The overall geometry and material composition enable the hub area to be constructed with minimal plastic wall thickness while optimizing the physical strength of the article and facilitating high production rate.