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 material inefficiency and potential structural weaknesses, particularly in the arm-to-hub connection area.
Innovation Solution
The chair base 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 strategically placing reinforcement elements between the arms and hub.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If material is evenly distributed throughout the chair base structure, then structural strength is maintained, but material usage increases and manufacturing cost increases
Solution Approach 1:
The patent applies local quality by concentrating material in specific high-stress regions (central hub, arm-to-hub connection areas, and between arms) rather than distributing material uniformly throughout the entire structure. This is achieved through strategic placement of ribs and coring patterns that provide reinforcement exactly where forces are concentrated, while using less material in lower-stress areas.
Solution Approach 2:
The patent segments the structural reinforcement into distinct functional elements: central hub reinforcement, arm-to-hub connection reinforcement, and inter-arm region reinforcement. Each segment addresses specific force concentration points identified in the force analysis, allowing material to be optimized for its specific structural role rather than providing uniform reinforcement throughout.
2Strength
If wall thickness is increased throughout the chair base, then structural strength and durability are improved, but manufacturing cost increases and cooling efficiency during injection molding decreases
Solution Approach 1:
The patent implements local quality in wall thickness by varying the thickness of structural walls based on local stress requirements. Thicker walls are provided at the central hub and arm-to-hub connection areas where forces are concentrated, while thinner walls are used in regions between arms where stress is lower. This optimized wall thickness distribution maintains structural strength while improving injection molding cooling efficiency and reducing material usage.
3Strength
If structural reinforcement is placed centrally within the arms, then arm strength is improved, but material usage increases and the design does not optimize the actual force distribution pattern
Solution Approach 1:
The patent inverts the conventional approach to arm reinforcement by placing reinforcement elements (ribs and coring patterns) not in the center of the arms where one might traditionally expect strengthening, but rather in the regions between the arms at the outer hub. This inverted placement strategy aligns with the discovered force concentration pattern that shows maximum stress occurs between arms rather than at the arm centers or at the hub connection points.
4Ease of manufacture
If uniform structural design is used throughout the chair base, then manufacturing simplicity is maintained, but structural efficiency decreases and material cannot be optimized for actual force patterns
Solution Approach 1:
The patent segments the chair base structure into distinct functional zones with different reinforcement characteristics: the central hub region with its specific rib patterns, the arm-to-hub connection zones with localized reinforcement, and the inter-arm regions with coring patterns. This segmentation allows each zone to be optimized for its specific structural role based on the force distribution pattern, achieving both manufacturing efficiency through systematic design and structural efficiency through localized optimization.
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.