Two-Axis Chair Backrest Joint Using Compressible Foam
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Solution Overview
Problem
Existing backrest designs with two-axis joints using rubber-elastic materials are prone to detachment, leading to safety hazards when the connection becomes loose, and they are too stiff for flexible movement due to the incompressibility of rubber, making them impractical for a compact and flexible connection.
Innovation Solution
The use of compressible foam elements, such as open-pored PUR foam, which are loaded in compression rather than tension, allowing for a flexible and secure connection without the need for fixed or vulcanized connections, and are designed to fill the receiving chamber without play, enabling a compact and resilient joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rubber-elastic material is used to hold the joint in a basic position, then the joint can move relative to one another, but the backrest falls off when the connection becomes loose
Solution Approach 1:
The patent changes the material parameter from rubber-elastic material to compressible foam material. This parameter change allows the material to be loaded exclusively in compression, fundamentally altering the loading conditions and eliminating the need for fixed connections while maintaining both flexibility and reliability.
Solution Approach 2:
The patent replaces the mechanical connection system (screws, vulcanized connections) with a compression-based elastic element system. The compressible foam elements are supported against the receiving chamber, eliminating the need for fixed mechanical connections at the interfaces between the joint plate and elastic elements.
2Ease of operation
If rubber-elastic material is used to hold the joint, then the joint can pivot, but the backrest plate cannot be pivoted compared to the backrest support due to incompressibility
Solution Approach 1:
The patent changes the material parameter from rubber-elastic material to compressible foam material. This parameter change enables the material to be compressed, allowing the joint to pivot while maintaining sufficient rigidity when compressed, thus resolving the contradiction between pivoting capability and joint stiffness.
3Ease of manufacture
If the elastic elements are accommodated loosely in the receiving chamber without fixed connections, then assembly is simplified, but the connection may become loose
Solution Approach 1:
The patent replaces mechanical fastening systems with a compression-based retention system. The compressible foam elements are retained by the geometry of the receiving chamber and the compression force itself, eliminating the need for screws or other fixed connections while maintaining reliability through the compressive load.
Solution Approach 2:
The patent changes the loading condition parameter from tension/compression to exclusively compression. This parameter change allows the elastic elements to be retained without fixed connections, as the compression force naturally retains the elements in the receiving chamber while maintaining connection stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design prevents the backrest from detaching and provides sufficient flexibility and rigidity, ensuring safety and a compact structure, while allowing for easy assembly and aesthetic alignment with the backrest support.
Implementation Method 1
the elastic elements are made of a compressible foam and are supported against the receiving chamber, so that they can pivot about the two pivot axes
Implementation Method 2
an element made of an elastic material holding the joint in a basic position
Data Source
Figure 1
Figure 2~3
AI summary
The backrest has a backrest carrier (10) and a backrest plate (30) fastened pivotably to the carrier by using a two-axle joint (20). The joint has a joint plate (21) that is connected with the backrest plate. Elastic units (22, 23) holding the joint in a normal position, and a retaining chamber (24) connected with the carrier. The joint plate is pivotable around two pivoting axes and is arranged in the retaining chamber between the elastic units that are supported against the retaining chamber. The elastic units are made from a compressible foam material e.g. polyurethane -foam material.