Chair with a tilting backrest
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Solution Overview
Problem
Designing chair flexible uprights that harmonize with the chair's line to allow backward bending of the backrest while preventing excessive material stress and ensuring comfort, without yielding at bending zones.
Innovation Solution
The chair features injection-molded plastic uprights with vertically oriented ribs and arched slot-shaped through-cuts that form multiple bending zones, allowing the backrest to move between rest and tilted positions, with stop surfaces that contact each other to prevent further deformation, reducing material stress and enhancing resistance to accidental impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the elasticity of deformable material is used to obtain bending of uprights, then the backrest can move between rest and tilted positions, but excessive stresses occur at the most stressed bending areas causing material yielding
Solution Approach 1:
The upright is divided into multiple segments by transverse through-cuts, creating a series of teeth. This segmentation allows controlled bending at the cut locations while the teeth engage to prevent excessive deformation and material yielding, resolving the contradiction between enabling backward tilt and preventing stress-induced failure
Solution Approach 2:
The through-cuts modify the structural parameters of the upright by creating localized bending zones. These cuts change the stiffness distribution along the upright, allowing elastic deformation in controlled regions while maintaining overall structural integrity and preventing excessive stress concentration
2Ease of operation
If the uprights are made flexible to allow backrest tilting, then comfort is improved, but the design complexity increases due to shaping requirements
Solution Approach 1:
The through-cuts segment the upright structure, creating standardized bending zones that simplify the design process. Instead of designing complex continuous flexible shapes, the segmentation approach allows using simpler upright forms with discrete cut features, reducing design complexity while maintaining comfort
Solution Approach 2:
The upright has different local properties: the regions with through-cuts provide flexibility and bending capability, while the teeth portions maintain rigidity. This local differentiation allows the upright to achieve the required comfort function without requiring the entire structure to be complexly shaped
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 achieves comfortable backward tilting of the backrest while minimizing material stress and risk of breakage, providing better stackability and resistance to accidental bumps compared to previous solutions.
Implementation Method 1
said at least one upright is elastically deformable to allow a movement of the backrest between a rest position and a backward tilted position
Data Source
AI summary
A chair comprising: a support structure, a seat fixed to the support structure, and a backrest connected to the seat by means of at least one upright of plastic material, wherein said at least one upright is elastically deformable to allow a movement of the backrest between a rest position and a tilted position, wherein said at least one upright is provided with at least one vertical rib having at least one localized bending zone wherein at least one through-cut is formed, which allows bending of the vertical rib, and wherein said at least one through-cut has a first and a second stop surface that come into mutual contact in the backwards inclined position of the backrest to stop the backward bending of the upright, wherein said at least one through-cut has the shape of a closed arched slot, which extends generally along a vertical axis of said upright.