Chair Backrest Elastic Joint Design for Increased Torque and Stability
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Solution Overview
Problem
Existing chair designs with elastic joints for pivoting backrests face limitations in providing sufficient elastic force to counteract backward thrust, as elastic elements like helical compression springs have limited lever arm and thus torque, making them ineffective in maintaining the backrest's position.
Innovation Solution
The chair incorporates an elastic joint design with a helical spring housed within a bushing, featuring a connecting rod and compression member with a forward-displaced articulation axis, increasing the lever arm and torque to counteract backward thrust, and includes a ring and upper attachment for enhanced stability and a protective element to prevent pinching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If helical compression springs are arranged coaxially to the side uprights of the backrest, then the structure is simple, but the lever arm for spring compression is limited and elastic torque is insufficient
Solution Approach 1:
The invention moves the articulation axis of the connecting rod forward, displacing it from the longitudinal axis of the spring. This dimensional displacement creates a perpendicular distance (lever arm) between the spring's longitudinal axis and the articulation axis, transforming the force application from a coaxial arrangement to an offset arrangement that generates torque through moment arm mechanics.
Solution Approach 2:
The connecting rod acts as an intermediary element between the helical spring and the backrest assembly. It transfers the axial compression force from the spring and converts it into rotational torque about the articulation axis, enabling the spring to effectively counteract the backward thrust on the backrest.
2Device complexity
If elastic elements deformable by bending are used, then the structure is simple, but the elastic force opposing backward thrust is limited
Solution Approach 1:
The invention replaces bending-deformable elastic elements with a helical compression spring system. The helical spring provides elastic force through axial compression rather than bending deformation, significantly increasing the available elastic force while maintaining structural simplicity through the well-established spring mechanism.
3Force
If the lever arm for spring compression is increased, then elastic torque increases, but the device complexity increases
Solution Approach 1:
The invention merges the spring housing (bushing) with the articulation mechanism for the connecting rod. The bushing serves dual functions: guiding the connecting rod's rotation and housing the helical spring. This integration achieves the torque multiplication function without adding separate complex components, as the articulation axis and spring mounting are combined in a single structural element.
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 significantly increases the elastic torque applied to the backrest, effectively counteracting user-applied backward thrust, ensuring robust and stable operation while preventing excessive backward inclination.
Implementation Method 1
an elastic element, which allows an inclination between the upper support and the lower support
Implementation Method 2
with helical compression springs arranged coaxially to the side uprights of the backrest
Implementation Method 3
The connecting rod 66 has a lower end 68 articulated to the compression member 46 and an upper end 70 articulated to the upper attachment 80 with an articulation axis C forward of the longitudinal axis A of the spring, increasing the lever arm
Data Source
AI summary
A chair having a fixed support structure including two side uprights, a backrest having two side portions, and a pair of elastic joints connecting said side portions of the backrest to said side uprights, wherein each of said elastic joints comprises: a bushing fixed to a respective side upright, a helical spring having a longitudinal axis, the helical spring having an upper end resting against a front wall of the bushing, a compression member resting against a lower end of the spring, an upper attachment fixed to a corresponding side portion of the backrest, and a rigid connecting rod having an upper end and a lower end.