Adjustable Chair Mechanism for Forward Tilt and Posture Alignment

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Solution Overview

Problem

Ergonomic chairs often fail to accommodate users' need for adjusting seating angles beyond the initial 90-110 degrees, leading to discomfort and potential injury due to lack of support and accessibility issues when trying to recline or lean forward.

Innovation Solution

A seating mechanism with a pivotally mounted thigh support and pelvic cradle that allows users to control seating angles without springs or force-balancing devices, using mechanical advantage to counterbalance torso weight, enabling forward tilting and maintaining spine and pelvis alignment, with optional stabilizing links for constant cradle attitude.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If synchronized linkages with heavy springs are used to counterforce the back support, then the chair back can move with the user's torso, but the device complexity increases

Engineering Contradiction:

Improvereclining capabilityVSAvoidmechanism complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates the complex synchronized linkage system with heavy springs from the chair mechanism. Instead, it uses a simpler pivotal connection between the thigh support and pelvic cradle, combined with the user's own body weight and gravity to achieve the reclining function. This reduces mechanical complexity while maintaining adaptability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The chair mechanism uses the user's own body weight and gravity to provide the counterbalancing force needed for reclining, rather than requiring external springs or force-balancing devices. The pelvic cradle pivots freely, allowing the user's torso weight to naturally drive the reclining motion, making the system self-regulating and mechanically simple.

Inventive Principle:

Principle #25Self-service

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

Enables users to adjust seating angles comfortably while maintaining proper posture, reducing thigh force required and ensuring back support throughout the range of motion, improving accessibility to work surfaces.

Implementation Method 1

The first and second pivot axes and the length of the forward end of the first segment are arranged to define a mechanical advantage sufficient to enable the user to use the weight of the thighs to counterbalance the weight of his torso and pelvis through the full range of seating angles

Methodology Applied

Scientific EffectMechanical advantage: Mechanical Advantage

Implementation Method 2

As the pivots approach vertical alignment the force of the thighs necessary to maintain position reduces progressively

Methodology Applied

Scientific EffectGravitational force: Gravitation

Data Source

PatentUS8944507B2Ergonomic adjustable chair mechanisms

Publication Date: 2015.02.03 MILLERKNOLL INC

AI summary

Seating mechanisms enable the user to vary the seating angle of a chair or stool by enabling at least the portion of the chair that supports the thighs to be tilted forwardly to controllably increase the seating angle while maintaining the spine and pelvic region in vertical alignment. The extent of forward tilt is controlled by pressure applied by the user's thighs that also serves to counterbalance the weight of the user's torso.