Office Chair Spring Force Adjustment With Stepwise Detent Locking

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Solution Overview

Problem

Existing office chair mechanisms for adjusting spring force to accommodate different user weights result in sudden engagement and jerking when the backrest is inclined, requiring precise alignment and additional user actions.

Innovation Solution

A device where the articulation axis is permanently locked in one of the locking recesses and adjusted step-by-step between adjacent positions using a manual drive with a planetary gear mechanism, ensuring smooth adjustment without sudden engagement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the articulation axis is designed to engage with detent depressions during backrest inclination, then the spring force can be adjusted for different user weights, but the engagement causes sudden jerking and requires precise alignment

Engineering Contradiction:

Improveadjustment of spring force for different user weightsVSAvoidsmooth operation during backrest inclination

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The detent bearing is segmented into multiple detent depressions arranged along its circumference, allowing the articulation axis to engage at different positions. This segmentation enables discrete adjustment of the spring force while maintaining smooth operation between adjustments, as the axis engages only at predetermined positions rather than continuously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A cam mechanism acts as an intermediary between the articulation axis and the detent depressions. The cam profile is designed to guide the articulation axis smoothly into engagement with the detent depressions, eliminating sudden jerking. The cam gradually transitions the axis from one engagement position to another, providing a smooth user experience while maintaining the adjustable spring force capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If the articulation axis is permanently locked in one position, then smooth operation is achieved, but the spring force cannot be adjusted between different user weights

Engineering Contradiction:

Improvesmooth operation during backrest inclinationVSAvoidadjustment of spring force for different user weights

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The system transitions from a static locked position to a dynamic adjustable position. The articulation axis is designed to be temporarily disengageable from one detent depression and engageable with another, allowing the spring force to be dynamically adjusted for different user weights. This dynamic capability is achieved through the cam mechanism that facilitates smooth transition between engagement positions without requiring forceful manipulation.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If manual adjustment mechanism is added to change articulation axis position, then spring force adjustment is enabled, but device complexity increases

Engineering Contradiction:

Improveadjustment of spring force for different user weightsVSAvoidcomplexity of adjustment mechanism

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The adjustment function is merged with the existing backrest inclination mechanism. The cam mechanism that guides the articulation axis into detent depressions during normal inclination is also used to facilitate adjustment between different detent positions. By combining these functions, the patent avoids adding a separate complex adjustment mechanism while still enabling spring force adjustment for different user weights.

Inventive Principle:

Principle #5Merging (Combining)

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 smooth adjustment of spring force without jerking, accommodating varying user weights without additional user actions, ensuring a comfortable and consistent reclining experience.

Implementation Method 1

A gear connected to a hand wheel engages the toothed inner surface of the elongate curved member. Turning the handwheel changes the position of the linkage axis relative to the detent bearing.

Methodology Applied

Scientific EffectPlanetary gear mechanism: Epicyclic Gearing

Data Source

PatentEP2070445B1Device to adjust the spring force of an office chair

Publication Date: 2010.10.20 SEDUS STOLL

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AI summary

The device has a detent bearing with detent recesses for an articulation axle of a spring (70). A sun gear, a hollow wheel and a slide bearing are coupled with a hand wheel and a drive axle such that the sun gear, the hollow wheel and the slide bearing are driven until the articulation axle is disengaged from one of the recesses, and the sun gear, a planet wheel and a pivoted lever are driven until the articulation axle is adjusted and engaged in the adjacent recess during the actuation of the hand wheel and the drive axle.