Chair Backrest Preload Linkage for Precise Tilt Resistance
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Solution Overview
Problem
Existing chair backrest adjustment systems fail to provide precise control over spring resistance, leading to uncomfortable tilt positions for users outside the standard weight range, due to complex constructions and limited adjustment capabilities.
Innovation Solution
A device featuring a first connecting rod and crank mechanism that allows for precise adjustment of spring preload by varying the point of application of the returning force, using a cam device to modulate the relationship between the user's weight and spring resistance, enabling comfortable tilt positions for users of different weights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a lever system with slider is used to adjust spring resistance, then the resistance can be adjusted for different user weights, but the construction becomes complicated and precise adjustment becomes difficult
Solution Approach 1:
The adjustment mechanism is segmented into discrete positions using a rack and pinion system, where the pinion gear engages with teeth on the rack to provide distinct, predetermined adjustment positions. This segmentation simplifies the construction compared to continuous adjustment systems while still providing multiple resistance levels for different user weights.
Solution Approach 2:
The patent replaces the complex slider-on-lever mechanical system with a gear-based mechanism. The pinion gear rotating on the fulcrum engages with the rack attached to the lever, substituting a simpler rotational motion system for the more complex linear sliding system, thereby reducing construction complexity while maintaining adjustment functionality.
2Device complexity
If a short lever is used in the adjustment system, then the construction is simpler, but precise adjustment becomes difficult because small pin displacements cause large resistance variations
Solution Approach 1:
The system uses a dynamic adjustment mechanism where the pinion gear can rotate to change the effective lever arm length. By rotating the pinion, the point of force application moves along the rack, dynamically adjusting the mechanical advantage. This allows precise control over the resistance adjustment sensitivity, enabling small adjustments even with a relatively short lever structure.
Solution Approach 2:
The patent changes the geometric parameters of the adjustment mechanism by allowing the pinion gear to rotate to different angular positions. This changes the effective lever arm length and the point of engagement with the rack, thereby adjusting the sensitivity of the resistance change. This parameter variation enables precise adjustment without requiring a long lever.
3Device complexity
If fixed backrest positions are used, then the system is simpler, but users outside standard weight ranges cannot achieve comfortable positions
Solution Approach 1:
The adjustment mechanism serves multiple functions: it adjusts both the backrest tilt angle and the spring resistance simultaneously. The single rack-and-pinion system controls both the lever position (affecting tilt) and the spring preload (affecting resistance), making the system universal for users of different weights without requiring separate adjustment mechanisms for each function.
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 easy and precise control over the backrest tilt resistance, allowing users of varying weights to achieve comfortable seating positions with fewer sturdy elements, ensuring reliability and cost-effectiveness.
Implementation Method 1
elastically constrained to the base frame in correspondence to at least one point of application of the returning force applied by the spring onto the backrest frame
Implementation Method 2
a cam device to modulate the relationship between the user's weight and spring resistance
Data Source
AI summary
A device for adjusting the tilt of a chair backrest having a backrest frame rotatable with respect to the base frame of the chair is provided. The device includes elastic means for returning the backrest and/or countering the rotation thereof, in addition to means for controlling the preload of the elastic means. The means for controlling the preload include at least one first connecting rod and at least one first crank. The first connecting rod is hinged to the first crank and constrained to the elastic means so as to move the point of application of the returning and/or countering force with respect to the backrest. Adjusting means to adjust the position of the first crank determine at least two distinct stable positions of the first crank corresponding to two distinct positions of the mentioned point of application of the returning and/or countering force with respect to the base frame.