Chair Seat-Back Linkage for Low-Effort Synchronized Tilt
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Solution Overview
Problem
Existing chair synchronizing devices are mechanically complex and uncomfortable for users, as they require significant force to oppose weight and do not effectively synchronize the tilt of the seat and back frames, leading to uneven adjustments and discomfort.
Innovation Solution
A device with a four-bar linkage system where the back frame is integral with the front crank and a rear crank is connected to the seat frame via a spring, allowing for adjustable tilt based on user weight, ensuring comfortable postures by synchronizing the tilt of the seat and back frames with a geometry that allows simultaneous raising or pulling down of both seat portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a four-bar linkage with a lever having a fulcrum on the base is used to synchronize the seat frame tilt, then the mechanical structure is simple, but the user must exert considerable force onto the chair back to oppose their own weight
Solution Approach 1:
The patent inverts the conventional four-bar linkage configuration by making the back frame integral with the front crank instead of the rear crank. This inversion changes the mechanical advantage distribution, allowing the user's weight to more effectively assist the tilting action rather than requiring the user to actively oppose their own weight through a lever system.
Solution Approach 2:
The patent modifies the geometric parameters of the four-bar linkage, specifically the lengths and positions of the cranks and links. By optimizing these parameters, the mechanical advantage is adjusted to reduce the effort required by the user while maintaining synchronization between the seat and back frame tilts.
2Device complexity
If the four-bar linkage geometry follows conventional designs, then the structure is straightforward, but the front and rear portions of the seat do not raise or pull down simultaneously and equally during back tilt variation
Solution Approach 1:
By making the back frame integral with the front crank rather than the rear crank, the patent inverts the force transmission path. This ensures that when the user tilts the back frame, the motion is transmitted through the four-bar linkage to simultaneously raise or pull down both the front and rear portions of the seat frame in a synchronized manner.
Solution Approach 2:
The patent employs asymmetric configuration of the four-bar linkage where the front and rear cranks are tilted in different directions relative to the vertical. This asymmetric design, with the front crank tilted anticlockwise and the rear crank tilted clockwise (or vice versa), creates the mechanical condition for simultaneous and equal movement of both seat portions during back tilt.
3Force
If the cranks are tilted in opposite directions relative to the vertical, then the linkage provides mechanical advantage, but the front portion of the seat raises while the rear portion pulls down, creating an unpleasant sensation for users
Solution Approach 1:
The patent inverts the conventional arrangement by making the back frame integral with the front crank. This inversion, combined with the specific asymmetric tilt directions of the cranks, ensures that both the front and rear portions of the seat move in the same direction (both raise or both pull down) during back tilt, eliminating the unpleasant sensation of one portion moving opposite to the other while still maintaining mechanical advantage.
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
The solution provides a mechanically simple and comfortable user experience by allowing effective tilt regulation of the chair back and seat, ensuring comfortable postures and preventing unpleasant sinking sensations during tilting, while maintaining precise control over seat configurations.
Implementation Method 1
elastic means for returning the seat frame towards the support, preferably composed of at least one spring
Implementation Method 2
at least one first - front - crank hinged to such a support and a front portion of the seat frame, and at least one second - rear - crank hinged to such a support and a rear portion of the seat frame, such first and second crank constituting a four - bar linkage with the seat frame
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Device (1 ) for synchronizing the tilt of the back and the seat of a chair, of the type comprising a back frame (13), a seat frame (2) and a support (5) constrained to, or coincident with, the base (14) of the chair, as well as at least one first crank (3) hinged (6, 7) to the support (5) and a front portion (2f) of the seat frame (2), and at least one second crank (4) hinged (8, 9) to the support (5) and a rear portion (2r) of the seat frame (2), so that the afore said at least one first and one second crank (3, 4) constitute a four - bar linkage with the seat frame (2). Advantageously, the device (1 ) provides that the back frame (13) is integral with the afore said at least one first crank (3).