Folding Chair Hinge Geometry for Passive Locking Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing folding chairs lack a secure locking mechanism in both the unfolded and folded positions, leading to instability and aesthetic issues, with existing solutions being cumbersome or obstructive.
Innovation Solution
A tubular structure with coaxial hinge pins featuring a rigid part with a cylindrical groove and cradles that lock the chair in the unfolded position, eliminating the need for straps and enhancing aesthetics by using a metal framework with plastic half-shells for added rigidity and visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lever handle with rack teeth is used to lock the chair in the unfolded position, then the chair can be locked, but the lever handle frequently leaves the rack when the chair is moved, causing the chair to tilt backward and become insecure
Solution Approach 1:
The patent removes the lever handle and rack teeth locking mechanism from the chair structure. Instead, it uses a passive geometric locking system where the hinge pin's position relative to the tube axes automatically locks the chair in the unfolded position through the specific angular arrangement (60-120 degrees) of the tubes, eliminating the need for active locking components that can fail during movement.
Solution Approach 2:
The chair's geometry itself provides the locking function. The hinge pin positioned at a specific distance from the tube axes creates an automatic mechanical lock when the tubes form the X-shape in the unfolded position, without requiring any additional locking mechanism. The structure locks itself through its own configuration.
2Reliability
If a lace or strap is used to lock the chair in the folded position, then the chair can be prevented from unfolding, but the operation is tedious for the user and the laces or straps are aesthetically displeasing
Solution Approach 1:
The patent completely removes laces, straps, or any external fastening elements from the chair design. The folding and locking functionality is achieved entirely through the inherent geometry of the tubular structure and hinge pin arrangement, eliminating the need for separate locking components.
Solution Approach 2:
The locking function is merged into the basic structural components of the chair. The hinge pin and tube arrangement simultaneously provide both the folding mechanism and the locking capability, eliminating the need for separate locking systems.
3Reliability
If link rods are used to lock the chair in the unfolded position, then the chair can be locked, but the link rods form obstacles making it difficult to access the chair, particularly for users with reduced mobility
Solution Approach 1:
The patent removes link rods and armrest structures from the design. The locking is achieved through the hinge pin geometry and tube arrangement, which do not protrude or create obstacles. The user can access and use the chair without encountering any blocking structural elements.
4Reliability
If a lever handle is used for locking, then the chair can be locked, but the lever handle is often not aesthetically pleasing and actuating it may pinch the user's fingers
Solution Approach 1:
The patent removes the lever handle completely from the design. The locking mechanism is passive and geometric, relying on the hinge pin position and tube arrangement rather than an active handle that the user must manipulate, thereby eliminating the risk of finger pinching.
Data Source
AI summary
A folding chair capable of being moved between a folded position and an unfolded position, includes: two units, each of which includes first and second tubes hinged together via a hinge pin; and a canvas sheet, where each assembly of two tubes includes a rigid part at the hinge pin thereof, said rigid part being arranged between two tubes and having: a groove for receiving a tube of the assembly without any degree of freedom; first and second cradles arranged on either side of the hinge pin, such that when the chair is in the unfolded position, the first cradle bears against the upper section of the other tube and the second cradle bears against the lower section of the other tube.