Toothed Locking Joint for Wheelchair Rest Position Stability
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Solution Overview
Problem
Existing lockable joints, such as ball joints, fail to maintain position under sustained loads and impacts, particularly in applications like wheelchairs for disabled individuals where stability is crucial.
Innovation Solution
A lockable joint design featuring a body with a concave surface and a clamp with moveable jaws, where at least one jaw has teeth that bite into the body's surface to resist movement, combined with a rod coupling the jaws and made of materials with varying hardness for enhanced locking and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional ball joints are used, then the structure is simple, but the joint cannot maintain position under sustained loads and impacts
Solution Approach 1:
The patent applies local quality by introducing teeth only at the engagement interface between the clamp and body, rather than modifying the entire joint structure. These localized teeth provide enhanced biting engagement and position maintenance under load, while the rest of the joint maintains its simple ball-and-socket geometry for ease of movement and adjustment.
Solution Approach 2:
The patent utilizes spherical surfaces for the ball joint components, with the clamp featuring a concave spherical surface and the body featuring a convex spherical surface. This curvature enables smooth multi-directional adjustment while the added teeth provide localized gripping engagement to prevent slippage under sustained loads and impacts.
2Strength
If teeth are added to the clamp jaws, then resistance to movement under load improves, but manufacturing complexity increases
Solution Approach 1:
The teeth are implemented as localized features only at the engagement surface of the clamp jaws, rather than modifying the entire clamp structure. This localized approach provides the necessary biting engagement to resist movement under severe loads while minimizing the increase in manufacturing complexity, as only a portion of the clamp requires tooth formation.
3Adaptability or versatility
If the aperture is made wider than the rod, then relative motion when not locked is enabled, but stability during operation may be compromised
Solution Approach 1:
The patent uses spherical engagement surfaces that provide natural stability through geometric constraint. The curved surfaces ensure that even with a wider aperture allowing rod movement, the joint maintains operational stability because the spherical geometry constrains the movement paths and prevents lateral displacement during loaded conditions.
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 joint effectively maintains position under severe loads and impacts, allowing for adjustable positioning of components like footplates and headrests in wheelchairs, ensuring stability and safety even during user spasms or changes in load direction.
Implementation Method 1
at least one jaw comprises at least one tooth configured to bite into the body as the clamping force is applied, thereby resisting movement between the body and the clamp
Implementation Method 2
the first and second jaws being configured to engage respectively the concave and convex surfaces of the body when applying a clamping force thereto
Implementation Method 3
The first jaw may be disc-shaped, while the second jaw may be annular. The disc may be configured to have such elasticity as to allow the joint to stay locked even if the clamp actuator slackens.
Data Source
AI summary
Apparatus for connecting together two objects comprises:a body for attachment to a first object and having a concave surface and a corresponding convex surface;a clamp for attachment to a second object and having a first jaw and a second jaw moveable relative to the first jaw, the first and second jaws being configured to engage respectively the concave and convex surfaces of the body when applying a clamping force thereto,wherein at least one jaw comprises at least one tooth configured to bite into the body as the clamping force is applied, thereby resisting movement between the body and the clamp.A chair, in particular a wheelchair for disabled persons, has one or more rests mounted on apparatus as detailed above.