Stretchable Bowden Cable Tensioning for Low-Friction Medical Aids

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Solution Overview

Problem

Conventional cable pulleys in medical and sports aids cause friction and jamming issues, particularly in deflection areas, leading to damage of the aid's fabric and potential skin irritation.

Innovation Solution

Employing a Bowden cable with a stretchable sheath, allowing the core to move with low friction and adapt to length changes, eliminating the need for a fixed sheath length.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a conventional Bowden cable with a non-stretchable sheath is used, then the cable can transmit tensile forces along curved paths, but the sheath cannot adapt to length changes when the core is used as a tensioning element

Engineering Contradiction:

Improveadaptability to length changesVSAvoidstructural stability of sheath

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The sheath is designed with a stretchable section that can dynamically change its length to accommodate the extension and retraction of the core during tensioning operations. This dynamic adaptation allows the sheath to maintain its functional relationship with the core while permitting the necessary length variations for effective tensioning.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The sheath is divided into different sections: a stretchable section that can expand and contract, and a pressure-resistant section that maintains structural integrity. This segmentation allows different parts of the sheath to perform different functions - the stretchable portion adapts to length changes while the rigid portion provides structural stability and force transmission.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If simple cable pulleys with ropes or cords are used, then the tensioning mechanism is simple, but the ropes rub against the medical device or sports aid causing friction, fabric damage, and skin irritation

Engineering Contradiction:

Improvesimplicity of tensioning mechanismVSAvoidfriction and skin irritation

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The Bowden cable acts as an intermediary between the tensioning mechanism and the medical device or sports aid. By enclosing the core in a sheath, the cable prevents direct contact between the tensioning element and the fabric or skin, thereby eliminating friction and irritation while maintaining a relatively simple overall tensioning mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The sheath functions as a flexible protective shell that encloses the core. This thin-walled structure allows the core to move and transmit force while preventing direct contact with surrounding materials, reducing friction and eliminating the harmful effects of rope contact with fabric and skin.

Inventive Principle:

Principle #30Flexible shells and thin films

3Adaptability or versatility

If the sheath is made stretchable to allow core displacement and length adaptation, then the Bowden cable can function as a tensioning element, but the friction between core and sheath increases

Engineering Contradiction:

Improveability to function as tensioning elementVSAvoidfriction between core and sheath

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The sheath is designed with different properties in different sections: the stretchable section has properties optimized for low-friction core movement and length adaptation, while other sections may have different characteristics. This local differentiation allows the sheath to minimize friction in the critical displacement areas while maintaining necessary structural properties elsewhere.

Inventive Principle:

Principle #3Local quality

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 Bowden cable reduces friction and prevents damage to the aid's fabric and skin irritation by distributing friction evenly, while maintaining mobility and flexibility.

Implementation Method 1

the sheath is stretchable at least in a partial area

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

reduces friction and prevents damage to the aid's fabric and skin irritation by distributing friction evenly

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP4352372B1Medical aid or sports aid comprising a bowden cable

Publication Date: 2025.08.06 BAUERFEIND GMBH & CO

Figure 1a~1b
Figure 2a~2b
Figure 3~4

AI summary

The invention relates to a medical aid or sports aid (100) comprising a Bowden cable (10, 40). The Bowden cable (10, 40) comprises a core (11, 41), said core (11, 41) running in a coating (12, 42) at least in a sub-region, and the coating (12, 42) can be stretched at least in a sub-region. The invention also relates to the use of a Bowden cable (10, 40) having a core (11, 41) for tensioning a medical aid or a sports aid (100), wherein the core (11, 41) runs in an at least partly movable manner in a coating (12, 42), and the coating (12, 42) is stretchable.