Constant Force Spring Tourniquet for Consistent Pressure

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Solution Overview

Problem

Existing pressure-application aids for venous access after hemodialysis are prone to incorrect pressure adjustment, affected by muscle tension and arm circumference changes, leading to potential damage or discomfort.

Innovation Solution

A pressure-exerting aid featuring a circumferential band with an adjustable circumference and a constant force spring, which maintains a consistent force over a specific range, along with a display element to indicate the spring's deflection and an optional emergency compression mechanism.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a conventional spring-loaded mechanism with rotary knob is used to adjust pressure, then the pressure can be adjusted, but the applied pressure can be incorrectly adjusted and is affected by muscle tension and arm circumference changes

Engineering Contradiction:

Improvepressure adjustmentVSAvoidpressure consistency

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The constant force spring automatically maintains a constant force within its elastic range without requiring continuous user adjustment. The system self-regulates the pressure applied to the puncture site, compensating for changes in arm circumference and muscle tension automatically.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent transitions from a variable force spring to a constant force spring, changing the fundamental parameter of force output from variable to constant. This ensures that the applied pressure remains within the ideal range regardless of travel variations caused by muscle tension or arm circumference changes.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a compressor and air cushion are used to dynamically apply pressure, then the applied force can be kept within the ideal range, but the device complexity increases and portability is reduced

Engineering Contradiction:

Improvepressure controlVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the complex electronic compressor and air cushion system with a simple mechanical constant force spring mechanism. This mechanical solution achieves reliable pressure control without requiring power sources, control software, or complex hardware components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The constant force spring mechanism is a simple, inexpensive mechanical component that can be easily manufactured and replaced if needed, eliminating the need for expensive electronic components, batteries, and complex control systems.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Device complexity

If a conventional spring is used, then the structure is simple, but the force applied varies with travel and can lead to too little or too much pressure

Engineering Contradiction:

ImprovestructureVSAvoidpressure accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent changes the force-travel characteristic from a linear relationship (conventional spring) to a constant force relationship (constant force spring). This parameter change ensures that the force remains constant within the elastic range, providing accurate pressure application without requiring complex control mechanisms.

Inventive Principle:

Principle #35Parameter changes

4Force

If the pressure-exerting aid is not flat, then the spring can provide sufficient force, but it does not fit well under the patient's clothing

Engineering Contradiction:

Improvecompression forceVSAvoidprofile

Core Design Contradiction:

ForceVSShape

Solution Approach 1:

The patent uses a flexible band structure that can be made thin and flat to fit under clothing, while still incorporating the constant force spring mechanism to provide sufficient compression force. The flexible nature of the band allows it to conform to the arm shape while maintaining a low profile.

Inventive Principle:

Principle #30Flexible shells and thin films

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 ensures consistent and reliable pressure application, reducing the risk of damage to the venous access and enhancing user comfort by compensating for muscle movements and providing emergency compression if needed.

Implementation Method 1

a constant force spring arranged in the circumferential band, which has the advantage that, unlike a conventional spring, it exerts or regulates a constant force over a specific travel or stroke

Methodology Applied

Scientific EffectConstant force spring mechanism: Spring

Implementation Method 2

a display element is preferably located on the outside of the constant-force spring, which is designed to directly or indirectly indicate the deflection of the constant-force spring

Methodology Applied

Scientific EffectVisual indication of deflection:

Data Source

PatentEP4114283B1Tourniquet

Publication Date: 2025.06.11 FRESENIUS MEDICAL CARE DEUTSCHLAND GMBH

Figure 1~2b

AI summary

The invention relates to a tourniquet for compressing the puncture site of a patient, the tourniquet comprising an all-around strap (10) the circumference of which can be varied and a constant-force spring (20) being arranged in the all-around strap.