Tape Measure Spiral Spring Profile to Reduce Retraction Whip
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Solution Overview
Problem
Conventional tape measures with spiral springs experience high retraction speeds and potential whip at the end of tape retraction due to uniform stress levels, leading to excessive force and impact on the housing.
Innovation Solution
A variably stressed spiral spring design with decreasing stress levels towards the outer end, reducing maximum torque and torque profile slope, thereby decreasing retraction speed and minimizing the force of tape blade impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a uniform stress spiral spring is used, then the spring provides consistent retraction force, but the tape blade experiences high retraction speed and whip at the end of retraction
Solution Approach 1:
The spring is designed with varying stress levels along its length, specifically with reduced stress in the outer end section. This creates different local properties: the inner section maintains higher stress for strong initial retraction, while the outer section has lower stress to reduce retraction speed and eliminate whip at the end of retraction.
Solution Approach 2:
The stress parameter of the spiral spring is changed along its length, with the outer end section having a different stress level than the inner section. This parameter variation allows the spring to provide controlled retraction speed and reduce impact force on the housing.
2Device complexity
If a uniform stress spiral spring is used, then the spring structure is simple, but excessive force and impact are applied to the housing
Solution Approach 1:
The spring structure incorporates a localized variation in stress levels, with the outer end section having reduced stress compared to the inner section. This local modification reduces the impact force on the housing without requiring a completely complex spring design.
3Speed
If the free coil diameter is increased along the first length section, then the stress decreases and retraction speed reduces, but the spring geometry becomes more complex
Solution Approach 1:
The free coil diameter is varied only in the outer end section of the spring, creating a local geometric variation that reduces stress and controls retraction speed. The rest of the spring maintains a simpler geometry, balancing performance requirements with manufacturing simplicity.
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 variably stressed spiral spring design reduces maximum retraction speed and eliminates whip, providing a smoother and gentler tape retraction process.
Implementation Method 1
the spring stores energy when the tape blade is extended from the housing and releases energy driving retraction of the tape blade
Data Source
AI summary
A tool, such as a tape measure, including a spring-based retraction system is shown. The spring-based retraction system is driven by a spiral spring, that has a variable preformed stress profile along the length of the spring.