Tape Measure Spiral Spring Stress Profiling to Prevent 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 when the tape hits 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 the tape hitting the housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a uniform stress spiral spring is used, then the retraction force is consistent, but the retraction speed becomes excessively high and causes whip and impact at the end of retraction
Solution Approach 1:
The spiral spring is designed with non-uniform stress distribution, where the stress varies along the length of the spring. Specifically, the spring has a first section with higher stress and a second section with lower stress, creating different retraction characteristics in different portions of the spring. This local variation in stress quality resolves the contradiction by preventing excessive retraction speed at the end while maintaining adequate retraction force throughout the process.
Solution Approach 2:
The patent changes the stress parameter along the length of the spiral spring, transitioning from a uniform stress design to a variable stress design. By modifying the stress parameter distribution (creating a gradient from high to low stress), the retraction speed is controlled to decrease progressively, eliminating the whip and impact problem at the end of retraction while maintaining overall retraction functionality.
2Device complexity
If a uniform stress spiral spring is used, then the spring structure is simple, but excessive force and impact occur when the tape hits the housing
Solution Approach 1:
The spiral spring incorporates local quality variation by having different stress levels in different sections. The first section has higher stress providing initial retraction force, while the second section has lower stress providing gentle final retraction. This local differentiation reduces the impact force when the tape reaches the housing without requiring a completely complex spring structure.
Solution Approach 2:
The variable stress design acts as a form of beforehand cushioning by progressively reducing the retraction force as the tape approaches the housing. The lower stress in the second section of the spring预先 (in advance) prepares for the final retraction phase, cushioning the impact before it occurs rather than allowing a sudden stop.
3Productivity
If high retraction speed is achieved, then the retraction process is fast, but whip is generated at the end of tape retraction
Solution Approach 1:
By changing the stress parameter distribution along the spring length, the patent controls the retraction speed profile. The higher stress in the first section enables fast initial retraction (high productivity), while the lower stress in the second section reduces speed progressively, preventing whip generation at the end of retraction.
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 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.