Tape Measure Spiral Spring Profile to Reduce Retraction Whip
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Solution Overview
Problem
Conventional tape measures with spiral springs often experience high retraction speeds and forces at the end of tape retraction, leading to potential damage and 'whip' due to constant torque profiles, which are not adequately managed by existing designs.
Innovation Solution
A variably stressed spiral spring is used, where the free coil diameter increases towards the outer end, reducing stress and torque, resulting in a lower maximum torque and flatter torque profile, thereby decreasing retraction speed and force, specifically designed to mitigate the issues of high retraction speed and potential damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional spiral spring with constant stress is used, then the tape measure provides sufficient retraction force, but the retraction speed and force become excessively high at the end of tape retraction, causing damage and whip
Solution Approach 1:
The spring is designed with varying stress distribution along its length, where the outer end portion has reduced stress compared to the inner end portion. This local quality variation allows the spring to provide sufficient retraction force overall while specifically reducing the excessive force and speed at the outer end that causes damage and whip.
Solution Approach 2:
The stress parameter of the spiral spring is changed along its length, creating a gradient where the outer end portion has lower stress than the inner end portion. This parameter change enables the spring to maintain adequate retraction force while eliminating the harmful high-speed whip effect at the end of retraction.
2Object-affected harmful factors
If the spring stress is reduced to decrease retraction speed, then damage and whip are eliminated, but the starting torque may become insufficient for efficient retraction
Solution Approach 1:
Different portions of the spring have different stress characteristics: the inner end portion maintains high stress to provide sufficient starting torque, while the outer end portion has reduced stress to eliminate damage and whip. This local quality differentiation resolves the contradiction between needing high power initially and preventing harmful effects later.
Solution Approach 2:
The spring is effectively segmented into two functional zones: an inner end portion with high stress for generating starting torque, and an outer end portion with reduced stress for controlling retraction speed and preventing whip. This segmentation allows each zone to optimize its function without compromising the other.
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 effectively decreases the maximum retraction speed and force of the tape blade, reducing the likelihood of damage and eliminating whip during the last few feet of tape retraction, while maintaining sufficient starting torque for efficient retraction.
Implementation Method 1
a spiral spring coupled between a tape blade and tape measure housing such that 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.