Eccentric Bushing for Double-Coil Spring Stress Reduction
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Solution Overview
Problem
The double-coil spring actuation mechanism in tarping systems for open-topped containers experiences stress and fatigue at transition points, leading to potential failure due to repeated deployment and loading, which is exacerbated by weight and cost constraints.
Innovation Solution
A bushing with an eccentric external periphery is integrated into the pivot shaft of the double-coil spring actuation mechanism, limiting deflection and providing support at the transition points between the coil portions, thereby reducing stress concentration and prolonging the life of the springs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a double-coil spring actuation mechanism is used to deploy the tarp cover, then the tarp can be automatically unfurled with sufficient deployment force, but the spring experiences stress concentration and fatigue at transition points leading to potential failure
Solution Approach 1:
A bushing is introduced as an intermediary component between the double-coil spring and the pivot shaft. The bushing has an eccentric external periphery that progressively limits deflection of the spring coils, providing support at the transition points between coil portions and the center anchor section. This intermediary structure distributes the stress more evenly throughout the spring, preventing stress concentration at the vulnerable transition points while maintaining the necessary deployment force.
2Reliability
If the spring size and number are increased to reduce stress and extend fatigue life, then reliability improves, but weight and cost increase
Solution Approach 1:
The bushing acts as a stress-distributing intermediary that allows the use of smaller, lighter springs while achieving the same fatigue life extension that would otherwise require larger or multiple springs. By providing structural support at the critical transition points, the bushing enables weight reduction without sacrificing reliability.
Solution Approach 2:
Instead of uniformly increasing the size of the entire spring system, the bushing provides localized support precisely where stress concentration occurs - at the transition points between the coil portions and the center anchor section. This localized reinforcement allows the rest of the spring system to remain lightweight while still achieving improved fatigue life.
3Reliability
If larger or more springs are used to reduce stress, then fatigue life extends, but manufacturing cost increases
Solution Approach 1:
The bushing is a relatively simple, inexpensive intermediary component that can be manufactured from common materials such as plastic or metal. It provides the same fatigue life extension benefits that would otherwise require expensive, large-sized or multiple springs, thereby reducing overall manufacturing cost while maintaining reliability.
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 bushing significantly reduces stress concentration at the transition points of the double-coil spring, extending its fatigue life while maintaining the mechanism's torsional capacity and being cost-effective.
Implementation Method 1
The mechanism includes an elastically deformable double-coil spring with two coil portions concentrically wound around each other
Implementation Method 2
The bushing has an eccentric external periphery that is progressively increasingly spaced from the coil portions of the spring as the coil portions diverge from the mounting portion of the spring. The eccentric external periphery limits the deflection of the spring at the transition points between the center portion and each of the coil portions.
Data Source
AI summary
An actuation mechanism for a tarping system includes a double coil spring mountable on a pivot shaft of the mechanism. A bushing is mounted on the pivot shaft and within the double coil spring. The bushing includes an eccentric external periphery that limits the deflection of the spring, particularly at the transition points between the center portion and each of the coil portions of the spring. As the spring winds or coils, the coil portions progressively contact the eccentric periphery of the bushing to not only limit further movement of the coil portions, but also to provide support for those portions under load.