Helical Spring Tether Structure for Peak Load Reduction
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Solution Overview
Problem
Conventional tether lines experience high maximum loading and potential damage when restraining heavy objects, leading to unpredictable motion and rebound, and require larger, heavier cable diameters, making them difficult to handle and maneuver.
Innovation Solution
An energy-absorbing structure incorporating a helical spring with a secure connector system, which reduces maximum loading by distributing force and preventing unscrewing, allowing for smaller, more flexible cable diameters and improved motion restraint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional wire rope tether line is used to restrain heavy objects, then the tether line can provide sufficient strength, but the maximum loading becomes excessively high (approximately 30 tons) causing damage and unpredictable motion
Solution Approach 1:
The patent incorporates an energy-absorbing structure (helical spring) into the tether line before use. This spring is pre-configured to compress and absorb kinetic energy during a fall event, cushioning the impact before it reaches the tether line. The spring reduces the maximum loading from approximately 30 tons to 700-800 kgf by converting kinetic energy into elastic potential energy during compression, thereby preventing damage and unpredictable motion while maintaining adequate restraint strength.
Solution Approach 2:
The patent changes the physical state and mechanical properties of the tether line system by introducing a compliant energy-absorbing element. The helical spring transforms the rigid tether line into a system with variable stiffness - soft during normal operation but providing progressive resistance during fall arrest. This parameter change allows the system to adapt its force characteristics, reducing peak loading while maintaining control.
2Strength
If a conventional wire rope tether line is used to restrain heavy objects, then the tether line can provide sufficient strength, but the cable diameter becomes larger and heavier making it difficult to handle and maneuver
Solution Approach 1:
The energy-absorbing spring is pre-installed in the tether line to cushion fall impacts. By absorbing kinetic energy through spring compression, the system reduces peak forces to 700-800 kgf, which allows the use of lighter, smaller diameter cables that would otherwise be insufficient for heavy object restraint. This enables handling of 300 kg objects with much more manageable cable dimensions.
Solution Approach 2:
The introduction of the energy-absorbing spring changes the force-parameter relationship in the tether line system. The spring allows the system to maintain adequate strength for heavy objects while operating at lower force levels during normal use, enabling the selection of lighter cable materials and smaller diameters that are easier to handle and maneuver.
3Device complexity
If the connector uses only an externally threaded portion for securing the spring, then the assembly is simple, but the spring may unscrew from the connector under turning moments
Solution Approach 1:
The tapered portion is pre-configured on the connector to prevent spring unscrewing before use. During assembly, the spring is threaded onto the externally threaded portion, and the tapered surface ensures that any turning moments or vibrational forces encountered during operation will cause the spring to wedge tighter against the taper rather than loosen. This beforehand geometric constraint reliably prevents unscrewing without adding complex locking mechanisms.
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 energy-absorbing structure significantly reduces maximum loading on the tether line, prevents unpredictable motion, and allows for smaller, lighter, and more manageable cable diameters, effectively restraining heavy objects without causing damage.
Implementation Method 1
a helical spring; providing the energy-absorbing structure as a separate component... reduces the maximum loading that the tether line is subject to
Implementation Method 2
a first connector for securing a first end of the helical spring to a first fastener, the connector having an externally threaded portion for threadedly receiving the first end of the helical spring
Implementation Method 3
the connector further comprises a tapered portion extending from the inner end of the externally threaded portion. If the spring should experience a turning moment that would cause the spring to start to unscrew from the connector
Implementation Method 4
a sleeve provided on the connector and extending over at least part of the first end of the helical spring and the external threaded portion of the connector for retaining the helical spring on the connector
Data Source
AI summary
An energy-absorbing structure for a tether line includes a helical spring and a first connector for securing a first end of the helical spring to a first fastener (such as a support cable section, an eye bolt or an eye nut). The first connector has an externally threaded portion for threadedly receiving the first end of the helical spring. A sleeve is provided on the connector, extending over at least part of the first end of the helical spring and the external threaded portion of the connector, for retaining the helical spring on the connector. Additionally or alternatively, the connector includes a tapered portion extending from the inner end of the externally threaded portion.