Asymmetric Nozzle for Retractable Fall Arrest Cable Wrapping
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Solution Overview
Problem
Standard nozzles in retractable fall arrest units cause cable wrapping in the center of the drum due to a short fleet angle, leading to incomplete retraction and potential cable breakage from friction, as the cable does not fill the drum evenly.
Innovation Solution
A nozzle with an elongate passage having a constricted portion and a dog-bone shaped opening, where the entrance and exit are flattened ovals, and the upper portion is made of a material to prevent cold welding, ensuring the cable fills the drum evenly by switching sides during retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a standard circular nozzle with hour-glass shaped inner surface is used, then the cable can pass through the nozzle easily, but the cable wraps in the center of the drum and does not fill evenly, causing friction and incomplete retraction
Solution Approach 1:
The nozzle passage is changed from a circular symmetric shape to an elongate asymmetric shape with a constricted middle section and wider end sections. This asymmetric geometry guides the cable to wrap around the drum in a specific pattern, preventing center wrapping and ensuring even distribution across the drum surface.
Solution Approach 2:
The nozzle passage extends in a specific directional dimension with an elongate shape rather than a circular cross-section. This dimensional change in the passage geometry creates a guiding effect that directs cable movement along a controlled path, ensuring proper drum filling pattern.
2Ease of operation
If the cable wraps in the center of the drum, then the cable can be easily pulled through the nozzle, but the cable rubs on the inner diameter of the housing and prevents full retraction
Solution Approach 1:
The elongate asymmetric passage shape with constricted middle section forces the cable to follow a specific wrapping path that distributes it across the drum width rather than concentrating it in the center. This prevents the cable from rubbing against the housing inner diameter.
Solution Approach 2:
The constricted middle section of the nozzle passage creates a localized narrowing that acts as a guide point, forcing the cable to pivot and wrap around the drum edges. This local geometric feature ensures proper cable distribution across the entire drum surface.
3Strength
If the cable wraps tightly in the center, then the cable can be securely held, but friction increases and can cause cable breakage
Solution Approach 1:
The asymmetric elongate passage with constricted section redistributes the cable wrapping pattern from a concentrated center wrap to a distributed pattern across the drum. This reduces contact pressure and friction between cable strands and between cable and housing.
Solution Approach 2:
By changing the passage geometry to an elongate shape rather than circular, the cable is guided to wrap in a distributed pattern across the drum surface. This dimensional change in wrapping geometry reduces friction by preventing concentrated cable stacking.
Data Source
AI summary
A nozzle for a retractable fall arrest defines a passage extending through the nozzle between a top surface and a bottom surface of the nozzle through which a retractable cable or lifeline can extend. The passage has a passage axis, an elongate entrance, and an elongate exit. The passage defines a constricted portion having opposed end sections and a middle section. The end sections of the constricted portion define a width greater than a width of the middle section of the constricted portion, and the width of the middle section of the constricted portion is less than a width of at least one of the entrance and exit to the passage. A perimeter of the passage defines a plane which intersects said passage axis at an angle greater than zero.