Variable-Stiffness Rope Gripper for Low-Shear Hoist Terminals
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Solution Overview
Problem
Elevator ropes with brittle or coated materials face challenges in reliable gripping due to sensitivity to deformation under stress, leading to creep and potential rupture, especially when subjected to shear stress and compression, which can result in loss of suspension.
Innovation Solution
A rope gripping member with an elongated gripping face that increases tensile stiffness non-linearly from the front edge to the rear edge, equalizing shear stresses and reducing the likelihood of ruptures by eliminating high shear stress peaks, suitable for use with materials like fiber-reinforced composites and coated ropes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the rope end is compressed with a straight and long compression face without bending, then the rope structure is preserved without severe damage, but the grip reliability deteriorates due to creep and shear stress in the surface material
Solution Approach 1:
The gripping member is designed with non-uniform thickness, where the thickness varies along the gripping face. This creates different local stiffness properties: the thicker rear portion provides structural support while the thinner front portion reduces shear stress concentration. This local variation in geometry directly addresses the contradiction by maintaining rope structure integrity while improving grip reliability through reduced creep and shear stress in the polymer coating.
Solution Approach 2:
The invention changes the geometric parameter of the gripping member by introducing a thickness gradient along the gripping face. This parameter change transforms the uniform compression into a distributed stress pattern that reduces peak shear stresses at the front edge. The thickness variation parameter directly influences the stress distribution, thereby resolving the contradiction between maintaining rope integrity and ensuring reliable grip.
2Ease of operation
If the surface material of the rope is subjected to continuous shear stress, then the rope can be gripped and compressed, but the surface material undergoes creep deformation and may rupture over time
Solution Approach 1:
The non-uniform thickness design creates zones of different stress characteristics along the gripping face. The varying thickness locally adjusts the stress distribution, reducing continuous shear stress concentration on the polymer coating while maintaining adequate gripping capability. This local quality variation prevents creep-induced rupture while preserving the ability to grip and compress the rope.
3Reliability
If the rope end section is firmly gripped to prevent sliding, then suspension reliability is maintained, but the surface material and load bearing members are subjected to excessive compression and shear stress
Solution Approach 1:
The varying thickness of the gripping member creates a gradient in contact pressure and shear stress distribution. The thicker regions provide necessary compression for firm gripping while the thinner regions reduce peak stresses. This local quality variation ensures suspension reliability without subjecting the rope materials to excessive harmful stresses that would cause creep or rupture.
Solution Approach 2:
By changing the thickness parameter of the gripping member along its length, the invention optimizes the balance between gripping force and stress induction. The thickness gradient parameter allows the system to achieve firm grip for suspension reliability while simultaneously reducing peak compression and shear stresses on the rope materials, thereby minimizing harmful effects.
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 provides a firm and reliable grip, reducing the risk of creep-related and internal stress-induced ruptures, ensuring safe and stable suspension of elevator ropes.
Implementation Method 1
By adjusting stiffness of the gripping member as described above, shear stresses can be made more equal over the contact length between the gripping member and the rope. Hereby, particularly existence of very high and thereby harmful shear stresses close to the front edge of the gripping face can be eliminated.
Implementation Method 2
The surface material is subjected to continuous shear stress, which may cause increasing deformation over time (creep). In long term, the creep phenomenon can lead to rupture of the surface material.
Data Source
Figure 1
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AI summary
The invention relates to rope gripping member (2) for a rope gripping device (1), the rope gripping member (2) comprising an elongated rope gripping face (3) for being pressed against an elongated side face of an end section of a rope (4), the elongated rope gripping face (3) having a longitudinal direction (L) and a front edge (5) and a rear edge (6);wherein tensile stiffness of the rope gripping member (2) in longitudinal direction (L) of the gripping face (3) increases non-linearly with accelerating rate from the front edge (5) towards the rear edge (6) of the gripping face (3). The invention also relates to a rope gripping device (1), a rope terminal arrangement (A) and a hoisting apparatus implementing the rope gripping member (2).