Elevator Sheave Belt Guiding Surface Profile
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Solution Overview
Problem
Elevator sheaves currently fail to optimize the longevity of load-bearing members like belts due to overload stresses and uneven loading, particularly with crowned surfaces that do not adequately accommodate tracking behavior under all circumstances.
Innovation Solution
A sheave design featuring a belt guiding surface defined by an nth degree polynomial equation, with a central parallel portion and side portions that extend towards the edges, providing distinct zones to enhance tracking performance and reduce stress on the load-bearing member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crowned sheave surface is used to improve belt-tracking behavior, then tracking performance is improved, but overload stress is introduced in the central region of the belt
Solution Approach 1:
The sheave surface is divided into distinct zones with different geometries: a crowned central portion for tracking and a linear tapered peripheral portion for stress reduction. Each zone has optimized local properties - the central crowned zone provides tracking stability while the peripheral linear zone reduces bending stress on belt cords, resolving the contradiction between tracking performance and stress distribution.
Solution Approach 2:
The sheave surface profile is segmented into multiple functional portions: a central crowned portion defined by polynomial equations and peripheral linear tapered portions. This segmentation allows each portion to perform its specific function independently - the central portion handles tracking while the peripheral portions handle stress distribution, eliminating the need for a uniform crowned surface that causes overload.
2Reliability
If conventional crown designs are used, then some tracking improvement is achieved, but they do not adequately accommodate tracking behavior under all circumstances
Solution Approach 1:
The sheave surface design incorporates dynamic adaptability through its composite geometry. The transition from the central crowned portion to the peripheral linear tapered portions creates zones that can accommodate varying belt positions and loading conditions. This dynamic design allows the belt to be guided effectively whether it is centered or shifted, and whether the system is under normal or overload conditions.
Solution Approach 2:
The surface profile parameters are optimized using polynomial equations (e.g., y = ax^4 + bx^2 + cx) that allow precise control over the curvature and transition zones. By adjusting these mathematical parameters, the sheave can be tailored to accommodate different belt widths, speeds, and loading conditions, providing universal tracking performance across all operational circumstances.
3Device complexity
If flat belts are used with conventional sheaves, then the system is simple, but the belts are subjected to overload stresses as they move over the sheave
Solution Approach 1:
Instead of using a uniformly complex crowned surface, the invention applies local quality by creating specific zones with different geometries. The central crowned zone maintains simplicity for basic tracking, while the peripheral linear tapered zones are added only where needed to reduce stress. This localized approach minimizes overall design complexity while effectively addressing the overload stress problem.
Data Source
AI summary
An elevator sheave (20) includes a belt guiding surface (26) having a surface profile along at least a portion of the belt guiding surface. The surface profile preferably is defined by an nth order polynomial equation where n is a number greater than 2. In one example, the reference point (40) is a central point along the width of the belt guiding surface (26). In one example, a central portion (42) of the surface profile preferably is aligned to be generally parallel with the central axis (34) of the sheave body. Some examples have curvilinear side portions (44,46) between the central portion (42) and the edges (28,30) of the sheave. Other examples also include second side portions (48,50) that have linear profiles.