Flat-Belt Linear Actuator Geometry for High-Reduction Sheave Alignment
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Solution Overview
Problem
Flat belts in linear actuator systems are sensitive to fleet angle misalignments, which significantly reduce their service life and power transmission efficiency, making it difficult to apply them in high-reduction block and tackle topologies where wire ropes perform better.
Innovation Solution
A linear actuator system design that eliminates fleet angles by using sheaves with non-constant spacing and different diameters, tilted to align their centerlines on a common circular profile, allowing for high-reduction block and tackle topologies with flat belts, enhancing service life and power transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wire ropes are used in block and tackle topologies, then high reduction ratios can be achieved, but fleet angle misalignments occur that reduce service life and efficiency
Solution Approach 1:
The system divides the block and tackle into multiple pulley blocks with multiple sheaves, where each sheave is independently positioned to eliminate fleet angles. The belt is segmented into multiple spans that run between the sheaves, allowing each span to be optimized for zero fleet angle while maintaining high reduction ratio through the cumulative effect of multiple pulleys.
Solution Approach 2:
The invention transitions from a planar arrangement to a three-dimensional configuration where sheaves are positioned at different locations in space. The sheave centers define a polygonal geometry rather than a simple linear or planar arrangement, allowing the belt to wrap around sheaves in a spatial configuration that eliminates fleet angles while achieving high reduction.
2Reliability
If flat belts are used in high-reduction block and tackle, then service life and efficiency improve, but fleet angle misalignments occur that prevent their use
Solution Approach 1:
The sheaves are intentionally positioned asymmetrically relative to each other, with their centers defining an irregular polygon rather than a symmetric arrangement. This asymmetric positioning allows each sheave to be optimally oriented to receive the belt at zero fleet angle, while the overall asymmetric configuration achieves the required high reduction ratio.
Solution Approach 2:
The invention changes the geometric parameters of the sheave arrangement, specifically the positions and orientations of sheave centers, to eliminate fleet angles. By adjusting the spatial parameters of the block and tackle configuration, the system optimizes for zero fleet angle at each sheave while maintaining high reduction through the cumulative mechanical advantage of multiple pulleys.
3Productivity
If conventional block and tackle design is used, then mechanical reduction is achieved, but fleet angles are introduced that substantially reduce expected system service life
Solution Approach 1:
The sheaves are pre-positioned in their optimal locations and orientations before the belt is installed. The block and tackle geometry is predetermined such that when the belt is tensioned, it naturally aligns with each sheave at zero fleet angle. This preliminary geometric configuration ensures that no fleet angle misalignment occurs during operation, maximizing service life.
Solution Approach 2:
The invention creates a geometric model or template for the optimal sheave arrangement that can be replicated. The relative positions and orientations of sheaves are designed as a standardized configuration that eliminates fleet angles, and this geometric pattern can be copied or replicated in different sizes and applications while maintaining the zero fleet angle property.
Data Source
AI summary
Disclosed herein are methods, systems, and components for the design of a flat belt based block and tackle design that is theoretically free of fleet angles. A mapping technique forms a set of planar positions for the centerlines of the free spans that provides a plurality of sheave geometries, which reside on a common axis and spans that are free of fleet angles at the sheave engagement interfaces. This permits the use of high-performing flat belts in high-reduction (e.g., 6:1 or greater) block and tackle topologies, with the principal benefits of an extended service life, high power transmission efficiency, more effective traction power transfer, and a compact machine design.