Flat-Belt Linear Actuator Sheave Layout to Eliminate Fleet Angles
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Solution Overview
Problem
Flat belts in linear actuation systems are sensitive to fleet angle misalignments, which significantly reduce their service life and prevent their use in high-reduction block and tackle topologies, unlike wire ropes that can tolerate such angles.
Innovation Solution
A linear actuator system design that uses a combination of sheaves with non-constant spacing and different diameters, tilted to eliminate fleet angles, allowing for the use of high-performing flat belts in high-reduction block and tackle systems by mapping sheave geometries onto a common axis, ensuring zero fleet angles at engagement interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If block and tackle topology is used for high reduction ratios, then mechanical reduction is achieved, but fleet angles are introduced that substantially reduce belt service life
Solution Approach 1:
The patent applies asymmetry by tilting alternate sheaves in opposite directions (e.g., +5 degrees and -5 degrees) rather than using symmetric alignment. This asymmetric tilting pattern allows the belt to follow a zigzag path that maintains proper engagement at each sheave while achieving the desired mechanical reduction ratio, thereby preventing fleet angle damage and extending belt service life.
Solution Approach 2:
The patent introduces a new dimensional approach by tilting sheaves about an axis perpendicular to the traditional plane of operation. Instead of keeping all sheaves in a single plane, the invention uses alternating angular orientations in three-dimensional space, creating a spatial arrangement that eliminates fleet angles while maintaining the block and tackle topology for high reduction ratios.
2Reliability
If flat belts are used instead of wire ropes, then maintenance-free operation and durability are improved, but sensitivity to fleet angle misalignments increases
Solution Approach 1:
The patent applies preliminary anti-action by pre-tilting the sheaves in alternating directions before the belt engages them. This predetermined angular configuration proactively prevents fleet angle misalignment from occurring during operation, rather than attempting to correct it afterward. The belt is guided into proper engagement at each sheave, eliminating the harmful fleet angles that would otherwise cause premature failure.
3Reliability
If sheaves are tilted to eliminate fleet angles, then belt service life is extended, but system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the sheave system into discrete, independently tiltable units. Each sheave can be tilted individually by a specific angle (e.g., 5 degrees) about its mounting axis, allowing precise control over the belt path. This modular approach simplifies the overall design compared to attempting complex continuous adjustments, as each sheave operates as an independent segment with a fixed angular offset.
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
This design extends the service life of flat belts, enhances power transmission efficiency, and enables compact machine designs, allowing for their use in applications like construction equipment and manufacturing machinery with high-reduction ratios without premature failure.
Implementation Method 1
They are now making their way into other oscillatory linear applications, such as scissor lifts, fork trucks, and gym equipment thanks to their ability to efficiently transmit power without maintenance for an extended period of time
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 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.