Linear Actuator Pulley Layout for Low-Bend Belt Durability
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Solution Overview
Problem
Belt-driven linear actuators face limitations in durability and maximum capacity due to belt wear and stress caused by excessive bending, which accelerates degradation and reduces service life, while maintaining a conventional form factor.
Innovation Solution
A pulley system with a configuration of fixed and traveling sheaves arranged to minimize belt bending, using large sheaves within a small cross-section, and ensuring belt tension is approximately coincident with the output shaft centerline to reduce stress and prevent contra-flexion, allowing for large loads and extended service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional pulley systems are used with smaller sheaves, then the actuator can maintain a compact form factor, but the belt experiences excessive bending which accelerates degradation and reduces service life
Solution Approach 1:
The patent arranges sheaves in a three-dimensional configuration where multiple sheaves are positioned at different depths along the actuator's longitudinal axis. This spatial arrangement allows the belt to bend in multiple directions rather than being constrained to a single plane, distributing the bending stress across larger effective radii while maintaining a compact external footprint. The sheaves are positioned such that the belt traverses through the actuator body in a complex path that minimizes cumulative bending cycles.
Solution Approach 2:
The patent employs a nested arrangement where smaller sheaves are positioned within the internal volume defined by larger outer sheaves. This nested configuration allows the belt to pass through multiple concentric or semi-concentric sheave arrangements, effectively increasing the bending radius without increasing the external dimensions of the actuator. The internal sheaves are housed within the actuator body, creating a compact nested structure that protects the belt from excessive bending while maintaining a small form factor.
2Strength
If large sheaves are used to reduce belt bending, then durability and load capacity improve, but the actuator size increases beyond conventional form factors
Solution Approach 1:
The patent divides the load-bearing function across multiple sheaves rather than relying on a single large sheave. The belt passes through several sheaves in sequence, with each sheave contributing to the mechanical advantage and load distribution. This segmentation allows the use of multiple moderate-sized sheaves instead of one excessively large sheave, distributing the stress and achieving high load capacity while keeping individual sheave sizes manageable and the overall actuator compact.
Solution Approach 2:
The patent combines multiple sheaves into a single integrated pulley system where the sheaves work together as a unified mechanism. The belt tension is distributed across multiple sheave contact points, and the combined mechanical advantage of all sheaves provides high load capacity. This merging of multiple sheave functions into one compact assembly achieves the strength of large sheaves while maintaining a compact form factor that fits conventional actuator dimensions.
3Volume of moving object
If the belt is subjected to excessive bending, then the actuator can maintain a compact design, but belt wear and stress increase leading to accelerated degradation
Solution Approach 1:
The patent introduces intermediate sheaves that act as mediators in the belt's path, allowing the belt to transition smoothly between different directions and planes. These intermediate sheaves are positioned to provide gradual bending transitions rather than sharp angles, reducing stress concentration points. The intermediate sheaves effectively distribute the bending action across multiple smaller, controlled bends rather than one large bend, protecting the belt from excessive stress while maintaining the compact actuator design.
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 enhances the durability and maximum load capacity of belt-driven linear actuators by minimizing belt bending, reducing stress, and preventing contra-flexion, thereby increasing the service life and load-bearing capability while maintaining a compact form factor.
Implementation Method 1
Bending a belt causes non-uniform internal stresses within the belt that can cause accelerated degradation. Thus, minimizing the amount of bend in the belt increases maximum load capacity and service life.
Implementation Method 2
The disclosed pulley configuration is designed to allow for large sheaves contained within a relatively small cross-section and does not contra-flex the belt.
Data Source
AI summary
In general, this disclosure involves a pulley system that includes a plurality of fixed sheaves arranged to at least partially encircle an output shaft, a plurality of traveling sheaves coupled to the output shaft. The output shaft can be configured to pass through the fixed sheaves and translate along an axis of travel and the plurality of traveling sheaves can be arranged such that a geometric average of belt tension created by spans of belt between the plurality of traveling sheaves and the plurality of fixed sheaves is approximately coincident with a centerline of the output shaft. The system further includes a belt extending between and around the plurality of fixed sheaves and the plurality of traveling sheaves such that the belt flexes toward a single surface of the belt.