Fluid Actuator Radial Expansion to Longitudinal Contraction
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Solution Overview
Problem
Conventional fluid injection type artificial muscles face issues with radial expansion not being fully translated into longitudinal contraction, leading to stress concentration and potential cracking or separation of fibers from the rubber film, especially under high pressure or heavy loads.
Innovation Solution
A fluid injection type actuator with a tubular body featuring annular fiber groups and additional fibers arranged radially outside or inside, coated in an elastic body, and optionally with rings to restrict radial expansion, allowing for uniform radial expansion and efficient translation into longitudinal movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick kite strings are used as restraining members to prevent longitudinal extension of the rubber tube, then the durability is improved by eliminating friction between fibers and rubber, but the radial expansion becomes concentrated between the kite strings causing stress concentration and potential cracking
Solution Approach 1:
The patent divides the single thick restraining fiber into multiple thin fibers arranged in an annular array. This segmentation distributes the restraining force across many contact points around the circumference, preventing stress concentration in any single location while maintaining overall durability.
Solution Approach 2:
The patent creates non-uniform fiber distribution by arranging fibers in an annular array with varying radial positions. Some fibers are positioned radially outside while others are radially inside, creating local variations in restraining characteristics that optimize both durability and expansion uniformity.
2Force
If the number of kite strings is increased to narrow the interval between them, then the restraining force is increased, but the stress concentration in the rubber film between the strings cannot be alleviated
Solution Approach 1:
The patent segments the restraining function across numerous thin fibers arranged circumferentially. This allows the total restraining force to be distributed over many small contact points, maintaining high overall force while avoiding stress concentration that would occur with fewer, thicker fibers.
Solution Approach 2:
The patent transitions from a single-dimensional arrangement (single thick fiber) to a two-dimensional annular array of multiple thin fibers. This dimensional change allows the restraining force to be distributed across both the radial and circumferential dimensions, effectively preventing stress concentration.
3Device complexity
If a single layer of fibers is used to restrain the rubber tube, then the structure is simple, but the radial expansion cannot be fully translated into longitudinal contraction especially under high pressure
Solution Approach 1:
The patent employs multiple fiber layers arranged at different radial positions (inside and outside the annular array). This multi-layer configuration translates radial expansion more effectively into longitudinal contraction by creating distributed restraining forces that act throughout the rubber tube wall thickness, improving contraction efficiency without excessive complexity.
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 enhances the durability and efficiency of converting radial expansion into longitudinal contraction, reducing stress concentration and preventing rupture, even under high loads, while allowing for precise adjustment of the tubular body's shape.
Implementation Method 1
a pressure of a fluid supplied into a space formed by the tubular body and the lid members expands the tubular body radially thereby contracting it longitudinally
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(d)
Figure 3
AI summary
An actuator (10) is provided whose expansion in the radial direction can be efficiently translated into longitudinal movement when its length is contracted and extended by injecting a fluid into the tubular body. The fluid injection type actuator includes an actuator body (11), which is an expansion and contraction section of the actuator (10). The actuator body is constructed of a cylindrical rubber tube (12)and annular fiber groups (13A-13C) inserted and extending longitudinally therein. The annular fiber groups (13A-13C) are each a group of fibers (13), such as glass roving fibers having a diameter of about 10 µm, arranged in an annular array along the circumference of the rubber tube. The arrangement allows the rubber tube (12) to be restrained over the entirety of the actuator body (11) longitudinally when it is expanded radially.