Open-celled TiNi Foam Actuators for Fast Response
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Solution Overview
Problem
Shape Memory Effect (SMA) actuators made from Nickel Titanium (TiNi) or Nitinol have limited applicability in large force applications due to high cost, difficulty in bonding, slow cycle times, and mechanical connection issues, which hinder their use in generating large actuation forces with fast response times.
Innovation Solution
The use of open-celled TiNi foam manufactured through High Temperature Self Propagating Synthesis (SHS) allows for net-shape actuators with rapid heat transfer via hot and cold fluids or gases, enabling large actuation forces and fast response times while reducing manufacturing complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If bundles of thin TiNi wires are used to generate large actuation forces, then the actuation force increases, but the complexity of bonding and mechanical connections increases
Solution Approach 1:
The actuator is divided into multiple thin TiNi wire bundles, each contributing to the total actuation force. This segmentation allows the system to achieve large forces while maintaining manageable bonding complexity through modular assembly
Solution Approach 2:
Multiple thin TiNi wire bundles are combined into a single integrated actuator structure with common bonding interfaces. This merging approach consolidates the bonding operations and mechanical connections, reducing overall complexity while maintaining the cumulative actuation force of all wire bundles
2Force
If bundles of thin TiNi wires are used to generate large actuation forces, then the actuation force increases, but the cost increases
Solution Approach 1:
The actuator uses multiple thin TiNi wire bundles instead of a single thick wire. Thin wires are less expensive per unit force and can be manufactured more efficiently, reducing the overall cost while achieving the required actuation force through cumulative effect
Solution Approach 2:
Instead of using one expensive thick TiNi wire, the design replicates the function across multiple thin wire bundles. This copying approach reduces material cost and manufacturing expense while maintaining the required performance through parallel contribution of each bundle
3Force
If indirect heating methods are used for large diameter SMA articles, then large actuation forces are achieved, but the response time increases
Solution Approach 1:
The large diameter actuator is segmented into multiple thin wire bundles, each with high surface-area-to-volume ratio. This segmentation enables rapid heat transfer to each individual wire, maintaining fast response times while the cumulative cross-sectional area of all bundles provides the required large actuation force
Solution Approach 2:
The actuator employs a porous or bundled structure with high surface area exposure. This porous configuration allows efficient thermal penetration and heat distribution throughout the material, enabling rapid phase transformation and fast response times even for large force generation
4Force
If the cross-sectional area of TiNi SMA element increases to generate large forces, then the actuation force increases, but the cyclic response times increase to minutes
Solution Approach 1:
The large cross-sectional area requirement is met by assembling multiple thin wire bundles in parallel rather than using a single large-diameter wire. Each thin bundle maintains fast thermal response characteristics, so the overall actuator achieves both large force capacity and fast cyclic response times
Solution Approach 2:
The bundled wire structure creates a porous configuration with high surface area-to-volume ratio. This porous structure enables rapid heat transfer throughout the entire actuator mass, reducing cyclic response times from minutes to seconds while maintaining the large cross-sectional area needed for high force generation
Data Source
AI summary
This invention relates to the exploitation of porous foam articles exhibiting the Shape Memory Effect as actuators. Each foam article is composed of a plurality of geometric shapes, such that some geometric shapes can fit snugly into or around rigid mating connectors that attach the Shape Memory foam article intimately into the load path between a static structure and a moveable structure.The foam is open-celled, composed of a plurality of interconnected struts whose mean diameter can vary from approximately 50 to 500 microns. Gases and fluids flowing through the foam transfer heat rapidly with the struts, providing rapid Shape Memory Effect transformations. Embodiments of porous foam articles as torsional actuators and approximately planar structures are disposed. Simple, integral connection systems exploiting the ability to supply large loads to a structure, and that can also supply hot and cold gases and fluids to effect rapid actuation are also disposed.