Shape Memory Alloy Actuation with Opposing Wires for Reduced Lateral Force
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Solution Overview
Problem
Existing SMA actuator systems face challenges in providing gain while minimizing the impact on the suspension system and overall size, as inclined SMA wires apply high lateral forces that increase friction, rolling forces, and spring forces, making it difficult to design compact and efficient devices.
Innovation Solution
The use of two lengths of SMA wire inclined at an acute angle with respect to the movement axis, applying forces in opposite directions, and a suspension system with flexures or bearings to resist the lateral couple, minimizing lateral forces and maintaining compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a single SMA wire is inclined at an acute angle with respect to the movement axis to provide gain, then the movement distance is amplified, but high lateral forces are applied to the suspension system increasing friction and rolling forces
Solution Approach 1:
The single inclined SMA wire is segmented into two opposing SMA wires that apply forces in opposite directions. This segmentation allows the lateral force components to cancel each other out while the axial components add up to provide the desired gain, resolving the contradiction between movement amplification and lateral force reduction
Solution Approach 2:
The second SMA wire acts as a counterweight to the first SMA wire, with both wires applying equal and opposite lateral forces that cancel each other out. This counterbalancing approach eliminates the net lateral force on the suspension system while maintaining the gain-providing inclination geometry
2Length of moving object
If mechanical means are used to amplify the distance moved by SMA wire, then gain is achieved, but the overall size of the apparatus increases and design complexity increases
Solution Approach 1:
The opposing SMA wire configuration serves multiple functions simultaneously: it provides gain through inclination, cancels lateral forces through opposition, and eliminates the need for separate mechanical amplification mechanisms. This multi-functionality achieves movement amplification without increasing apparatus size or design complexity
3Force
If opposing SMA wires are used to reduce lateral forces, then lateral force components cancel out, but a couple is applied to the movable element perpendicular to the movement axis
Solution Approach 1:
The couple applied by the opposing SMA wires, which initially appears as a harmful effect, is converted into a beneficial feature by designing the suspension system to resist this couple. The suspension system's resistance to the couple becomes a mechanism for maintaining precise control and stability of the movable element, transforming the potential problem into a design advantage
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 configuration achieves high gain with reduced lateral forces, allowing for a compact and efficient SMA actuation apparatus that maintains the functionality of the suspension system, suitable for miniature devices.
Implementation Method 1
two lengths of shape memory alloy wire each connected at one end to the support structure and at the other end to the movable element and arranged to apply forces to the movable element
Data Source
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AI summary
An SMA actuation apparatus (1) comprises a support structure (2) and a movable element (3) supported thereon by a suspension system (8, 10) that supports the movable element on the support structure and guides movement of the movable element along a movement axis. Two closely spaced lengths of SMA wire (4) that are close to parallel and inclined at the same acute angle with respect to a plane normal to the movement axis are connected to the support structure and to the movable element so as to apply respective forces to the movable element with respective components parallel to the movement axis that are in opposite directions. The two lengths of shape memory alloy wire apply a couple to the movable element perpendicular to the movement axis and the suspension system includes a pair of flexures or bearings that resist the resultant couple applied to the movable element by the lengths of SMA wire.