SMA Wire Anchor with Curved Clamping for Stress Relief
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Solution Overview
Problem
Shape memory alloy (SMA) wires in devices experience failure due to uneven stress distribution and slide-through at attachment points when heated, leading to fatigue and pull-out, as all portions of the wire contract, including those attached to structural members.
Innovation Solution
A thermally and electrically conductive anchor with a configurable clamping component that engages a thermally responsive ligature, limiting deformation in the engaging segment by reducing current flow and heat transfer, preventing contraction and maintaining communication with the anchor body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the SMA wire is heated to cause contraction and movement, then the actuator achieves desired displacement, but the attached portions of the wire experience uneven stress distribution and fatigue leading to failure
Solution Approach 1:
The wire is segmented into an engaging segment (attached to structural member) and a free segment (not attached). The engaging segment is designed with a curved portion that engages with the anchor body, while the free segment performs the contraction function. This segmentation prevents the attached portion from experiencing contraction stress, eliminating fatigue failure while maintaining actuator functionality.
Solution Approach 2:
The anchor body serves as an intermediary between the wire and the structural member. It provides a thermal sink that limits temperature increase in the engaging segment, preventing deformation at the attachment point while allowing the free segment to contract and generate force.
2Force
If the SMA wire is heated to cause contraction, then force is applied to move members, but the wire slides through the attachment point leading to pull-out failure
Solution Approach 1:
The clamping component is configured to secure the engaging segment to the anchor body before the wire is heated and subjected to contraction forces. This preliminary anchoring action prevents slide-through and pull-out failures during subsequent actuation cycles.
Solution Approach 2:
The engaging segment is formed with a curved portion that engages with a corresponding curved surface on the anchor body. This curved geometry increases the contact area and mechanical interlocking, preventing slide-through at the attachment point while allowing the wire to transmit force effectively.
3Force
If current is passed through the entire wire to cause heating and contraction, then the wire generates sufficient force, but the engaging segment deforms due to temperature increase
Solution Approach 1:
The anchor body is made of thermally conductive material to create a localized thermal sink at the attachment point. This ensures that the engaging segment remains cool and maintains its shape, while the free segment can be heated to the required temperature for contraction and force generation.
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 effectively prevents deformation in the engaging segment of the ligature, reducing stress on attachment points and preventing failure by ensuring even force distribution, thus enhancing the reliability of SMA-based actuators.
Implementation Method 1
the temperature increase in the engaging segment of the ligature is sufficiently limited by heat transfer to the anchor body
Implementation Method 2
by reduction of current passing through the engaging segment of the ligature because of current passing through the anchor body
Implementation Method 3
portions of the clamping component proximate to the clamping portions of the engaging segment of the ligature can be moved towards the anchor body to reconfigure the clamping component so that the portions of the clamping component press the clamping portions of the engaging segment of the ligature against the anchor body
Implementation Method 4
passing current through SMA wire, thereby causing it to heat, resulting in contraction of the wire and the application of force to the members it is attached to
Data Source
AI summary
The present invention is an anchor for a thermally responsive ligature that deforms when heated. The ligature has an engaging segment for engaging the anchor with two clamping portions and a curved portion. The anchor is made from a thermally and/or electrically conductive material and has an engaging surface for engaging a curved portion of the ligature. The clamping portions of the engaging segment of the ligature pass between the body and the clamping component when the curved portion of the engaging segment is engaging the engaging surface of the anchor body. Then, portions of the clamping component can be moved towards the anchor body to reconfigure the clamping component so that the portions of the clamping component press the clamping portions of the engaging segment of the ligature against the anchor body and maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body.