SMA Actuator Wire Optical Assembly End-Stop Design
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Solution Overview
Problem
Existing optical assemblies with SMA actuator wires face reliability issues due to excessive strain during impacts, as conventional end-stop surfaces either limit movement or fail to prevent wire damage, especially when SMA actuator wires are inclined with respect to the optical axis.
Innovation Solution
Incorporating end-stop surfaces that extend substantially orthogonally to the direction of SMA actuator wires, preventing excessive strain while allowing desired movement, and positioning them in line or not in line with the wires to restrict strain or rotation, respectively, to enhance protection without restricting movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional end-stop surfaces extending perpendicular or parallel to the optical axis are used, then the structure is simple, but the SMA actuator wire experiences excessive strain during impacts causing damage
Solution Approach 1:
The end-stop surface is oriented specifically perpendicular to the SMA actuator wire direction rather than using a universal perpendicular-to-optical-axis orientation. This local adaptation ensures that each end-stop is optimally positioned to protect the specific SMA wire it constrains, preventing excessive strain during impacts while maintaining overall structural simplicity.
2Reliability
If end-stop surfaces are positioned to prevent excessive SMA actuator wire strain, then wire protection is improved, but the desired degree of movement is restricted
Solution Approach 1:
The system uses multiple end-stop surfaces oriented perpendicular to each SMA actuator wire direction, creating a dynamic constraint system. This allows the optical element to move freely within the operational range defined by the intersection of multiple constraint planes, while preventing excessive movement in any single direction that would strain the SMA wires beyond their safe limits.
3Reliability
If end-stop surfaces extend orthogonally to the SMA actuator wire direction, then wire strain is minimized during impacts, but the end-stop must be precisely positioned in line with the wire
Solution Approach 1:
The end-stop structure is segmented into multiple independent end-stop surfaces, each oriented perpendicular to a specific SMA actuator wire direction. This segmentation allows each end-stop surface to be independently positioned and oriented to match its corresponding wire, distributing the precision requirement across multiple discrete elements rather than requiring a single complex precisely-positioned component.
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 effectively prevents SMA actuator wire damage from impacts while maintaining the desired degree of movement, ensuring the wires operate within their safe strain limits and extending their lifespan by reducing fatigue.
Implementation Method 1
an optical assembly comprising at least one optical element and at least one shape memory alloy (SMA) actuator wire connected between a static portion of the optical assembly and the optical element, wherein the SMA actuator wire is inclined with respect to the optical axis of the optical element
Data Source
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AI summary
Broadly speaking, the present techniques are concerned with improving protection against impact in an actuator assembly wherein a moveable element is driven by shape memory alloy (SMA) actuator wires. The actuator assembly may be an optical assembly comprising a static portion, an optical element capable of movement with respect to the static portion, and at least one shape memory alloy actuator wire connected between the static portion and the optical element and inclined with respect to the optical axis of the optical element. End- stop surfaces arranged to limit said movement extending substantially orthogonally to the direction along the respective shape memory alloy actuator wires, thereby providing improved impact protection compared to end-stop surfaces extending orthogonally to the optical axis.