Sacrificial Strut Assembly for SMA Actuator Crimping
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Solution Overview
Problem
The crimping process for assembling shape memory alloy (SMA) actuators in miniature devices, such as cameras, requires precise control of SMA wire length and attachment points, which is challenging due to variations in distance between attachment points, limiting miniaturization and increasing design complexity.
Innovation Solution
A method involving a sacrificial strut element with crimp tabs, where the SMA wire is crimped onto the strut before attachment to static and moving parts, allowing for accurate length maintenance and space-saving design by removing the need for crimp tool access, enabling compact SMA actuator arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the SMA wire is crimped directly onto the static and moving parts in situ, then the attachment is simplified, but space must be allowed for crimp tools to access both sides of the crimp tab which restricts miniaturization
Solution Approach 1:
The assembly process is segmented into two distinct phases: first, crimping the SMA wire onto a separate support structure (fret) in an accessible area, and second, attaching the pre-crimped assembly to the static and moving parts. This segmentation eliminates the need for crimp tool access during final assembly, resolving the contradiction between ease of manufacture and miniaturization.
Solution Approach 2:
The crimping operation is performed in advance on a support structure before the SMA wire assembly is installed in the final position. By completing the crimping action preliminarily when tool access is not constrained, the design achieves both easy manufacture and compact dimensions without requiring space for crimp tools at the final assembly location.
2Manufacturing precision
If the SMA wire length is tightly controlled to meet operational requirements, then proper operation is ensured, but variations in distance between attachment points cause corresponding variations in wire length which cancel the error
Solution Approach 1:
A support structure (fret) serves as an intermediary element that mechanically defines and maintains the precise distance between crimp locations. This intermediary component absorbs and compensates for variations in attachment point distances, ensuring consistent SMA wire length regardless of tolerances in the static and moving part mounting positions.
Solution Approach 2:
The support structure is designed with built-in dimensional tolerance compensation that cushions against variations in attachment point distances. By incorporating this compensatory mechanism in advance during the support structure design phase, the system maintains reliable operation despite manufacturing variations in the final assembly.
3Ease of manufacture
If space is allowed for crimp tool access during assembly, then the crimping process can be completed, but the design of the SMA actuator assembly is restricted and miniaturization becomes more difficult
Solution Approach 1:
The manufacturing process is divided into a preliminary crimping stage on an open support structure and a final assembly stage. This segmentation allows crimp tools to access the SMA wire freely during the first stage without constraining the compact design of the final actuator assembly, as the crimping occurs before components are positioned in their space-constrained final locations.
Solution Approach 2:
The crimping operation is performed preliminarily on a support structure that provides unobstructed tool access. By completing this manufacturing step before final assembly, the design achieves both ease of manufacture (with full tool access) and design flexibility (compact final configuration), as the support structure can be designed for manufacturability independently of the space constraints in the final assembly.
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 method ensures precise SMA wire length and attachment without hindering the design, facilitating miniaturization and reducing manufacturing time and cost, particularly beneficial in SMA actuator arrangements with multiple wires for applications like autofocus and optical image stabilization in portable devices.
Implementation Method 1
at least one shape memory alloy wire extending therebetween
Data Source
AI summary
An SMA actuator arrangement is assembled using a strut element shaped to comprise a sacrificial strut body and crimp tabs held apart by the sacrificial strut body. A SMA wire is laid across the crimp tabs which are folded and pressed to form crimps holding the SMA wire. The crimps are then attached to static and moving parts, after which the sacrificial strut body is removed. The method allows the crimping to be performed without hindrance from the static and moving parts, the sacrificial strut body holding the relative locations of the crimps prior to attachment.