Helical SMA Actuator Assembly for Long-Stroke Linear Motion
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Solution Overview
Problem
Existing actuator assemblies using shape memory alloy (SMA) wires for translational movement in miniature devices, such as camera lenses, face challenges in achieving a higher stroke without compromising accuracy and repeatability, and require mechanisms to prevent rotational movement in non-rotationally symmetric components.
Innovation Solution
An actuator assembly with a support structure, first and second movable parts, and bearing arrangements that convert rotational movement into helical movement, incorporating anti-rotation mechanisms to prevent rotational displacement and enhance translational stroke, using SMA elements to drive rotation and biasing arrangements for stable positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a single helical bearing arrangement is used to convert rotation to helical movement, then the actuator can achieve translational movement, but the stroke is limited and normal forces on the bearing arrangement increase
Solution Approach 1:
The single helical bearing arrangement is segmented into two separate bearing arrangements: a first helical bearing arrangement that converts rotation to helical movement, and a second bearing arrangement that provides rotational constraint. This segmentation allows the stroke to be increased by distributing the mechanical functions across separate components, reducing the normal forces on any single bearing arrangement while maintaining the desired translational movement capability.
Solution Approach 2:
A second movable part is introduced as an intermediary element between the first movable part and the support structure. This intermediary component undergoes rotational constraint while allowing translational movement, thereby increasing the overall stroke of the actuator assembly without directly increasing the normal forces on the first helical bearing arrangement. The intermediary part acts as a mechanical lever that amplifies the movement range.
2Length of moving object
If the second movable part is allowed to rotate freely during actuation, then the stroke can be increased, but rotational displacement occurs in non-rotationally symmetric components
Solution Approach 1:
The rotational degree of freedom is extracted and isolated from the translational movement path. The second bearing arrangement is specifically designed to constrain rotation while allowing translation, thereby separating these two degrees of freedom. This extraction ensures that the second movable part can move along the desired translational path without introducing unwanted rotational displacement into non-rotationally symmetric components.
Solution Approach 2:
The rotational constraint function is replaced by a dedicated bearing arrangement (second bearing arrangement) that provides rotational limitation. This specialized mechanical component substitutes for what would otherwise require complex geometric constraints or additional actuators, achieving rotational stability through dedicated mechanical guidance while maintaining translational freedom.
3Length of moving object
If SMA actuator wires are angled at an acute angle to the movement direction, then the amount of movement is increased, but the actuator extent in the movement direction increases
Solution Approach 1:
The actuator configuration transitions from a single-dimensional linear arrangement to a multi-dimensional arrangement involving rotational movement around a primary axis. By introducing rotational freedom in a different dimension and using helical bearing arrangements to convert this rotation into translational movement, the system achieves increased stroke without requiring the SMA wires to be angled excessively, thereby controlling the actuator extent in the movement direction.
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 assembly achieves increased stroke and accuracy in translational movement while maintaining stable, non-rotational positioning of components, suitable for applications requiring precise optical adjustments.
Implementation Method 1
a first bearing arrangement (supporting the first movable part on the support structure) configured to convert said rotation of the first movable part into helical movement of the first movable part around the primary axis relative to the support structure
Implementation Method 2
an actuator arrangement configured (on actuation) to drive rotation of the first movable part around a primary axis relative to the support structure
Data Source
AI summary
An actuator assembly is disclosed. The actuator assembly comprises a support structure (2): a first movable part (10): a second movable part (12): an actuator arrangement configured to drive rotation of the first movable part around a primary axis (O) relative to the support structure: a first bearing arrangement (20, 21) configured to convert said rotation of the first movable part into helical movement of the first movable part around the primary axis relative to the support structure: a rotation control arrangement capable of limiting rotation of the second movable part around the primary axis relative to the support structure; and a second bearing arrangement (30, 31) configured such that, when the first movable part undergoes said helical movement and the second movable part undergoes said rotation limitation, the second movable part undergoes translational movement along the primary axis relative to the support structure and/or the first movable part.