SMA Actuator Lens Tilt and Stress via Flexure Compression
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Solution Overview
Problem
Existing SMA actuation systems for miniature cameras face challenges in achieving precise movement of camera lens elements with minimal tilt and maximum range while maintaining mechanical stress within material limits, due to constraints on stress distribution and stiffness in the suspension system.
Innovation Solution
A shape memory alloy actuation apparatus with a suspension system comprising flexures arranged at different positions along the movement axis, where the SMA wire applies a force component perpendicular to the movement axis, compressing the flexures and allowing them to apply a force in the same direction as the SMA wire, thereby reducing tilt and increasing the range of movement without exceeding material limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the SMA wire is arranged at an acute angle to the movement axis, then the actuation force is improved, but the stress distribution becomes unbalanced causing tilt
Solution Approach 1:
The patent introduces a biassing element that applies a counter-force to balance the unbalanced stress distribution caused by the acute-angled SMA wire. This counter-weight principle allows the system to maintain both the actuation advantage of acute-angle wiring and the stability required to prevent tilt during lens element movement.
Solution Approach 2:
The patent applies different mechanical properties to different parts of the suspension system by using flexures with varying stiffness characteristics. Specific flexures are designed with higher or lower stiffness to locally compensate for stress imbalances, allowing precise control over force distribution and tilt prevention while maintaining overall system stability.
2Length of moving object
If the range of movement is increased, then the focusing capability is improved, but the mechanical stress exceeds material limits
Solution Approach 1:
The patent employs a dynamic suspension system using flexures that can adapt their stiffness characteristics during movement. The flexures are designed to provide higher stiffness when stress approaches material limits and lower stiffness when additional movement range is needed, enabling the system to achieve extended focusing range while preventing excessive stress that would exceed material strength limits.
3Stability of the object's composition
If the stiffness of the suspension system is increased, then the tilt control is improved, but the friction and resistive force increase
Solution Approach 1:
The patent implements non-uniform stiffness distribution across the suspension system by designing flexures with different stiffness values at different locations. This allows high stiffness in directions where tilt control is critical while maintaining low stiffness in directions where movement freedom is needed, thereby achieving effective tilt control without introducing excessive friction and resistive forces throughout the entire system.
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 allows for high minimum stress in the SMA wire for operation at high temperatures, reduces maximum stress to prevent fatigue, and increases the range of movement achievable while minimizing tilt, enhancing the optical performance of miniature cameras.
Implementation Method 1
Actuation may be achieved by control of the temperature of the SMA actuator over an active temperature range in which the SMA actuator changes between martensite and austenite phases in which the stress and strain of the SMA actuator changes
Implementation Method 2
at high temperatures the SMA actuator transforms into the austenite phase which induces a deformation causing the SMA actuator to contract
Implementation Method 3
a suspension system comprising a plurality of flexures coupled between the support structure and the movable element to support the movable element on the support structure and to guide movement of the movable element along a movement axis by deflection of the flexures
Implementation Method 4
a biassing element, in addition to said flexures, connected between the support structure and the movable element and arranged to apply a biassing force to the movable element in a second direction along the movement axis opposite to said first direction
Data Source
Figure 1~2
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Figure 5
AI summary
An SMA actuation apparatus comprises a camera lens element supported on a support structure by a plurality of flexures. An SMA wire at an acute angle to the movement axis and a biassing element are connected between the support structure and the movable element. A component of the force applied by the SMA wire perpendicular to the movement axis compresses the flexures causing them to apply a force to the movable element having a component along the movement axis in the same direction as the SMA wire. An end-stop limits the movement of the movable element, and the moment applied by the end-stop to the movable element about the centre of stiffness is equal to the moment applied by the SMA wire about the centre of stiffness at the point when the movable element loses contact with the end-stop on contraction of the SMA wire.