SMA Autofocus Actuator with Optical Axis Return Force
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Solution Overview
Problem
Existing SMA-based camera module autofocus actuators face issues with frictional forces between the housing and lens barrel, leading to premature failures and increased stress on the structure, which are not adequately addressed by prior solutions that introduce a constant perpendicular force component.
Innovation Solution
A camera module autofocus actuator design utilizing a shape memory alloy wire with a return elastic element exerting force only in the optical axis direction, combined with guide channels and rolling spheres to manage friction, and an optional Flexible Printed Circuit board with a magnet and Hall sensor for position feedback, minimizing stress and enhancing actuator longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oblique return spring is used to ensure contact between rolling members and lens barrel, then frictional force management is improved, but a constant perpendicular force component is generated causing stress on the structure and leading to premature failures
Solution Approach 1:
The return spring is configured to exert force only in the optical axis direction (vertical direction in the patent), creating an asymmetric force distribution that eliminates the harmful perpendicular component while maintaining the necessary contact between rolling members and lens barrel
Solution Approach 2:
Rolling members (spheres) are introduced as intermediary elements between the housing and lens barrel, with the return spring acting on these rolling members to transmit force only in the optical axis direction, thereby managing friction without generating structural stress
2Reliability
If rolling members are introduced to manage friction, then frictional force management is improved, but the structure becomes more complex requiring making and reciprocal coupling of sub-assemblies
Solution Approach 1:
The guide channels are integrated directly into the housing structure, and the rolling members are positioned within these channels such that the entire friction management system can be assembled as a unified structure rather than separate sub-assemblies, reducing manufacturing complexity
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 reduces stress on the actuator structure, improves friction management, and extends the lifespan of the SMA-based autofocus mechanism by aligning forces with the optical axis, ensuring precise focusing without premature failures.
Implementation Method 1
The controlled heating via Joule effect of the shape memory alloy wire causes its contraction and the movement of the lens holder with respect to the housing
Implementation Method 2
a shape memory alloy wire in contact with the lens holder (sometimes referred in the field as lens barrel) and fixed to the camera module housing
Implementation Method 3
a return elastic element, and in which actuator the return elastic element is mounted between the housing and the lens carrier, the return elastic element exerting a force only in the optical axis direction
Implementation Method 4
at least four spheres, a bottom plate, two electric terminals at a different height with respect to the protrusion apex
Data Source
AI summary
An autofocus actuator for camera modules and control method thereof, the autofocus actuator incorporating a shape memory alloy wire as actuating element, at least 4 spheres as sliding aids, and including a return elastic element mounted between an autofocus housing and a lens carrier and exerting a force only in the optical axis direction.