MEMS Piston-Tube Actuator Autofocus for Image Sensor
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Solution Overview
Problem
Traditional autofocus mechanisms in miniature cameras, which rely on lens barrel actuation, suffer from slow speed, large size, and optical lens tilt due to the heavy load on actuators, compromising image quality and speed.
Innovation Solution
The implementation of MEMS electrostatic piston-tube actuators that translate and rotate the image sensor along the optical axis and bi-axial tilt axes, enabling compact autofocus with improved image quality by canceling lens tilt and accommodating image sensor packaging and electrical wiring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If lens barrel actuation is used to achieve autofocus, then the autofocus function is achieved, but the module size becomes large and the actuator speed becomes slow
Solution Approach 1:
Instead of moving the lens barrel forward to achieve focus, this invention moves the image sensor backward along the optical axis. This inversion of the traditional autofocus approach allows the use of a compact MEMS actuator with stroke of 5-15 micrometers to move the image sensor (mass of several tens of milligrams), achieving both high speed and small module size. The lens barrel remains stationary, eliminating the need for large actuators and complex mounting structures.
Solution Approach 2:
The invention replaces the traditional mechanical lens barrel actuation system with a MEMS-based electrostatic actuator system. The MEMS actuator uses electrostatic fields to move the image sensor, eliminating the need for large mechanical components. This substitution enables high-speed autofocus (response time of several milliseconds) while maintaining a compact module size suitable for portable devices.
2Manufacturing precision
If lens barrel actuation is used to achieve autofocus, then the autofocus function is achieved, but optical lens tilt occurs and image quality deteriorates
Solution Approach 1:
By inverting the autofocus mechanism to move the image sensor instead of the lens barrel, the invention eliminates the need to mount the lens barrel on a moving stage. This removes the source of lens tilt (0.2° mentioned in background) and associated image quality deterioration. The lens barrel remains firmly mounted in a fixed position, ensuring optimal optical alignment throughout the autofocus range.
3Volume of moving object
If image sensor actuation is used to achieve autofocus, then the module size is reduced and speed is improved, but the actuator must handle image sensor mass and electrical wiring compatibility
Solution Approach 1:
The invention merges the MEMS actuator and image sensor into a single integrated package. The actuator is designed with built-in electrical connections (spring contacts or flex cables) that maintain continuous electrical connectivity with the image sensor during movement. This integration simplifies manufacturing by eliminating separate mounting steps and ensures reliable electrical wiring compatibility while maintaining the compact form factor.
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 solution provides a compact, high-speed autofocus mechanism that enhances image quality by effectively addressing the limitations of traditional lens barrel actuation systems, including reduced size and improved handling of image sensor motion.
Implementation Method 1
MEMS electrostatic piston-tube actuators that are developed by the applicants and described in patent application U.S. application Ser. No. 14/449,544 and PCT/IB2014/001498 are able to meet such requirements for autofocus using image sensor actuation.
Implementation Method 2
The actuator provides 3 degrees-of-freedom motion: translation along the optical axis (i.e. z axis) and bi-axial tilt about the in-plane x and y axes.
Data Source
AI summary
A miniature camera module that achieves autofocus (AF) by applying actuation to the image sensor using MEMS (Micro Electro Mechanical System) actuators comprising of a piston-tube electrostatic actuators. The camera comprises of a MEMS piston-tube actuator, an image sensor die, an IC package, a housing, and a lens barrel. The image sensor die is attached and is electrically bonded to the moving rotor of the MEMS electrostatic piston-tube actuator, which is, in turn, attached and electrically bonded to a semiconductor device package. The packaged piston-tube actuator with the image sensor attached to it is covered with a transparent protection lid which could be an IR filter.