Micro Lens Actuator Scaled-Up Prototype — MASASHI KARASAWA DESIGN

Camera vibration could lead to blurry still images when taking pictures in low-light situation where slower shutter speed is used. For videography, it could lead to footages showing unpleasant frame-to-frame jitter. Since more and more cameras are made in compact form factors and are meant to be hand-held, optical image stabilization could be utilized to compensate the inevitable hand shake and minimize the negative effects it induces. However, the stabilizer cannot take up too much footprint, as gadgets today are often designed with thin profiles and are tightly packed with other electronics. A collaborative development project by UBC Control Engineering Laboratory and Micro-Electro-Mechanical System (MEMS) Laboratory seek to solve the problem by developing a flexure-mechanism-based micro-size lens actuator that can tilt the optics in yaw and pitch orientations to achieve 2-axis optical image stabilization. I was the designer of the scale-up version of of the micro-lens actuator, and the functional prototype was successfully used for preliminary characterization works and controller development.

Micro Lens Actuator

Scaled-Up Prototype

For the scaled-up actuator prototype, the platform movement is tracked using laser doppler velocimetry (LDV). However, a much more compact and economical solution, such as capacitive sensors, would be needed for the actual product.

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Optical Stabilization for Sharper Image

The camera movement causes the light to move along the image sensor pixels during exposure, which results in false images. Optical image stabilization could be utilized to counter-act the camera movement to keep the light still with respect to the image sensor during exposure.

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Actuator Concepts

The micro lens actuator design (approximately 10 mm by 10 mm footprint) was inspired by flexure mechanism often seen in a MEMS device. By varying the current at the 4 coils which push or pull the flexure platform, the actuator can achieve 3 degrees of freedom, which include 2 tilts and a linear motion along the optical axis. The tilting actions could be used for 2-axis optical image stabilization, while the linear motion could be utilized for focusing.

Flexure mechanism has several advantages over traditional multi-component mechanism. Since flexure mechanism relies on deformation to articulate, it is not susceptible to typical problems like friction, backlash, or hysteresis found in traditional mechanisms. Furthermore, due to its simple and single-piece architecture, it is possible to achieve low manufacturing cost during mass production.

Scaled-Up Actuator Prototype

In order to perform preliminary studies to identify the characteristics of the mechanism and to plan for the implementation strategies, an 8X scaled-up prototype was designed and fabricated. Compared to the actuator of actual compact size, the scaled-up prototype is less challenging to build, and its movement could be tracked without a need to develop new expensive sensing solution.

The prototype consists of a water-jet-cut flexure lens platform (with 4 magnets glued on the bottom side), 4 hand-wound coils, and a robust base to house the components. The air gap between the magnets and the coils could be adjusted by changing the mounting heights of the coils.

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Multiple Flexure Lens Platforms Tested

The scale-up prototype’s flexure lens platform can be easily swapped out. Thus multiple platforms with different beam widths and plate thicknesses are designed and fabricated for physical testing. I also conducted modal analysis in COMSOL Multiphysics FEA software to predict the vibration modes for each design.

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Experimental Setup

During the preliminary experiment, the prototype’s velocity and speed was tracked using LDV, and a classical controller (PI + notch filter) was implemented using a dSPACE microcontroller. However, due to the actuator’s inherent non-linearity and non-uniformity of the hand-wound coils, a classical controller fails to control it in certain scenarios (lower figure). Thus robust controllers (LPV) are designed in the later stage to account for these issues.