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Robust control of miniaturized optical image stabilizers for mobile phone cameras

University of British Columbia

Cameras in mobile phones are the most popular due to their availability and portability; however, image blur caused by involuntary hand-shakes of the photographer degrades their image quality as mobile phones become lighter, smaller, and high-resolution. The optical image stabilizer (OIS) is a hardware-based alternative to conventional software-based de-bluring algorithms that offer superior de-blur; however, they are set back for mobile phone applications by cost, size, and power limitations. The magnetically-actuated lens-tilting OIS is a novel miniaturizable and low-power conceptual design which is suitable for low-cost micro manufacturing methods; however, significant product variabilities caused by these methods, along with the strict performance requirements to outperform software-based algorithms, and the limited controller implementation capabilities of mobile phone devices pose a challenging control problem that is solved by the modeling and controller design method proposed in this thesis. To solve the problem, practical manufacturing tolerances are simulated through computer-aided design and analyzed by finite-element methods to obtain the structure of the dynamics of OIS and uncertainties in dynamics. A dynamic uncertainty model is developed based on the analysis results and the robust H∞ control theory is applied to guarantee the closed-loop stability and optimize the closed-loop performance against uncertainties with constrained controller order. The proposed method is demonstrated in two steps. First, it is applied to a set of large-scale OIS prototypes to demonstrate its feasibility in an experimental setting and its capability to deal with physical product variabilities. Then, it is applied to a set of small-scale OIS prototypes containing mass-produced parts to verify its applicability to real OISs. In both cases, the experimental results suggest that the robust H∞ controller outperforms the conventional nominal controllers and the μ-synthesis controller. By dealing with control challenges of the magnetically-actuated lens-tilting OIS, the application of this conceptual design to mobile phone cameras is expanded. Substitution of the conventional post-processing algorithms in mobile phone cameras with OIS has significant impact on their image quality.

Text

2019-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/58778

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/