Optimized actuation of resonant MEMS mirrors for laser beam scanning applications

The present paper on regards the improvement of the way one resonant MEMS (Micro Electro-Mechanical System) micro-mirror is usually controlled to project the wanted laser beam scanning image/pattern, with the goal of creating a fast-response application able to reach as fast as possible the wanted projection aperture and to maintain it with discrete voltage pulses, minimizing the angle amplitude error and with a look to the power consumption of the architecture. On top of that a self-adapting actuation system was realized, able to comply to any mirror design obtaining, thus, a driving system which no longer requires to be initialized according to the mirror parameters. The previous architecture, in fact, leveraged the well-known resonant frequency of the driven mirror, to set two square-wave signals with the same frequency and shifted by 180 degrees for the two mirror's electrodes, and with a certain voltage amplitude to reach a specific aperture. This technique, otherwise, fails to ensure a fast initial opening of the mirror to get to the target angle and requires a continuous excitation during its operation time to hold the same oscillation amplitude, even more if we consider the low damping coefficient that characterize these high-Q mirrors and that, despite the benefits, makes the device less stable due to its high responsivity. For these reasons the project was born to overcome these limitations and to create a design based on larger but sporadic pulses, thinking about boosting the initial opening and controlling it without a continuous change in driving amplitude voltage. The paper will detail a first modelling of the architecture, designing with Simulink the features of the new driving system and testing them with the model of a generic resonant mirror, a various Q factor. Once the simulations results were satisfying and some design solutions were identified, will be described a RTL implementation of an architecture on an FPGA (Field Programmable Gate Array), mounted on an custom evaluation board. A discussion of experimental results will follow, to verify experimentally the stability of the architecture designs identified on a board that manages the full control of a mirror, actuating and sensing its oscillation, especially in comparison with the legacy driving mode.