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Position encoding and closed loop control of MOEMS translatory actuators

: Lenzhofer, M.; Tortschanoff, A.; Frank, A.; Sandner, T.; Schenk, H.; Kraft, M.; Kenda, A.


Schmid, U. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Smart Sensors, Actuators, and MEMS IV : 4 May 2009, Dresden, Germany
Bellingham, WA: SPIE, 2009 (SPIE Proceedings Series 7362)
ISBN: 0-8194-7636-6
ISBN: 978-0-8194-7636-4
ISSN: 0277-786X
Paper 736212
Conference "Smart Sensors, Actuators, and MEMS" <4, 2009, Dresden>
Fraunhofer IPMS ()
MOEMS; translatory micro-mirror drive; FTIR spectrometer; Michelson Interferometer; closed-loop control

We present a new method for detecting the accurate position of micro-electro-opto-mechanical system (MOEMS) devices, thus enabling the implementation of closed-loop controls. The ensuing control mechanism allows building robust MOEMS-based Fourier-transform infrared (FTIR) spectrometers with large mechanical amplitudes and thus good spectral resolutions. The MOEMS mirror device, a rectangular 1.65 mm metalized plate mirror suspended on bearing springs and driven by comb-structured electrodes, is driven by a rectangular signal with a duty cycle of 50% and high voltage levels up to 140 V at a frequency near twice its mechanical resonance frequency. Out-of-plane mirror displacements of up to ±100 µm have thus been achieved. To handle the high bandwidth of the sinusoidal mirror position reference signal, which is generated by a laser reference interferometer, an analog position detection circuit is necessary. This dedicated circuit demodulates the reference signal and generates a highly accurate control signal returning the zerocrossing position of the mirror. This permits the implementation of a closed-loop control, which ensures optimally stable MOEMS mirror movement and maximal mechanical amplitude, even under varying environmental conditions. While this solution has been developed for a specific MOEMS device, the principle is widely applicable to related components.