No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Optical Position Feedback and Phase Control of MOEMS-Scanner Mirrors
Abstract
Resonantly driven oscillating MOEMS mirrors are used in various fields in optics, telecommunications and spectroscopy. One of the important challenges in this context is to assure stable resonant oscillation with well controlled amplitude under varying environmental conditions. For this reason, we developed a compact device comprising a resonant MOEMS micro-mirror, optical position sensing, and driver electronics, with closed loop control, which ensures operation close to the mirror resonance. In this contribution we present this device and show experimental results with a 23 kHz MOEMS mirror, which demonstrate its capabilities and limitations.
... Underneath the mirror plate and the torsional springs the bulk silicon is removed. Therefore, the deflection angle is not limited geometrically 4 . The vertical sides of the comb driving electrodes form with the mirror plate a variable capacitance, which value depends on the deflection angle. ...
... The scan angle indexing measurement is performed as depicted inFig. 4. Contrary to related approaches [13] [14] only one index mark is needed: The MEMS mirror deflects the laser beam, which passes the scan head window and is reflected there partially. When the reflected beam passes the micro motor position sensor magnetic strip spring guides guide spring lensFig. ...
Precise and robust perception of the environment is crucial for highly integrated and autonomous robot systems. In this paper the dedicated design of a triangulation based laser range scanner optimized for 3D-modelling and autonomous exploration in robotics is presented. The presented laser scanner design is based on an extremely small MEMS scan head permitting a compact, lightweight and highly integrated implementation allowing for hand-eye operation. Special capabilities like variable range and confidence rating of the measuring values increase robustness. The design considerations and a prototype are described and experimental results are presented.
This paper proposes a novel self-sensing control concept for resonant MEMS mirrors solely based on the comb-drive current generated by the mirror movement and simple circuitry. Phase errors are immediately compensated by asynchronous switching of the driving voltage using the precise zero crossing detection by the steep current gradient. The mirror amplitude is detected based on the time difference between a comparator threshold crossing of the current signal and the zero crossing of the mirror, while it is controlled by the duty cycle of the driving voltage signal. The proper threshold setting is analyzed regarding the obtained sensitivity and uncertainty of the amplitude detection and is verified by measurements. It is found that even for symmetric out-of-plane comb-drives the scanning direction can be determined utilizing the mode coupling phenomenon of a lightweight MEMS mirror design with reinforcement structure. Experiments show that the proposed control concept results in a low optical pointing uncertainty of 0.52mdeg, which allows 10000 pixels with a precision of 10 sigma at a scanning frequency of 2kHz. Thus a lightweight and simple design of a high performance MEMS mirror is precisely controlled in its oscillation without any additional sensors or complex circuitry.
This paper presents a novel method to derive and identify an accurate small perturbation model of a comb-actuated resonant MEMSmirror with highly nonlinear dynamics. Besides the nonlinear stiffness and damping, the comb-drives add nonlinearities due to their electrostatic nature and their effect on the dynamic mirror amplitude over frequency behavior. The proposed model is based on a period to period energy conservation and applies for most nonlinearities present in an oscillator such as MEMS mirrors. It is shown that for specific nominal operation points with square wave excitation, the small perturbation model is linear for a wide range. The full dynamics of the derived linear model are parametrized by three constants, that can be estimated by the PLL, performing a proposed identification method only based on phase measurements. An analysis of control laws usually applied in a PLL provides important information for the proper design of controllers to meet the desired behavior for individual applications. (An open access post-print version of the article can be found at https://publik.tuwien.ac.at/files/publik_288425.pdf)
Assuring stable resonant oscillation with well controlled amplitude under varying environmental conditions is a major challenge for electrostatically driven MOEMS mirrors. For this reason, we developed a compact device comprising a resonant MOEMS micro-mirror, optical position sensing, and driver electronics with closed loop control, which ensures operation close to the mirror resonance. Closed loop control is realised by adjusting the driving frequency to minimize the phase offset of the mirror oscillation, which is notably applicable for high frequency devices. Here we present our position encoding and feedback scheme, and show first experimental results, which demonstrate the capability of our device.
Resonantly driven oscillating MOEMS mirrors are of high interest for various fields in optics, telecommunications and spectroscopy. For stable oscillation with large amplitude, operation close to resonance must be ensured under varying environmental conditions. For this reason, we have developed a compact device comprising optical position sensing, and driver electronics, with closed loop control, capable of driving resonant 1D-MOEMS micro-mirrors. Very recently, we extended our approach to 2D scanner mirrors. In this contribution we present the position encoding and feedback scheme of the novel 2D device.
Position feedback of resonant scanning micromirrors plays a key role for various applications like portable laser projection displays or scanning grating spectrometers. The SOI device layer without an additional surface implantation is used for the piezoresistive sensor design. It assures the full compatibility to microscanner technology and requires no additional technological efforts. The necessary asymmetry of the current field density is achieved by the geometrical design of the sensor and its contacting. Integrated 2D position sensors with amplitude sensitivities of 0.42mV/V° were fabricated. FEA simulation and measured data correlates well with variations of
This work deals with the development of a novel MOEMS-based platform for miniaturised 1D or 2D light barrier systems. As outlined below, such a device could be used to project a classical linear light barrier, but could equally be used to produce curved perimeters and/or even full-volume light barriers. Target applications of this technology are security and surveillance, e.g. for access, tampering or theft control, or vehicle interior presence detection.
Recently, there has been substantial progress in the development of ultra-compact image projection systems with di-mensions clearly below the size of products based on DMD™ technology. This has been enabled by the availability of electrically modulated laser sources for all three elementary colors and a two-dimensional resonant micro scanning mir-ror as MOEMS device for light deflection. The laser beam formed by collimator optics is directed onto the micro scanning mirror. Then, the reflected beam describes a highly complicated Lissajous figure on the projection screen with flare angles of up to 20 degrees. By driving the mirror and electrically modulating the intensity of the laser beam in a synchronous manner, projection of images can be achieved. In this contribution we will present the theoretical back-ground of the projection system as well as the latest achievements in system design. Both monochrome and full color systems are currently available. The latter use a separate laser bank as RGB light source, which is coupled with the pro-jection head comprising the micro-optics and the micro scanning mirror. For monochrome red systems, the laser diode can be integrated into the projection head as well, whose volume could be reduced to 15mm x 7 mm x 5mm. All sys-tems have VGA (640 x 480 pixels) resolution and operate with 8 bit color depth per pixel and 50 frames per second. This degree of miniaturization makes laser projection systems attractive for integration into mobile devices and over-comes limitations of display size in such appliances.
This paper presents a complete portable laser-based projection system using two one-dimensional magnetic actuated MEMS linear scanning micro-mirrors. Dedicated high speed electronics was developed to drive the MEMS, detect the mirror scanning position at any time and synchronize the two mirrors and the laser pulsation. The achieved projection system head is 3 cm3 and is able to project static images and videos with projection size of 50 cm diagonal at 50 cm distance with 32x32 px resolution, the resolution is only limited by current optical setup. The circuit building blocks itself can project image with resolution up to QVGA (320x240 px), suitable for information display applications. © 2009.
A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65deg and 53deg are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting thetas<sub>opt </sub>D product of 79.5 degmiddotmm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 times 1024) resolution scanned beam displays
We present an ASIC for synchronized excitation of electrostatically driven resonant micro scanning mirrors which have been developed and fabricated at the Fraunhofer IMS for several years. The mirror oscillation is excited with a rectangular driving signal and operated close to the characteristic frequency or higher. Deflection amplitude is maximum if the driving voltage is switched off precisely at the cross-over of the oscillation. We have developed and fabricated a mixed signal ASIC that starts the oscillation and runs the mirror with high efficiency by detecting the oscillation cross-over. For that, the ASIC senses the varying capacitance of the actuator"s comb-drive electrodes and converts it with a clocked charge amplifier into a voltage. The amplified capacitance signal is processed by a synchronization module which detects the minimum of the capacitance signal corresponding to the cross-over of the oscillation. An integrated charge pump provides the driving voltage. The ASIC has been fabricated at the facilities of the IMS with a 1.2 μm CMOS process. Tests with a demonstrator PCB have shown that the synchronization works highly efficient with a value of appr. 96 %. A mechanical deflection angle of ± 13° was achieved for a micro-mirror with a characteristic frequency of 250 Hz at a driving voltage of 13.5 V, only.
The domain of micromechanical systems is an extensive, useful and yet largely unexplored area. It is likely that, in many applications, small mechanisms will prove to be faster, more accurate, gentler and less expensive than the macro systems presently used. This paper explores the advantages of micromechanical systems and analyzes the scaling of forces in the micro domain.
In the last few years the importance of Micro Opto Electro Mechanical Systems (MOEMS) increased significantly in technical applications. This is caused by the possibility of combining micro optical elements with micromachining technology that makes it feasible to develop new systems with high volumes and low prices. In this article, we report on the realization of a NIR (near infrared) spectrometer in the range of 900 - 2000 nm using MOEMS technology. It is based on a scanning mirror chip, which mirror plate is structured with a diffractive aluminium layer on top. This offers the possibility to fabricate a spectrometer, which needs only one single InGaAs detector photo diode. In contrast to common CCD arrays, the obtained resolution is only limited by the performance of the spectrometer (entrance slit, exit slit, focus length, diffractive element). The scanning grating chip operates at a frequency of 500 Hz, at an optical scan range of +/- 4°. The whole spectrometer has a size of 90 x 60 x 50 mm. For first investigations of the performance, IR LEDs (light emitting diode) with 1300, 1450 and 1550 nm wavelength have been measured.
Assuring stable resonant oscillation with well controlled amplitude under varying environmental conditions is a major challenge for electrostatically driven MOEMS mirrors. For this reason, we developed a compact device comprising a resonant MOEMS micro-mirror, optical position sensing, and driver electronics with closed loop control, which ensures operation close to the mirror resonance. Closed loop control is realised by adjusting the driving frequency to minimize the phase offset of the mirror oscillation, which is notably applicable for high frequency devices. Here we present our position encoding and feedback scheme, and show first experimental results, which demonstrate the capability of our device.
We describe a spectrometer employing a microelectromechanical system (MEMS). A torsional micromirror device, which was originally designed for laser scanner applications, has been modified to act as a diffraction grating in a Czerny-Turner setup. This spectrometer system combines the working principle of a scanning monochromator with the compactness of a microsystem. The micromirror device is operated in a harmonic scanning mode at a resonant frequency of 500 Hz, enabling the system to acquire a spectrum per half cycle in one millisecond. The spectra of a calibration source in the visible and near-infrared spectral range as well as simulations concerning the optical system demonstrate the performance of the spectrometer.
We describe the design and fabrication of micromachined resonant scanners that have large scan angles at fast scan speeds. Driven by an electrostatic combdrive actuator, these 200 /spl mu/m/spl times/250 /spl mu/m micromirrors have a maximum scan angle of 28/spl deg/ (optical) at a resonant frequency of 3 kHz when driven by a sinusoidal voltage of 9.5 V (amplitude) superimposed on a 30-V dc bias. Fabricated with a four-layer polysilicon-surface-micromachining process, these resonant scanners are compact, extremely light in weight, potentially very low in cost, and operate at very low power levels. Using the scanner as a laser-beam deflector, we have demonstrated a barcode reader system.