KEYWORDS: Digital image correlation, 3D metrology, Laser soldering, 3D tracking, Optical spheres, Calibration, 3D image processing, Cameras, Engineering, Imaging systems
3D DIC is an optical noncoherent full-field optical technique that enables the measurement of shape, displacements (u,v,w) and strains (εxx, εyy, εxy) of a mechanical structure subjected to an external force. During investigations of large engineering structures (e.g., wind turbine blades), a single 3D DIC system is insufficient to deliver the information from the entire object. Hence multi 3D DIC systems should be used and the output information from all systems must be combined into a single coordinate system. This task is relatively simple if each system’s Field-of-Views (FoV) partially overlap. The task gets much more complicated if the FoVs of each system are separated. In such a case, an additional system defining reference coordinate system is required. In this work, we analyse the possibility of using a laser tracker system, an optical ranging method that provides a common reference coordinate system to FoVs distributed in space. Such an approach supporting multi-3D DIC measurements requires specific calibration targets and additional calibration procedures to deliver reliable and accurate results. The work presents the full calibration and data processing path and an experimentally estimated accuracy for the technique.
Time averaging technique applied to different interferometric methods is one of the most commonly used measurement technique in vibration testing. The information on amplitude of vibration is encoded in so called fringe envelope function described by the J0 Bessel function in case of harmonic motion. In the presented paper the author proposes novel solution for amplitude distribution evaluation. It is based on the analysis of the Bessel pattern modulation distribution. For modulation evaluation and Directional Spatial Carrier Phase Shifting (DSCPS) method are used. Conducted error analysis prove usefulness of the proposed approach.
Time averaging interferometry is one of the techniques that allows to investigate a dynamic behaviour of MEMS elements. The information of the maximum amplitude of vibration is encoded in the argument of Bessel function. Many different approaches enable evaluation of this value. Due to the fact that accuracy of the result depends on the quality of the input data, Bessel function of a good quality must be calculated first. Wide range of modulation distribution calculation methods enable to obtain absolute or square value of J0. These results are more difficult in processing than pure Bessel function because of gradient function discontinuity or poor SNR. For ensuring smaller errors one may normalize absolute values of J0 by the sign of the function. In this paper, several different algorithms for determining the sign of Bessel function were investigated and compared. For each approach accuracy of the method was calculated. In the end, the best solution was found.
Classical time-averaging is widely used for MEMS/MOEMS dynamic behavior investigations. In order to evaluate the information on maximum amplitude at a given load of vibrating object one needs to evaluate the argument of Bessel function that encodes the useful information. For this purpose many different approaches were presented. Among them Temporal Phase Shifting applied to Bessel fringes is of special interest since it provides most accurate results. It, however, requires additional cumbersome pixelwise correction routine via specially designed look-up-table. In this paper we investigate, through extensive numerical simulations, the possibility of reduction of phase evaluation error (without correction routine) by different strategies of phase shifting. Two different 5 step algorithms are investigated for that purpose. Additionally, quick and robust correction procedure based on evaluated phase distribution is presented.
Time averaging technique applied to different interferometric methods is one of the most commonly used measurement technique in vibration testing. The information on amplitude of vibration is encoded in so called fringe envelope function described by the J0 Bessel function in case of harmonic motion. In the presented paper the author proposes novel solution for amplitude distribution evaluation. It is based on the analysis of the Bessel pattern modulation distribution. For modulation evaluation Temporal Phase Shifting method was used. Conducted numerical error analysis prove usefulness of the proposed approach.
Classical Time Averaging and Stroboscopic Interferometry are widely used for MEMS/MOEMS dynamic behavior
investigations. Unfortunately both methods require an extensive measurement and data processing strategies in order to
evaluate the information on maximum amplitude at a given load of vibrating object. In this paper the modified strategies
of data processing in both techniques are introduced. These modifications allow for fast and reliable calculation of
searched value, without additional complication of measurement systems. Through the paper the both approaches are
discussed and experimentally verified.
Modern tendencies of higher education require development of master programs providing achievement of learning outcomes corresponding to quickly variable job market needs. ITMO University represented by Applied and Computer Optics Department and Optical Design and Testing Laboratory jointly with Warsaw University of Technology represented by the Institute of Micromechanics and Photonics at The Faculty of Mechatronics have developed a novel international master double-degree program “Optical Design” accumulating the expertise of both universities including experienced teaching staff, educational technologies, and experimental resources. The program presents studies targeting research and professional activities in high-tech fields connected with optical and optoelectronics devices, optical engineering, numerical methods and computer technologies. This master program deals with the design of optical systems of various types, assemblies and layouts using computer modeling means; investigation of light distribution phenomena; image modeling and formation; development of optical methods for image analysis and optical metrology including optical testing, materials characterization, NDT and industrial control and monitoring. The goal of this program is training a graduate capable to solve a wide range of research and engineering tasks in optical design and metrology leading to modern manufacturing and innovation. Variability of the program structure provides its flexibility and adoption according to current job market demands and personal learning paths for each student. In addition considerable proportion of internship and research expands practical skills. Some special features of the “Optical Design” program which implements the best practices of both Universities, the challenges and lessons learnt during its realization are presented in the paper.
Classical time-averaging and stroboscopic interferometry are widely used for MEMS/MOEMS dynamic behavior
investigations. Unfortunately both methods require an amplitude magnitude of at least 0.19λ to be able to detect resonant
frequency of the object. Moreover the precision of measurement is limited. That puts strong constrains on the type of
element to be tested. In this paper the comparison of two methods of microobject vibration measurements that overcome
aforementioned problems are presented. Both methods maintain high speed measurement time and extend the range of
amplitudes to be measured (below 0.19λ), moreover can be easily applied to MEMS/MOEMS dynamic parameters
measurements.
The paper presents the novel approach to an interferometric, quantitative, massive parallel inspection of
MicroElectroMechanicalSystems (MEMS), MicroOptoElectroMechanical Systems (MOEMS) and
microoptics arrays. The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under
test. The probing wafer is exchangeable and contains one of the micro-optical interferometer arrays based on:
(1) a low coherent interferometer array based on a Mirau configuration or (2) a laser interferometer array
based on a Twyman-Green configuration. The optical, mechanical, and electro-optical design of the system
and data analysis concept based on this approach is presented. The interferometer arrays are developed and
integrated at a standard test station for micro-fabrication together with the illumination and imaging modules
and special mechanics which includes scanning and electrostatic excitation systems. The smart-pixel approach
is applied for massive parallel electro-optical detection and data reduction. The first results of functional tests
of the system are presented. The concept is discussed in reference to the future M(O)EMS and microoptics
manufacturers needs and requirements.
The authors of the paper propose a novel approach to the analysis of fringe patterns described by the Bessel function.
This kind of patterns can be met while using Time Averaging Interferometry for vibration investigations. The directional
spatial carrier phase shifting technique (one of the automatic fringe pattern analysis methods) is proposed to decode the
information encoded in the function argument. With additional correction process (the analyzed J0 function differs from
the sinusoidal one) the investigated object vibration amplitude may be evaluated. An unquestionable merit of the
proposed technique is its processing simplicity and single pattern analysis scheme. The paper presents features of the
proposed approach as well as its possible measurement errors, via extensive numerical simulations. Performed
experiments corroborate the theoretical findings.
KEYWORDS: Cameras, Demodulation, Interferometers, Interferometry, Imaging systems, Inspection, Signal detection, Signal processing, Data processing, Modulation
The paper presents the electro-optical design of an interferometric inspection system for massive parallel inspection of
Micro(Opto)ElectroMechanicalSystems (M(O)EMS). The basic idea is to adapt a micro-optical probing wafer to the
M(O)EMS wafer under test. The probing wafer is exchangeable and contains a micro-optical interferometer array: a low
coherent interferometer (LCI) array based on a Mirau configuration and a laser interferometer (LI) array based on a
Twyman-Green configuration. The interference signals are generated in the micro-optical interferometers and are applied
for M(O)EMS shape and deformation measurements by means of LCI and for M(O)EMS vibration analysis (the
resonance frequency and spatial mode distribution) by means of LI. Distributed array of 5×5 smart pixel imagers detects
the interferometric signals. The signal processing is based on the "on pixel" processing capacity of the smart pixel
camera array, which can be utilised for phase shifting, signal demodulation or envelope maximum determination. Each
micro-interferometer image is detected by the 140 × 146 pixels sub-array distributed in the imaging plane. In the paper
the architecture of cameras with smart-pixel approach are described and their application for massive parallel electrooptical
detection and data reduction is discussed. The full data processing paths for laser interferometer and low coherent
interferometer are presented.
Although low coherence interferometers are commercially available (e.g., white light interferometers), they are generally
quite bulky, expensive, and offer limited flexibility. In the paper the new portable profilometer based on low coherence
interferometry is presented. In the device the white light diode with controlled spectrum shape is used in order to
increase the zero order fringe contrast, what allows for its better and quicker localization. For image analysis the special
type of CMOS matrix (called smart pixel camera), synchronized with reference mirror transducer, is applied. Due to
hardware realization of the fringe contrast analysis, independently in each pixel, the time of measurement decreases
significantly. High speed processing together with compact design allows that profilometer to be used as the portable
device for both in and out door measurements. The capabilities of the designed profilometer are well illustrated by a few
application examples.
The paper introduces different approaches to overcome the large ratio between wafer size and feature size in micro
production. The EU-project SMARTIEHS develops a new concept for high volume M(O)EMS testing. The design of the
test station is presented and the advancements compared to the state of the art are introduced within the following fields:
micro-optical laser interferometer (LI) design, DOE-based microinterferometer production, smart-pixel camera and
signal processing for resonance frequency and vibration amplitude distribution determination. The first experiments
performed at LI demonstrator are also reported.
The surface flatness of transparent plates is frequently tested in a conventional Fizeau interferometer. In case of quasiparallel
plates, however, a common problem is the additional reflection from the plate rear surface. Unwanted parasitic
intensity distribution modulates the two-beam interferogram of the plate front surface and makes the application of phase
methods for automatic fringe pattern analysis inefficient. On the other hand parasitic fringes contain the information on
the light double passage through the plate (i.e., optical thickness variations). Several methods to suppress unwanted
fringe modulations are available. However, these methods require either modification of a sample or sophisticated
equipment and complicated data analysis. In this paper we present our proposal of processing the three-beam
interferograms obtained in a Fizeau interferometer when testing quasi-parallel optical plates. The modulation distribution
of acquired pattern encodes the information of the plate optical thickness variations, whereas the phase distribution
contains the information about the sum of profiles of both surfaces (uniform refractive index distribution is assumed).
Both maps can be derived using a combination of different interferogram analysis techniques such as Temporal or
Spatial Carrier Phase Shifting and Vortex Transform. As the result separate information about both surfaces from a
single measurement can be obtained.
In this paper we present our proposal of processing three-beam interferograms obtained in a Fizeau interferometer when
testing quasi-parallel optical plates. If the intensities of three interfering beams reflected from the front and back surfaces
of the investigated plates and from the reference flat are nearly equal, the modulation distribution of the pattern encodes
the information of the plate optical thickness variations, whereas the phase distribution contains the information about
the sum of profiles of both surfaces (uniform refractive index distribution is assumed). Both maps can be derived using a
combination of different interferogram analysis techniques such as Temporal or Spatial Carrier Phase Shifting and
Vortex Transform. As a result separate information about both surfaces from a single measurement can be obtained. The
situation complicates, however, when noticeable difference of the beam intensities occurs. We prove that in this case the
modulation still contain useful information on the optical thickness of the investigated plate. Numerical studies of the
method working principle are complemented by experimental results.
The paper deals with a common problem in measuring surface flatness of transparent quasi-parallel plates in a Fizeau
interferometer. The beam reflected from the rear surface leads to a complicated interferogram intensity distribution. The
application of phase shifting for the plate front surface flatness determination becomes ineffective. We propose a new
computation approach to suppress spurious modulations. First we find a two-beam-like interference pattern relevant to
plate thickness variations using either temporal or spatial phase shifting. Its distribution is calculated using the Hilbert
transform. The residual spherical aberration of the illuminating beam and the shape of the reference flat (determined by
an absolute flatness testing conducted with the same interferometer) are subtracted from the plate thickness distribution.
In this way the shape of the front surface is obtained. Numerical studies are complemented by experimental results.
The paper deals with the calibration error of unequal phase changes across the interferogram in phase shifting interferometry, i.e., tilt-shift error. For its detection the lattice-site representation of phase shift angles is used. The error can be readily discerned using (N+1) algorithms. Four and five frame algorithms are considered. The influence of experimental parameters on the error detection sensitivity is discussed. Numerical studies are complemented by experimental results.
This work is devoted to two-beam interferogram intensity modulation decoding using spatial carrier phase shifting interferometry. Single frame recording, simplicity of experimental equipment and uncomplicated data processing are the main advantages of the method. A comprehensive analysis of the influence of systematic errors (spatial carrier miscalibration, non-uniform average intensity profile, nonlinear recording) on the modulation distribution determination using automatic fringe pattern analysis techniques is presented. The results of searching for optimum calculation algorithm are described. Extensive numerical simulations are compared with laboratory findings obtained when testing vibrating silicon microelements under various experimental conditions.
The phase shifting method is an effective tool to determine the intensity modulation distribution of a two-beam interferogram. We present numerical studies of the influence of two experimental errors on the results obtained using temporal phase stepping, i.e., the phase step miscalibration and average intensity changes between the component interferograms. Experimental studies of vibration mode patterns by time-average interferometry provide excellent verification of numerical findings. Comparative analysis of interferogram contrast and intensity modulation determination is included.
Two-beam interferometry enables information coding in the shape/orientation and contrast/intensity modulation of the fringes. There exists an abundant literature on decoding the interferogram phase whereas there are only a few studies dealing with the second type carrier decoding. This paper is focused on the two-beam interferogram intensity modulation analysis using temporal phase shifting. The influences of most important experimental errors are studied using computer simulations and laboratory works. Null and finite-fringe detection modes are compared. Phase-shift histograms and their lattice-site representations are investigated to aid the experimental error identification.
The paper presents numerical and experimental investigations of two errors having pronounced influence on the results of interferogram intensity modulation calculations using temporal phase stepping, i.e., the phase step miscalibration and average intensity changes between component interferograms. Experimental studies of sinusoidal vibration mode patterns by time-average interferometry provide excellent verification of numerical findings.
Numerical simulations of the influence of the phase step miscalibration and average intensity changes between the registered frames on the time-averaged interferogram contrast calculated using the temporal phase-shifting (TPS) method are presented. The amplitude of sinusoidal vibration studied by the time-averaged method is encoded in the interferogram contrast or intensity modulation described by the zero-order Bessel function. The properties of the TPS method used for contrast determination are established. Experimental studies of vibration mode patterns of silicon microelements with specular reflection surfaces provide corroboration of theoretical and numerical findings.
Numerical simulations of the influence the phase step miscalibration and average intensity differentiation between the frames on the calculated interferogram contrast using the temporal phase shifting method (TPS) are presented. The fringe function includes in its argument the amplitude of vibration studied by the time-average method. Some features of the TPS method known from the interferogram phase calculations are confirmed and properties characteristic to contrast determination are established. Experimental studies of vibration resonant mode patterns of silicone microelements provide corroboration of theoretical and numerical findings.
We present a methodology for static and dynamic testing of mechanical properties of microelements. The measurement path includes temporal phase shifting interferometry for quantitative static shape elements analysis. This is followed by determination of the resonance frequency by means of modified time average interferometry and transient amplitude and phase maps of vibrating micromembrane capturing and evaluation by phase shifting stroboscopic interferometry. Proper application of combination of these methods allows for quick and accurate analysis of micromembranes and optimization of their manufacturing conditions.
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