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Optical Measurement Solutions
InFocusISSUE 2015
Boost Your QualityOptical Measurement Technology for Production and Quality Control
More Precise than GPS Page 4
Two Million Measurements within Seconds
Page 12
When the Atmosphere is Vibrating ...
Page 22
Deep Impact Page 28
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Editorial
Dear Readers,
Quality Wins the Day
The ISO norm defines quality as the degree to which a product fulfills specified stan-dards. Defined tolerances have to be sustained in order to meet customer expectations of guaranteed properties.
In production processes, the quality of components is expressed by quantitative val-ues. Determining them as precisely as possible helps reduce costs, makes optimal use of resources and increases customer satisfaction.
Polytec sensors prove themselves time and again even under harsh production envi-ronments. All over the world, they deliver dependable measurement data to assess and ensure product quality.
This InFocus edition includes details about many of the different ways our measure-ment instruments are used for quality control.
We hope you enjoy reading this issue!
Eric WinklerVice PresidentBusiness Unit Optical Measurement Systems
Polytec News Page 3
More Precise than GPS Page 4
Interview with Dr. Ivo Milev, technet-rail Page 7
Polytec LSV - When The Going Gets Tough Page 8
Two Million Measurements within Seconds Page 12
Separating the Wheat from the Chaff Page 17
Interview with Dipl.-Ing. Holger Marschner, Continental Page 20
When the Atmosphere is Vibrating... Page 22
Deep Impact Page 25
Interview with Lisa Kadner, KSOP Page 28
Unveiling Wave Patterns in Complex Geometries Page 32
Product News Page 36
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News
Polytec ChinaNew subsidiary opens in Beijing
Polytec continues to expand, and recently opened a new subsid-iary in Beijing, China. Polytec China Ltd. CEO Walter Gao and his colleagues serve the growing demands of the worlds largest economy. Besides subsidiaries in the USA, Japan, France, Great Britain and Singapore, China is our sixth overseas office offering products and services based on optical measurement technology.
ExcellenceInnovation award goes to Polytec
Polytec received the Innovation Award of the state of Baden-Wuerttemberg for the development of the MSA-100-3D Micro System Analyzer on the 1st of December 2014. This prize is awarded for successful implementation of outstanding technical innovations. The new instrument from Polytec enables 3D vibra-tion measurements on microstructures with picometer resolution for both out-of-plane and in-plane motion.
For further information visit our News section at: www.polytec.com
Sharing Experiences13th user conference laser vibrometry
Users of laser vibrometers met at Polytec’s headquarters in Wald-bronn, Germany on November 18th and 19th, 2014. The partici-pants discussed current challenges, new applications and recent advances in laser vibrometry.
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More precise than GPSUnconventional use of Polytec’s LSV-2000 for the capture of 3D data on the tracks of Deutsche Bahn
Infrastructure
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Demand has risen in recent years for fast response railroad track surveying technology. The goal is to facilitate rapid and decisive actions regarding the maintenance of railway infrastructure.
To enable this fast deployment, the company technet-rail 2010 utilizes laser surface velocimetry in its mobile variant (MLS). Whether using a specially designed trolley for short recordings, a mobile self-propelled platform or a track-installed measurement train (Figure 1) – the MLS guarantees short term, fast deployment anywhere on the track.
The precision of localization, fundamentally important for the absolute evaluation of the data, must be ensured whether measuring with scanners or other 3D recording instruments. The applied technology has to meet the requirements of this complex measurement method.
A prerequisite for the monitoring and control of railroad tracks with associated infrastructure objects are measurements with a recording accuracy which is typical in the engineering design. This precision must also be attained in the data analysis and subsequent data comparison in order to achieve exact results.
The MLS system comprises a trolley, a profile laser scanning instrument, an inertial system (INS), a displacement sensor (Polytec Laser Surface Velocimeter LSV-2000) and possibly a GNSS (Global Navigation Satellite System) receiver. An advantage of this system is its flexible structure. The assembly of the trolley on the tracks and the installation of the measurement instruments can be carried out within a very short time. Another advantage is the fact that laser scanning instruments from various manufacturers can be applied. Past measurements with different terrestrial scanners provided precision consistently in the millimeter range. This complete and highly accurate 3D capture enables multi-disciplinary use in the quality control of railway infrastructure.
One primary application area of the MLS is in tunnel systems, which make up a significant part of the railway network. Frequent analyses of deformations, collision areas and tunnel clearance activities are required because of environ-mental conditions and tunnel
constructions, which are often complex. These analyses are an integral part of tunnel monitoring and require a quick and precise determination of the track geom-etry characteristics in relation to the building.
Measured data are correlated with a precise geolocation during the recording process. This must be given even at low or missing GNSS signal strength. In open areas, the differential of the GNSS, the INS and a non-contact LSV-2000 define the geoposition with the aid of simultaneous post-processing of data records.
The MLS system calculates that GNSS sensors are a dependent part of the subsequent data synchroni-zation and data adaptation system. A specific modification of the MLS system and the data synchroni-zation is applied in areas with low, missing or insufficient GNSS signal. With this modification, the INS, developed algorithms and LSV-2000 measurement tech-nology ensure a high precision in rail measurement and data synchronization. ►
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Infrastructure
Polytec’s LSV-2000 non-contact laser surface velocimeter offers high precision and sensitivity when capturing the movement on the rail in areas with no GNSS signal. The LSV-2000 guarantees minimal geometric error, offsets and errors in the axial position in the stationing alignment direction. The INS and LSV-2000 ensure contin-uous data capture and complete coverage of the scanner section.
In contrast to the GNSS that generates geoposition signals only under certain circumstances, the LSV-2000 provides a consistent signal from which the exact rail position and geoposition can later be precisely determined by the differential method. Discrepancies in the GNSS trajectory based on bad or missing signal coverage can therefore be prevented or reme-died. Furthermore, data ambiguity (overlap or duplication) caused for example by wheel slippage is avoided by using non-contact LSV-2000 technology.
The data measured by all sensors including the LSV-2000, and their subsequent analysis, are improved even in areas where the GNSS signal is not available. The linking of recorded data guarantees uninterrupted traceability during post-processing.
Thanks to specially developed mathematical algorithms, the indi-vidual scan data are correlated with
highly precise LSV-2000 informa-tion during data synchronization, providing precise geoposition for the scans. This is particularly important for synchronized scans of the INS data sets which contain the camber values as well as the gradients. The located results of the georeferenced point clouds are precise to the millimeter. These are essential to the adaption of the track geometry concerning driving dynamics as well as for deformation and clearance analysis.
Because of the improved preci-sion provided by the LSV-2000, comparisons of target and actual complete railroad geometry values are possible in tunnel constructions or on the open track. Therefore we can determine the actual position of the geometry and the behavior
relative to the predefined target axis.
Deployment of the LSV-2000 in railway monitoring guarantees increased precision and quality, which for infrastructure issues offers a fast payback. ■
Figure 1: Measurement train with LSV-2000
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Contact
Dr.-Ing. Ivo MilevManaging Directortechnet-rail 2010 GmbH, Germanywww.technet-rail.com
Dr. Milev, how did you get to know Polytec?
I learned about Polytec’s prod-ucts when I was conducting research into non-contact displacement measurement. I quickly found out that Polytec has rich experience in this area.
How is the support and how satisfied are you with the instruments?
The instruments are character-ized by excellent processing and signal quality. All applica-tions have so far met withour total satisfaction and have delivered very good results.
How do you see future cooperation with Polytec?
We continue to see the cooper-ation between technet-rail and Polytec as very positive and also look forward to the future with optimism. This open cooperation leads continually to new ideas and areas of application. Both companies benefit from this close and fruitful cooperation. New innovative products and services will emerge, without neglecting targeted basic research.
We spoke with Dr. Ivo Milev from technet-rail 2010 GmbH about his experiences with Polytec.
„TotallySatisfied“
Dr. Milev, we thank you for the interview.
Interview
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Steel Industry
Polytec LSV – When The Going Gets Tough To measure glowing steel from short distance is a challenge that only few instruments can cope with
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Laser Doppler velocimetry has since its introduction been in regular daily use in steelworks. Laser Surface Velocimeters (LSV) are found in many applications ranging from measurements on red-hot slabs or billets coming from the continuous caster to measurements of the cold finishing level and of the length at coils in cold rolling mills. The environments in which sensors such as the LSV are deployed are harsh and present a major challenge for high precision measurement instruments such as the LSV.
A lot of effort goes into protecting sensors, especially in hot environ-ments such as continuous casting. For LSVs there are enclosures offering cooling and ingress protection. However, these enclo-sures typically have to be installed by customers at substantial expense to protect these highly sensitive sensors.
The cooled protective housing specifically offered by Polytec, on the other hand, is so sturdy and robust that there is no need for additional protective measures. It consists of a large aluminum housing with cast-in tubes made of
stainless steel that are flooded with cooling water. The cooled housing is designed for ambient tempera-tures of up to 200° C.
Because the inexpensive protective housing’s design enables opera-tion in hot environments, Polytec performed a test together with Arcelor-Mittal in Eisenhüttenstadt at a continuous casting plant. The LSV-2000 operating at a distance of 1,500 mm was installed in an LSV-A-121 cooled housing, with just a standard plate to protect against radiated heat (Figure 3). ►
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Three thermocouples captured the temperature: One of them measured the ambient temperature at the back outside the housing. This thermocouple was installed in such a way that there was no exposure to frontal heat radiation. The other two thermocouples were installed inside the housing directly on the LSV. One of them was placed in front by the window frame, the other at the rear near the bottom of the housing.
The system was installed on a cross beam near the outlet of the cast strand, directly in front of the torch cutters (Figure 5). At first, used water from the water cycle cooled the LSV at a temperature of 31° C. The temperature curves from the three sensors for the casting period are shown in Figure 1. It was apparent that despite the high inlet temperature, the
Figure 1: Temperature curve during the casting period. Temperatureof the cooling water is about 31° C. The temperature OUTSIDE shows anincrease each time the bridge with the torch cutters moves withthe strand.
Figure 2: During an interruption of the cooling water supply the tempera-turesincrease significantly. When the water supply is opened again, thetemperatures drop immediately. The temperature at the LSV head showsa higher inertia.
Steel Industry
cooling performance in this case was sufficient to protect the LSV. It was helpful that the bridges with the torch cutters absorbed a part of the radiation heat when they were in their rest position in front of the LSV. This effect can be seen on all of the external sensor temperature curves: The temperature increases when the bridge is moving with the strand and decreases again when the bridge has returned to its starting position.
In order to simulate a problem with the cooling water supply, supply was interrupted and the tempera-ture trend observed. The tempera-ture reached a critical value for the sensor only after approximately 15 minutes. When the cooling water was flowing again, the temperaturedropped to a safe level within a few minutes (Figure 2).
As the used water temperature can increase up to about 40° C, tap water was used instead. The temperature variations over the course of a day are illustrated in Figure 4 as an example. The temperature in the cooled protec-tive housing never exceeds 25° C. Therefore, the temperature in the measurement head, which must not exceed 45° C, is less than 30° C. This means that a safe operation is possible without any problems even if the lateral heat radiation is not absorbed.
The tests carried out over the strand showed clearly that Poly-tec’s massive cooled protective housing without any additional enclosure offers sufficient protec-tion in order to cool the LSV at the continuous caster. However, this housing has sufficient reserves to work reliably in even higher
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Figure 3: Open cooled protective housing with LSV and the position of the temperature sensors.
Figure 5: LSV positioned above the strand. A part of the bridge with the torch cutters can be seen at the front to the left.
Figure 4: Development of the temperatures during a day after water supply had been changed to tap water supply
Contact
Peter Groß[email protected], Germany
temperature environments than in this test. Because there is no need for additional protection, there are essentially no costs for its design, manufacturing, installation and operation. Therefore customers save a significantly amount of money, and the acquisition and operation of non-contact length measurement becomes even more efficient. ■
Polytec LSV
Position of temperature sensor „FRONT“
Position of temperature sensor „REAR“
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Two Million Measurements in SecondsOptical characterization of surfaces
Surface Metrology
The requirement for checking fine tolerances in quality control is a challenge for metrology.In addition to being precise, the sensor cannot over-look any relevant information. Therefore, the entire functional surface has to be characterized. Contact-ing measurement methods are time consuming and because of this only a few random samples can be examined on the manufacturing line in the time avail-able. If problems emerge, a short reaction time is desirable. So, there is a great potential to achieve cost savings by implementing a full-field optical method.
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give the height information. On ring shaped surfaces, the instru-ment can create circular profiles. Figure 2 shows such a profile which runs midway between the outer and inner edges that has a flatness deviation of +/-100 nm. The align-ment at anchor points and edge lines ensures a high reproducibility
This applies also, of course, when the step height between two surfaces is important, as shown in Figure 3. Looking separately at both surfaces, one can see that the lower (outer) one has differ-ences in height of several μm, while the upper (inner) surface, which is located 425 μm higher, has a conical shape (Figure 4). Measurements of step heights between two points can vary considerably, depending on which
Optical surface measurement instruments offer a solution that quickly characterizes an entire surface. Each camera pixel acts as a sensor – this means that two million pixels equals two million measurements. In addition, inter-ferometric methods offer the same high accuracy in the vertical direc-tion, regardless of the measure-ment area, the so-called field of view.
Therefore, a white-light interfer-ometer determines quickly and reliably, for example, flatness, parallelism or step heights. Below, we present the results of two different types of white-light inter-ferometers, namely a white-light interferometer which is able to measure large surfaces for shape measurements and a white-light
interferometer microscope for revealing finer structures. The microscope also determines texture parameters such as roughness or structural parameters.
SURFACE PROFILE VERSUS LINE PROFILE
Compared with line profiles, surface measurements provide more information, for example when flatness must be determined. It ensures that both the highest and the lowest points as well as local unevennesses are reliably recorded. Where there are contact surfaces, localized surface wavi-ness can result in high local loads, which in turn affect the life of a component. Figure 1 shows such a measurement with a white-light interferometer where the colors
Figure 3: Two circular surfaces (measured by a TMS-300 TopMap in.Line).
Figure 2: Surface and line profile of a ring-shaped surface (measured by a TMS-300 TopMap in.Line).
Figure 1: Flatness measurement of a contact surface.
Surface Metrology
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multiple surfaces with large height differences. In addition to flatness and parallelism, they determine radii, inclination angles and lateral distances.
Examples show that considerably more information can be obtained with an optical surface measure-ment than with conventional tactile methods. The coin example in Figure 6 illustrates this. The tactile probe surface measurement (left) is composed of individual lines. The interferometer measurement on the right is much more compre-hensive. The tactile measurement required thirty minutes, the surface measurement less than one.
points were selected on each of the two surfaces. With the help of surface measurements, the centers of gravity of both surfaces and their parallelism can be determined.
The TMS-100 and TMS-500 have a telecentric optical configuration, which means that no shadowing will occur. It is therefore possible to characterize surfaces that are at the bottom of deep holes. Figure 5 shows such a measurement of a slightly curved and crooked surface which is positioned 40 mm down inside a hollow cylinder. The TMS-100 and TMS-500 white light interferometers from Polytec, designed for large measurement surfaces, have a scan depth range of up to 70 mm, which means they are capable of characterizing
Figure 5: Characterization of a deep-set surface.Figure 4: Details of the circular surfaces. Left: surface measurement with a probe; right: surface measurement with an interferometer.
SHORT MEASUREMENTTIMES ARE REQUIRED
In quality assurance, it is often not only measurement times that play a major role, but also reproducibility, traceability and comparability. The comparability of results measured at different sites must be ensured, regardless of the operator. Further-more, the measurement proce-dures should be automatable for integration into the production line as well as for routine measure-ments. The following example on small wheels will illustrate this.
To increase the clock rate, several wheels are placed in the field of view and measured at the same time (Figure 7). The initial set-up is made at one sample, and the measurement procedure and evaluation algorithms are then ►
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Figure 7: Simultaneous measurement of several small wheels; the framed wheel was used for set-up (measurement with TMS-500 TopMap).
Figure 8: Visually inspected individual measurement.
Surface Metrology
determined. The sensor simultane-ously learns the shape of the first component and with this infor-mation the sensor recognizes and automatically measures the other components. In this case the initial set-up took less than two minutes. The initial set-up can be stored and is available for all subsequent measurements, regardless of the operator.
After measurement, the results are either exported or displayed in a good/bad table. If desired, bad parts once again can be inspected visually (Figure 8). Measurements and analyses can be defined and retrieved even without optional shape recognition.
INTERNATIONALSTANDARDIZATION
Tactile methods have until now been the most popular approach for surface measurements, with nearly all international standards referring to this technique. Mean-while, optical measurement instru-ments are becoming more popular, so it is therefore only logical that international standardization pays attention to optical methods.
HIGH PRECISION
As illustrated, white-light inter-ferometers measure with great precision. The resolutions (smallest distinguishable step height) are in the sub-nanometer range Texture parameters such as roughness, flat-ness or step height can be deter-mined with nanometer precision. ■
Figure 6: Comparison of tactile (left) with an optical measurement (TMS-100 TopMap Metro.Lab) (right) on a coin..
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Separating the Wheat from the ChaffVibrometers spell success for quality assurance
It’s not so advisable these days to leave the good/bad decision to the wind, not just because it blows so rarely in factories and laboratories. It has become more important than ever to quick-ly and reliably differentiate the good from the bad.
The economic success of a product, in both the consumer and capital goods industries, is deter-mined to a large extent by how well quality, production processes and costs are optimized. Quality assurance in manufacturing relies on fast, automated and robust test methods. Structural defects can be revealed by analyzing the dynamic properties of components,
assemblies or the final product. Features such as changes in natural frequencies, amplitudes and mode shapes are characteristic quality markers. Therefore, with a suitable measurement, evaluation and classification of these parameters a fast and automatic good/bad selec-tion is possible on the product or component level. For many such applications in the final inspection
of production, laser vibrometers are particularly suitable because they offer considerable advantages compared with conventional sensors such as accelerometers or microphones. In addition to the wide dynamic range and the large bandwidth of vibrometers, their non-contact measurement principle and ability to target with pinpoint precision are crucial.
Vibrometry
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Non-contact means that the measurement method doesn’t influence the data being acquired. Integration becomes easier because there is no physical contact with the samples. The method is not susceptible to ambient noise etc. because the vibrometer captures the vibrations directly on the sample surface. Operational costs are further reduced by fast change-over, easy calibration and lower repair expenses.
HOUSEHOLD APPLIANCES AND MEDICAL TECHNOLOGY
Electrically driven household appliances, medical devices or their components which generate unwanted vibrations and noise, can be identified in production with laser vibrometers for removal from the line. Examples are washing machines, vacuum cleaners, electric toothbrushes, dental instruments or motors for medical devices. Vibrometers confirm the proper function of hi-tech medical products such as membrane inhala-tion systems with 100% testing.
Thanks to 40 years of close coop-eration with the world’s largest washing machine manufacturers, the Loccioni Group is a leader in the development of automatic quality control systems for labora-tory and in-process applications. Their MUSA test station (Measure-ment Unit in Sound-proof Area) is a
fully automated turnkey installation for vibration and noise testing on washing machines, which tradition-ally is carried out in the laboratory.
Experience has shown that spot checks on systems selected at random do not result in a reliable outcome. Only 100% testing on the finished products guarantees a high quality standard. Vibra-tion tests are a good method for distinguishing good from faulty products. Therefore, the use of vibration analysis for quality control of household appliances is highly recommended. Laser vibrometry has firmly established itself as the non-contact method of choice for in-line testing. With the help of the laser vibrometer, the system reli-ably detects possible defects such as faulty or loose components or machine tub unbalance.
AUTOMOBILE INDUSTRY AND MECHANICAL ENGINEERING
Laser vibrometers are alreadywidely used for manufacturinginspection in these fields. They perform noise and failure analyses on components with moving parts such as combustion engines, gear drives, A/C systems, injection valves, steering systems, adjusters and miniature drives, as well as for material testing, e.g. on camshafts or light bulbs.
Roller bearings are high-precision components manufactured in large numbers. SKF is the world market leader, continuously expanding its lead in manufacturing and quality technology. SKF noise inspects 100% of manufactured roller bearings. Highly efficient test systems are required to achieve goal cycle times of a few seconds. Therefore, the measurement technology center of the SKF Group (QTC – Quality Technology Center) decided in 2010 to rely on optical measurement technology employing IVS sensors from Polytec. Advantages for SKF are the non-contact principle, signal quality, as well as lower opera-tional costs from the quick sample changeover, simple calibration and lower repair expenses.
Vibrometry
Figure 1: Testing of washing machines (Loccioni)
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INFORMATION AND MICROSYSTEMS TECHNOLOGY
Vibrometers are used in the manu-facture of hard drives as highly sensitive detectors of unwanted deviations in the dynamic behavior of read-write heads and other fine structures. Another related appli-cation is the component testing of DVD players or bubble-jet printers.
The static and dynamic properties of microsensors, microactuators and other MEMS components can be tested during manufacture on the wafer level with the MSA Micro System Analyzer or other micro-scope-based vibrometers.
In many MEMS, critical geometric and material parameters, which can’t be measured directly with other non-destructive methods, can be deduced from the results of a vibration measurement. Examples
are the determination of membrane thickness of MEMS pressure sensors or the spring thickness of MEMS Fabry-Perot interferometers which are used as tunable IR filters. The procedure can be completely automated: The structure to be examined is excited in broadband mode on an automatic probe station by a special probe card with a transparent electrode made of indium tin oxide (ITO) and an electrostatic stray field on the wafer. The mechanic vibrations stimulated in this way are measured by means of a laser vibrometer. The frequency response function and selected resonance frequencies are determined very precisely from the measured data and known exci-tation signal.
A MEMS model, comprising poly-nomials, is adapted to the reso-nance frequencies by parameter adaptation. Thereby, the required geometry and material parameters are calculated very precisely. The polynomials can be extracted from the parametric FE simulations before starting the measure-ments. The calculations which are necessary during the series tests for parameter adjustment can be carried out very efficiently. The measurement is fully automated for all devices on the wafer. The procedure is therefore well suited for 100% inspection during MEMS fabrication. ■
Figure 2: Testing of roller bearings (SKF)
Figure 3: Automated testing of Fabry-Perot MEMS sensors (FHG ENAS)
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Mr. Marschner, at the Eurobrake 2014 in Lille you received the “Best Presentation Award” for your talk at last year’s conference in Dresden. The participants gave the highest marks for your contribution “Appropriate Test Configurations for Noise Matrix Tests on Inertial Dynamometers“. Congratu-lations on that! What was the content of your presentation?
These days, customers expect their car’s brake system to have optimized vibro-acoustic behavior. In the process of developing a new passenger car it is important to be able to reproduce exactly the noise characteristics of the brake in order that no undiscovered noises will occur later in real vehicle operation. My presentation dealt with the capture of brake squeal on flywheel mass dynamometers. It compared different methodologies
and described new ways that we at Continental approach the field of brake development.
Continental as an internationally active supplier is a sought-after partner for the automotive industry. Which proposal could you present, what was the core message of your presentation?
The wheel loads and lateral forces experienced when cornering influence the noise characteristics significantly and should therefore be simulated on dynamometers. In this way the risk of setbacks is reduced during later driving tests. Such a dynamometer has existed since the last Eurobrake. We like to share results and participate in working groups, for example the expert group Brake Noises. This group summarizes dynamometer
specifications included in VDA recommendations. Ultimately everyone benefits when costs can be saved by standardized test specifications. This product can of course be a platform for more improvements in the future.
When you think back, what haschanged in recent years with regardto the requirements and the under-standing of the acoustics of brakes?
The demands on the brake system have increased continuously. It should fulfill its duties comfortably, reliably and unobtrusively. Electric vehicles and low-noise drives will continue this trend. Vehicle manu-facturers and system suppliers are therefore faced with new challenges.
Interview with Dipl.-Ing. Holger Marschner, Principal Technical Expert NVH, in the Hydraulic
Brake Systems Business Unit of the Chassis & Safety Division of Continental at Eurobrake 2014.
Interview
„The helpful support is exemplary“
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How can Polytec contribute regarding this challenge?
Polytec has already made a valu-able contribution through consis-tent customer-oriented product development. In 2008 for example we combined for the first time scanning vibrometer measurement data with data from accelerometers that were placed directly in the rotating brake disk. I was pleased that Polytec had no problem with also giving tactile sensors a chance. I appreciate Polytec’s willingness to cooperate with Continental. This willingness, which continues today, always serves the measure-ment task and allows us to achieve the best possible result. Also, the helpful support provided by your team is exemplary. At this point I’d like to thank our distribution partner at Polytec, Mr. Staniewicz, for his assistance.
Which impressions and what ideas for new developments did you take withyou from this year’s Eurobrake?
The presentations on joint patch damping and contact stiffness in particular have impressed me. I am now aware that such effects have a dominant influence on the noise when driving around curves. It is not at all easy to reproduce these effects in computer models. However, it would certainly be worthwhile.
What role will test compared with simulation play for you in future?
The more detail we want to calcu-late, the more precisely we must be able to validate the processes metrologically. Therefore with increasing simulation quality the demands for the measurement systems are increasing too. More-over, there are still a number of other noise phenomena that should be explored.
What are those NVH (noise, vibration, harshness) problems specifically and which measurement technology is required?
Squealing is just one of the chal-lenges. There is also moan and creep groan. Laser vibrometry is again used in all of these cases. Time domain measurements are necessary here because these are transient processes. It would be desirable to have a 3D multi-point laser vibrometer, with of course the ability to combine multi-channel measurements with accelerometer data.
Mr. Marschner, thank you for talking with us and we wish you every success. Your approaches will certainly be discussed at length during our next user conference.
Contact
After 19 years with the company, Dipl.-Ing. Holger Marschner left Continental in March 2015. He accepted a chair at Frankfurt University of Applied Sciences as professor for automotive engineering and NVH.
www.frankfurt-university.de
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Climate Research
When the Atmosphere is Vibrating...Airborne imaging Fourier spectroscopy
The design and operation of airborne instrumentation for study of the atmosphere is a challenging task, especially with optical systems highly sensitive to vibrations. Vibration measurements with Polytec’s RoboVib® system have been used to understand and improve the dynamic behavior of the airborne instrument, GLORIA.
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Gimballed Limb Observer for Radiance Imaging of the Atmo-sphere (GLORIA) aims to study atmospheric dynamics and trace gas composition in the upper troposphere and lower strato-sphere. GLORIA is the result of the evolution from a limb scanning to limb imaging instrument, which enables measurements of meso-scale processes in the atmosphere. The instrument is designed to fly in an instrument bay on the German High Altitude and LOng Range Research Aircraft (HALO) and on the Russian Myasishchev M55 Geophysica. GLORIA is equipped with a very sensitive optical system, a Michelson interferometer, which is cooled to 215 K with the help of solid carbon dioxide snow. This is necessary to reach the sensitivity required for atmospheric emis-sion measurements. The covered spectral range is in the mid and thermal infrared (780 -1,400 cm-1). This infrared radiance originates from the emission of vibrating and oscillating molecules in the atmosphere generating typical
spectral fingerprints. GLORIA has already successfully completed two campaigns with very promising results.
POINTING AND CONTROL SYSTEM
GLORIA relies on a flexible concept to support different scientific scenarios and goals. The 3-axis compensation of aircraft movements is necessary to guar-antee precise limb pointing. It is required as the target points are quite far away (up to 350 km) and small angle errors of the instrument cause large deviations at the target points. Stabilization errors can produce artefacts in the measurements. Therefore, a good stabilization is paramount during acquisition times of 1.5 to 30 seconds. The 3-axis control is achieved with a gimbal frame as depicted in the picture on page 22. This illustration of GLORIA shows the spectrometer in light blue, the gimbal frame in red, the shield in green, the mounting structure in
olive, the calibration sources in pink and the schematic footprint of the viewing beam in red. The visual image and corresponding infrared image is depicted also.
INFLIGHT VIBRATION ANALYSIS
During the 1st research flight on HALO, 7 accelerometers (PCB Piezotronics, Model: 356A17) and a microphone measured vibrations with a sampling frequency of 1 kHz. Extensive lab measurements could not reproduce the most significant vibrations measured inflight at 200 - 240 Hz, depicted in Figure 2. So far, the origin of the observed inflight oscillations could not be clearly determined. However, it is very likely that they are initiated by aerodynamic forces, which in turn originate at the instrument bay opening. ►
Figure 1: GLORIA mounted in the open HALO instrument bay (left) and HALO aircraft with instrument bay.
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eigenfrequencies of the interfer-ometer and gimbal structure. Most importantly, the measurement allows the determination of the input parameters for an FEM model designed for fatigue analysis and its validation.
RESULTS
The RoboVib® measurements were executed with mechanical excitation via a shaker and with acoustic excitation to simulate the aerodynamic forces during flight. Due to the extensive number of measurement points, it was possible to reproduce the motion inside GLORIA with the high quality
Figure 3: RoboVib® image of the instrument motion at 45 Hz.
MOTIVATION FOR ROBOVIB® MEASUREMENTS
The unexpectedly high level of vibrations during the flights made further investigations necessary. The impact of vibrations on the quality of pointing stabilization and on the spectroscopic measure-ments had to be reviewed. For the airworthiness certification process, the question of fatigue also arises in light of the measured vibration levels.
Therefore it was decided to pursue RoboVib® measurements to allow analysis of relative motions within the instrument and
Contact
Felix Friedl-VallonGLORIA, Germanygloria.helmholtz.de
Climate Research
Figure 2: Accelerometer data over flight time and frequency.
shown in Figure 3. The RoboVib® measurements have been a valu-able asset to our vibration analysis and led to mechanical improve-ments. The parameters necessary for the FEM model could also be derived. The modifications of GLORIA and the instrument bay will be finally evaluated during test flights in 2015. ■
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Mrs. Kadner, where do you come from?
I come from the city of Jena and study at the KSOP in Karlsruhe.
What are you studying?
I study Optics & Photonics.
You are studying at the Karlsruhe School of Optics & Photonics. What do you like most about it?
The KSOP is an international program and so the students are from various countries. For me, the best thing about the KSOP is
In the 2013 issue of InFocus we presented Polytec’s cooperation with the Karlsruhe School of Optics & Photonics – KSOP. For this issue we interviewed Lisa Kadner who studies at the Karlsruhe School of Optics & Photonics and is writing her master’s thesis here at Polytec.
„I am interested in everything that has to do with light“
meeting so many great people from all around the world. What I also like about the program is the combination of theory and prac-tice. For me this is very important.
You are writing your Master’s thesis at Polytec’s headquarters in Waldbronn. What is it about?
It is about improving the reso-lution of a vibrometer with a so called open optical resonator. This consists of an arrangement of mirrors that forms a standing wave cavity resonator for light waves. I investigate this new method in theory as well as in experiment.
The goal of my research is to improve non-contact laser-based measurement of vibrations by achieving attometer resolution.
Why did you chose Polytec for your thesis?
Last year I did an internship at Polytec where I could work on a project on my own. Plus the working atmosphere was very friendly. I chose to come back for my thesis because that internship was such a positive experience.
Interview
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KSOP Karlsruhe School of Optics & Photonics
The Karlsruhe School of Optics & Photonics was founded in 2006 within the Karlsruhe Institute for Technology (KIT) under the umbrella of the KIT International Department. Since then, it has proven to be one of the leading research and education institutes in the field of optics & photonics in the world.
Additionally, KSOP is involved in the Erasmus Mundus EUROPHOTONICS Program, which offers mobile MSc and PhD programs at different European universities.
The School is situated in Karlsruhe in the German state of Baden-Wuerttemberg, near the French border. The so called Karls ruhe Technology Region is located in the heart of one of Europe’s most produc-tive and innovative industrial regions.
Since its foundation, the Karlsruhe School of Optics & Photonics has been funded under the German Excellence Initiative that was launched to support world class research and education at German universities.
www.ksop.de
ContactB.Eng. Lisa KadnerKarlsruhe School of Optics & Photonics (KSOP)KIT – Karlsruhe Institute of Technology, Germanywww.ksop.de
How important is practical experience for your studies?
Practical experience is highly important because all the theory is worth nothing if you cannot apply it to something real. During studies it is motivating because you see what can be done with the knowl-edge from the lectures and in turn it also deepens that knowledge.
What are your future plans? Are you planning to work in this field when you have graduated?
Yes, I can imagine working in this field, but I would also like to gain experience in other branches of optics & photonics. I am especially interested in the fields “Advanced Photonic Materials” and “Integrated Optics”. Since I am interested in everything that has to do with light there are many other optics topics that might draw my attention.
Mrs. Kadner, we thank you for this interview and wish you the very best for your future.
Interview
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„Direct contact with students“
We also talked with Dr.-Ing. Christian Rembe, Manager of Optics Development at Polytec, about the cooperation with the Karlsruhe School of Optics & Photonics.
Contact
Dr.-Ing. Christian RembeManager Optics DevelopmentCorporate Research and Development Polytec GmbHwww.polytec.de/karriere
Dr. Rembe, how long has Polytec been working with the KSOP?
Polytec has been an industrial partner of the KSOP since its foundation in 2006. However we have been cooperating more closely with them for about the past five years. First, we partic-ipated in internships and the execution of master’s theses, but more recently we started to cooperate specifically with the Steering Committee of the KSOP.
What do you like best about this cooperation?
By working with the KSOP we have direct contact with students of the Karlsruhe Institute for Tech-nology (KIT) whose main focus is education in optical systems. Addi-tionally, via the KSOP, Polytec has developed excellent connections with the other facilities at the KIT.
How does Polytec benefit from this cooperation?
Because of the KSOP, optics and photonics have grown consider-ably in significance as main focal points in the Karlsruhe area. The number of potential partners for cooperation on various projects is increasing and there are more engineers and physicists in this area with extensive experience. For a globally active optical measure-ment company like Polytec, it is of course a great advantage to be based in a technology region rich with optics and photonics. A partic-ularly important aspect for Polytec is that, through our engagement with the KSOP, the awareness level of Polytec among the students at the KIT has considerably increased, and as a consequence we receive many applications from students and graduates.
With regard to the cooperation, what would you desire for the future?
At Polytec, we are already very satisfied with the cooperation. Industry-sponsored doctor-ates, for example, would be a possibility to further expand the cooperation in future.
Dr. Rembe, thank you very much for this conversation.
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Deep ImpactLDV measurements of impacts with fluids
Experimental Physics
An outer sphere (left) is released by an electro-magnet, it is measured with 2 LDVs from both sides.
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The concept of a bistable shift valve was investigated in a bio-medical research project. The shifting is caused by a mechanical impact. A test set-up was built for the detailed investigation of impacts and the desired impulse transmission into the valve housing. This goal of this experiment is to develop an understanding of the fundamental physical behavior of the impact. Furthermore, numerical simulation models are validated using the results. Experiments are carried out with different impacting bodies, different materials and also with fluids.
EXPERIMENTAL SET-UP AND IMPLEMENTATION
The set-up comprises a frame with a clamped plate and two spheres, one on each side. One sphere is initially deflected and hits the clamped plate perpendicularly. On the other side, which represents the inside of the shift valve, the
Impacts with solids are processes that last for very short periods of time. Non-contact measurement methods are particularly well suited for this kind of experiment. The impact between two spheres, separated by a plate, is measured with two LDVs, both with and without the influence of fluids. Measurements in a fluid container cause interesting physical phenomena which have to be considered to obtain correct measurements.
sphere is at rest, touching the plate. At the frame, a fluid container can be mounted, where the inner sphere is submerged. The impacting sphere is released by an electromagnetic mechanism to achieve high repeatability. The sphere has just before it hits the plate a velocity of approximately v0 = 600 mm/s. It hits the plate with this velocity and causes it to deform and vibrate. This causes the inner sphere to accelerate. Experimental evaluation requires
the velocity and displacement of both spheres. Two Laser Doppler vibrometers (OFV-302/ OFV-3000) are therefore used. They have the advantage that the non-contact measurement itself does not influ-ence the experiment. In addition, because of the high sensitivity and high resolution of the signals, the very brief impact time is resolved in great detail. What is challenging is that the outer sphere enters the laser beam just before impact ►
Figure 1: Prototype with two piezo actuators.
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and a useful measurement is only expected if the laser is almost perpendicular to the sphere surface. On the other side of the plate, the sphere is at rest at the beginning and is therefore easier to measure.
Alternatively, an acrylic tank can be mounted on the frame which holds the plate in order to fully submerge the inner sphere and study the influence of different fluids. The inside surface of the plate is in contact with the fluid, which could be either water or oil. Filling the tank with a fluid changes the measurement results considerably. These changes comprise influences that the fluid has on the impact and the movement of the sphere, and influences of the optical refractive index of the fluid on the measure-ment technique.
Figure 2: Close-up view of the acrylic tank
Experimental Physics
Figure 3: Velocity signal of both spheres with a super-imposed vibration caused by the movement of the
fluid tank.
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The laser Doppler vibrometer relies on the physical principle of the Doppler Effect, measured with an optical interferometer. An interfer-ometer can be used to determine the frequency shift of the laser reflected from a moving surface as well as interference fringes caused by a change in optical path length. If measurements are performed in any medium other than air or a vacuum, the refractive index of that different medium must be taken into account. This correction has to be applied in order to determine the velocity of the sphere in the fluid. However, the movement of the fluid tank causes a change in length of the optical path if different media are on both sides of the casing, leading to an additional superimposed vibration as shown in Figure 3.
RESULTS AND CONCLUSIONS
By taking into account the different refractive indices (n), we can measure in the presence of fluids and modify the signal with the equation vcorr= v/n. The measure-ments demonstrated that we could successfully determine the velocity of both spheres before and after impact. ■
Contact
Dipl.-Ing. Christian Fischer, Prof. Dr.-Ing. Prof. E.h. Peter EberhardInstitute of Engineering and ComputationalMechanics, University of Stuttgart, Germanywww.itm.uni-stuttgart.de
Figure 4: The completely submerged inner spheretouches the plate.
32 |
Lattice structures are well known for a range of exotic dynamic properties, including the ability to work as band-gap filters and to propagate anisotropic waves with frequency-depen-dent directionality. In order to verify experimentally the anisotropy of the spatial propagation patterns, we need a non-intrusive measurement technique that allows acquiring in-plane velocity values at multiple locations. The Polytec PSV-400-3D is the perfect device for the job.
Unveiling Wave Patterns in Complex GeometriesLaser-enabled reconstruction of in-plane wavefields in cellular periodic structures
Structural Dynamics
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Periodic cellular materials, such as metallic or composite honeycombs, are widely used in aerospace, automotive and civil structures, primarily in virtue of their high strength-to-weight ratio. However, their technolog-ical potential extends far beyond their remarkable static properties. A widely discussed effect is the formation of phononic band-gaps, i.e., intervals of forbidden wave propagation that can be ascribed to the deconstructive interference between incident and scattered waves. Additionally, some wave modes propagate conforming to
anisotropic patterns, a property known as wave directivity. This spatial effect, if properly harnessed, presents significant opportunities for spatial wave manipulation, with applications including energy deflection, rerouting, trapping and harvesting, and acoustic cloaking.
Our overarching research theme revolves around the design and characterization of new lattice architectures with unconventional wave manipulation capabilities (Celli and Gonella, J. Appl. Phys. 115, 103502 (2014)). In support of this investigation, we need
an experimental approach that allows testing structures featuring significant topological complexity and composed of thin structural elements. Here we discuss a methodology revolving around the in-plane wave reconstruction capabilities of the Polytec 3D Scan-ning Laser Doppler Vibrometer, by which we can collect in-plane velocities at the nodes of an ad-hoc scanning grid that conforms exactly to the lattice shape of a cellular structure. Here we test the methodology against the bench-mark case of a regular hexagonal lattice, whose phononic behavior
Figure 2: Experimental setup for transient wavefield measurement in a regular hexagonal honeycomb specimen. Note, on the screen, the hexagonal scan-ning grid with three scan points per link.Figure 1: Regular hexagonal honeycomb specimen.
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34 |
has been extensively investigated with analytical and numerical models (Phani et al., J. Acoust. Soc. Am. 119, 4 (2006), Gonella and Ruzzene, J. Sound Vib. 312 (2008)).
THE EXPERIMENT
Our specimen is the regular hexa-gonal honeycomb shown in Figure 1, consisting of a 31.2 cm by 30 cm (20 by 18 cells) lattice, manufac-tured via wire-EDM cutting of a 0.95 cm thick aluminum plate. The lattice beams have an in-plane thickness of 0.67 mm. The spec-imen is clamped along the bottom edge and the excitation is applied by means of a transducer placed at the mid-point of the structure’s upper boundary, as to simulate a scenario in which the honeycomb is used as the truss core of a sand-wich panel whose skin is excited by a point force. The transient signal used for the analysis is a 5-cycle narrow-band tone burst, with variable carrier frequency and a
sufficiently-long relaxation time to allow the structure to return to its stress-free state in between acqui-sitions at consecutive scan points. Three measurement locations for each lattice beam are selected, for a total of 1811 nodes. Time aver-aging (100 averages) is carried out to reduce the influence of noise on the signal. The experimental setup is depicted in Figure 2.To fully study a structure with such topological complexity with the ambition to obtain accurate in-plane measurements at a multitude of sensing points, it is necessary to develop a sophisti-cated sensing strategy that allows agile in-plane measurements from non-uniform scanning grids. The Polytec PSV-400-3D Scanning Laser Doppler Vibrometer provides the perfect platform for this type of task. Nonetheless, the limited thickness of the lattice structural features that need to be scanned poses severe challenges even for state-of-the-art 3D vibrometers;
overcoming these challenges requires a special combination of procedural expedients (in terms of specimen preparation and data post-processing).
The main challenge during the data acquisition stage is posed by the difficulty in obtaining convergence of the three laser beams on the thin exposed surface of the individual lattice links. Only one of the three lasers need to miss the target surface (a scenario represented in Figure 3a) to completely compro-mise the quality and reliability of the measurement at that node. Unfortunately, video triangulation, which is designed to improve beam convergence, cannot be applied directly, as it is known to fail on edges (note that our struc-ture can be de-facto viewed as the collection of edge-like elements).
Our solution to this problem consists of placing patches of reflective tape at the lattice points
Figure 3 : Laser beam positioning improvement process: (a) A possible default situation in which one of the three laser beams is missing the target surface, due to the inapplicability of video triangulation on structural edges; (b) The three beams successfully land on the reflective tape patch; (c) Beam converge on the patch attainable via video triangulation.
Structural Dynamics
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corresponding to the nodes of the scanning grid. Figure 3b shows how the laser beams are forced to land on the patch and Figure 3c depicts the kind of optimal beam convergence that is obtained using video triangulation of the three coplanar laser points.
RESULTS
Two signals have been employed in the analysis: a burst with carrier frequency belonging to the S-mode (3.1 kHz), and one with carrier frequency belonging to the P-mode (27.9 kHz). The results for the S-mode are reported in Figure 4, where experimental (Figure 4a) and numerical (Figure 4c) wavefields, corresponding to the same time instant, are obtained via interpolation of the nodal vertical displacements. We observe that, at this frequency, the S-mode prop-agates with a spatially-anisotropic pattern. The frequency content of the wavefields is extracted via
2D-DFT of the data and reported in Figure 4b and 4d. We note that the results reported here for the S-mode have undergone frequen-cy-domain filtering to eliminate a spurious feature not conforming with the S-mode characteristics and ascribable to the dynamics of the tape patches. The results for the P-mode are reported in Figure 5: the propagation patterns feature circular-crested fronts and confirm the isotropy of this mode. The agreement between experimental and numerical results for both frequencies is remarkable, both in terms of wavelength and directionality.
CONCLUSIONS
In our study, we have confirmed experimentally the inherent frequency-dependent anisot-ropy of the wave propagation patterns in two-dimensional lattice-like phononic crystals (Celli and Gonella, J. Sound Vib. 333
(2014)). The study also demon-strates the applicability of the Polytec 3D-SLDV for the analysis of transient dynamic events in phononic crystals and, more in general, in structures with complex geometries and thin structural constituents. The use of reflective tape patches has been proposed as a way to overcome the chal-lenge of achieving laser beam convergence on thin structural elements while enhancing reflec-tivity and signal-to-noise ratio. ■
Figure 4 : Experimental and numerical results for
the S-mode (3.1 kHz). The experimental wavefield
(vertical displacement) at a relevant time instant, upon
filtering in the DFT plane, is shown in (a). The corre-
sponding numerical wavefield, obtained via a finite-element
simulation, is shown in (c). The experimental and
numerical spectral signatures, obtained via 2D-DFT of the
respective wavefields, are shown in (b) and (d).
Figure 5 : Comparison between experimental (a) and numerical (c) wavefields for the P-mode (27.9 kHz), at the same time instant. The experimental and numerical spectral signatures are shown in (b) and (d), respectively.
Acknowledgement
This work is supported by NSF (grant CMMI-1266089).
For more details, please refer to: P. Celli, S. Gonella, Laser-enabled experimental wavefield reconstruction in two-dimensional phononic crystals, J. Sound VIb., v. 333, pp. 114-123, 2014.
Contact
Paolo Celli, Stefano [email protected] of Civil, Environmental, and Geo- EngineeringUniversity of Minnesota, USA
36 |
Product News
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Forever YoungNew Polytec software
Our software support ensures that your Polytec measurement system investment continues to pay for itself many times over.
Fixed release cycles guarantee that you always use the most advanced measurement and analysis technology.
New versions of PSV Scanning Vibrometer Software, VibSoft Vibrometer Software, Planar Motion Analyzer Software and TMS Software are available now.
38 |
Product News
Family GrowsNew accessories for microscope systems
The right accessories enable users to take full advan-tage of their measurement instruments.
Polytec introduces a whole new family of accesso-ries for microscope-based measurement systems that measure static and dynamic properties of microsystems.
Active vibration damped tables with a portal for the sensor head convey a professional working environ-ment. Automated positioning further guarantees optimal operation.
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Measure Vibrations on the Lab BenchNew x, y, z positioning stage
A new x,y,z stage system for OFV-534 sensor heads extends the application range of our proven Single-Point Vibrometers significantly. This system enables vibration measurements on small objects that need to be positioned precisely.
The A-STD-BAS-01 compact basic stage ensures a secure mounting for the sensor head. A large work space is guaranteed with the integrated 150 mm range z-axis, which improves the flexibility for a broader range of measurement scenarios.
Optical accessories for the OFV-534 sensor head are compatible with the basic stage system, such as micro-scope objectives with 10X and 20X magnification that enable measurements on tiny structures. The VIB-A-510 illumination module ensures optimal viewing of the measured object and the clearest possible video images from the available sensor head camera.
The A-PST-050S x,y stage positions the measured object via software for seamless operation.
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ImprintPolytec InFocus · Optical Measurement SolutionsIssue 2015 – ISSN 1864-9203 · Copyright © Polytec GmbH, 2015Polytec GmbH · Polytec-Platz 1 - 7 · 76337 Waldbronn · Germany
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