Polytec Scanning Vibrometer PSV-300 Principle of Operation and Applications This Powerpoint presentation informs you about operation of the Polytec s Scanning Vibrometer PSV-300 and presents some typical measurements carried out in the automotive industry. As this material contains several AVI movie files a fast CD ROM is recommended for viewing.
Polytec Scanning Vibrometer PSV-300 Basic Configuration of a Scanning Vibrometer The PSV-300 comprises an optical scanning head incorporating the laser interferometer sensor, beam steering optics and a video camera. Data from the scanning head are processed by the OFV-3001 vibrometer controller. A Windows NT workstation is responsible for scan point definition, data acquisition and control of the entire system. Sensor Head OFV-056 Test object Scan Electronics Video Vibrometer Sensor OFV-303 Scanning Mirrors Vibrometer Controller OFV-3001 Data Management System with NT Workstation
Polytec Scanning Vibrometer PSV-300 The OFV-056 Sensor Head features: Scan angle 40 x 40 degrees with 0.02 degrees resolution. Important feature for measurements of large objects in limited space areas 72 x zoom color video camera for measuring large and/or small objects without re-positioning the sensor head. Video camera, laser focus, range settings: All remote controlled for easy operation, e.g. with the scan head installed in an engine test chamber. Large range of working distance 0.2 m to > 50 m Coaxial attachment for scanning small objects down to 1 x 1 mm, e.g. injector nozzles
Polytec Scanning Vibrometer PSV-300 PSV-300-H Data Management System designed for the specific needs of our automotive customers 6 velocity ranges up to 10 m/s. Important for measurements on tires, shafts and other rotating parts. 4 channel data acquisition with 80 khz bandwidth. Up to 3 reference channels are recorded together with the vibrometer data. Full remote control of all hardware Scanning speed up to 100 points per second, reducing the brake squeal measurement time Build-in multiple channel signal generator Optional order tracking software for run-up measurements.
Polytec Scanning Vibrometer PSV-300 Making a PSV measurement On the following pages we will demonstrate how easy a PSV measurement is set-up and carried out. The experienced PSV user may use our new Visual Basic Macro feature to generate his own macros for automation of the entire measurement routine. Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Presentation of Data Export
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Presentation of Data Export Like in a drawing program the user defines the scan points on the structure. Different objects may have different types of meshes and mesh densities. Single points can be defined as well as lines of points (e.g. for scanning a drive shaft) with densities up to 512 x 512 points per object! The laser beam is clearly visible on screen and perfectly matching with the scan points in the video image.
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Presentation of Data Export If you have ever used an FFT analyzer the selection of acquisition parameters will be self explaining. The PSV data acquisition features Zoom- FFT, time domain data storage and FastScan for single frequency measurements (e.g. brake noise). In Multi Frame Mode the vibration data are synchronized with the engine and scanning results may be displayed for each cylinder separately.
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Presentation of Data Export During the scan the data quality is verified for each point. The Signal Enhancement algorithm will automatically increase the number of averages for points with low SNR. Data with too low SNR are rejected or re-measured resulting in perfectly clean measurement data. If you are using modal analysis software you will appreciate the high quality of the PSV-300 data.
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Export After the scan is finished the power spectrum is shown either averaged over all scan points or for individual data points. The user selects frequencies (modes) of interest for the on screen presentation of the results. Data can be presented for the entire frequency band (rms), for selected frequency bands (rms) or for individual frequencies.
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Data are presented in 2-D color coded, 3-D mesh or isoline displays. Even the video image of the test object may be animated. Presentation of Data Export
Polytec Scanning Vibrometer PSV-300 Define Scan Area Adjust Parameters Select Scan Mode Scan Select Frequency Bands Presentation of Data Export For the vibrometer and all 3 reference channels the the complex spectra are saved to hard disc during the scan. The Universal File Format (UFF) option allows easy export of these data to all common modal analysis programs.
Polytec Scanning Vibrometer PSV-300 Selected Automotive Applications On the following pages we present some examples of automotive measurements carried out with the PSV system. Please note that the list of applications mentioned here is not complete. Many of our customers applications are confidential and cannot be discussed in this presentation. If you have questions about your particular application please do not hesitate to contact Polytec for more information.
Polytec Scanning Vibrometer PSV-300 Panel vibration on doors, bonnet and inside of the vehicle Vibration testing on panels is a classical PSV applications in the automotive industry. The panels are excited either by mounting onto a shaker, by rolling road or by mounting the entire vehicle onto a shaker system. This application includes also tests inside of the car such as on the dashboard or on the car seats.
PSV-300 for panel vibrations The animation shows the color coded vibration of the bonnet at 103 Hz. Green data areas are standing for negative and red areas for positive velocities. The data are super-imposed to the video image. The bonnet (0.7 mm sheet metal) is supported by beams which can resonate like organ pipes. Stoppers are placed into the beams for closing open cavities. The PSV helps to identify the best location for these stoppers. Furthermore the effects of additional dumping materials is studied. In this measurement the bonnet is freely suspended and excited by a set of loudspeakers. A period chirp signal generated by the PSV-300 is applied to the loudspeakers for simultaneous excitation of the entire frequency band.
PSV-300 for panel vibrations Same measurement on a bonnet, but data shown at 153 Hz. The animation of the video image provides an easy understanding of how a structure is vibrating.
PSV-300 for panel vibrations In some experiments vibration measurements are carried out on objects excited by their own running engine. A once per revolution trigger pulse from the engine may be acquired simultaneously by the PSV system for synchronization of the data. The vibration of the rear part of the car is shown at 2 different frequencies. In the lower case the video image itself with super-imposed measurement data is animated.
PSV-300 for panel vibrations Bonnet vibration of the new VW Beetle car. For these measurements the vehicle was mounted onto shakers and excited by a periodic chirp signal.
PSV-300 for panel vibrations Vibration measurements on car doors are a traditional application for Polytec scanning vibrometers. Best results are achieved on a freely suspended door coupled to a vibration shaker as shown on the left.
PSV-300 for panel vibrations Measurements on the dashboard as shown above are routinely performed with the PSV-300. In above example the dashboard is mounted to a vibration shaker. The customer had problems to identify the source of vibrations on the glove box. The PSV helped to locate a part (dumper) behind the glove box causing the unwanted vibrations.
PSV-300 for panel vibrations From time to time measurements on highly reflecting parts (mirrors) or on windows are requested. Such measurements require a special surface treatment as otherwise the PSV would not receive any return signal. Polytec provides a special spray (powder) for scattering enhancement which can easily be removed after the measurement without any damage to the surface.
Polytec Scanning Vibrometer PSV-300 Vibration Testing of Braking Systems All major brake manufacturers are using Polytec vibrometer systems for measurements of brake noise, squeal and modal testing. This includes not only the Scanning Vibrometer, but also the Polytec 3-D vibrometer and fiber optical systems. For more details about brake testing please refer to the other presentation on this CD prepared by our customer Bosch.
PSV-300 for brake testing PSV-300 measurements on a test stand for brake pads. Data for used and new pads are acquired and compared to each other. During the scan the brake disc is slowly rotating.
PSV-300 for brake testing Deflection shape of brake disc under squeal condition. The squeal appears once per revolution and may disappear once the brake is running hot. Polytec provides an acoustical trigger unit comprising a microphone, DSP filter and gate unit. With this trigger unit the scan is paused while no squeal is present. As the squeal appears at single frequencies FastScan mode with scan speeds of up to 100 points per second is normally used for this kind of measurements.
PSV-300 for brake testing In most measurements the brake disc is mounted to a brake dynamometer. In above example the brake was driven by the tire running on the rolling road. Optical access was very difficult to achieve and only possible via mirrors. The Polytec trigger unit with microphone was used to synchronize the scan with the brake squeal.
Polytec Scanning Vibrometer PSV-300 Vibration Testing on Rotating Systems Many automotive measurements are performed on moving surfaces such as brakes, tires, pulleys, fan belts etc. Such tests are only possible with non-contact methods like laser vibrometry. While scanning the vibrometer will not only see the vibrational out-ofplane, but also the DC in-plane velocity component. Here the high velocity capability of the PSV-300 (10 m/s) is an important feature. A system with lower velocity limit would easily go into saturation when the scan angle, i.e. the DC velocity component increases.
PSV-300 for rotating objects Axial vibration measurements on an engine pulley and on an alternator. For such measurements a once per revolution signal from the engine is frequently used for triggering the data acquisition. An accelerometer on the engine/alternator provides a phase reference for the PSV data. The PSV can acquire up to 3 reference signals simultaneously.
PSV-300 for rotating objects Although in these examples the tires are mounted to a shaker and non-rotating, measurements on rotating tires are a major application for Polytec Vibrometers. Engineers at leading tire manufacturing companies are using the PSV-300 for modal testing on stationary tires and ODS measurements on rotating tires. Tire measurements are a demanding application requiring a high velocity capability of the laser vibrometer as the circumferential velocity of the tire might otherwise saturate the vibrometer system.
Polytec Scanning Vibrometer PSV-300 Vibration Testing for other automotive applications Not all applications of the PSV in the automotive industry can be addressed in this presentation. Measurements on engine components, testing in wind tunnels, exhaust systems, car seats and even measurements on all the electrical motors of a vehicle are other popular applications. In addition some applications require non-scanning vibrometers, e.g. valve train testing on engines, common rail injection nozzles and more.
PSV-300 for other automotive applications Above animation prsents data measured on a yellow glowing hot exhaust system. Even if surface temperatures are approaching 900 C no special precautions are needed. For exhaust measurements frequently a PSV-300 and a single point vibrometer are combined. One for scanning the exhaust and the other as a stationary reference. The reference vibrometer is fully remote controlled by the PSV software as well.
PSV-300 for other automotive applications A large portion of all PSV systems are used by suppliers of automotive components and not by the motor companies themselves. The images are showing an inlet manifold made of plastics. The manufacturer of these plastics parts is routinely using PSV systems for achieving data for their modal analysis workstation.
Polytec Scanning Vibrometer PSV-300 Vibration Testing on large structures The PSV-300 system can be used for measurements on untreated surfaces for distances exceeding 20 m. Hence the PSV is capable of scanning large structures such as complete cars or even trucks. In some situations the scattering properties are too poor and surface enhancement is required, e.g. on very reflective paints, when measuring via poor quality mirrors etc. The next example shows that even if surface preparation is required a huge amount of time will be saved by using the PSV.
PSV-300 for large structures Measurement on a 20 m wide rail way wagon from ca. 20 m distance. The set-up for a large truck or bus would be similar. Instead of using powder spray for enhancing the scattering properties of the surface a total of 700 reflective marks was attached. Preparation of the measurement took ca. 3 hours, the measurement itself less than 10 minutes. When using conventional accelerometers time needed for the preparation of the test was more than 1 week.
Measurement of turbine blade vibrations. Experimental setup and scan grid on the A320 wheel
Jet Engines
Inflatable 4x6-meter communications antenna concept.
Squealing Brakes Three views of a deflection shape of a brake disk
New Method for Non-destructive Testing of Materials and Structures using Non-linear Acoustics Higher harmonics (40 khz excitation) at a simulated defect: Delamination in carbon fibre reinforced plastics (CFRP) Flaw detection in aluminum: 4th Harmonic (excitation frequency 20 khz)
3D animation and time trace of Input Shaped step response MEMS Accelerometer spring elbow at 23 khz
Bending mode of HGA at 5114 Hz Torsion mode of HGA at 6650 Hz Applications to Data Storage Dynamics
Laser Doppler Vibrometry Brings Insight into the Functioning of Fruit Fly Ears
Loudspeaker Development The Balanced Mode Radiator is a new approach to loudspeaker design with unique visual and acoustic features. Tight control of the membrane properties is essential to providing proper acoustic fidelity from the device. Polytec s Scanning Vibrometer enabled insitu measurements on operating devices with no contact or loading of the panel membrane, successfully accelerating the development and manufacturability of the new Sounds Good Vibration Analysis is a Valuable Tool for Loudspeaker Development loudspeaker. 90 85 80 75 70 65 60 55 50 45 1k On-axis SPL [db] SPL 2k 3k 4k 5k 6k 7k 10k 20k 30k 40k 50k Frequency [Hz] Release Sample Golden Sample Fig. 1: On-axis Sound Pressure Level (SPL) spectra from tested BMR s. Introduction The Balanced Mode Radiator (BMR) represents a new class of loudspeaker with distinct design features and acoustical properties that distinguish it from the traditional, well-known electrodynamic loudspeaker design based on conical membranes. The most obvious difference between traditional conical speakers and the BMR is the use of a suspended flat circular disc as the radiating membrane panel (see title image). The drive unit features a clean appearance and a plane front that allows for innovative industrial designs with unique sound properties. Acoustically, the BMR is designed as full-range driver which supports almost the entire audible spectrum. For frequencies above the panel s first eigenmode, the BMR operates as a bending-wave device where its acoustic behavior is predominantly determined by the panel s mass density, bending stiffness, damping, and shear. These parameters are of paramount importance for the acoustic performance of the BMR. From Prototype to Mass Production The design of the BMR was done in Germany. But, due to cost constraints in the consumer market, most drive units had to be manufactured in China. During the product development phase, all required parts were tooled and made in China then assembled and tested in Germany. Each part s geometry and material was changed until satisfactory performance was achieved. A construction manual was written and sent to China together with the final drive unit. This Gold Standard called Golden Sample serves as a reference when setting up the production line. An initial set of prototype drive units known as Release Samples were sent back to Germany for approval. In the case study presented here, unexpected changes in the panel s material composition degraded the acoustic performance. A Release Sample was found to produce a less bright sound than the Gold Standard, although both units were built according to the same nominal specifications. Thus, the task was to identify the source of this difference. On-axis Frequency Response To begin the drive unit assessment, the acoustic on-axis frequency response was measured (Fig. 1). Above 18 khz the Release Sample is slightly louder than the Gold Standard, indicating a somewhat brighter sound. This measured result was the opposite of what was subjectively noted when auditioning both units. 20 10 5 2 1 0.5 0.2 0.1 0.05 1k Averaged velocity & acceleration spectrum Velocity [mm/s] Acceleration Release Sample Golden Sample Velocity Release Sample Golden Sample Acceleration [m/s 2 ] 2k 3k 4k 5k 6k 8k 10k 20k 30k 40k 50k Frequency (Hz) Fig. 2: Average velocity and acceleration spectra from tested BMR panels. 20 15 10 5 0 5 10 Source: Polytec InFocus 1/2008 Polytec GmbH www.polytec.com/infocus
Consequently, the next step was to try to resolve this apparent contradiction by spatially measuring the dynamic response of the BMR panels of both units using the Scanning Vibrometer. Vibration Analysis of Drive Units Vibration analysis was performed using a Polytec PSV-300 Scanning Vibrometer. For sample excitation, the vibrometer generated a swept sine wave signal ranging from 150 Hz to 50 khz, and acquired the velocity frequency response data from 1781 measurement points that were evenly distributed in a circular symmetric mesh across the panel. The average spectrum calculated using the Scanning Vibrometer software allowed quick access to mean velocity and mean acceleration data. In Fig. 2, the acceleration spectra of both units are plotted in Fig. 3: Out-of-plane deflection shapes for BMR panels at 10 khz, Release Sample (left), Gold Standard (right). the upper half of the diagram with the associated ordinate axis positioned to the right, while the velocity spectra are located in the lower half with the associated ordinate axis to the left. The most obvious deviations occur in the 7 12 khz range as opposed to the 12 18 khz range identified by the on-axis Sound Pressure Level (SPL) measurements. Differences in this frequency range (7 12 khz) are more likely to be judged as bright or dull. The brighter sounding Gold Standard shows higher activity in both average spectra than the Release Sample, supporting the results of the informal subjective evaluation. Modal Analysis The results shown in Fig. 2 suggest that the two drive units have different panel materials. In Fig. 3, the operational deflection shapes (ODS) at 10 khz are compared. It is obvious that the Release Sample shows a bending mode with circular symmetry on its panel (left) while the Gold Standard features rotationally symmetric structures that break circular symmetry (right). The results confirm the previous findings. The Gold Standard BMR panel shows a much less isotropic bending stiffness than the Release Sample panel. Obviously, the panel manufacturer had actually tried to improve the panel quality by making it more isotropic. Release sample 10 khz velocity profile Momentary value [um/s ] 300 200 GoldenSample 10kHz velocity profile Momentary value [um/s ] 400 200 Conclusions Structural response data taken with Polytec s Scanning Vibrometer allowed in-situ identification and characterization of dynamic material properties in loudspeakers and clarified inconsistent preliminary SPL measurements and auditory tests. The net result of the vibration analysis was an improved understanding of the BMR and reduced development time by eliminating trial-and-error approaches. 100 0 100 200 4 0 30 2 0 10 0 10 2 0 30 4 0 raidal position [mm] Release Sample: 10 khz-velocity-profile @ 0 -axis Release Sample: 10 khz-velocity-profile @ 90 -axis Fig. 4: Plots of orthogonal cuts through Fig. 3 deflection shapes, Release Sample (left), Gold Standard (right). 0 200 400 4 0 30 2 0 10 0 10 2 0 30 4 0 raidal position [mm] Golden Sample: 10kHz-velocity-profile @ 0 -axis Golden Sample: 10kHz-velocity-profile @ 90 -axis Authors Contact Dipl.-Ing. Charalampos Ferekidis, Karl-Heinz Fink Fink Audio Consulting, Essen, Germany; AudioPlus, Sutton SM1 2SG, UK lampos@ferekidis.de; karl-heinz@fink-audio.com Source: Polytec InFocus 1/2008 Polytec GmbH www.polytec.com/infocus