FORD automotive (1990): Holographic interferometry for automotive engineering.

FORD automotive (1990): Holographic interferometry for automotive engineering.


holography in art is a form of playing with a perfect illusion these bananas look as if they were within reach but they can’t be grasped [Music] the John Andrews engineering Center of Ford in Cologne here our engineers use holography as an effective optical measuring technique with no other technology is it possible to register even minimal vibrations and deformations of vehicle parts so precisely in one of the laboratories an Orion model is being prepared for measurement the results help to optimize construction of vehicle components the technical jargon for this special application by the way is holographic interferometry Ford pioneered its use in automobile development but let’s first have a look at the fundamentals of holography [Music] we can stay with the car for this when a gearbox is being tested on the torque stand it’s very important for the designers to know how the housing stands up to stresses a hologram decodes the deformation interference structures into visible deformation contours and these provide information on the level of stress in vibration analyses to make the picture clearer the interference line structure can be converted by computer animation into a three-dimensional vibration movement how is a simple hologram made to start with you need single color pure light with the individual electromagnetic waves exactly in phase no normal light source meets this requirement only a laser provides this totally artificial light the experts call this monochromatic coherent light a model makes the path of the laser light clearer the light is split by a beam splitter into an object beam and a reference beam let’s first follow the onward path of the object beam it’s deflected by a mirror towards a divergent lens the lens transforms the originally sharp laser beam into a kind of searchlight whose light cone illuminates the whole object in our model the toy car the car reflects the light cone and this reflected light falls directly onto a holographic photo plate now let’s follow the path of the split off reference beam this also goes to a mirror and a divergent lens but then falls directly on the photographic plate without touching the object being photographed and it’s the interplay of the object and reference beams that’s decisive in making a hologram the process once again in detail the laser-light is split at the beam splitter the object beam is first deflected by the mirror and then expanded by the lens before falling on the object the pure laser light of which the individual electromagnetic waves were originally in phase is reflected in random phase by the toy car one could say that in this way a body print of the object is taken on the holographic plate the reflected in coherent wave fields of the object beam cross with the in phase light waves of the reference beam this overlapping of object and reference beams produces a distinct interference pattern on the holographic plate and this pattern contains complete information on the exterior form of the object photographed rather like a fingerprint to make this visible the reference laser beam is required now we remove the car and switch on the laser beam on the very same spot where the real toy car just stood we see a perfect three-dimensional image we can look at it from any angle we like the division between illusion and reality is no longer clear [Music] let’s return to the application of holography as a laser measurement technique in automobile design in day-to-day driving cars are often subjected to very considerable stresses yet even on bumpy roads their occupants should feel safe and comfortable body vibrations as well as oscillations produced by powertrain components can result in objectionable noises a holographic vibration analysis can help to detect disturbing noise sources and eliminate them through improved design we’re now in the pulse laser laboratory an Orien model is just being installed on a specially developed hydrostatic test rig with which driving condition on the road can be very precisely simulated here the oil sump is being prepared for measurement with the aid of holographic interferometry exact data on the vibration behavior of the oil sump during actual driving conditions can be obtained the whole optical system takes up relatively little room the engineers actuate the test stand and the pulse laser holography system from a control room additional apparatus for measuring noise and vibration is used to back up the holographic analysis the success of the experiment depends on both exposures being made at measuring points that are characteristic of the components vibration behavior only in this way can its dynamic deformation be correctly assessed so before producing the hologram the engineers measure the vibrations at an appropriate spot here it’s being done with a laser Doppler vibrometer the screen displays the representative vibration signal that will activate the laser flashes preparations are now complete and the laboratory is vacated from the control room the test rig is started up the vehicle is driven up to the precisely defined and predetermined level at which the objectionable noise commences the high-energy Ruby laser works like a photographic flashlight with two short flashes one after the other that capture the object on the holographic photo plate owing to the extremely short interval between the two flashes the human eye can recognize one flash only the double exposure not only permits a simple hologram but provides a three-dimensional image of the deformations of the oil sample course by driving vibrations and this is what’s really important for the subsequent measurement evaluation and the secret by means of the double exposure interference patterns are produced they can be perceived as contour lines emanating from the center of vibration a video camera scans the completed interferogram and relays the digital image information to a computer which evaluates it in terms of measuring technology the image evaluation program can precisely register vibrations to ten thousandth of a millimeter electronically colored the interference patterns become even more distinct the vibration center of this engine unit can easily be recognized but the computer can do even more it converts the vibration data into a three-dimensional grid pattern which serves as a reference for optimizing design the vibration form in slow motion shown without phase shift permits conclusions concerning sound radiation pulse laser technology as a non damaging non-contact laser measuring technology linked with computer-aided evaluation processes is a valuable means of analyzing vibration in realistic conditions it provides component engineers with precise and accessible information and able to solve any vibration problems arising in a vehicle faster and more easily [Music] gear shifting in a modern transmission system should be smooth and precise and under all driving conditions transmission must be quiet and reliable a challenge to the designer the stresses on material should never be such that they lead to eventual damage through fatigue that’s why we subject units like gearboxes engines or additional components like alternators – holographic analysis in the continuous-wave laser laboratory one frequently applied method of this continuous-wave laser technology is the real time process this process offers above all one great advantage all surface deformations caused by static forces torque pressures and temperature fluctuations can be directly observed and analyzed [Music] a gearbox is being firmly anchored to a vibration-free table the table prevents the distortion of measurement data by external vibrations through the floor in ordinary driving conditions diverse input and output forces put a strain on the transmission these forces are simulated on the test stand with the aid of a worm drive and a pneumatic cylinder the technicians can subject the driving shaft to any given talk [Music] the resulting output torque is transmitted through a shaft to the test control unit [Music] a technician sets the gearbox unit in position for the hologram to be made of the required aspect he then produces the desired torque in the driving shaft all preparations for the holographic shot are now complete the laboratory light is switched off and for a brief moment the laser exposes a photographic plate on which the surface structure of the gearbox casing is now captured the hologram developed in the darkroom is remounted in exactly the same position in further testing it serves for comparative image or to stick to the technical jargon as a reference hologram [Music] the reference beam of the laser makes it visible the surface structure of the real gearbox is superimposed on the one captured in the basic hologram a change of torque results in deformation of the gearbox housing it can be seen directly in the video picture in the form of interference lines this is why we speak of the holographic real-time process the interference fringes can be interpreted like the elevation lines on a contour map the real-time interferogram obtained in this way is fed into a digital image processing program the computer calculates the deformation data contained in the interference fringe pattern a false colors graphic makes the structure of the deformation even clearer a really concise 3-dimensional image of the deformation structure is given by a pseudo 3d graphic the measurement values provide further evidence on deformation in the gearbox housing under examination all the weak points in construction are revealed with the aid of this technique for designers the holographic real-time process is an important aid to effective optimization of vehicle components with regard to deformation and stress at Ford the various applications of holographic interferometry have already contributed to a series of technical improvements in the case of our example with the aid of holographic measuring technology certain weak points were discovered in the gearbox housing consequently additional reinforcing ribs were incorporated into the housing which led to quality improvements even at the development stage as we can see effective technical innovation is a matter of detail and being technically ahead assures as the goodwill of our customers [Music]


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