Laser Measuring Techniques In Commercial Vehicle Construction And Mechanical Engineering

Laser measuring techniques in commercial vehicle construction and mechanical engineeringB. BreuckmannMaschinenfabrik Augsburg- Nurnberg AGDachauer Strase 667, 8000 Munchen 50AbstractThis paper explains the specific advantages and disadvantages of interferometricmeasuring and testing techniques using the example of holographic interferometry.Applications from commercial vehicle construction and mechanical engineering are given forthe most important fields in which holographic measuring techniques are used. Particularattention is thereby paid to considering the techniques from the point of view of theindustrial user: to their availability outside special laboratories, to their reliabilityin day -to -day industrial use and to their economy. The present state of the art and theexpected developments in the field of automatic evaluation are also discussed.IntroductionThe invention of the laser has fired man's imagination like few other innovations beforeit. Although many of the initial hopes and expectations have not been realised, there aretoday many processes which were not technically possible or economically feasible until theadvent of the laser. The industrial applications of the laser can be divided into three maingroups:- telecommunications- material processing- measuring and testing techniques.In the first of these areas, laser diodes are being used more and more often. The demandsmade on typical laser properties - low spectral width, small divergence of ray - should how-ever been seen here in relation to the corresponding properties of other optical transmittersand are thus in general less strict than they are in measuring technology, for example. Inmaterial processing, the CO2 and Nd -Yag lasers, which have in the meantime become very reli-able, are used in order to generate the required high energy densities in a specified,closely restricted space. In measuring technology, various properties of the laser areexploited according to the particular application and the most varied types of laser areaccordingly in use. The necessarily higher demands made on the devices for measuringpurposes are however in many cases not met. The lack of technical maturity frequently meanslow reliability and time -consuming preparations, which means that many types of laser canbe eliminated as unsuitable for industrial applications from the start. Laser -based measu-ring and testing techniques also often prove to be unsuitable for the same reason althoughapplications and a demand exist. In view of this, the following sections are devoted to adiscussion of the question of the availability of laser -based procedures in measuringtechniques specifically from the point of view of the industrial user. The example taken isholography.Holography in industrial practiceHolography, the application of which is particularly closely linked to the developmentof the laser, has been the object of great expectations since the mid- 1960s. A large numberof groups concerned themselves with the new technology and so after only a few years notonly the physical principles but also the necessary requirements for lasers, opticalstructure and recording material were known and had also been realised for most of thepresent fields of application. Unfortunately, many of the dreams of this time have onlybeen fulfilled in laboratory set -ups, if at all, such as holographic films or even 3 -Dscreens, all of which means that holography has not yet made an impact on everyday life.In the field of measuring techniques, the situation is similar, although the physicalprinciples, the measuring set -up, the stability requirements and the equations forevaluating have been known for a long time. The possibilities of combining holography withother optical measuring techniques such as speckle technique, moire technique and optics ofstress and strain have also been shown. All these procedures have been used and can showsome success in solving problems of measurement. However, a large proportion of holographicmeasuring techniques are still only applied in university institutes or in research anddevelopment laboratories of the larger companies. Their use in series production or inquality control has to date been confined to only a few instances such as tyre checks andmeasuring of optical elements. Using as examples three important applications, the followingsections will examine the possibilities offered by holographic measuring and testingtechniques in industrial use, the limitations to which they are at present subject and the