Siemens Rail could buy multiple tachymeters, or just one API tracker

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The railcar manufacturer’s quality control department was especially intrigued with the ability to automate measurement processes, thereby allowing the API tracker to take a more complete measurement, capturing the specific data that they needed.

With its locomotives, Siemens makes an efficient operation possible for its customers while protecting the environment and resources at the same time; the well-established locomotive platforms Eurosprinter and Eurorunner are already in successful operation. With the new Vectron locomotive generation, a highly flexible vehicle is available that covers all the applications from pure AC and DC locomotives up to multi-system locomotives. In addition, Siemens also offers individual solutions on the basis of proven concepts and components that can be precisely tailored to specific customer requirements.Furthermore, the global presence and many years of experience of Siemens make it possible to build locomotives in cooperation with local vehicle manufacturers.

The central component of every locomotive is the car body, which is realized as a self-supporting structure due to the requirements for high strength; it consists of three main assembles: the under- frame, the driver’s cab and the engine room side panels, which are manufactured in the context of the component manufacture in the steel construction area of the locomotive factory. Folded, lasered or drilled steel plates are built, which are then assembled in jigs and welded together.

Robotic welding systems are also used in the car body production, one of the core skills of the Munich factory. In the measurements, there is not only interest in the dimensions of the box, such as length, width and height, but also in the inclinations of the side panels for the frame, the roof widths and other interface measurements. Up to a few years ago, the standards applicable at the time permitted the carrying out of all basic measurements with string, tape measures and leveling instruments. As the (theoretical) car body center began to establish itself as the reference point over the course of time, a point that could no longer measured, but only constructed, measurement technicians experienced increasing problems.

Tachymeters have been displaced

Up to now, tachymeters have been the means of measurement of choice. Whereby, as a pure user, Siemens only carries out the measurements; the measurement tasks and the measurement processes were programmed by an engineering office, which also carried out the evaluations. A production run-up gives the user a choice: to either expand existing measurement processes or to switch to an alternative. Thomas Osterauer, Quality Manager in the Steel Construction department of the locomotive factory comments:

“At that time, we had to significantly increase our mea- surement capacities; either through the procurement of a second tachymeter or by switching to more advanced measurement equipment. Our attention was drawn to laser trackers at an industrial fair, and we then considered them in more detail. It was immediately clear to us that a switch to laser trackers would entail changes to our existing measurement programme.“

But the advantages of the laser tracker spoke for themselves. After a selection process, it was decided to obtain two OmniTrac laser trackers from Automated Precision Inc. (API). These laser trackers, in this model without the interferometer that is normally integrated into laser trackers, are the ideal candidates for the replacement of the tachymeter, which was showing its age. Even the principle of operation of the automatic targeting of the measurement ball, which differed from that of the tachymeter, promised considerable time savings; in addition, the measurement errors that are other- wise normal and that can arise from the imprecise targeting of the ball, are avoided by the automatic tracking. There was an additional advantage in addition to the significant time savings: while measurements were previously carried out by two persons, these measurements could now be carried out by one man using a laser tracker.

It has now also become possible to carry out special measurements, such as the measurements of the free clearance profile of the locomotive, as well as checking jigs and templates. When it comes to exclusively optical quality checks, such as the detection of scratches and welding spatter and checking evenness, however, rulers are still used.

The switch to laser tracker provided yet another opportunity: From now on, components could be checked using automated measurement procedures, whose measurement programmes could be created by ourselves. This also applied to the measurement of steel motor mounts. Here also, self-created, photo-documented measurement plans can be used to process measurement programs with up to 500 measurement points. In this way, all the external measurement services could be saved – and we were more flexible with regard to special measurements. This became possible through the use of the SpatialAnalyzer software, which permits a convenient self programming by the user. An initial training course, in which the first self-made programs are also created, was carried out by the employees of Automated Precision Europe (API) in Heidelberg.

Flexibility is everything

The locomotives built by Siemens in Munich can weigh 90 tonnes or even 130 tonnes; their weight depends on their intended pur- pose and is largely determined by the thickness of the steel plates used, which can be 20 mm or 200 mm. The longest structures that have to be measured in the locomotive factory are related to the underframe manufacture, in which the components are assembled and welded together.

An important role in the selection of the new measurement system was the requirement that it should be able to be used as flexibly as possible; not only should the installation at different stations (shell and underframe manufacture, component manufacture, test and assembly equipment) take place as quickly as possible, but the installation location itself was also an important factor for the suit- ability of the system.

Unlike conventional measurement systems and all other systems, the laser tracker from API could also be mounted directly under- neath the underframe thanks to its minimal installation height. This was the decisive factor in the selection, because one measurement location could be completely saved as a result, which considerably shortened the total measurement time. With a height of 36 cm and a weight of only 8.6 kg, the tracker is more compact than other systems that were out of the question for this installation location due to their size.

Both laser trackers are constantly on the move between their three deployment locations in the factory – over short distances as hand luggage thanks to their low weight, and on roller trolleys for longer distances. The laser trackers are also used when customers come to the factory and want to see the measurement processes; incorrect measurements are then demonstrated in order to check the process reliability. The reproducibility of measurements helps here, as well as the automatic reports from the documentation.

In retrospect, Thomas Osterauer agrees that the replacement of the tachymeter by the laser tracker from API was exactly the right decision. “With our trackers, we now measure much more accu- rately and very much faster than before. We were also impressed by the unmatched compactness of the system and the possibility of even installing them under our underframes – whereby we were able to save a considerable amount of measurement time. We have freed ourselves from our dependency on external service providers and can now program all the measurements ourselves – with lower costs.”