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Industrial series measurement

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Industrial series measurement - What is it and how does it work?

Digitalization does not stop at surveying. Precise recording of geometric and spatial information about plants, machines, components and products is becoming increasingly important, especially for industry. To ensure that the data can be made available promptly and with the appropriate density and accuracy, companies are making use of increasingly modern technology. For example, the latest 3D serial measurement can be used to perform precise measurements on objects with complex geometry. Industrial serial measurement is part of industrial computed tomography. 

What is industrial series measurement? Industrial series measurement enables accurate, cost-efficient and almost automated measurement of components, products or devices. Accurate results and short cycle times are important. Accuracy is guaranteed by measurement plans and repeated measurements on one and the same product, component or fixture.

But what exactly is industrial serial measurement and why is it so popular in the industry?

What is industrial surveying?

Industrial surveying includes all metrological services that industrial companies have to provide. This includes, for example, the measurement of plants and the creation of 3D models of the plants. Settlement measurements are also part of industrial surveying. Here, large, heavy structures such as bridges and their effects on the subsoil - as a result of loading - are investigated and analyzed. Particularly important in the field of industrial surveying, however, is the measurement of components. These are examined by means of industrial series measurement.

What does industrial series measurement mean?

In industrial series measurement, large quantities of one and the same product, component or device are repeatedly measured. The shortest possible cycle times and reliable measurement results are important here. By means of individually developed measurement plans, the highest possible degree of automation is to be achieved in industrial series measurement. The aim is to keep the time and cost factor for the measurements as low as possible. Therefore, the repetitive measurement tasks should be designed as simple as possible. Furthermore, the measurements should not be influenced by operator errors. The measurement plans, which can be called up again and again, help against this.

Where is the origin of industrial series measurement?

Ever since man has existed, he has tried to explore and measure the earth and its shape. In addition to land surveying, engineering surveying and measurements in medicine also developed. 

History of computed tomography

With the discovery of X-rays on November 8, 1895, by German physicist Wilhelm Conrad Röntgen, people began using electromagnetic waves to shine light through bodies and objects.

The absorption behavior of the various materials is used for this purpose. The absorption behavior is based, on the one hand, on the density of an object. On the other hand, it is based on the chemical composition. Accordingly, elements with many protons in the atomic nucleus are hardly penetrable for X-rays. On the other hand, the rays can penetrate elements with few protons more easily. Due to the different tissue density of the illuminated objects, a two-dimensional shadow image resulted.

It was not until 1971 that the first CT scanner was introduced. The prototype was developed by Godfrey Newbold Hounsfield, an electrical engineer at Electric and Musical Industries Ltd.

Over the years, the prototype has been developed further and further. In addition to medicine, computed tomography is now also used in materials science fields. Since this often involves X-raying materials that have a stronger absorption than the human body, for example metals, higher radiation energies must be used in industrial computed tomography.

How does industrial series measurement work? 

For industrial series measurement of smaller objects, these are usually mounted on rotating plates. Unlike medical CT, in industrial CT the X-ray source does not rotate around the object to be examined, but the objects rotate around their own axis. In this process, an X-ray source and a detector remain in position.

While the X-ray source, generates X-rays, the detector measures the intensities of the radiation, converts them first into visible light and then into electrons with a photodiode. The pixel size and spatial resolution of the object is determined by the spacing of the individual measurement points on the detector. Afterwards, all pixels of the industrial series measurement are combined to form a 2D overall image or projection. Depending on the intensity, each pixel is displayed with different gray values. The result is a black and white image. The following applies: The denser an object is at a point, the greater the attenuation of the output radiation and the less clear the images of the detector are.

In addition to the understanding of the detector and X-ray device, the rotating plate also plays an important role in industrial series measurement. This does not rotate continuously around its own axis. Rather, it continues to rotate by a tenth of a degree after each individual measurement until the object has been completely measured once. The result is up to 2,000 X-ray images taken from a wide variety of angles. As a rule, 180° is sufficient as a rotation, since everything beyond that has already been measured once. Only from the other side.

How does the 2D model become a 3D model?

Once the projections have been created from all angles, special software, with the help of an algorithm, calculates a 3D object. The result is the so-called reconstruction. Not only the measured intensities are needed for this. The geometry of the measurement setup also plays a role. In other words, how far apart were the X-ray source, object and detector. 

After reconstruction, the measured object is available as a gray-scale image stack. Depending on the size of the object to be measured, several hours may pass. Reconstruction also takes some time. However, once the digital object is available, the image pixels can be converted to volumetric pixels using a graphics program. These are also called "voxels". 

At first glance, a massive, gray block appears. This is because in industrial series measurement, everything that has been defined as a non-object but is in the measurement volume is also measured. This can be, for example, a container in which the object to be measured is located, or a cushioning material in the case of fragile objects. The computer program cannot distinguish between the different materials here. 

Only by masking out certain gray values can properties be made visible that were previously hidden. In general, reducing the image volume is always advantageous for further processing. This works with a so-called segmentation: Here, all gray values that mark or represent the object are marked. All other values are removed.

But how do you turn the gray structure into a colorful 3D model?

In order to be able to view the inner workings of the object and possibly detect air pockets or errors in production, certain value ranges must be color-coded. Contrast settings can also be helpful in the visualization. 

This sub-step in industrial series measurement is rendering. To render something roughly means to reproduce or present something. Incidentally, this method is also used in the visualization of computer games. In this way, virtual spatial models are created that artistically generate the viewing direction, lighting effects and depth of field on the basis of raw data. In this way, color and material properties, such as surface reflections independent of an object, can be represented or changed at will. For example, to detect an air pocket in metal parts or tools, the transparency of the surrounding material must be increased for this purpose. The results can then be used to make changes in the production process.

Why is industrial series measurement so important?

The industrial serial measurement includes the professional and precise inspection as well as realization of measurements for industrial plants. Thus, entire production lines or individual machines can be checked for proper functionality. Especially the target geometry is checked at regular intervals during industrial serial measurement. This is because regular inspections are indispensable for quality assurance and proper monitoring of large plants. For this purpose, among other things

  • digital precision levelers, 
  • 3D laser scanner, 
  • or laser printers are used. 

Only in this way can

  • Quality testing of assemblies,
  • Quality testing of homogeneous materials,
  • Quality testing of inhomogeneous materials
  • and reverse engineering 

be carried out.

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