Only what can be measured can be optimized

In modern production processes, measurement and sensor technology is indispensable. Continuous monitoring of defined quality parameters in random samples or directly in the production process ensures maximum quality and minimum scrap. This is one of the reasons why optical measurement methods in the semiconductor and optics industries now work in the sub-nanometer range. In the interview, the new head of the Institute of Applied Optics at the University of Stuttgart in Germany, Professor Stephan Reichelt, and Manuel Hüsken, CEO of the Mahr GmbH, based in Göttingen, Germany, discuss the latest trends in measurement and sensor technology, the influences of transformation in the automotive industry, and the outlook for measurement and sensor technology in the development and expansion of a European manufacturing basis for semiconductor chips, high voltage batteries, and photonics solutions.

Professor Reichelt, you took charge of the ITO a few months ago. What are your plans for the institute and collaboration with industrial partners?

Professor Stephan Reichelt: The ITO has been collaborating with industrial partners for a long time with a great deal of success and we intend to continue along this path. It is fruitful for both sides. We get a sense of the challenges and issues bothering the companies and we can then align our research in that direction. From time to time, we have been able to contribute solutions from earlier projects immediately. Each project is a platform to present our competences and technological possibilities. As an institute with around 40 employees, we take a holistic approach: From planning the measurement methods and dimensioning the optical systems to producing the core components, such as diffractive optical elements or 3D-printed microoptic systems, and then characterizing them with our measurement process and testing them in prototypes, we are able to optimize our solutions systematically and continuously.

Can you give us an example?

Reichelt: I can point out the joint development of a tilted wave interferometer together with Mahr. It responds to the demand for more flexible measurement engineering for aspheric lenses. These were previously measured with computer-generated holograms to create a test wave for interferometric zero tests. To make this more efficient, we came up with the idea of simultaneous surface measurement using tilted wavefronts. The ITO developed this approach to the prototype stage before Mahr transformed it into a marketable product in the course of further joint development. This example illustrates how many years of research collaboration encourages expertise that can solve specific problems. At the same time, our students and Ph.D. candidates get to know what the main issues are—and they evolve into sought-after experts. Qualification is and will remain a key task of our institute.

Mr. Hüsken, you also have been CEO of Mahr for a relatively short time. What are your plans?

Manuel Hüsken: The matter of further digitalization is high up on the agenda. We want to offer more digital and networked products in the future. Artificial intelligence is part of this: It should enable users to increase their productivity, prevent failures, and detect critical developments at an early stage. To this end, we are developing appropriate user interfaces that can adapt to the respective user with the help of AI. Another digitalization topic is predictive maintenance, for which we are taking new approaches. We want to get an idea of the machine’s condition even before it reaches the customer: How well does it work and in what state does it leave our factory? This also implies offering customers extended digital options, such as a digital twin of their machine. Another very important goal is to manage the current transformation in the vehicle industry. The aim is to generate profitable sales growth and further expand the other business areas to achieve this. What many aren’t aware of is that Mahr not only manufactures measurement technology, but also gear metering pumps, mixing and metering machines, and stroke bearings. But what is also very important to me is to offer our employees prospects for the future and a modern working environment. In addition, we are focusing on reducing complexity within the company and acquiring new customers. These are the big issues we want to work on over the next five years. And, of course, there are other technological subtopics.

The tilted wave interferometer that Professor Reichelt mentioned and the takeover of NanoFocus AG clearly show that Mahr is focusing on optical methods. Will tactile measurement processes be a thing of the past?

Hüsken: No, not at all. We will continue to rely on both technologies in the future—on both tactile and optical measuring devices. These are technologies that can co-exist as they complement each other. Optical processes are an important element for the future. Demands on structures and topographies of surfaces are constantly increasing in the fields of medical technology, the semiconductor industry, optics and many other sectors. Therefore, it is necessary for the portfolio to comprise the appropriate technology. Let me just make a basic remark here: It isn’t always easy to choose the right measurement method for a specific application. In general, the two-dimensional stylus method is an excellent choice for rapid surface validation of known products and processes. This technology is accepted worldwide from a financial and technical point of view. On the other hand, contactless 3D measurements are a better choice when the surface is technically complex, additional statistical security is required, or the material is very sensitive. In addition, the measurement recording is significantly faster and enables large-scale 3D recordings.

And what does the scientist have to say about that?

Reichelt: I believe that tactile and optical measurement processes will exist side by side. The importance of optical methods is increasing, as they enable contactless, very fast line and area scans in order to capture complex 3D surfaces. This is an advantage compared to tactile measurement methods where the point clouds subsequently have to be analyzed. But there are applications where optical processes struggle. This could be due to contamination or the surface properties of the object to be measured or due to unfavorable vibration and light influences. For example, whether coherent lighting generated by laser helps or obstructs depends on the individual case and the objective. With every measurement project, a lot of issues and parameters have to be clarified beforehand so that the correct measurement strategy can be chosen from the variety of optical and tactile methods.

In many industrial processes, the trend is towards 100 percent control and, consequently, to inline processes. What challenges does this pose for your research?

Reichelt: If measurements are to be carried out close to the process, particularly robust methods and sensors are required, which have to be fast, small, flexible and adaptable in many different applications and—importantly—they must be relatively inexpensive. These are the stipulations that we base our research on when developing new methods. The aim is to create added value, for instance, when the measurements provide additional information about the measured object, reduce throughput times, or provide realtime data in the process in order to adjust running processes on the fly. But for that, you cannot just move the component into the measurement room and check its dimensional stability there. A lot of what we do at ITO is aimed at inline measurements. These include single shot methods that generate information in realtime with one shot instead of evaluating measurement sequences. This also has the advantage that single shot methods minimize the effect of vibrations and drifts, which becomes more important when the measurement is carried out close to the process. These inline methods are a key component of Industry 4.0. to be able to monitor and readjust processes and ensure the quality in a fully automated production world.

Is Mahr also involved with inline measurement methods?

Hüsken: This is a hugely growing market that is an important factor for our future. Professor Reichelt’s description of the requirements for inline measurement methods hit the mark. We already offer a wide range of sensors for these processes. And it is clear that the measurement technology is moving out of the measurement rooms towards the line, which is why we will also expand the existing sensors and technologies for this area in the future. Not every characteristic will be measurable with precision directly inline in the process. But it must be possible to integrate measurement engineering into the manufacturing world so that production can take place in a closed loop.

At ITO measurement engineering is moving deep into the sub-wavelength range. We are talking about aspheres, 3D-printed microoptics, and artificial intelligence. Where are these high-end solutions used?

Reichelt: Since optical technologies moved on from being a special area for crossover technology some time ago, they are now used in a large number of applications. For example, these days it is difficult to imagine how manufacturing engineering, image processing, data transfer, medical engineering, biotechnology, energy and environmental engineering, and transport would function without the contributions made by optical technologies. EUV lithography with 13 nanometer (nm) wavelength enables microprocessors with ten billion transistors on an area the size of a fingernail. Mechanical manufacturing processes are replaced by high-precision laser material machining. Autonomous vehicles function in traffic with the help of optical sensors. And at the ITO we produce the 3D-printed microoptical systems I mentioned before, which are used, for instance, in miniaturized endoscopes to look for build-up in blood vessels. The lenses for this are pressed directly onto optical fibers to enable multimodal imaging and sensors. In this way, we are constantly shifting the boundaries of what is feasible—and for this we need extremely precise measurement methods. After all, you can only produce and optimize something that can be measured.

Mahr also offers nano resolutions, digitally driven measurement processes and measurement engineering for battery and fuel cell factories. How does the upheaval in the automotive industry affect the measurement and sensor engineering market?

Hüsken: The automotive sector will remain of great importance for Mahr in the future. Some of the existing production lines in the automotive industry are currently being modernized in terms of metrology, and we are benefiting from this. But many investments are already now subject to very strict cost control in the combustion sector. The industry is shifting its resources toward electromobility—here, too, we are well positioned. Overall, the market for measurement technology in e-mobility has a different complexity. We need to respond to this in order to take advantage of the opportunities it presents. And expertise in surface measurement technology is a key requirement here. I expect that the demand for optical measurement methods will continue to grow and that its contributions to greater system efficiency will be in demand in many new areas of automotive engineering. There are also demands for the highest possible precision in electric drive trains. Among other things, measurement technology helps to optimize surfaces: More precise bearings, minimized friction in the sense of reduced energy consumption and wear. This goal ensures continuously growing demand for optical measurement methods. And the expertise is also important when electric motors or fuel cells are used as drive systems.

Reichelt: We look forward to the challenges this will pose for measurement engineering. We have been pressing ahead with digitization and using AI methods for some time. In high-resolution measurement engineering it has been common practice to combine different measuring procedures and model-based methods for some time. This is the only way to determine geometrical and material-specific properties of nanostructures. For this purpose, we use the variety of information provided by light: wavelength, intensity, phase, coherence properties, polarization, and angular spectrum. Based on models, we obtain the information that is relevant for the respective measurement task. Another important approach in this respect are digital twins of the measurement set-up, including the object to be measured, in order to reproduce and simulate measurements virtually. This helps estimate measuring uncertainties of actual systems—and, in the long term, will change our approach. When deep learning methods are able to think for themselves, in many cases it will not be necessary to translate measurement signals into image data for humans.

Finally, a look to the future. In Europe and, ultimately, worldwide the production basis for semiconductors and batteries will be expanded. Photonics will be used in many new areas. Will demand for high-precision measurement and sensor engineering also increase?

Reichelt: From many aspects, it is important that these significant technologies are increasingly produced here in Germany and Europe. We must keep pace with developments. Global supply chains have been shown to be fragile in times of crisis. And we should be less dependent on some suppliers. This opens up enormous opportunities for measurement and sensor engineering. The miniaturization fields, such as the manufacture of semiconductors, MEMS, and optical elements, especially cannot function properly without high-precision measurement engineering. Also, the quality, range, and costs of electric drive systems will depend largely on their production being supported by continuous measurement. I think we can expect to see many fascinating issues and measurement tasks in the future. We look forward to the corresponding requests from these future fields.

Hüsken: I can only underline these statements, even though I continue to see many advantages in global business relationships. But the new technologies offer great opportunities for Germany as a business location. Wherever proof of very high precision is required, you need measurements to determine the position of the object being measured—and, importantly, the exact calibration of the measurement systems themselves. We have the necessary know-how here in Germany. Especially in microsystem technology, although manufacturing has often not taken place in Europe in the past. A change is on its way here, in the course of which the demands on us as a manufacturer of measurement and sensor technology will also increase. Therefore, the proximity to the industry and the institute landscape is very important.