Vibrations occur when drives move machines. Because these vibrations are often unwanted, damping them as effectively as possible is a key issue in automation. “Every industry has its own specific issues when it comes to adapting the automatic control of its machines for fast, error-free production,” says Schäfers, who – together with his team – works on custom solutions for automation systems. “I don’t usually have to reinvent the wheel,” he says. “Instead, I can take existing components, such as special motors or sensors, and combine them in new ways.” Because Siemens has extensive expertise in all areas of automation –including drives, sensors and materials – as well as a virtually complete range of products, Schäfers can try out many solutions in his search for the optimal combination.

Take modern harbor cranes, for example. Although they are taller than in the past, they are lighter. At the same time, they must not occupy a greater surface area than previously, otherwise transport vehicles wouldn’t have enough space to unload their freight. When the crane operator’s cabin moves back and forth along the jib in order to lift containers off the ship and onto the wharf, this movement causes the crane to vibrate. The entire crane oscillates several centimeters back and forth, making it much more difficult for the crane operator to work precisely. So-called passive dampers, such as a 40-ton mass suspended from a pendulum, are currently used to reduce these vibrations. The oscillation frequency of the pendulum is determined by its length. Because energy is withdrawn from the swinging mass by means of a damper, such as a hydraulic cylinder, the disruptive crane vibration is ultimately damped.

However, it is very difficult to integrate such a large passive damper into a crane’s design, a significant amount of material is required, and the damping effect is limited. Schäfers and his team therefore went looking for a more effective method. They developed an active damping method in which a linear motor is intelligently moved back and forth. It, too, is mounted on the jib and equipped with a weight, which is, however, ten times smaller than that of a passive damper. The linear motor runs back and forth on guide rails mounted on the jib. During acceleration and braking, the reaction forces are passed into the jib. The vibration is reduced more quickly and effectively than with the conventional method. A sensor measures the motion of the jib, and the algorithms developed by Schäfers use these values to precisely compute how much force the linear motor must apply to damp the vibration. In collaboration with a crane builder, Siemens wants to introduce active vibration damping using a linear motor to the market in the middle of next year.

Schäfers has also developed a vibration damping solution for another field of business: the production of machine tools. For many products, the surfaces must be as free as possible from irregularities. Because every motor in the production process induces vibrations in the parts connected to it, workpieces in surface finishing are processed at a very low speed to avoid surface irregularities. “That costs a lot of time and thus a lot of money,” says Schäfers. “That’s why we went looking for a method that makes an allowance for the vibrations in the control technology, thus enabling more precise processing within a shorter amount of time.” Today’s automation systems from Siemens already offer the option of automatically measuring the vibration behavior of a machine during the course of commissioning. The result of this measurement is a machine behavior fingerprint. Equipped with this fingerprint, it is possible to derive mathematical models that reproduce the vibration behavior very accurately. These mathematical models are used in algorithms developed specifically for the machine controller. The aim is to prevent vibrations from hardly ever occurring. Schäfers calls this method “model-based precontrol.” It is currently being tested and optimized at several machine tool makers.

Schäfers, who has a PhD in electrical engineering, is head of a motion control systems development department at the Drive Technologies Division’s Industry Sector in Erlangen, Germany. He finds it ironic that he is so involved with mechanical engineering. “I chose electrical engineering over mechanical engineering as my major because I didn’t have any particular affinity for design drawings and spatial conceptualization,” he explains. After studying at the Karlsruhe Institute of Technology from 1988 to 1993, he earned his doctorate at the Institute for Open and Closed-loop Control Systems with a thesis in the field of artificial intelligence. Schäfers has worked at Siemens since 1999. He now really enjoys working together with the mechanical engineers. “We always manage to push the limits of what is physically possible,” he reports. Schäfers has already registered 49 inventions, resulting in 36 granted individual patents and 34 IPR families. Schäfer’s personal life is dedicated primarily to his family, which will soon be welcoming a third child.