In the field of space technology, Centre Suisse d’Electronique et de Microtechnique (CSEM) has been a partner of the European Space Agency (ESA) for many years. One focus of their joint research is eliminating vibration emissions originating from components aboard satellites. In addition to limiting the precision of attitude control for satellites, these micro-vibrations lead to higher energy consumption and (in the case of imaging missions) cause deterioration of image quality.
There are different ways to counter unwanted vibrations either at the source or the payload. As part of its exploration of different approaches, CSEM currently has several projects focusing on numerical models, active-passive mitigation, and algorithm-based notching. In one of these projects, CSEM and its partners are working with an innovative technology based on magnetic levitation.
“With support from Kistler measurement technology, we examined a reaction wheel prototype with a magnetic bearing,” said Leopoldo Rossini, who heads the micro-vibration facility at CSEM. “This technology from Celeroton, a Swiss company, offers many advantages such as no friction, a virtually infinite lifetime, the possibility of actively suppressing unwanted vibrations by control, and the opportunity to achieve higher performance at higher speeds,” Rossini added.
The CSEM engineers use a measuring chain from Kistler to examine the vibrations of the reaction wheel prototype. The custom dynamometer comprises four three-component force sensors sandwich-mounted between two steel plates — a design that achieves maximum mechanical stiffness. This measuring instrument is mounted on a granite block suspended over four pneumatic isolators so that environmental influences are eliminated as far as possible.
Because the micro-vibrations occur in the millinewton range, a highly sensitive measuring chain with very low noise is required. Actuators such as a stepper motor and a cryo-cooler can be placed on the instrumentation table to perform the desired measurements.
For the magnetically levitated reaction wheel prototype, a speed range of –20,000 to 20,000 rpm was covered. This allowed full characterization of the effectiveness of a multiple-harmonic force rejection algorithm capable of suppressing the main vibrations generated during operation. “The lack of physical contact due to magnetic levitation opens up some very interesting opportunities,” according to Guzmán Borque Gallego, an R&D Engineer at CSEM. “It leaves us almost free to position the rotor in such a way that the vibrations are minimized — for instance, by letting the rotor rotate about its main axis of inertia to suppress any vibration related to the rotor unbalance, which reduces these emissions to near zero,” he said.
“The equipment from Kistler is ideal, and it provided us with results of very high quality,” Borque Gallego said. “We’re measuring rather small forces in the millinewton range — but even in micronewtons, we can still see differences. This allows comfortable judgment of all the measurements, leading to high-quality data in the process.”
Data acquisition is handled by a rapid prototyping system at 20 kHz and thanks to the accurate measurements, the effect of the control algorithm can be clearly identified.
Although the researchers initially intended to use the modern LabAmp 5167A with a digital output, they finally opted for the 5080A charge amplifier from Kistler, which allows even more accurate measurements and has higher real-time capability due to analog signal transmission.
“We’re pleased to have new Kistler technology here, because our partners at ESA and in Germany also use it for qualification purposes,” Rossini added. “This equipment is very robust and did not break down even when stressed beyond the given constraints. Now that it has proven its abilities, we will definitely use it for future projects in the field of vibration characterization — where we already operate accelerometers from Kistler.”
“The advantages of magnetic bearing reaction wheels are obvious: they can generate far lower vibrations and rotate faster than conventional wheels — which means improved performance as well as reduced size and weight. And thanks to the absence of friction, there is no wear and the wheel’s lifetime is virtually unlimited,” Borque Gallego said. “This is a fascinating project, and we hope to move ahead to the next steps: practical use, testing, and maybe even validation together with our partners.”
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