Radar-based collision protection moves closer to the shop floor

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Technische Universität München Umwelthygiene

Colour signal provides visualisation of collision danger

But even the relative speed already offers plenty of information about the target object, particularly if the object is observed not only by one sensor, but by a number of sensors around the tool. The chronological pattern of frequency change can be represented in so-called spectrograms. These represent in colour code the results of the Fourier analysis of a short excerpt from the signal, and the analysis window is permanently updated. One thus receives, thanks to the calculating power of today’s field-programmable gate array (FPGA) building blocks, a precise millisecond-by-millisecond picture of the spectral composition of the received signal and thus of all objects in the monitoring field of the radar. The image above shows such a spectrogram, recorded during experiments with a test machine at the PTW Institute in Darmstadt, Germany. Here the motor spindle initially moves towards the obstacle and then draws away from it. These two motion phases are recognisable by the high amplitude (red) at a certain frequency. The moment of motion reversal can also be pinned down very precisely. As individual sensors in the radar ring are not lone warriors but collect and compare centrally information and observations, the observed objects can be followed through the area, even though none of the sensors ever carries out a distance measurement. It is enough to know that target objects cannot move completely arbitrarily, but only according to the laws of physics. The whole is thus more than the sum of its parts, and the sensors together recognise when the tool is too close to an obstacle.

The research project will continue to make the signal processing ever more reliable and accurate with experiments on real machines. The chances are therefore rising that such “intelligent” miniature radar systems will in the near future help prevent expensive damage to processing centres, which can occur from lack of attention or a careless error. By eliminating the costs of lost production and follow-on expenditures, even avoiding one collision could allow such a system to pay for itself.

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