Safer human-robot collaboration with 360° radar
Nowadays, it is impossible to imagine industry without robots. Safety laser scanners mostly safeguard dangerous areas and protect people from collisions. But optical sensors have their limitations — for instance, when plastic surfaces, dust or smoke obstruct their line of sight. Fraunhofer researchers have developed a high-frequency radar scanner that cuts through these obstacles. It can monitor its environment in a 360° radius, making it suitable for safety applications wherever people and robots work together.
Increasing connectivity of production systems in ‘smart’ Industry 4.0 operations is driving the interaction between people and machines. The trend is moving towards industrial robots that operate without protective barriers. A prerequisite for this level of co-working is that people must not be endangered at any time — but that is precisely the Achilles’ heel of collaboration between people and robots. Currently, laser scanners are used to monitor the danger zone around machinery and to stop the machine as soon as a person enters the zone. However, optical sensors do not always achieve reliable results under changing light conditions. They also do not work if smoke, dust or fog limits visibility.
Researchers at the Fraunhofer Institute for Applied Solid State Physics IAF have developed a compact, modular, 360° radar scanner that is claimed to be superior to optical sensors in many respects. This makes it a good choice for safety applications for human-machine collaboration. The radar works with millimetre waves that are reflected by the objects to be observed, such as people. Transmitted and received signals are processed and evaluated using numerical algorithms. Based on the calculations, it is possible to determine the distance, position and speed of the objects. If several radar units are used, an object’s location in the room can also be determined as can the direction in which it is moving.
The human eye cannot see through wood, paper or plastic. But the radar developed by Fraunhofer IAF now makes it possible to see the invisible: the radar works with millimetre waves at a frequency of 94 GHz and a bandwidth of 15 GHz. In contrast to optical sensors, millimetre waves penetrate all dielectric materials — and therefore optically non-transparent materials such as clothing, plastics, surfaces and paper, as well as dust, rain, snow and fog.
“Our radar is not focused on one point. Instead, it sends out millimetre waves in a club shape. Unlike a laser scanner, the signals are reflected even when visibility is obstructed by an object,” explained IAF scientist Christian Zech. The laser scanner can reliably measure the distance and the position of a target — a person, for instance — only if the target is working in an unobstructed line of sight. However, IAF’s 360° radar can penetrate optically opaque material, which means it can identify the employee even if there are boxes, cardboard walls or other obstacles in the way.
This makes it possible to use the W band — that is, the frequency range between 75 and 110 GHz — to detect small objects several kilometres away, even in conditions with poor visibility. The higher the frequency and bandwidth, the better the spatial resolution. The system’s distinctive feature is that it detects and visualises its surroundings in a 360° view, making the scanner suitable for a broad range of applications — from area monitoring and access surveillance to industrial sensor technology, logistics and flight safety through to non-destructive materials testing.
High-frequency board technology for cost-effective systems
Previous millimetre wave radar systems — based on waveguides — are bulky and expensive. IAF’s scanner has a diameter of only 20 cm and is 70 cm high. The high-frequency module, featuring indium gallium arsenide semiconductor technology, is no larger than a pack of cigarettes and is located in the base of the scanner.
“These days, millimetre-wave applications are dominated by waveguides that are extremely expensive to produce. Thanks to a cost-effective mounting and interconnection technology, as well as specially developed circuit boards, we can replace the waveguides with our high-frequency module that has been integrated onto a board measuring just 78 x 42 x 28 mm,” said Zech.
The high-frequency module, which is the key component of the radar scanner, was developed by IAF researchers in close collaboration with the Fraunhofer Institutes for Reliability and Microintegration IZM and for Manufacturing Engineering and Automation IPA.
In addition to the signal processor, the complete system comprises a transmitting and receiving antenna with a dielectric — that is, electric non-conducting — lens. A self-turning mirror affixed at a 45° angle deflects the millimeter waves, guides them and evaluates the entire room. Thanks to the use of a dielectric antenna, the angle of aperture can be freely selected. That means nearby objects as small as a centimetre in size can be detected as easily as large surfaces that are far away. The system‘s range of operation is dependent on the application and can be up to several hundred metres. The scanner includes an ethernet interface and is therefore suitable for Industry 4.0 applications.
Precise distance measurement
In order to evaluate the measurement accuracy and reliability of the 360° radar, the researchers carried out hundreds of measurements in the lab. Maximum deviation from the mean was less than 1 µm; standard deviation was 0.3 µm.
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