Signals from the ceiling lighting connect the factory floor
Driverless transport systems, conveyor belts, engines, robots, sensors, drones, mobile terminals, a wide variety of machines and systems – they all communicate with each other in the Industry 4.0 factory floor, exchange vast amounts of data. They are often mobile components, which makes wireless networking indispensable. But WiFi and Bluetooth only offer limited bandwidth, and the increasing number of users renders the radio spectrum overcrowded. Although 5G is expected to alleviate this problem, the challenges of communication in production environments can be overcome more effectively without a license-free technology.
Researchers at Fraunhofer IOSB-INA in Lemgo (Germany) are therefore taking a different approach: they chose the visible spectrum of light for wireless data transmission. Visible Light Communication (VLC) is what experts call the technology. “The light spectrum is about 4000 times wider than the entire available radio spectrum, ranging from 380 to 800 nanometers wavelength,” says Fraunhofer scientist Daniel Schneider. Together with colleagues and the Technical University OWL, he is working on the project “Visible Light in Production” to make VLC fit for the requirements of industry.
Compared to WiFi, VLC offers a number of advantages. It offers a higher bandwidth; data security is also guaranteed: Radio signals penetrate walls, so communication can be intercepted and manipulated outside the factory floor. This is not possible with light. Another bonus: 1000 or more devices will be able to be networked wirelessly with each other via VLC. “Once we have optimally designed our VLC system on the basis of our measurement campaign, we will be able to operate more than 1000 devices at one location – energy-saving, tap-proof and insensitive to electromagnetic influences,” summarizes the researcher. In addition to the ceiling lighting, the system requires only an Internet access and a transceiver that is connected to the terminal device. The researchers have developed a demonstrator that is currently being tested in the Lemgo SmartFactoryOWL under real-world conditions. Both large and medium-sized companies are expected to benefit from the system as early as mid 2021.
VLC is already used in office, home and laboratory environments. In factory environments, however, the hurdles for communication technology are high or have not yet been sufficiently researched due to the particular disruptive factors. “As an alternative to conventional wireless network access, we will use commercially available, energy-efficient LEDs for VLCs,” explains Schneider. Such a system can be considered reliable if coverage problems caused by walls, metallic objects, machines and other interfering signals can be overcome. Artificial light sources, shadows and reflections can affect data transmission via light. The systematic detection and quantification of these influences is a sub-task of the project. The measurement campaign focused on a total of three influencing variables: Ambient light sources, particles and ambient reflections (multipath propagation).
The tests so far proved that dust particles do not pose a problem for optical signals, since today’s factory buildings are usually well ventilated. Even persons and vehicles moving slowly at 0.2 m/s have little effect on the quality of the signal. Ambient light sources, on the other hand, interfere with data transmission, and this over the entire optical spectrum. The project partners have identified a total of ten models to whose lighting conditions VLC systems react. These include welding processes and fluorescent tubes, but also optical tracking systems. However, they only occur locally and not across locations. VLC systems, and this is one of the results of the tests, must therefore be able to react adaptively to the lighting conditions and minimise such disturbing influences.