Predictive safety for pedestrians
The future of the automotive industry is being shaped by developments such as predictive pedestrian protection. Yet before the first models can actually be equipped with intelligent systems to prevent collisions, the necessary sensors must first be tested in realistic conditions. To do this, a pedestrian dummy installed in a test rig is pulled out of danger at the last second with a force of over 14 g. These test rigs are developed and built by 4a engineering GmbH and rely on control and drive technology from B&R.
Hoisting the dummy up and out of danger protects it and the vehicle from harm and is one of many technological challenges in this sophisticated experimental design. The system itself was designed and built by 4a engineering, a technology-oriented R&D company based in the Austrian town of Traboch that specializes in developing and optimizing new products and procedures through a profound understanding of physical and mechanical processes. Hence, the 4a motto: "In physics we trust". The company's employees, the majority of whom have academic backgrounds, contribute expertise from diverse areas ranging from method development and simulation to end product development. One example of the innovation made possible by this diverse team is a metal-plastic laminate that was developed here, manufactured by an affiliated company and is now being used in approximately 15% of all mobile phone speakers worldwide. Nearly 50% of revenue generated by 4a engineering comes from the automotive industry, with the remaining share coming from the fields of aerospace, electronics, consumer goods, sporting equipment, medical technology and mechanical engineering. Their expertise in plastics engineering and materials science is particularly sought after in these industries.
It was this expertise in the field of polymer materials that helped 4a engineering win the contract to design the new test rig for active pedestrian protection. The detection systems installed in vehicles are often based on radar, and one requirement was that the test rig be virtually invisible to these systems. To achieve this, 95% of the rig is constructed from special composite materials that minimize radar echo. In addition, the color of the test rig was also designed to blend into the surroundings. The result is that the vehicle's sensors register only the crash test dummy and nothing else.
The test rig resembles a gantry crane with a dual-rail track and trolley system that moves the dummy at speeds of up to 25 km/h. "In the initial task description from 2007, implementation time was limited to just 11 weeks," reports engineering director Martin Fritz. "This meant that we had to make a few compromises, which were later replaced with more permanent and technologically advanced solutions during a subsequent upgrade." This included the mechanism used to hoist the dummy out of danger in just 100 milliseconds. The resulting acceleration exceeds a force of 14 g, which a human would not survive. In initial testing, this was achieved by harnessing the dummy to a pre-loaded elastomer band that was then released when triggered.
Minimal power consumption
This design was not ideal due to the acceleration curve and the inability to effectively control the process. In the meantime, it has since been replaced by a pole-mounted dummy connected to a motorized drive. This pole is fastened to a crossbar, which is moved up and down by two synchronized servo motors. "Synchronizing this process was also a considerable challenge for the drive technology," recalls Fritz. "Synchronization is absolutely essential to ensuring that the dummy will be lifted 2 meters in just 160 to 180 ms." The horizontal trolley is also driven by a B&R servo motor, with the vertical mechanics controlled using drives from B&R's ACOPOSmulti series.
Sequential control is handled by a CPU and I/O modules from B&R's X20 controller series, which – like the ACOPOSmulti servo drives – are extremely compact and energy-efficient. These compact devices made it possible to build a low-profile control cabinet and further reduce radar echo. The active attenuation required to hide the control cabinet from radar becomes considerably more difficult with larger cabinets. In addition, the exceptionally dynamic movements can cause sudden motor currents of up to 170 A. The power supply on remote testing grounds can be relatively weak and, in some cases, a mobile generator is even required to power the system. The technicians from 4a engineering worked together with B&R to design the system so that reliable operation could be guaranteed even if the power supply is weak. "The robust ACOPOSmulti units proved themselves once again by running reliably even with voltage dips down to less than 300 V," praises Fritz.
The system sends live data to the vehicle via WLAN about the positions of both the vehicle and the dummy. The driver is provided with a terminal that displays the pre-defined scenarios and that can be used to begin the sequence. A system of symbols was also designed to ensure that the driver can quickly identify the respective scenario. "Once we developed the concept, Visual Components in Automation Studio made it easy to implement a graphical representation of each scenario."
There is still a long way to go before vehicles demonstrate sufficient intelligence to anticipate pedestrian behavior and reliably avoid collisions. Nevertheless, predictive safety systems that pre-activate the brakes when danger is detected (to dry the discs and improve braking performance) will soon be much more common. Whether we're behind the wheel or on the crosswalk, with testing made possible by advanced polymer technology from 4a engineering and state-of-the-art automation technology from B&R, we're well on the road to a safer future.
Bernecker + Rainer Industrie-Elektronik Ges.m.b.H.
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