Ouch! When humans and robots collide, literally

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German researchers are exploring a new dimension of human-robot interaction: the "interaction" that occurs when a 200-kilogram industrial robot accidentally strikes a 90-kilogram person in the head, torso, or pelvis.

Susanne Oberer and Rolf Dieter Schraft at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart are conducting human-robot "crash tests" to understand what kind of injuries result in such cases and how safety could be improved.

They reported their latest findings in a paper titled "Robot-Dummy Crash Tests for Robot Safety Assessment," presented at the 2007 IEEE International Conference on Robotics and Automation in Rome early this year. "Dummy" in their study is not the poor individual who gets smashed by a heavy robotic manipulator. Rather, dummy is a crash test dummy, or actually a crash test dummy computer model called FAT ES-2, developed by DYNAmore GmbH and other companies in collaboration with the German Association for Automotive Research.

As for the robot, the researchers used a computer model of the the Comau SMART NS 16 industrial manipulator and welding robot. To make the two models "interact," they used finite-element software (LS-DYNA by the Livermore Software Technology Corp.), originally designed to study car crash tests.

In the first scenario, a seated worker is struck by the robotic arm on the left side of the head, the robot moving with a rotational velocity of up to 50 degrees/second around its vertical axis. The collision results in a head acceleration of about 65 g's. In the second scenario, the robot hits the dummy on the left side of its ribcage. For a rotational speed of 50 degrees/second, the ribs deflects 1 centimeter inward. Finally, in the third scenario, the dummy is hit at its pelvis, with forces measured at its pubic symphysis, which experiences forces of more than 0.15 kilonewtons.

Now, what does that all mean? Would the robot have killed the person? The researchers don't have a definite answer, mainly because there's no reliable way to figure that out. Existing injury criteria (the methods to translates head acceleration, rib deflection, and pelvis force into medical assessments like minor bruise, severe concussion, fracture, death) were developed for car accidents, which usually involve impact intervals of around 15 to 30 milliseconds. Human-robot collisions of the type studied by the German researchers happen in intervals of 5 to 10 seconds.

"The assessment scheme for robotics has to be specifically designed for the characteristic stiffness and impact intervals arising in robot-human crash," they write.

The injury criteria for car crashes was developed by biomechanics researchers by performing a variety of experiments using cadavers, animals like pig carcasses, and human volunteers. Abruptly decelerate a cadaver on a crash-simulator sled and see if the aorta rips open -- that kind of thing. This knowledge of the human body and its dynamic behavior now needs to be extended to the types of collisions we can expect from people and robots. It may take a while, so for now watch out for that swinging 200-kilogram robotic arm.

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