Robot joint makes human-robot interaction safer

August 25, 2020 //By Christoph Hammerschmidt
Robot joint makes human-robot interaction safer
When humans interact physically with robots, one aspect always requires special attention: Additional sensors and algorithms ensure that the robot with its gripper arm does not injure humans. Now, researchers at Chemnitz University of Technology (Germany) have invented a special joint that reduces the danger: The joint is pliable; it can absorb collision energy.

Since 2016, doctoral student Hongxi Zhu and Professor Ulrike Thomas, head of the robotics professorship at Chemnitz University of Technology, have been working on this new robotic joint. Previous joints have been equipped with sensors, mostly force sensors, to measure the contact forces in the event of a collision and to be able to avoid them if necessary. Other techniques use external optical sensors to monitor the distance between robot and human. The new joint can absorb energy thanks to a spring. This allows collision energy to flow away and the robot can move faster in the vicinity of a human without endangering the human.

The challenge is to be able to adjust the spring hardness in a non-linear way so that the robot can adjust the spring hardness independently and adaptively for work that requires high force, for example, to hammer a nail into a wall. "With the joint, we have succeeded in covering a very large area and at the same time offering a compact design for the robot joint," says Thomas. Another advantage of the compliant joints is that the stored energy can also be used to accelerate the movement, so that a humanoid robot can throw balls or jump.

Thomas had the initial idea for such a design when he looked at a harmonic-drive gear - a shaft gear with a high transmission ratio - which also uses an elliptical shape so that a non-linear behavior can be realized. Thomas' colleague Hongxi Zhu then quickly developed the initial ideas into working prototypes.

In the last five years, a new robotics team has been established at Chemnitz University of Technology under the direction of Professor Ulrike Thomas, which is conducting intensive research in the field of humanoid robotics, in particular perception and cognition, human-robot interaction and walking robotics. The professorship develops new mechatronic systems, applies modern methods from AI research and thus improves the capabilities of robots,

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