Super Strong Robotic Arm Withstands High Shocks

The joints of each finger are driven by two tendons, each attached to one motor. When the motors turn in the same direction, the joint moves; when they turn in opposite directions, the joint stiffens. By changing the tension in the tendons, the hand is able to absorb high impact shocks, such as being hit with a baseball bat.

The DLR hand has the shape and size of a human hand, with five articulated fingers powered by a web of 38 tendons, each connected to an individual motor on the forearm. The fingers can exert a force of up to 30 newtons at the fingertips, which makes the hand one of the strongest ever built. Another key element in the DLR design is a spring mechanism connected to each tendon. These springs give the tendons, which are made from a super strong synthetic fiber called Dyneema, more elasticity, allowing the fingers to absorb and release energy. This capability is key for achieving robustness and for mimicking the kinematic, dynamic, and force properties of the human hand.

During normal operation, the finger joints can turn at about 500 degrees per second. By tensioning the springs, and then releasing their energy to produce extra torque, the joint speed can reach 2,000 degrees per second. This means that this robot hand can do something few others, if any, can: snap its fingers. The new hand can also catch a ball thrown from several meters away, since the actuation and spring mechanisms are capable of absorbing the kinetic energy without structural damages.

"Existing robot hands built with rigid parts, despite their Terminator-tough looks, are relatively fragile. Even small collisions, with forces of a few tens of newtons, can dislodge joints and tear fingers apart,” said mechanical engineer Markus Grebenstein of the DLR Institute of Robotics and Mechatronics, and the hand's lead designer. "If every time a robot bumps its hand, the hand gets damaged, we'll have a big problem deploying service robots in the real world.”

The researchers are now building a complete two-arm torso called the DLR Hand Arm System. Their plan is to study innovative grasping and manipulation strategies, including bimanual manipulations.

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German Aerospace Center