Robotic hand gets a grip using string artificial tendons

While the quest for robotic grippers with a light, yet firm touch has led to innovative approaches, such as the universal jamming gripper, it’s still hard to go past the four fingers and opposable thumb form factor honed by millions of years of evolution. While the technology is available to create a robotic hand that is both powerful and delicate, cramming it inside a compact arm is still difficult. But European researchers have done just that by using a novel string actuator to act as an artificial tendon. Each of the five fingers of the robotic hand are comprised of three segments, each of which can be precisely controlled by an artificial tendon. These tendons consist of a 20 cm (7.87 in) long polymer string that is twisted by a small, high-speed electric motor generating five Newton-millimeters of torque to tighten the tendon. The strings are extremely strong and can lift a five-kilogram (11 lb) load 30 mm (1.2 in) in a split second.

The artificial tendons provide precise control to each of the finger segments and allow the sensorized robotic hand to grip and lift a diverse range of objects and gently place them in a new position. The mechanics also fit in a form that is only slightly larger than a human arm. The hand has been demonstrated lifting a delicate Easter egg and a heavy glass bottle. Its developers say the technology could be employed in home-helper, industrial or search and rescue robots. “The capability of the robotic hand is so near to that of humans that the vision of robots as personal assistants in the household, in the operating room as well as in industrial settings is becoming ever more realistic,” says Chris May, scientist at the Laboratory of Actuation Technology in Germany’s Saarland University. “We presume that the combination of small electric motors with twisted string is interesting for other applications as well.” The robotic hand was developed as part of the European DEXMART (DEXterous and autonomous dual-arm/hand robotic manipulation with sMART sensory-motor skills) project by researchers at Saarland University together with colleagues in Bologna and Naples.