Countless industrial tools and robots need to grip things, and because we humans learn to grip since infancy, we can easily underestimate how complex gripping actually is. If our grip is too rigid, we can snap or shatter our payload; if our grip is too soft, our payload may slip from our fingers or exceed lift capacity. Human hands have advantages: rigid bones covered in pliable skin and muscles. So, what’s a poor mechanism to do when it simply wants to lift?
The solution is biomimicry. Various engineers seeking superior grip performance have employed biomimicry in their designs, which have been inspired by seed pods, elephant trunks, lobster tails (in fact, using actual lobster tails), and, of course, octopus limbs. In theirCyborg and Bionic Systems paper, researchers from Peking University in Beijing, National University of Singapore, Zhejiang University, and the Beijing Institute of Technology describe how their Octopus-Inspired Upward Transport Robot (OUT-Robot) outperforms previous gripping systems.
The OUT-Robot’s advantage is its unprecedented ability to shift swiftly to its pliable state (in 1.3 seconds) and into its rigid state (0.8 seconds). Deploying six arms featuring this rapidly tunable stiffness, the OUT-Robot mimics the multimodal grasping strategy of cephalopods, allowing it to sort through and grip objects of varying shapes, pliability, and weight.
Made from a shape memory polymer (SMP) of polylactic acid (the same PLA plastic used in many 3D printers), the arms soften during application of voltage, and become inflexible once electrical heating ceases. The quick tuning from flexible to rigid is possible because of the OUT-Robot’s thermal interface of three layers which synergizes the robot’s shape and materials with the watery environment for fast cooling.
According to Professor Xie Guangming at Peking University, the leader of the international research team, typical SMP grippers require tens of seconds for air-cooling, a massive underperformance compared with the operation of the OUT-Robot. “The inner silicone layer diffuses heat uniformly, the outer layer acts as a transient barrier during heating, and the surrounding water becomes an active heat sink during cooling,” says Xie. “Our stiffness transition time is substantially faster than [that of] any previously reported actuator.”
Like real octopuses, the OUT-Robot can maneuver through its liquid environment by shooting jets of water, and also by using its tentacles to crawl at up to 70 cm (27.6 inches) in 55 seconds. When those tentacles are pliable – and each one can function independently using a different grasping mode – they can use suction or gripping along irregular surfaces, using positive pressure to drive the arms before rigidity locks the hold without any added energy.
As Xie says, “This zero-energy shape-locking is a game-changer for long-duration underwater missions.” His team’s experiments back his bold claim: an SMP tentacle is approximately 25 times more rigid than a non-SMP arm, allowing the OUT-Robot’s six arms to exceed 4 Newtons (more than 400 g, or 0.88 lb). In a pool 2 m (6.6 ft) deep, the OUT-Robot alternated pliability to sort among debris at the bottom (including rocks, bottles, scallops, and sea cucumbers) and remove a light fishing net less weighing less than a gram, collect fragile biological samples, and lift a glass bottle. “Our robot,” says Xie, “can handle objects from extremely light debris to heavy solid waste over 500 grams, all in one continuous operation.”
Once the OUT-Robot has firmly grasped its cargo, it employs active buoyancy control by inflating its soft-shelled “head” like a balloon, allowing zero-fuel vertical lift that massively reduces energy consumption compared with previous systems that use power continuously. “The grasping phase consumes about 75 joules for 1.3 seconds,” says Xie, “while the subsequent ascent uses almost zero energy.”
According to Xie, the OUT-Robot – perhaps operating in swarms – offers numerous applications for oceanic protection, restoration, and recovery, as well as resource exploitation. “We are providing a robust, efficient, and quiet solution to protect our oceans,” says Xie, “one grasp at a time.”
Source: Beijing Institute of Technology Press Co. Ltd. via EurekAlert
