MSGID: 1:317/3 64129b75   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Resilient bug-sized robots keep flying even after wing damage    
    New repair techniques enable microscale robots to recover flight   
   performance after suffering severe damage to the artificial muscles that power   
   their wings.    
      
     Date:   
         March 15, 2023   
     Source:   
         Massachusetts Institute of Technology   
     Summary:   
         Researchers have developed resilient artificial muscles that can   
         enable insect-scale aerial robots to effectively recover flight   
         performance after suffering severe damage.   
      
      
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   FULL STORY   
   ==========================================================================   
   Bumblebees are clumsy fliers. It is estimated that a foraging bee   
   bumps into a flower about once per second, which damages its wings   
   over time. Yet despite having many tiny rips or holes in their wings,   
   bumblebees can still fly.   
      
      
   ==========================================================================   
   Aerial robots, on the other hand, are not so resilient. Poke holes in   
   the robot's wing motors or chop off part of its propellor, and odds are   
   pretty good it will be grounded.   
      
   Inspired by the hardiness of bumblebees, MIT researchers have developed   
   repair techniques that enable a bug-sized aerial robot to sustain severe   
   damage to the actuators, or artificial muscles, that power its wings --   
   but to still fly effectively.   
      
   They optimized these artificial muscles so the robot can better isolate   
   defects and overcome minor damage, like tiny holes in the actuator. In   
   addition, they demonstrated a novel laser repair method that can help the   
   robot recover from severe damage, such as a fire that scorches the device.   
      
   Using their techniques, a damaged robot could maintain flight-level   
   performance after one of its artificial muscles was jabbed by 10 needles,   
   and the actuator was still able to operate after a large hole was burnt   
   into it. Their repair methods enabled a robot to keep flying even after   
   the researchers cut off 20 percent of its wing tip.   
      
   This could make swarms of tiny robots better able to perform tasks in   
   tough environments, like conducting a search mission through a collapsing   
   building or dense forest.   
      
   "We spent a lot of time understanding the dynamics of soft,   
   artificial muscles and, through both a new fabrication method and a   
   new understanding, we can show a level of resilience to damage that is   
   comparable to insects. We're very excited about this. But the insects   
   are still superior to us, in the sense that they can lose up to 40   
   percent of their wing and still fly. We still have some catch-up work   
   to do," says Kevin Chen, the D. Reid Weedon, Jr. Assistant Professor in   
   the Department of Electrical Engineering and Computer Science (EECS),   
   the head of the Soft and Micro Robotics Laboratory in the Research   
   Laboratory of Electronics (RLE), and the senior author of the paper on   
   these latest advances.   
      
   Chen wrote the paper with co-lead authors and EECS graduate students Suhan   
   Kim and Yi-Hsuan Hsiao; Younghoon Lee, a postdoc; Weikun "Spencer" Zhu,   
   a graduate student in the Department of Chemical Engineering; Zhijian   
   Ren, an EECS graduate student; and Farnaz Niroui, the EE Landsman   
   Career Development Assistant Professor of EECS at MIT and a member of   
   the RLE. The article will appear in Science Robotics.   
      
   Robot repair techniques The tiny, rectangular robots being developed in   
   Chen's lab are about the same size and shape as a microcassette tape,   
   though one robot weighs barely more than a paper clip. Wings on each   
   corner are powered by dielectric elastomer actuators (DEAs), which are   
   soft artificial muscles that use mechanical forces to rapidly flap the   
   wings. These artificial muscles are made from layers of elastomer that   
   are sandwiched between two razor-thin electrodes and then rolled into a   
   squishy tube. When voltage is applied to the DEA, the electrodes squeeze   
   the elastomer, which flaps the wing.   
      
   But microscopic imperfections can cause sparks that burn the elastomer and   
   cause the device to fail. About 15 years ago, researchers found they could   
   prevent DEA failures from one tiny defect using a physical phenomenon   
   known as self-clearing. In this process, applying high voltage to the   
   DEA disconnects the local electrode around a small defect, isolating   
   that failure from the rest of the electrode so the artificial muscle   
   still works.   
      
   Chen and his collaborators employed this self-clearing process in their   
   robot repair techniques.   
      
   First, they optimized the concentration of carbon nanotubes that comprise   
   the electrodes in the DEA. Carbon nanotubes are super-strong but extremely   
   tiny rolls of carbon. Having fewer carbon nanotubes in the electrode   
   improves self- clearing, since it reaches higher temperatures and burns   
   away more easily. But this also reduces the actuator's power density.   
      
   "At a certain point, you will not be able to get enough energy out of   
   the system, but we need a lot of energy and power to fly the robot. We   
   had to find the optimal point between these two constraints -- optimize   
   the self-clearing property under the constraint that we still want the   
   robot to fly," Chen says.   
      
   However, even an optimized DEA will fail if it suffers from severe damage,   
   like a large hole that lets too much air into the device.   
      
   Chen and his team used a laser to overcome major defects. They carefully   
   cut along the outer contours of a large defect with a laser, which causes   
   minor damage around the perimeter. Then, they can use self-clearing to   
   burn off the slightly damaged electrode, isolating the larger defect.   
      
   "In a way, we are trying to do surgery on muscles. But if we don't use   
   enough power, then we can't do enough damage to isolate the defect. On   
   the other hand, if we use too much power, the laser will cause severe   
   damage to the actuator that won't be clearable," Chen says.   
      
   The team soon realized that, when "operating" on such tiny devices, it is   
   very difficult to observe the electrode to see if they had successfully   
   isolated a defect. Drawing on previous work, they incorporated   
   electroluminescent particles into the actuator. Now, if they see light   
   shining, they know that part of the actuator is operational, but dark   
   patches mean they successfully isolated those areas.   
      
   Flight test success Once they had perfected their techniques, the   
   researchers conducted tests with damaged actuators -- some had been   
   jabbed by many needles while other had holes burned into them. They   
   measured how well the robot performed in flapping wing, take-off, and   
   hovering experiments.   
      
   Even with damaged DEAs, the repair techniques enabled the robot to   
   maintain its flight performance, with altitude, position, and attitude   
   errors that deviated only very slightly from those of an undamaged   
   robot. With laser surgery, a DEA that would have been broken beyond   
   repair was able to recover 87 percent of its performance.   
      
   "I have to hand it to my two students, who did a lot of hard work when   
   they were flying the robot. Flying the robot by itself is very hard,   
   not to mention now that we are intentionally damaging it," Chen says.   
      
   These repair techniques make the tiny robots much more robust, so Chen   
   and his team are now working on teaching them new functions, like landing   
   on flowers or flying in a swarm. They are also developing new control   
   algorithms so the robots can fly better, teaching the robots to control   
   their yaw angle so they can keep a constant heading, and enabling the   
   robots to carry a tiny circuit, with the longer-term goal of carrying   
   its own power source.   
      
   This work is funded, in part, by the National Science Foundation (NSF)   
   and a MathWorks Fellowship.   
      
       * RELATED_TOPICS   
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       * RELATED_TERMS   
             o Nanorobotics o Robot o Humanoid_robot o Industrial_robot   
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             Absolute_zero   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Massachusetts_Institute_of_Technology. Original written by Adam   
   Zewe. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * Resilient_bug-sized_robot   
   ==========================================================================   
   Journal Reference:   
      1. Suhan Kim, Yi-Hsuan Hsiao, Younghoon Lee, Weikun Zhu, Zhijian   
      Ren, Farnaz   
         Niroui, Yufeng Chen. Laser-assisted failure recovery for dielectric   
         elastomer actuators in aerial robots. Science Robotics, 2023; 8   
         (76) DOI: 10.1126/scirobotics.adf4278   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230315143816.htm   
      
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