At the IEEE International Conference on Robotics and Automation (ICRA) last year, Harvard's Sam Felton introduced us to his printed, self-folding inchworm robot. With some external infrastructure and the addition of a motor, the inchworm could autonomously transform from a flat sheet to a crawling robot by folding itself into a 3D structure with flexible joints.
Today, Felton and colleagues from Harvard and MIT are publishing a new paper in Science featuring a much more complex self-folding robot that can go from flat to folded and walking in four minutes without any human intervention at all.
Let's be clear about what's autonomous here, and what's not: the folding process by which the robot changes from flat to less flat is completely autonomous, and this includes the ability to begin walking on its own, as shown in the video above.
But the layered structure of the robot takes a lot of work to prepare (printing, bonding, laser cutting, and so on), and the motors, batteries, and some electronic components all need to be installed by hand—a series of steps that take almost 2 hours:
That's a very long and complex process [see illustration below], but what's most relevant is to think about how much of it can be made autonomous. The researchers say that "the assembly time could be substantially reduced and completely automated with the use of pick-and-place electrical component assembly machines and automated adhesive dispensers." And if that's the case, we're looking at potentially very cheap, easily mass-produceable robots.
The secret sauce that allows this robot to structure itself from a flat piece of cardboard is a very carefully computed folding design, combined with a structure comprised of resistive circuits embedded in a flexible PCB between layers of paper and heat-activated shape-memory polymer (the "PSPS" in the above image). This sandwich is laser cut where the joints will be, and when the embedded resistors heat up, the shape-memory polymer around them contracts.
Depending on where and how the cuts are made, this contraction can result in permanent (when cooled) controlled bending of up to 120 degrees in either direction. Flexible joints (like hinges) come from cutting out both the paper and the PSPS, leaving just the flexible circuit board to connect two structural elements. And by combining flat elements, rigid bends, and flexible joints, you can create complex linkages that can translate (say) the rotary motion from a motor into the cyclical motion of a set of legs. (DASH is an excellent example of this.)
The motor and alignment mechanism of the robot: (A) The linkages are fabricated in plane with the composite, and the crank arms are oriented upward. (B) The legs and linkages fold into position, and the alignment tab folds into place. (C) The motor rotates 180°, pushing the crank arm pin into the alignment notch. (D) The locking tab folds over the pin, coupling the pin to the linkage. In (C) and (D) the obscuring linkage is displayed in outline only for clarity. self-folding process with shape-memory composites: (A) The self-folding shape-memory composite consists of five layers: two outer layers of PSPS, two layers of paper, and a layer of polyimide (PCB) bearing a copper circuit in the middle. Cutting a gap into the upper paper layer allows controlled folding of the polyimide, and slits in the bottom layers of paper and PSPS prevent antagonistic forces. (B) A structural hinge, designed to fold once when activated and then become static. (C) When activated, the PSPS on the concave side pulls the two faces together, bending the polyimide along the hinge. (D and E) A dynamic hinge, designed to bend freely and repeatably. (F) A self-folding crawler built with the shape-memory composite. This robot includes both (G) self-folding and (H) dynamic hinges.
The really hard part here is the design of the origami structure (which is done by a computer program) and the manufacturing of the composite sheet. Once the composite is completed, the final assembly step just involves attaching the batteries, motors, and microcontroller to the robot using a 3D printed motor mount and some screws. Still, arriving at the right design required over 40 iterations of the robot's structure.
The microcontroller took care of sending current through the series of embedded resistive traces at the right time, to ensure that the folding process took place in the correct order. A particularly clever bit is how the motors attach to the structure of the robot, using tabs that sequentially fold to align the motor and then lock it into place [right].
Overall, creating a structural fold using this technique had a success rate of about 97 percent. The researchers tried to make three robots, and were successful with just one, but that was due to one single hinge not folding with the necessary precision on each of the failures. The robot itself can walk at 5.4 centimeters per second (0.43 body lengths per second) and turn at about 320 degrees per second.
برچسبها: Self Folding Origami Robot Goes From Flat to Walki