Have you ever wondered why robots cannot walk and move their bodies with the same smoothness that we do? Some robots can run, jump, or dance more efficiently than humans, but their body movements still seem mechanical. The reason lies in the bones they lack.
Lack of Bones in Robots
Unlike humans and animals, robots do not have real bones or the flexible tissues that connect them; instead, they have artificial joints and links made from materials like carbon fibers and metal tubes. According to Robert Katzschmann, a robotics professor at ETH Zurich, these internal structures allow robots to perform movements, grasp objects, and maintain different postures. However, since the joints and links are made of rigid materials, robots’ bodies are not as flexible, agile, and soft as human bodies. This is what makes their body movements stiff.
3D Printing Technology for Robotic Hands
However, they may not have to remain stiff for long. A team of researchers from the Swiss Federal Institute of Technology (ETH) Zurich and the U.S. startup Inkbit has developed a way to 3D print a robotic hand that features an internal structure resembling bones, ligaments, and tendons similar to humans. What makes the hand even more distinctive is that it was printed using a completely new method of 3D ink deposition called “Vision-Controlled Jetting” (VCJ).
3D Printing Technology vs. Robots
Currently, 3D-printed robots are typically made using fast-curing polymers. These polymers quickly bond during deposition. However, to avoid any irregularities, “every printed layer requires mechanical leveling [a process for leveling an uneven surface using mechanical force], which limits the smoothness levels and types of materials that can be used,” the researchers state. This is why standard 3D-printed robots are not very flexible and are limited in their shapes and materials.
Due to the rapid hardening of the printed material, scientists do not have time to make adjustments across different layers, and they must use separate manufacturing steps and assembly to create different components of a single robot. Once they finish printing each part, they assemble these different pieces and test them rigorously, making the process time-consuming and tedious.
VCJ Technology: Rethinking 3D Printing for Robots
The proposed VCJ method could make a significant difference. This process involves using soft, slow-curing thiol polymers. Katzschmann, one of the authors of a new paper describing the new method, stated: “These polymers have good elastic properties and return to their original state much faster after bending than polyacrylate polymers.”
In the VCJ system, in addition to a 3D printer, there is a laser 3D scanner that visually inspects each layer to detect surface irregularities during deposition. “This visual inspection makes the printing process completely non-contact, allowing for a wider range of polymers to be deposited. For example, we printed thiol polymers because they allowed us to create structures that are resistant to UV light and moisture,” Katzschmann told Ars Technica.
After inspection, there is no mechanical leveling of the deposited layer. Instead, the next layer is printed in a way that compensates for all the irregularities in the previous layer. “The feedback mechanism compensates for these irregularities when printing the next layer by calculating any necessary adjustments to the amount of material to be printed in real-time and with high precision,” said Wojciech Matusik, one of the study’s authors and a computer science professor at MIT.
Moreover, the researchers claim that this closed-loop system allows them to print the entire structure of the robot in one go. “Our robotic hand can be printed all at once, with no assembly required. This greatly accelerates the engineering design process — a person can go directly from an idea to a functional and durable prototype. It avoids the expensive costs of tooling and intermediate assembly,” Katzschmann added.
Future
VCJ Technology
Using VCJ technology, researchers have successfully printed a robotic hand with internal structures similar to a human hand. The hand is equipped with touch devices and pressure sensors and contains 19 tendon-like structures (in humans, tendons are the fibrous tissues that connect bones to muscles) that allow it to move the wrist and fingers. The hand can feel touch, grasp objects, and stop the fingers when they make contact with something. (Researchers used MRI data from a real human hand to model its construction.) Future of VCJ Technology
In addition to the hand, they also printed a robotic heart, a six-legged robot, and a material capable of absorbing vibrations in its surroundings. The researchers note that all these robots function as hybrid soft-rigid systems (robots made from soft and rigid materials) that can outperform rigid robots in terms of flexibility and overcome design and scaling issues faced by soft robots.
Since soft robots are made from flexible materials like fluids or rubbers, it is challenging for scientists to maintain their engineering and strength at larger scales, as materials may struggle to retain their physical properties and adapt to the structure. Additionally, controlling and providing power to a soft robot on a centimeter or millimeter scale is much easier; for this reason, they tend to be miniaturized. On the other hand, VCJ technology has the potential to produce scalable hybrid soft-rigid robots.
Katshman told Ars Technica: “We expect VCJ technology to replace all contact-based ink printing methods. With VCJ, you can start producing functional parts for robots, medical implants, and many other industries. The high precision, suitable material properties, and long lifespan of the prints make the VCJ system extremely useful for research and commercial applications.”
Source: Nature, 2023. DOI: 10.1038/s41586-023-06684-3
Rohindra Prahambat is an experienced journalist and filmmaker. He covers science and culture news and has worked in the last five years with some of the most innovative news agencies, magazines, and media brands operating in various parts of the world.
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