Have you ever wondered why robots can’t walk and move their bodies as smoothly as we do? Some robots can run, jump, and dance more efficiently than humans, but their body movements still seem mechanical. The reason lies in the fact that they do not have real bones.
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 such as carbon fiber and metal tubes. According to Robert Katzschmann, a robotics professor at ETH Zurich, these internal structures enable the robot to perform movements, grasp objects, and maintain different postures. However, since the joints and links are made from rigid materials, robots’ bodies are not as flexible, quick, and smooth as human bodies. This is what makes their movements stiff.
3D Printing of Robotic Hands
However, they may not have to stay stiff for long. A team of researchers from the Swiss Federal Institute of Technology (ETH) Zurich and the American startup Inkbit has developed a method for 3D printing the world’s first robotic hand that features an internal structure made of bones, ligaments, and tendons similar to those of humans. What makes the hand particularly unique is that it was printed using a new method called “optical control 3D ink printing.”
3D Ink Printing Technology
Currently, robots are typically 3D printed using rapid-curing polymers. These polymers are durable and cure quickly during printing. However, to avoid any irregularities, “each printed layer requires mechanical leveling [a process of sorting an uneven surface using mechanical force], which limits the smoothness levels and material qualities that can be used,” the researchers note. For this reason, 3D-printed robots are generally not very flexible and are limited in their shapes and materials.
Due to the rapid curing of the printed material, scientists do not have time to make adjustments across different layers, and they must use separate manufacturing steps and assemble them to create different components for a single robot. Once all parts are printed, they assemble these different pieces and test them meticulously, making the process time-consuming and tedious.
Optical Control 3D Ink Printing Method
This is where the VCJ method can make a significant difference. This 3D ink printing process involves using slow-curing soft thiol-based polymers. “These polymers have good elastic properties and return to their original state much faster after bending compared to polyacrylate polymers,” Katzschmann, one of the authors of a new research paper describing the new method, said.
In the VCJ system, there is a 3D laser scanner that visually inspects each layer to detect surface irregularities during printing. “This optical inspection makes the printing process completely non-contact, allowing for a wider range of possible deposited polymers. For example, we printed using thiol polymers because they allowed us to create UV-resistant and moisture-resistant structures,” 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 in the amount of material to be printed in real-time and with high precision,” said Wojciech Mateusz, one of the study authors and a professor of computer science at MIT.
Furthermore, the researchers claim that this controlled closed system allows them to print the entire structure of the robot in one go. “Our robotic hand can be printed in one piece, requiring no assembly. This significantly speeds up the engineering design process – an individual can move directly from an idea to a functional and durable model. You can avoid costly tooling and intermediate assembly costs,” Katzschmann added.
Future
3D Ink Printing with Optical Control
Using VCJ technology, researchers have successfully printed a robotic hand that contains internal structures similar to a human hand. Equipped with touch panels and pressure sensors, the robotic hand has 19 tendon-like structures (in humans, tendons are the fibrous tissues that connect bones to muscles) allowing it to move the wrist and fingers. The robotic hand can sense touch, grasp objects, and stop its fingers upon contact with something. (The researchers used MRI data from a real human hand to model its construction.) The Future of 3D Ink Printing with Optical Control
In addition to the hand, they also printed a robotic heart, a six-legged robot, and a morphing material capable of absorbing vibrations in its surroundings. The researchers note that all these robots function as hybrid soft-hard systems (robots made of both soft and hard materials) that can outperform rigid robots in terms of flexibility and overcome design and scale issues faced by soft robots.
Since soft robots are made from flexible materials such as liquids or elastomers, it is challenging for scientists to maintain their engineering and strength at a larger scale, as these materials may not retain their physical properties and structural integrity. Furthermore, controlling a soft robot sized in centimeters or millimeters is easier; this is why they are often miniaturized. On the other hand, VCJ technology has the potential to produce scalable hybrid soft-hard robots.
According to Katzschmann, “We expect VCJ technology to eventually 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 print longevity make the VCJ system extremely useful for research and commercial applications,” he told Ars Technica.
Source: Nature, 2023. DOI: 10.1038/s41586-023-06684-3
Rubendra Brahamabhatt is an experienced journalist and filmmaker. He covers science and culture news, and over the past five years, he has actively worked with some of the most innovative news agencies, magazines, and media brands operating in different parts of the world.
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