We often take our hands for granted, easily accomplishing tasks that remain challenging for even advanced robotics, such as pouring coffee without spilling or folding laundry without damaging delicate materials.
The main reason we can perform these tasks effortlessly is the sophisticated structure of our hands. A human hand is a marvel of biological engineering that includes a rigid skeleton that provides shape and allows fingers to bear weight. Soft tissues like muscles and ligaments bestow them with dexterity. These biomaterials have naturally evolved to work together in a complex assembly.
Mimicking these structures synthetically, however, is a daunting task.
Scientists have attempted to recreate intricate structures, such as hands and hearts, using additive manufacturing technology, or more commonly known as 3D printing. But these technologies face difficulties when incorporating multiple materials in a single printing process. For instance, creating a robotic hand with 3D printing would need multiple printers – one for the hard skeletal structure, another for the soft tissues – and then assembly of the various components. This multi-step process escalates both the timeframe and the complexity of production.
It has long been an objective for scientists to merge various materials in a single 3D printing process. A breakthrough from the soft robotics lab at ETH Zurich provides a solution.
The researchers successfully enhanced a 3D inkjet printer—similar to everyday office printers— with machine vision. This addition enables it to quickly adjust to assorted materials. This method named vision-controlled jetting, is a constant source of structure details during the printing process and helps the printer precisely lay down the next layer, irrespective of the material used.
In the experiment carried out, the team succeeded in 3D printing a synthetic hand in one go. This hand, designed with a skeleton, ligaments, and tendons, is capable of holding different objects when it detects pressure on its fingertips.
Additionally, they constructed a 3D print of a structure that resembles a human heart. Replete with chambers and one-way valves, it has the capability to pump fluid at a rate approximating 40 percent of the capacity of an adult human heart.
The study is “very impressive,” stated Dr. Yong Lin Kong from the University of Utah, who wasn’t involved in the research but authored an accompanying commentary, as he reported to Nature. According to him, 3D inkjet printing is already a solid technology but this research suggests that machine vision can extend its abilities to more intricate structures and diverse materials.
Reproducing a structure using traditional methods is painstaking and liable to mistakes. Engineers typically use a mold to achieve the needed shape, like the bone structure of a hand, then merge the initial shape with other materials.
This method is a painfully exact process. Analogous to setting up a cabinet door, any inaccuracies can result in an imbalanced outcome. And when it comes to intricate designs like a robotic hand, the effect could be quite chaotic.
Conventional techniques also make it challenging to incorporate materials with diverse features. Furthermore, they tend not to have the precision needed for intricate designs like a synthetic hand. These constraints hinder what a robotic hand, and other useful structures, can accomplish.
3D inkjet printing emerged as a breakthrough technology. Essentially, this kind of printers extrude a liquid resin substance through hundreds of thousands of autonomously operated nozzles, almost like a standard office printer crafting a high-resolution photograph. Every printed layer is then solidified from liquid form by the application of UV light. This process repeats layer after layer, allowing formation of a 3D object at a microscopic level.
However, despite its efficiency and precision, the technology encounters some challenges. For instance, it struggles in binding diverse materials together. To 3D print a functional robot, engineers have two options. They can either print components using multiple printers and assemble them afterwards, or print an initial structure, surround the part with a cast, and subsequently introduce additional materials with the required properties.
One significant limitation is the inconsistency in the thickness of individual layers. Variations in the velocity of the ‘ink’, interference from nozzles, and shrinkage during the solidifying phase can all contribute to slight differences. However, accumulated over numerous layers, these disparities can lead to defects in the resulting objects and printing failures.
Engineers strive to overcome this issue by incorporating a blade or roller. This works somewhat like levelling freshly poured concrete during road construction, wherein every layer is flattened before the onset of the next one. However, this solution also introduces its own set of complications. Since the rollers are not uniformly compatible with all materials and certain ones can clog the scraper, the selection of usable materials gets restricted.
Could we possibly eliminate this step?
The team proposes the use of machine vision. Instead of stripping off excess material, monitoring each layer during printing allows the system to identify and adjust for minor errors instantly.
The machine vision module incorporates four cameras and a pair of lasers to scrutinize the entire print platform at a microscopic level.
The printer is capable of self-modification, clarified the team. By determining the areas where material is excessive or deficient, the printer can alter the quantity of ink used in the subsequent layer, effectively repairing previous “potholes”. The result is an efficient 3D printing system where surplus material doesn’t have to be removed.
This is not the first instance where machine vision has been leveraged in 3D printers. However, this new system can scan at a pace 660 times faster than older models and is capable of analyzing the physical shape of the object being printed in less than a second, according to Kong. Such capabilities enable the 3D printer to tap into a broader range of materials, inclusive of those that support intricate structures during printingand are removed afterward.
In simpler terms, this system can speedily print a novel generation of bio-inspired robots which was not possible with previous technologies.
As a way of testing, the team used the printer to create a synthetic hand comprising two distinct materials: a solid, load-supporting substance acting as the skeleton and a soft, flexible substance used for tendons and ligaments. They structured air pressure-controlled channels throughout the hand while concurrently incorporating a touch-sensitive membrane which essentially functioned as the fingertips.
After connecting the hand to an array of external electrical components, it was integrated into a small, mobile robot. Due to its pressure-responsive fingertips, the robot could pick up a variety of objects such as a pen or an empty plastic water bottle.
The system also produced a structure resembling a human heart, complete with various chambers. This artificial heart functioned much in the same way as a real one, pumping fluid when pressurized.
The entire structure was printed in a single operation.
The outcome is quite remarkable and feels like significant progress for a technology that’s already quite advanced, according to Kong. He mentioned that despite being commercially accessible for several years, just the addition of machine vision gives the technology a fresh lease on life.
Interestingly, Kong noted that these diverse examples were produced using only a handful of materials. The team’s goal is to enhance the range of printable materials and to simultaneously incorporate electronic sensors for detection and activity during the printing process. Additionally, the system could make use of different fabrication techniques – for instance, by spraying a layer of biologically active molecules onto the surface of the printed hands.
Robert Katzschmann, a professor at ETH Zurich and an author on the new paper, is optimistic about the system’s broader use. “You could think of medical implants…[or] use this for prototyping things in tissue engineering,” he said. “The technology itself will only grow.”
Credit: ETH Zurich/Thomas Buchner
“Why did the 3D printer go to therapy? Because it had too many layers of unresolved issues!”
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