With 3D inkjet printing systems, engineers can make hybrid structures with soft and rigid components, such as robotic grippers strong enough to grip heavy objects but soft enough to interact safely with humans.
These multi-material 3D printing systems use thousands of nozzles to deposit tiny droplets of resin, which are smoothed with a scraper or roller and cured with UV light. But the smoothing process could crush or smudge the slowly hardening resins, limiting the types of materials that can be used.
Researchers from MIT, MIT spinout Inkbit and ETH Zurich have developed a new 3D inkjet printing system that works with a much wider range of materials. Their printer uses computer vision to automatically scan the 3D print surface and adjust the amount of resin deposited by each nozzle in real time to ensure that no area contains too much or too little material.
Since it does not require mechanical parts to smooth the resin, this contactless system works with materials that harden more slowly than the acrylates traditionally used in 3D printing. Some slower-curing material chemistries may offer improved performance over acrylates, such as greater elasticity, durability, or longevity.
Additionally, the automatic system makes adjustments without stopping or slowing down the printing process, making this production printer approximately 660 times faster than a comparable 3D inkjet printing system.
Researchers have used this printer to create complex robotic devices combining soft and rigid materials. For example, they made a fully 3D printed robotic gripper shaped like a human hand and controlled by a set of reinforced but flexible tendons.
“Our key idea here was to develop a machine vision system and a completely active feedback loop. It’s almost like giving a printer eyes and a brain, where the eyes observe what is being printed, and then the machine’s brain tells it what should be printed next,” explains the author. co-correspondent Wojciech Matusik. , a professor of electrical engineering and computer science at MIT who leads the computer design and manufacturing group within the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL).
He is joined in the article by lead author Thomas Buchner, a doctoral student at ETH Zurich, co-corresponding author Robert Katzschmann PhD ’18, an assistant professor of robotics who directs the Soft Robotics Lab at ETH Zurich ; as well as others at ETH Zurich and Inkbit. The research appears today in Nature.
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This paper relies on a low-cost multi-material 3D printer known as MultiFab which researchers introduced in 2015. Using thousands of nozzles to deposit tiny droplets of UV-cured resin, MultiFab enabled high-resolution 3D printing with up to 10 materials at a time.
With this new project, the researchers were looking for a contactless process that would expand the range of materials they could use to make more complex devices.
They developed a technique, known as vision-controlled jetting, that uses four high-frame-rate cameras and two lasers that scan the print surface quickly and continuously. Cameras capture images while thousands of nozzles deposit tiny droplets of resin.
The computer vision system converts the image into a high-resolution depth map, a calculation that takes less than a second. It compares the depth map to the CAD (computer-aided design) model of the part being manufactured and adjusts the amount of resin deposited to keep the object on target with the final structure.
The automated system can make adjustments to any individual nozzle. Since the printer has 16,000 nozzles, the system can control the smallest details of the device being manufactured.
“Geometrically, it can print almost anything you want, from multiple materials. There are virtually no limits to what you can send to the printer, and what you get is truly functional and durable,” says Katzschmann.
The level of control offered by the system allows it to print very precisely with wax, which is used as a support material to create cavities or complex networks of channels inside an object. The wax is printed under the structure as the device is manufactured. Once completed, the object is heated so that the wax melts and flows, leaving open channels throughout the object.
Because it can automatically and quickly adjust the amount of material deposited by each of the nozzles in real time, the system does not need to drag a mechanical part across the print surface to keep it level. This allows the printer to use materials that harden more gradually and would be stained by a scraper.
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The researchers used the system to print with thiol-based materials, which cure more slowly than traditional acrylic materials used in 3D printing. However, thiol-based materials are more elastic and do not break as easily as acrylates. They also tend to be more stable over a wider temperature range and don’t degrade as quickly when exposed to sunlight.
“These are very important properties when you want to make robots or systems that need to interact with a real environment,” says Katzschmann.
The researchers used thiol-based materials and wax to fabricate several complex devices that would otherwise be nearly impossible to make with existing 3D printing systems. On the one hand, they produced a functional, tendon-driven robotic hand with 19 independently actuable tendons, flexible fingers with sensor pads, and rigid, load-bearing bones.
“We also produced a six-legged walking robot capable of detecting and grasping objects, which was possible thanks to the system’s ability to create airtight interfaces of soft and rigid materials, as well as complex channels through it. ‘inside the structure,’ Buchner explains.
The team also demonstrated the technology through a heart-shaped pump with integrated ventricles and artificial heart valves, as well as metamaterials that can be programmed to have non-linear material properties.
” It’s only a beginning. There are an incredible number of new types of materials you can add to this technology. This allows us to introduce completely new families of materials that could not previously be used in 3D printing,” explains Matusik.
The researchers now plan to use the system to print with hydrogels, used in tissue engineering applications, as well as silicon-based materials, epoxies and special types of durable polymers.
They also want to explore new application areas, such as printing customizable medical devices, semiconductor polishing pads and even more complex robots.
This research was funded in part by Credit Suisse, the Swiss National Science Foundation, the US Defense Advanced Research Projects Agency and the US National Science Foundation.
