With 3D inkjet printing systems, engineers can produce hybrid structures composed of supple and fixed components, such as robot grippers that are robust enough to grip bulky objects but supple enough to safely interact with humans.
These multi-material 3D printing systems apply thousands of nozzles to deposit small resin droplets, which are smoothed with a scraper or roller and hardened with UV delicate. However, the smoothing process can crush or smear the resins, which cure slowly, limiting the types of materials that can be used.
Scientists from MIT spinout Inkbit and ETH Zurich have developed a modern 3D inkjet printing system that works with a much wider range of materials. Their printer uses computer technology to automatically scan the 3D printing surface and adjust the amount of resin deposited through each nozzle in real time to ensure there is not too much or too little material in any area.
Because no mechanical parts are needed to velvety the resin, this non-contact system works with materials that cure slower than acrylates, which are traditionally used in 3D printing. Some slower-curing material chemistries may provide improved performance compared to acrylates, such as greater flexibility, durability, or durability.
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.
Scientists used this printer to create intricate robotic devices combining supple and fixed materials. For example, they made a completely 3D-printed robotic gripper in the shape of a human hand, controlled by a set of reinforced yet elastic tendons.
“Our key insight was the development of a machine vision system and a fully lively feedback loop. It’s almost like giving a printer a set of eyes and a brain, where the eyes observe what’s being printed, and then the machine’s brain directs it what to print next,” says corresponding co-author Wojciech Matusik, a professor of electrical engineering and computer science at MIT who directs the Computational Design and Manufacturing Group at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL).
He was joined on the paper by lead author Thomas Buchner, a PhD student at ETH Zurich, co-corresponding author Robert Katzschmann PhD ’18, an assistant professor of robotics who directs the Soft Robotics Laboratory at ETH Zurich; as well as others at ETH Zurich and Inkbit. The study appears today in .
No contact
The article used an inexpensive, multi-material 3D printer known as MultiFab, which scientists introduced to the market in 2015. Using thousands of nozzles to deposit tiny UV-curable resin droplets, MultiFab enabled high-resolution 3D printing with up to 10 materials at a time.
For this new project, scientists were looking for a non-contact process that would expand the range of materials they could use to make more complex devices.
They developed a technique known as vision-guided spraying, which uses four high-frame-per-second cameras and two lasers that quickly and continuously scan the print surface. Cameras capture images as thousands of nozzles deposit tiny droplets of resin.
A computer vision system transforms the image into a high-resolution depth map, and the calculation takes less than a second. It compares the depth map with the CAD (computer-aided design) model of the part being manufactured and adjusts the amount of resin deposited to keep the object in target structure with the final structure.
The automated system can adjust any individual nozzle. Because the printer has 16,000 nozzles, the system can control the smallest details of the device being produced.
“Geometrically it can print almost anything you want, made of many materials. There are almost 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 provided by the system allows for very precise printing using wax, which serves as a support material to create cavities or complex networks of channels inside the object. Wax is printed underneath the structure when the device is manufactured. Once completed, the object is heated to allow the wax to melt and float away, leaving open channels throughout the object.
Because it can automatically and quickly adjust the amount of material deposited by each nozzle in real time, the system does not have to drag a mechanical part across the print surface to keep it level. This allows the printer to use materials that cure slower and could be smeared by a scraper.
Excellent materials
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 flexible and do not break as easily as acrylates. They are also more stable over a wider temperature range and do not degrade as quickly when exposed to sunlight.
“These are very important properties if you want to produce robots or systems that need to interact with a real environment,” Katzschmann says.
The researchers used thiol-based materials and wax to fabricate several complex devices that would otherwise be nearly impossible to make using existing 3D printing systems. First, they developed a functional tendon-powered robotic hand that has 19 independently actuated tendons, soft fingers with sensor pads, and stiff, load-bearing bones.
“We also produced a six-legged walking robot that can sense and grab objects, which was made possible by the system’s ability to create hermetic connections between soft and rigid materials, as well as complex channels inside the structure,” says Buchner.
The team also demonstrated technology in the form of a heart-like pump with integrated chambers and artificial heart valves, as well as metamaterials that can be programmed to have nonlinear material properties.
“This is just the beginning. There are an incredible number of new types of materials that can be added to this technology. Thanks to this, we can introduce completely new families of materials that could not be used in 3D printing before,” says Matusik.
Scientists are currently considering using the system to print hydrogels used in tissue engineering, as well as silicon materials, epoxies and special types of tough polymers.
They also want to explore modern application areas, such as printing customizable medical devices, semiconductor polishing pads, and even more intricate robots.
This research was funded in part by Credit Suisse, the Swiss National Science Foundation, the U.S. Defense Advanced Research Projects Agency and the U.S. National Science Foundation.