With 3D inkjet printing systems, engineers can build hybrid structures that have soft and rigid components, such as robotic grippers that are strong enough to grasp heavy objects but soft enough to safely interact with people.
These polymaterial 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. However, the smoothing process could squish or stain slow-curing 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 on each nozzle in real time to ensure no area has too much or too little material.
Since it requires no mechanical parts to smooth the resin, this non-contact system works with materials that harden more slowly than the acrylics traditionally used in 3D printing. Some slower curing chemicals can offer improved performance over acrylics, such as greater elasticity, durability or longevity.
Additionally, the automatic system makes adjustments without interrupting or slowing down the printing process, making this production-grade printer approximately 660 times faster than a comparable 3D inkjet printing system.
The researchers used this printer to create complex, robotic devices that combine soft and rigid materials. For example, they built a fully 3D robotic gripper shaped like a human hand and controlled by a set of reinforced, yet flexible tendons.
“Our key insight here was to develop a machine vision system and a completely active feedback loop. This is almost like giving a printer a set of eyes and a brain, where the eyes observe what is being printed and then the machine’s brain directs it as to what to print next,” says co-corresponding author Wojciech Matusik . , a professor of electrical engineering and computer science at MIT who leads the Computational Design and Fabrication Group at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL).
He is joined on the paper by lead author Thomas Buchner, PhD student at ETH Zurich, co-author Robert Katzschmann PhD ’18, assistant professor of robotics who leads the Soft Robotics Laboratory at ETH Zurich. as well as others at ETH Zurich and Inkbit. The research appears today at Nature.
Contact for free
This paper builds on a low-cost, multi-material 3D printer known as MultiFab that the researchers introduced in 2015. Using thousands of nozzles to deposit tiny droplets of UV-curable resin, MultiFab enabled high-resolution 3D printing with up to 10 materials simultaneously .
With this new project, the researchers sought 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-controlled jetting, which uses four high-frame-rate cameras and two lasers that rapidly and continuously scan the print surface. Cameras capture images as 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 to perform. 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 fine details of the device being manufactured.
“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 really functional and long-lasting,” says Katzschmann.
The level of control the system provides allows it to print very precisely with wax, which is used as a support material to create cavities or complex networks of channels within an object. The wax is printed under the structure as the device is manufactured. Once complete, the object is heated so that the wax melts and drains, 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 to the print surface to keep it flat. This enables the printer to use materials that harden more gradually and will be stained by a scraper.
Superior materials
The researchers used the system to print with thiol-based materials, which mature more slowly than the traditional acrylic materials used in 3D printing. However, thiol-based materials are more flexible and do not break as easily as acrylics. They also tend to be more stable over a wider range of temperatures and don’t degrade as quickly when exposed to sunlight.
“These are very important properties when you want to build robots or systems that need to interact with a real environment,” says Katzschmann.
The researchers used thiol- and wax-based materials to make several complex devices that would otherwise be nearly impossible to make with existing 3D printing systems. First, they produced a functional robotic tendon arm that has 19 independently actuated tendons, soft fingers with sensor pads, and rigid, load-bearing bones.
“We also produced a six-legged robot that can detect and grasp objects, which was possible because of the system’s ability to create airtight interfaces of soft and rigid materials, as well as complex channels within the structure,” says Buchner.
The team also demonstrated the technology through a heart-like pump with built-in ventricles and artificial heart valves, as well as metamaterials that can be programmed to have nonlinear material properties.
“This is just the beginning. There are a surprising number of new material types that you can add to this technology. This allows us to bring whole new families of materials that could not be used in 3D printing before,” says Matusik.
The researchers are now looking at using the system to print with hydrogels, which are used in tissue engineering applications, as well as silicon 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.