Singapore University of Technology and Design (SUTD), Southern University of Science and Technology (SUSTech) and Zhejiang University (ZJU) have collaborated on the development of process flow guides for 3D printing miniature soft robotic actuators.
Demonstrating the applicability of their additive manufactured actuators, the researchers have produced a soft debris remover with an integrated miniature gripper. The team believes their work offers potential applications in jet-engine maintenance and minimally invasive surgery.
Miniature soft robots
Made from compliant materials, soft robots are capable of safely adapting to complex environments and moving like living organisms. As the field is under rapid growth, soft robotics now come in a variety of designs, spanning multiple length scales from meters to sub-micrometers. Recently, scientists have 3D printed soft robots for drug delivery, tissue engineering and space exploration.
Miniature soft robots are of particular interest to the team. This class of soft robots can be designed as a combination of miniature actuators simply driven by pneumatic pressure. These millimeter scale robots exhibit excellent safety and deformability. Such properties are highly desirable for applications such as navigation in confined areas and manipulation of microscale objects.
For greater flexibility in manufacturing these robots, scientists would like to adopt additive manufacturing over traditional methods such as molding and soft lithography. However, successful examples of 3D printing miniature soft pneumatic robots are rare. The design complexity of the millimeter-sized robots require great delicacy in fabrication. When scaling down soft pneumatic robots to microscale, finer features are lost by more than one order of magnitude during the process. Furthermore, it is also challenging to 3D print components essential for pneumatic actuation, such as microscale voids and channels, without causing clogging.
Digital Light Processing of microscale soft robots actuators
Digital Light Processing (DLP) is a 3D printing process similar to stereolithography which uses a projector instead of laser as light source. “We leveraged the high efficiency and resolution of DLP 3D printing to fabricate miniature soft robotic actuators,” said Qi (Kevin) Ge, lead researcher of the research project from SUSTech.
During DLP, photo-absorbers are usually added into polymer solutions to enhance the printing resolutions. At the same time, overly increasing the dose leads to rapid degradation in the material’s elasticity, which is crucial for soft robots to sustain large deformations.
“To ensure reliable printing fidelity and mechanical performance in the printed products, we introduced a new paradigm for systematic and efficient tailoring of the material formulation and key processing parameters,” Ge explained.
The process flow guide starts with selecting a photo-absorber with good absorbance at the wavelength of the projected UV light and determining the appropriate material formulation. Based on mechanical performance tests, these steps ensure a reasonable trade-off between print resolution and elasticity. Next, the researchers characterized the curing depth and XY fidelity to identify the suitable combination of exposure time and sliced layer thickness.
The tailored results are then applied to a self-built multi-material 3D printing system. Using their DLP 3D printer, the researchers produced an assortment of soft pneumatic robotic actuators with overall size of 2-15mm and feature size of 150-350 μm. The team also managed to introduce various structures and morphing modes into the actuators.
Getting to grips with 3D printed miniature actuators
To exemplify the potential applications of 3D printed miniature actuators, a soft debris remover was devised. The remover is composed of a 3D printed miniature soft pneumatic gripper and a continuum manipulator. Made by this miniature soft robot 3D printing technique, the device can navigate through a confined space and collect small objects in hard-to-reach positions.
The proposed approach paves the way for 3D printing miniature soft robots with complex geometries and sophisticated multi material designs. “The same methodology should be compatible with commercial stereolithography (SLA) or DLP 3D printers as no hardware modification is required,” Ge added.
Integration of 3D printed miniature soft pneumatic actuators into a robotic system can lead to applications such as jet-engine maintenance and minimally invasive surgery.
“Miniature Pneumatic Actuators for Soft Robots by High‐Resolution Multimaterial 3D Printing“ is published in Advanced Materials Technologies. It is co-authored by Yuan‐Fang Zhang, Colin Ju‐Xiang Ng, Zhe Chen, Wang Zhang, Sahil Panjwani, Kavin Kowsari, Hui Ying Yang Qi Ge.
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