Have you ever pondered why robots struggle to replicate the graceful and fluid movements of humans? While some robots can exhibit impressive feats like running, jumping, or dancing more efficiently than humans, their motions often appear mechanical. The key to this lies in the absence of a skeletal structure.
In contrast to humans and animals, robots lack genuine bones and the pliable connective tissues found in biological organisms. Instead, their bodies consist of artificial links and joints constructed from materials such as carbon fiber and metal tubes. According to Robert Katzschmann, a robotics professor at ETH Zurich, these internal components enable robots to execute movements, manipulate objects, and assume various postures. However, due to the rigid nature of these artificial links and joints, robot bodies lack the flexibility, agility, and softness inherent in human bodies, resulting in their somewhat stiff and mechanical movements.
However, rigidity might not be a long-term requirement. Scientists from the Swiss Federal Institute of Technology (ETH) Zurich, in collaboration with the US-based startup Inkbit, have developed a groundbreaking method to 3D print the world's inaugural robotic hand. This robotic hand boasts an internal structure that mimics human bones, ligaments, and tendons, setting it apart from conventional designs. Notably, the hand was created using an innovative 3D inkjet deposition technique known as vision-controlled jetting (VCJ).
3D printing vs. robots
Presently, 3D-printed robots typically utilize fast-curing polyacrylates, known for their durability and quick solidification during the deposition process. However, a drawback is the necessity for mechanical planarization to smooth each printed layer, restricting the softness levels and material chemistries that can be employed. Consequently, conventional 3D-printed robots lack elasticity and face limitations in terms of shapes and materials.
The swift solidification of the printed material poses challenges for making modifications in different layers, leading to the adoption of separate manufacturing steps and assembly for various components of a single robot. This results in a time-consuming and labor-intensive process, where each part is printed individually, assembled, and rigorously tested.
The proposed Variable Compliance Joint (VCJ) method presents a revolutionary approach. This 3D printing technique utilizes soft, slow-curing thiolene polymers that exhibit excellent elastic properties. According to Katzschmann, one of the authors of the new paper outlining the method, these polymers return to their original state much faster after bending compared to polyacrylates. The VCJ method holds the promise of overcoming the limitations of traditional 3D printing, allowing for greater elasticity, versatility in shapes, and efficient assembly of robot components.
Rethinking 3D printing for robots
In a Variable Compliance Joint (VCJ) system, accompanied by a 3D printer, there exists a 3D laser scanner that meticulously examines each layer for surface irregularities during deposition. This visual inspection transforms the printing process into a fully contactless operation, expanding the scope of printable polymers. For instance, thiol-based polymers were utilized, offering the advantage of creating structures resistant to UV light and humidity, as explained by Katzschmann in conversation with Ars Technica.
Following the scanning process, there is no subsequent mechanical planarization of the deposited layer. Instead, the subsequent layer is printed in a manner that compensates for any irregularities present in the preceding layer. The researchers implement a feedback mechanism to dynamically adjust the amount of material to be printed in real-time with exceptional precision, ensuring the compensation for irregularities, as elucidated by Wojciech Matusik, a study author and professor of computer science at MIT.
Furthermore, the researchers assert that this closed-loop controlled system empowers them to produce the entire structure of a robot in a single printing session. Katzschmann emphasizes the efficiency of this approach, noting that their robotic hand can be printed seamlessly without the need for assembly. This streamlined process accelerates engineering design, enabling a direct transition from concept to a functional, durable prototype. It eliminates the necessity for costly intermediate tooling and assembly, presenting a significant advancement in the manufacturing workflow.
Variable Compliance Joint future
The researchers not only utilized the hand but also employed it to print diverse creations such as a robotic heart, a hexapod robot, and a metamaterial with the ability to absorb vibrations in its environment. These robots operate as hybrid soft-rigid systems, combining both soft and hard materials. This innovative approach allows them to outperform rigid robots in terms of flexibility and overcome the challenges related to design and scale that often hinder soft robots.
Soft robots, constructed from pliable materials such as fluids or elastomers, face difficulties in maintaining their geometry and strength at larger scales. The physical properties and structural integrity of these materials may become compromised. While controlling and powering smaller soft robots at centimeter or millimeter scales is more manageable, scalability poses a significant hurdle. The Variable Compliance Jetting (VCJ) method, however, holds the promise of creating scalable hybrid soft-rigid robots.
The researchers envision VCJ as a potential replacement for all contact-based inkjet printing methods. This cutting-edge technique opens avenues for producing functional components for robotics, medical implants, and various industries. The VCJ system's high resolution, suitable material properties, and extended lifespan render its prints highly valuable for both research and commercial applications, as highlighted by Katzschmann in a statement to Ars Technica.