Additive Manufacturing Bio-Inspired: 3D-Printed Elephant Robot

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Ecole Polytechnique Fédérale de Lausanne (EPFL)

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Researchers at EPFL have developed a programmable lattice structure for robotics that can be 3D-printed and mimics the vast variety of biological tissues—from flexible body stems to rigid bones—using a single foam material.

The powerful sprint of a cheetah, the smooth glide of a snake, or the skillful grip of a human: all of this is made possible by the seamless interaction of soft and solid tissues. Muscles, tendons, ligaments, and bones work together to provide the energy, precision, and freedom of movement necessary for the complex motions throughout the animal kingdom.

Replicating this diversity of the musculoskeletal system in robotics is a tremendous challenge. So far, 3D printing with multiple materials has enabled the creation of soft-rigid robots. While this approach can mimic the diversity of biological tissues, it means that crucial properties such as stiffness or durability cannot be continuously controlled across the entire robot structure.

Now, a team led by Josie Hughes from the Computational Robot Design and Fabrication Lab (CREATE) at EPFL’s School of Engineering has developed a lattice structure that combines the diversity of biological tissues with robotic control and precision. The lattice, made from a simple foam, consists of individual units (cells) that can be programmed to take on different shapes and positions. These cells can adopt over a million different configurations and even be combined into infinite geometric variations.

Construction of Lightweight, Adaptable Robots

"We used our programmable lattice technology to build a musculoskeletal-inspired elephant robot with a soft trunk that can twist, bend, and rotate, as well as stiffer hip, knee, and foot joints," says postdoctoral researcher Qinghua Guan. "This demonstrates that our method provides a scalable solution for designing unprecedentedly lightweight, adaptable robots." The research findings were recently published in Science Advances.

The team's programmable lattice can be printed with two main cell types with different geometries: the body-centered cubic (BCC) cell and the X-Cube. When each cell type is used for the 3D printing of a robotic "tissue," the resulting lattice exhibits different stiffness, deformation, and load-bearing properties. However, the CREATE Lab's method also allows for printing lattices from hybrid cells whose shape lies somewhere between BCC and X-Cube.

"This approach enables the continuous spatial blending of stiffness profiles and allows for an infinite range of blended unit cells. It is particularly well-suited for mimicking the structure of muscle organs like an elephant trunk," says doctoral student Benhui Dai.

In addition to modulating the shape of each cell, the scientists can also program its position within the lattice. This second programming dimension allows them to rotate and translate each cell along its axis. The cells can even be stacked on top of each other to create entirely new cell combinations, giving the resulting lattice an even broader range of mechanical properties. To give an idea of the virtually infinite range of possible variations: a lattice cube with four stacked cells can yield around 4 million possible configurations, while five cells result in over 75 million configurations.

Gallery

Complex Movement of the Muscular Elephant Trunk Replicated

For their elephant model, this dual programming capability enabled the creation of various tissue types with unique ranges of motion, including a sliding joint (found in the small bones of the foot), a uniaxial bending joint (found in the knee), and a biaxial bending joint (found in the toes). The team was even able to replicate the complex movement of an elephant's muscular trunk by developing separate lattice sections for twisting, bending, and rotational movements, ensuring smooth and continuous transitions between them.

Hughes says that their foam lattice technology offers many exciting possibilities for future robotics research beyond modifying the foam material or incorporating new cell shapes. "Like a honeycomb, the lattice's strength-to-weight ratio can be very high, enabling extremely lightweight and efficient robots. The open foam structure is well-suited for movement in fluids and even offers the potential to integrate other materials, such as sensors, into the structure to imbue the foams with additional intelligence."

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