3D Printing for Humanoid Robots

Humanoid robots have recently become a very hot topic. In the past few months, we’ve seen significant advances in motion control algorithms for humanoid robots. The latest advancements in AI have been harnessed to create large-scale learning models for robotics, like NVIDIA’s ISaac lab. Given the rapid pace at which AI is advancing, it will likely lead to the development of full-scale, general humanoid robot foundation models in the very near future. This is truly exciting! We will soon be able to replace most routine, difficult, and dangerous labor with machines.

The full-scale control model was certainly the biggest bottleneck in the development of humanoid robots. Now, as it seems we are nearing a solution, we can explore other topics related to the various systems of these complex machines.

Similar to the human body, humanoid robots include different functional systems, such as Integumentary System (sensors), Skeletal System (structure or frame), Muscular System (motors), Nervous System (electronics), and other systems, like energy storage and distribution. Where can 3D printing come at hand? Which systems of a humanoid robot can 3D printing contribute to?

Most notably, the structure. 3D printing allows for the creation of complex geometries that are often impossible to achieve with traditional manufacturing methods. With advancements in 3D printing, it’s possible to integrate electronic components directly into the structure of humanoid robots. This could include circuits, sensors, and actuators, which are essential for the robot’s functionality. The integration process can lead to more compact and efficient designs, as well as potentially lower production costs. The additive nature of 3D printing means that it can be more sustainable than subtractive manufacturing processes. It reduces waste by using only the necessary amount of material to create a part. Moreover, the ability to print on-demand aligns with lean manufacturing principles, reducing inventory and storage needs. The design flexibility offered by 3D printing enables rapid design iterations, on-demand production, and mass customization of products.

While 3D printing offers many advantages, there are also challenges to overcome, such as improving the strength-to-weight ratio of printed materials and enhancing the precision of printed components. Future research may focus on developing new materials and printing techniques that can produce parts that are more lightweight and strong compared to traditional manufacturing techniques.

The structure, or skeleton, accounts for a significant portion of the overall machine weight, and the ratio of body weight to battery weight determines the energy capacity of the system. The lighter the body weight, the less energy is needed to provide motion. Additionally, a lighter skeleton can be moved with less powerful and lighter motors, which will further contribute to overall energy efficiency. Therefore, the weight of the skeleton is extremely important in ensuring the machine’s efficiency.

Conversely, the skeletal system determines the robot’s durability and its ability to withstand external loads, such as carrying weight, jumping, running, applying force to other objects (Newton’s third law still applies), or resisting external impacts. This sets the structural requirements. Thus, we need a system that is both lightweight and stronger than any other application.

When discussing humanoid robots, it’s logical to seek inspiration from human anatomical structures. Our skeletal system is primarily an endoskeleton, lacking a hard protective outer layer. Instead, we have the integumentary system, including skin, which is soft, regenerative, and renewable. The skeleton, composed of various bone types and tissues, provides a strong, stiff, and lightweight support structure, while the skin offers protection. Certain skeletal parts, like the ribs and chest, safeguard the body’s vulnerable internal organs. Essentially, the human torso acts as a load-bearing, protective rib cage with non-load-bearing skin, and the limbs are akin to simple rods connected by movable joints. The human head features an exoskeletal structure, where the brain is encased within a skeletal form from the inside, offering enhanced protection.

Examining the materials used in human systems, we find that bone is a complex structure serving multiple functions, and as a living tissue, it can grow and regenerate. The structure of the bone is made up of osteons?—?tubular structures composed of collagen lamellae and fibers aligned along the bone’s direction. Consequently, bones display significant anisotropic behavior, providing exceptional tensile, compressive, and bending strength while maintaining a very low weight. Conventional fiber-reinforced composites represent a similar hierarchical structure, based on different types of molecules and orientation schemes.

A similar approach could be employed for humanoid robot structures. Firstly, we require a lightweight, directional material, such as fiber-reinforced composite. Secondly, we need a structure that represents a load-bearing endoskeleton, like a rib cage and hinged beams for limbs. This could be achieved with anisoprinting, coupled with the in-situ embedding of electrical wires, artificial muscles to replace motors and other integrated systems like sensors.

The exterior of the robot could be modeled after human skin, serving as a non-load-bearing, easy-to-maintain layer that doesn’t compromise the support and mobility functions of the robot if damaged. For this purpose, a heat-shrink film could be utilized, which is straightforward to apply and mend.

This approach could yield the most efficient design for a humanoid robot’s structural and protective systems, potentially reducing the weight of the structure several times compared to traditional metal exoskeleton designs.

In summary, the field of materials science and structural engineering for humanoid robots is rich with potential for innovation. By drawing inspiration from the human body and advancing material technologies, we can create robots that are more efficient, versatile, and capable of seamlessly working alongside humans in a variety of settings.