3-D Printing Helps Robots Conquer Stairs 

So far the mission of designing human-like robots has been more or less successful, with many experts claiming that artificial robots will replace one third of the work force by 2030. And the field is becoming even more advanced as robotics venture into ‘flexible’ territory. One of the main actions performed by animals from mantises to kangaroos is jumping. However, incorporating a jumping mechanism into autonomous robots requires a lot more technicality than just simple design. One of the main challenges for robots is still travelling efficiently over rugged surfaces and obstacles – climbing stairs? A big no, no! And if your robot can conquer the stairs it rules!

The benefits of a jumping robot are many fold: it could provide access to areas that are inaccessible to traditional mobile wheeled or legged robots. In the case of some search-and-rescue or exploration missions, in collapsed buildings for example, such a robot might even be preferable to unmanned aerial vehicles (UAVs) or quadcopter “drones”.

A new approach to robots explored by researchers at the University of California San Diego and Harvard University uses a robot with a partially soft body. The robot was fabricated using 3D printing technology to produce a design which seamlessly incorporates rigid and soft parts. The main segment comprises two hemispheres nestled inside one inside the other to create a flexible compartment. Oxygen and butane are injected into the compartment and ignited, causing it to expand and launching the robot into the air. Pneumatic legs are used to tilt the robot body in the intended jump direction.

There has been progressing research in the robotics field to take on the challenges of designing a mobile platform capable of jumping. Different techniques have been implemented for jumping robots such as using double jointed hydraulic legs or a carbon dioxide-powered piston to push the robot off the ground. Other methods include using “shape memory alloy” – metal that alters its shape when heated with electrical current to create a jumping force – and even controlled explosions. But currently there is no universally accepted standard solution to this complex task.

Most robots have largely rigid frames incorporating sensors, actuators and controllers, but a specific branch of robotic design aims to make robots that are soft, flexible and compliant with their environment – just like biological organisms. Soft frames and structures help to produce complex movements that could not be achieved by rigid frames.

Unlike many other mechanisms, this allows the robot to jump continuously without a pause between each movement as it recharges. For example, a spring-and-clutch mechanism would require the robot to wait for the spring to recompress and then release. The downside is that this mechanism would be difficult to mass-manufacture because of its reliance on 3D printing.

The invention of the “multi-extrusion” printers with multiple print heads means that two or more materials can be used to create one object using whatever complex design the engineer can come up with, including animal-like structures. For example, Ninjaflex, with its high flexibility could be used to create a skin or muscle-like outer material combined with Nylon near the core to protect vital inner components, just like a rib cage.

In the new robot, the top hemisphere is printed as a single component but with nine different layers of stiffness, from rubber-like flexibility on the outside to full rigidity on the inside. This gives it the necessary strength and resilience to survive the impact when it lands. By 3D printing and trialling multiple versions of the robot with different material combinations, the engineers realized a fully rigid model would jump higher but would be more likely to break and so went with the more flexible outer shell.


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