This quadruped relies on a series of valves that open and close in a specific sequence to walk. | Credit: UCSD

Engineers at the University of California San Diego have created a four-legged soft robot that doesn’t need any electronics to work. The quadruped only needs a constant source of pressurized air for all its functions, including its controls and locomotion systems.

The team, led by Michael T. Tolley, a professor of mechanical engineering at the Jacobs School of Engineering at UC San Diego, details its findings in the journal Science Robotics.

“This work represents a fundamental yet significant step towards fully-autonomous, electronics-free walking robots,” said Dylan Drotman, a Ph.D. student in Tolley’s research group and the paper’s first author.

Applications include low-cost robotics for entertainment, such as toys, and robots that can operate in environments where electronics cannot function, such as MRI machines or mine shafts. Soft robots are of particular interest because they easily adapt to their environment and operate safely near humans.

Most soft robots are powered by pressurized air and are controlled by electronic circuits. But this approach requires complex components like circuit boards, valves and pumps – often outside the robot’s body. These components, which constitute the quadruped’s brains and nervous system, are typically bulky and expensive. By contrast, the UC San Diego robot is controlled by a light-weight, low-cost system of pneumatic circuits, made up of tubes and soft valves, onboard the robot itself. The robot can walk on command or in response to signals it senses from the environment.

“With our approach, you could make a very complex robotic brain,” said Tolley, the study’s senior author. “Our focus here was to make the simplest air-powered nervous system needed to control walking.”

The quadruped’s computational power roughly mimics mammalian reflexes that are driven by a neural response from the spine rather than the brain. The team was inspired by neural circuits found in animals, called central pattern generators, made of very simple elements that can generate rhythmic patterns to control motions like walking and running.

To mimic the generators’ functions, engineers built a system of valves that act as oscillators, controlling the order in which pressurized air enters air-powered muscles in the robot’s four limbs. Researchers built an innovative component that coordinates the robot’s gait by delaying the injection of air into the robot’s legs. The robot’s gait was inspired by sideneck turtles.

The quadruped is also equipped with simple mechanical sensors – little soft bubbles filled with fluid placed at the end of booms protruding from the robot’s body. When the bubbles are depressed, the fluid flips a valve in the robot that causes it to reverse direction.

The paper builds on previous work by other research groups that developed oscillators and sensors based on pneumatic valves, and adds the components necessary to achieve high-level functions like walking.

How it works

The quadruped is equipped with three valves acting as inverters that cause a high pressure state to spread around the air-powered circuit, with a delay at each inverter.

Each of the robot’s four legs has three degrees of freedom powered by three muscles. The legs are angled downward at 45 degrees and composed of three parallel, connected pneumatic cylindrical chambers with bellows. When a chamber is pressurized, the limb bends in the opposite direction. As a result, the three chambers of each limb provide multi-axis bending required for walking. Researchers paired chambers from each leg diagonally across from one another, simplifying the control problem.

A soft valve switches the direction of rotation of the limbs between counterclockwise and clockwise. That valve acts as what’s known as a latching double pole, double throw switch—a switch with two inputs and four outputs, so each input has two corresponding outputs it’s connected to. That mechanism is a little like taking two nerves and swapping their connections in the brain.

The legs are angled down 45 degrees and composed of three parallel, connected pneumatic cylindrical chambers with bellows. | Credit: UCSD

Next steps

In the future, researchers want to improve the robot’s gait so it can walk on natural terrains and uneven surfaces. This would allow the robot to navigate over a variety of obstacles. This would require a more sophisticated network of sensors and as a result a more complex pneumatic system.

The team will also look at how the technology could be used to create robots, which are in part controlled by pneumatic circuits for some functions, such as walking, while traditional electronic circuits handle higher functions.

Editor’s Note: This article was republished from the UC San Diego.

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Roboticists at the University of California San Diego have developed flexible feet that can help robots walk up to 40 percent faster on uneven terrain such as pebbles and wood chips. The work has applications for search-and-rescue missions as well as space exploration.

“Robots need to be able to walk fast and efficiently on natural, uneven terrain so they can go everywhere humans can go, but maybe shouldn’t,” said Emily Lathrop, the paper’s first author and a Ph.D. student at the Jacobs School of Engineering at UC San Diego.

“Usually, robots are only able to control motion at specific joints,” said Michael T. Tolley, a professor in the Department of Mechanical and Aerospace Engineering at UC San Diego and senior author of the paper. “In this work, we showed that a robot that can control the stiffness, and hence the shape, of its feet outperforms traditional designs and is able to adapt to a wide variety of terrains.”

The feet are flexible spheres made from a latex membrane filled with coffee grounds. Structures inspired by nature? such as plant roots? and by man-made solutions? such as piles driven into the ground to stabilize slopes? are embedded in the coffee grounds.

The feet allow robots to walk faster and grip better because of a mechanism called granular jamming that allows granular media, in this case the coffee grounds, to go back and forth between behaving like a solid and behaving like a liquid. When the feet hit the ground, they firm up, conforming to the ground underneath and providing solid footing. They then unjam and loosen up when transitioning between steps. The support structures help the flexible feet remain stiff while jammed.

It’s the first time that such feet have been tested on uneven terrain, like gravel and wood chips.

An off-the-shelf six-legged robot equipped with the feet designed by UC San Diego engineers can walk up to 40 percent faster than when not equipped with the feet. | Credit: UC San Diego

The feet were installed on a commercially available hexapod robot. Researchers designed and built an on-board system that can generate negative pressure to control the jamming of the feet, as well as positive pressure to unjam the feet between each step. As a result, the feet can be actively jammed, with a vacuum pump removing air from between the coffee grounds and stiffening the foot. But the feet also can be passively jammed, when the weight of the robot pushes the air out from between the coffee grounds inside, causing them to stiffen.

Researchers tested the robot walking on flat ground, wood chips and pebbles, with and without the feet. They found that passive jamming feet perform best on flat ground but active jamming feet do better on loose rocks. The feet also helped the robot’s legs grip the ground better, increasing its speed. The improvements were particularly significant when the robot walked up sloped, uneven terrain.

“The natural world is filled with challenging grounds for walking robots — slippery, rocky, and squishy substrates all make walking complicated,” said Nick Gravish, a professor in the UC San Diego Department of Mechanical and Aerospace Engineering and study coauthor. “Feet that can adapt to these different types of ground can help robots improve mobility.”

In a companion paper co-authored by Tolley and Gravish with Ph.D. student Shivan Chopra as first author, researchers quantified exactly how much improvement each foot generated. For example, the foot reduced by 62 percent the depth of penetration in the sand on impact; and reduced by 98 percent the force required to pull the foot out when compared to a fully rigid foot.

Next steps include incorporating soft sensors on the bottom of the feet to allow an electronic control board to identify what kind of ground the robot is about to step on and whether the feet need to be jammed actively or passively.

Researchers will also keep working to improve design and control algorithms to make the feet more efficient.

Editor’s Note: This article was republished from UC San Diego.

The soft robotic foot conforms to the surfaces on which it steps, allowing the robot to walk faster. | Credit: UC San Diego

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Current methods of guiding flexible surgical robots within the human body are often expensive and require exposure to radiation. Engineers at the University of California San Diego said they have developed an easy-to-use system to track the location of flexible medical robots that performs as well as current state-of-the-art methods but is much less costly and does not involve radiation.

The system was developed by Tania Morimoto, a professor of mechanical engineering at the Jacobs School of Engineering at UC San Diego, and mechanical engineering Ph.D. student Connor Watson. Their findings were published in the April 2020 issue of IEEE Robotics and Automation Letters.

Flexible medical robots can minimize impact

“Continuum medical robots work really well in highly constrained environments inside the body,” Morimoto said. “They’re inherently safer and more compliant than rigid tools. But it becomes a lot harder to track their location and their shape inside the body. And so if we are able track them more easily, that would be a great benefit both to patients and surgeons.”

The researchers embedded a magnet in the tip of a flexible medical robot that can be used in delicate places inside the body, such as arterial passages in the brain.

“We worked with a growing robot, which is a robot made of a very thin nylon that we invert, almost like a sock, and pressurize with a fluid, which causes the robot to grow,” Watson said. Because the surgical robot is soft and moves by growing, it has very little impact on its surroundings, making it ideal for use in medical settings.

The 2020 Healthcare Robotics Engineering Forum is coming in September.

Magnetic localization works like GPS

The researchers then used existing magnet localization methods, which work very much like GPS, to develop a computer model that predicts the robot’s location. GPS satellites ping smartphones and based on how long it takes for the signal to arrive, the GPS receiver in the smartphone can determine where the cell phone is.

Similarly, researchers know how strong the magnetic field should be around the magnet embedded in the flexible medical robot. They rely on four sensors that are carefully spaced around the area where the robot operates to measure the magnetic field strength. Based on how strong the field is, they are able to determine where the tip of the robot is.

The whole system, including the robot, magnets, and magnet localization setup, costs only around $100.

Roboticists have used magnet localization to develop a model for locating the tip of a flexible medical robot. Credit: David Baillot, UC San Diego

Neural network improves localization

Morimoto and Watson then trained a neural network to learn the difference between what the sensors were reading and what the model said the sensors should be reading. As a result, they improved localization accuracy to track the tip of the flexible medical robot.

“Ideally, we are hoping that our localization tools can help improve these kinds of growing robot technologies,” said Morimoto. “We want to push this research forward so that we can test our system in a clinical setting and eventually translate it into clinical use.”

About the author

Ioana Patringenaru is associate media relations director at the Jacobs School of Engineering at UC San Diego.

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