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Artificial Robot Motion

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Soft artificial muscles designed for motion control in robots

Recently, ETH Zurich researchers developed artificial muscles for mobility in robots. In comparison to earlier technologies, their system has the following advantages: It can be applied in situations where robots must interact with their surroundings with more sensitivity or where they must be pliable rather than stiff.

Many roboticists want to create robots that are softer and more flexible in addition to being made of motors and metal or other hard materials.

Soft robots may engage with their surroundings very differently; for instance, they might carefully grab an object or cushion impacts like human limbs do. In terms of energy usage, this would also be advantageous because soft systems have a better capacity to store energy than robot motion, which often takes a lot of energy to hold a position. So what could be more clear than trying to replicate human muscle using it as a model?

Thus, biology underpins how artificial muscles operate. Artificial muscles contract in response to an electrical input, much like their natural counterparts. Nevertheless, the artificial muscles are made of a pouch filled with a liquid (often oil), the shell of which is partially covered in electrodes, rather than cells and fibers.

Upon receiving an electrical signal, these electrodes pull together and force the liquid into the remaining portion of the pouch, causing it to flex and have the ability to support a weight. An individual pouch may be thought of as a little bundle of muscle fibers; many of these can be joined together to create a whole propulsion element, which is also known as an actuator or just an artificial muscle.

Too much voltage

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Although the concept of creating artificial muscles is not new, there has been a significant barrier to its implementation up until now: electrostatic actuators could only operate at very high voltages, often between 6,000 and 10,000 volts. This need has a number of drawbacks, such as the muscles’ need to be attached to bulky, heavy voltage amplifiers, their inability to function in the water, and their partial safety for human use.

Professor of robotics at ETH Zurich Robert Katzschmann, along with Stephan-Daniel Gravert, Elia Varini, and other researchers, has recently created a novel solution. Their version of an artificial muscle, which has several benefits, has been described in Science Advances.

The pouch’s shell was created by Gravert, a scientific assistant at Katzschmann’s laboratory. HALVE actuators is the term the researchers have given to the new artificial muscles.The acronym HALVE represents “hydraulically amplified low-voltage electrostatic.”

The electrodes in other actuators are external to the shell. In ours, the shell is made up of many layers. We paired a layer of electrodes with a high-permittivity ferroelectric material—that is, a material with a reasonably high electrical energy storage capacity. Afterwards, we covered it with a polymer shell, which improves the mechanical qualities and increases the stability of the pouch,” says Gravert.

Because the ferroelectric material has a significantly greater permittivity and can withstand big stresses at low voltages, the researchers were able to lower the needed voltage. Together, Gravert and Varini not only designed the HALVE actuators’ casing, but they also constructed the actuators in the lab for use in two robots.

Fish and grippers demonstrate the muscle’s capabilities.

A gripper with two fingers that measures 11 centimeters in height is one of these robotic examples. Three series-connected pouches of the HALVE actuator move each finger. Robot power comes from a tiny battery-powered power supply that delivers 900 volts.

The battery and power source weigh only fifteen grams combined. The gripper’s total weight, including the control and power electronics, is 45 grams. When an object is raised into the air via a cable, the gripper can hold onto a smooth plastic object securely enough to sustain its own weight.

Additionally, it signifies that we’ve made significant progress toward our objective of developing integrated muscle-operated devices,” adds a pleased Katzschmann.

The second item is a swimmer that resembles a fish and is around 30 cm long. It has no trouble moving through the water. It is made up of a flexible “body” that holds the HALVE actuators and a “head” that houses the electronics. The swimming motion is created by the rhythmic, alternating movements of these actuators. Even in regular tap water, the self-governing fish can accelerate from a standstill to three millimeters per second in just 14 seconds.

Both watertight and self-closing

This second example illustrates still another novel aspect of the HALVE actuators, which makes it noteworthy: The artificial muscles are waterproof and may be utilized in conductive liquids since the electrodes are no longer exposed outside the shell.

An overall benefit of these actuators is exemplified by the fish: on the one hand, the environment is shielded from the electrodes, and on the other, the electrodes are shielded from the environment. Thus, for example, you may touch or operate these electrostatic actuators in water,” says Katzschmann. Another benefit of the pouches’ multilayer nature is that the new actuators are far more durable than previous artificial muscles.

The pouches should ideally be able to move swiftly and with a lot of mobility. But even the tiniest production mistake, like a dust particle between the electrodes, might cause an electrical breakdown, which is similar to a little lightning strike.

In previous iterations, this would cause the electrode to burn and leave a hole in the shell. As a result, the liquid was able to escape, rendering the actuator inoperable,” claims Gravert.

Because of the protective plastic outer layer, a single hole in the HALVE actuators effectively seals itself, solving this problem. Consequently, even in the event of an electrical malfunction, the pouch often retains all of its functions.

Although the two researchers are obviously happy to have made a significant advancement in the creation of artificial muscles, they are also pragmatic.

Katzschmann states, “We need to prepare this technology for larger-scale manufacturing, but we are unable to do it at the ETH lab at this time. I can tell that we’re already receiving interest from businesses want to collaborate with us, without giving too much away.”

Artificial muscles, for instance, may be utilized in the future in wearables, prosthetics, and innovative robots—that is, in technologies that are worn on the human body.

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