Humanoid Robots: Artificial Muscle Moves and "Feels" Simultaneously
Scientists have artificially replicated the function of a biological muscle, combining motor and sensory capabilities within it.
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An engineering team from the College of Engineering at Seoul National University has developed an artificial muscle for humanoid robots that can move robot joints while simultaneously measuring internal forces and length changes in real time. The “intelligent artificial muscle,” as the researchers themselves call it, essentially consists of a structure with two channels made of liquid metal, each integrating a special liquid crystal elastomer (LCE). One is heated by applied current, contracts, and expands again. The other measures the state of the muscle.
Conventionally, in robots powered by artificial muscles or actuators, the drive functions are separated from the sensory systems. Accordingly, sensors must first be elaborately connected to the drive system via control systems. Biological muscles, on the other hand, combine the simultaneous processing of motor signals via the somatic and sensory signals via the sensory nervous system. Inspired by this, the researchers wanted to design an artificial muscle that functions similarly to its biological counterpart to power robots that can act more delicately and perceive their environment sensitively. The scientists have summarized their findings in the study “Bio‐Inspired Artificial Muscle‐Tendon Complex of Liquid Crystal Elastomer for Bidirectional Afferent‐Efferent Signaling,” which was published in Advanced Materials.
Two elastomers with different tasks
The artificial muscle consists of a structure with two channels made of liquid metal, which run parallel to each other to some extent. The channels contain isotropic and nematic LCE, which fulfill different tasks. One material acts as an actuator, which heats up through applied current, contracts, and returns to its original shape upon cooling. This allows it to move joints. The other LCE serves as a sensor. It perceives the contraction state in real time, measures the resulting force and length, for example, so that the artificial muscle can be precisely controlled without the need for additional external sensors.
The researchers arranged their artificial muscle as an antagonistic muscle pair consisting of an effector muscle and a counter-muscle and integrated it into robotic fingers and gripping systems. The scientists demonstrated that the grippers can pick up objects gently while simultaneously perceiving their size and firmness and reacting to them autonomously. The muscle system can be precisely controlled in its contraction and tension through the antagonistic arrangement.
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The researchers now intend to improve the artificial muscle in further research work. This includes structural optimizations and active cooling of the muscle for faster return to its original shape. The muscle could be used in a wide range of applications, such as in humanoid (soft) robots and in medical applications.
(olb)
