Self-Sensing Artificial Muscle With Capabilities That Can Revolutionize Soft Robotics

Since the 1960s, machine automation has rapidly increased using robots in various industries. Some experts claim that a robot revolution has occurred at the intersection of technology and labor.

Despite the advancements in robotics, it still seems difficult to achieve a performance comparable to that of humans due to some challenges in motor skills. Robots are expected to perform complex tasks, yet their artificial muscles are limited in providing them with the degrees of freedom they need.

A Groundbreaking Advancement in Bionics

In response to this challenge, a research group from the School of Engineering and Materials Science at Queen Mary University of London (QMUL) developed a new electric artificial muscle demonstrating variable stiffness. Led by Dr. Ketao Zhang, the team took inspiration from nature in creating muscle-like actuators.

The self-sensing artificial muscle was fabricated using a simple and reliable process. It begins with using ultrasonic dispersion technology to mix carbon nanotubes and liquid silicone. The nanotubes are then uniformly coated with a film applicator to make the thin-layered cathode sensing part of the artificial muscle. The actuation layer is placed between the cathode and the anode made from a soft metal mesh cut. Finally, a complete artificial muscle with self-sensing variable-stiffness technology is formed.

According to Dr. Zhang, variable stiffness technology is a significant element in empowering robots made of flexible materials. The artificial muscle they created can resist more than 200% stretch along the length direction, demonstrating exceptional durability with its striped structure. It also exhibits flexibility and stretchability comparable to a natural muscle. Such properties make the artificial muscle an ideal element in complex soft robotic systems and adapting to different geometric shapes.

When different voltages are applied, the muscle-like actuator can quickly adjust its level of stiffness. It can achieve continuous modulation with stiffness adjustments more than 30 times. Moreover, its voltage-driven behavior offers benefits in terms of response speed compared with other artificial muscles. Most of all, the newly developed actuator can effectively monitor its deformation by observing the changes in resistance. This eliminates the need for more sensor arrangements while simplifying the control mechanism with less cost.

The Role of Stiffness Technologies for Soft Robotics

Soft robots have proven more effective than traditional rigid robots, especially in industries requiring safety and dexterity. However, these robots are known for having inherent low stiffness that could affect their ability to generate higher amounts of force and stability when needed.

In the bionics industry, soft robotic manipulators refer to robots made of soft materials and flexible elements. Such manipulators need to be adaptive to the shapes of their environment and have safer interactions with humans. However, challenges are still encountered in using soft robotic manipulators in practical applications. Such challenges include stiffness control along with structure design and function control.

Stiffness variation benefits soft robots, especially for manipulators with a high slenderness ratio. The stiffness variation technologies can be separated into interactions between structural elements and the direct material rigidity tuning approach.