Speed of polymer artificial muscles increased

دست مصنوعی

Tehran (ISNA) - Researchers at the University of Texas at Dallas controlled artificial muscles that are made of silver coated polymer.

The term “artificial muscles” refers to components that contract, expand, or rotate when they connect to a source of energy. Artificial muscles are already being explored for use many. Shape memory alloys, such as a mixture of nickel and titanium, are common artificial muscles. But these alloys have wide hysteresis. The more powerful artificial muscles have been made from yarns spun from hollow carbon fibers called single-walled nanotubes. However, there is no cheap way to make these nanotubes on an industrial scale.

Researchers at the University of Texas at Dallas report that they have controlled affordable artificial muscles that are made of silver coated polymer. Twisted and coiled polymer (TCP) muscles also known as supercoiled polymer (SCP) are coiled polymers that can be actuated by electric power. TCP muscles are usually made of silver coated Nylon thread. By twisting the thread, it creates coils, like a helical spring. TCP muscles are fabricated by annealing the coiled silver coated polymer thread in a high temperature (near melting point). The TCP muscles should be under a load to keep the muscles extended. When the muscle connected to the electrical source, the electrical energy transforms into thermal energy due to the electrical resistance of the muscles (Silver), which also known as Joule heating or resistive heating. As the temperature of the TCP muscle increases by Joule heating, the polymer contracts and it causes the muscle contracts.

Mohsen Jafarzadeh, a PhD candidate in electrical engineering and his colleagues at the University of Texas at Dallas, have spent two years work on control of several types of artificial muscles. In one of their works, they studied the dynamic behavior of TCP muscle when the input is electrical voltage. They found that TCP muscles can be represented by first-order state space models. The TCP muscles are very slow in compare natural muscles. So, a sharp improvement in speed and robustness of controllers is a significant progress in using the TCP muscle in practice. In their last work that published in journal Mechatronics, they used linguistic rules to design a fuzzy inference system to speeds up the control of the TCP muscles. The controller is digital (discrete-time) and can be implemented on most of low-cost available microcontrollers and microprocessors in the market. This solution elegantly addresses some of the existing challenges of control of TCP muscles, in terms of the speed, accuracy, robustness, and affordability. Potential applications for this controller in practice could include prosthetic hands, medical devices, robots, and various wearable exoskeletons, according to the researchers.

Reference:

Jafarzadeh, Mohsen; Gans, Nicholas; Tadesse, Yonas. "Control of TCP muscles using Takagi–Sugeno–Kang fuzzy inference system". Mechatronics (August 2018). Volume 53, pages 124–139. https://doi.org/10.1016/j.mechatronics.2018.06.007

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