IF ROBOTS are ever going to be part of our homes, they will need to become a lot quieter. Building them with artificial muscles that run on hydrogen, instead of noisy compressed-air pumps or electric motors, could be the answer.
Kwang Kim, a materials engineer at the University of Nevada in Reno, came up with the idea after realising that hydrogen can be supplied silently by metal hydride compounds.
Metal hydrides can undergo a process called reversible chemisorption, allowing them to store and release extra hydrogen held by weak chemical bonds. It’s this property that has led to the motor industry investigating metal hydrides as hydrogen “tanks” for fuel cells.
To make a silent artificial muscle, Kim and his colleague Alexandra Vanderhoff first compressed a copper and nickel-based metal hydride powder into peanut-sized pellets. They then secured them in a reactor vessel and pumped in hydrogen to “charge” the pellets with the gas. A heater coil surrounded the vessel, as heat breaks the weak chemical bonds and releases the stored hydrogen.
The next step was to connect the vessel to an off-the-shelf artificial muscle, which comprises an inflatable rubber tube surrounded by Kevlar fibre braiding. Two of these placed either side of a robotic joint can mimic the push/pull action of muscles by being alternately inflated and deflated.
Turning the heater on and off controls the flow of hydrogen into the rubber tube causing the muscle to move silently.