A Soft Bi-Stable Valve For Autonomous Control Of Soft Actuators

In recent years, an entirely new class of robot inspired by natural forms and built using soft, flexible elastomers has taken the field by storm, with designs capable of gripping objects, walking, and even jumping.

In one demonstration, Rothemund explained, the valve was built into a multifingered gripper, but a small vent was added to allow air pressure to escape the valve's bottom chamber. When the gripper was lowered onto a tennis ball, however, the vent was closed, causing the bottom chamber to become pressurized, activating the valve, and putting the gripper into action.

"So this integrates the function into the robot," he said. "People have made grippers before, but there was always someone standing there to see that the gripper was close enough to activate. This does that automatically."

The team was also able to build a "feedback" system that, when fed by a single, steady pressure, caused the valve to rapidly oscillate between states.

Essentially, Preston said, the system fed air pressure through the top chamber and into the bottom. When the valve popped into the raised position, it cut off the pressure, allowing the bottom chamber to vent, releasing the pressure and causing the membrane to return to the down position, starting the cycle again.

"We took advantage of the fact that the pressure that causes the membrane to flip up is different than the pressure that's required for it to flip back down," he explained. "So when we feed the output back into the valve itself, we get this oscillatory behaviour."

Using that behaviour, the team was able to build a simple "inchworm" robot capable of locomotion based on a single valve receiving a single input pressure.

"So with one constant pressure, we were able to get this walking motion," Preston said. "We don't control this walking at all—we just input a single pressure and it walks by itself."

Going forward, Rothemund said, more work needs to be done to further refine the valve so it can be optimized for various uses and various geometries.

"This was just a demonstration with the membrane," he said. "There are many different geometries that show this type of bistable behaviour so now we can actually think about designing this so it fits in a robot, depending on what application you have in mind."

Preston also hopes to explore whether the valve, because it is always in one of two states, could be used as a type of transistor to form logic circuits.

"It's kind of like a transistor in a way," he said. "You can have an input pressure come in and switch what the output is going to be … in that sense we could think about this almost like a building block for a completely soft computer."

Source: Science Robotics
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