Just Go with the Flow

Soft robots are an intriguing and rapidly developing field of robotics that offer several unique benefits over their traditional rigid-body counterparts. Unlike conventional robots constructed with rigid materials like metals and plastics, soft robots are made using flexible and compliant materials such as elastomers and textiles. This flexibility enables soft robots to interact with their environment in a remarkably lifelike manner.

One of the primary reasons engineers are enthusiastic about creating soft robots is their ability to navigate and manipulate complex, unstructured environments with ease. Traditional robots often struggle to adapt to irregular or unpredictable surroundings, but soft robots excel in these scenarios. Their compliant bodies allow them to deform and squeeze into tight spaces, traverse uneven terrain, and interact safely with delicate objects or humans. Soft robots can achieve tasks that were previously challenging or impossible for rigid robots, including tasks in healthcare, exploration, and human-robot interaction.

But it is exactly these desirable properties, especially their soft and compliant nature, that makes them challenging to construct. Designing and manufacturing components that can bend, stretch, and deform while still maintaining structural integrity is a complex task. The creation of actuators, or the devices responsible for generating movement, is particularly challenging in a soft form. Engineers have to develop soft actuators that can produce the necessary forces and motions while being flexible and durable. Traditional rigid actuators, such as motors and gears, do not easily translate into soft robotics.

Robert Wood’s lab at Harvard’s School of Engineering and Applied Sciences has long been at the forefront of the soft robotics revolution, having previously developed many soft components like valves and sensors. But actuators have remained a major sticking point, at least until now. Researchers in the Wood lab have recently reported on the development of a centimeter-scale, soft peristaltic pump. Unlike previous efforts, there are no rigid components involved, the pump is powerful enough to actuate a robot, and it is very versatile in the types of fluids it can pump.

The pumps are composed of arrays of high power dielectric elastomer actuators (DEAs), each weighing just 1.7 grams. These DEAs serve the role of the rollers in a traditional peristaltic pump — they line a length of tubing and alternately squeeze and release portions of the tube in a programmed sequence to create vacuums to draw, then push, fluids through the tube. Since the pumped fluid never touches the components of the pump, it can be incredibly versatile in the types of fluids it pumps.

Testing showed the pump to be powerful, exhibiting a maximum blocked pressure of 12.5 kilopascals and a run-out flow rate of 39 milliliters per minute. It was also fast, with an observed response time of less than 0.1 second. Through careful control of the DEA triggering patterns and voltage levels, it was demonstrated that the pumps can range from a continuous flow, to just pumping droplets. And due to the relative simplicity of the design, the pumps can run for hundreds of thousands of cycles.

After all of their hard work, the team put their device to good use pumping out gin, juice, and coconut milk to serve as a robotic bartender. Oh sure, and also to prove that the pump can work with liquids of various viscosities. Ahem, yes, very serious research indeed.

In another demonstration, a soft robotic finger was also actuated by the pump to show it has a broad range of application areas. The researchers envision many use cases for their invention, ranging from food handling and manufacturing to biomedical therapeutics.