Coiled Linear Actuators for Soft Robotics

Jul 12, 2023

Northern Arizona University, Flagstaff

In the field of robotics, researchers are continually looking for the fastest, strongest, most efficient, and lowest-cost ways to actuate robots to make the movements needed to carry out their intended functions.

The quest for new and better actuation technologies and "soft" robotics is often based on principles of biomimetics, in which machine components are designed to mimic the movement of human muscles and ideally, to outperform them. Despite the performance of actuators like electric motors and hydraulic pistons, their rigid form limits how they can be deployed. As robots transition to more biological forms and as people ask for more biomimetic prostheses, actuators need to evolve.

Researchers have developed high-performance artificial muscle technology that enables more human-like motion due to its flexibility and adaptability. They call the actuators "cavatappi" artificial muscles, based on their resemblance to cavatappi pasta.

Because of their coiled (helical) structure, the actuators can generate more power, making them an ideal technology for bioengineering and robotics applications. In the team's initial work, they demonstrated that cavatappi artificial muscles exhibit specific work and power metrics ten and five times higher than human skeletal muscles, respectively, and as they continue development, they expect to produce even higher levels of performance.

The cavatappi artificial muscles are based on twisted polymer actuators (TPAs), which were powerful, lightweight, and inexpensive when they were introduced; however, they also were very inefficient and slow to actuate because they had to be heated and cooled. Additionally, their efficiency is only about 2 percent. The new cavatappi actuators use pressurized fluid to actuate, enabling them to respond much faster; as a result, they are far more likely to be adopted. They also demonstrate contractile efficiency of up to about 45 percent, which is very high in the field of soft actuation.

The technology could be used in soft robotics applications, conventional robotic actuators such as walking robots, or potentially in assistive technologies like exoskeletons or prostheses.

Future work will include the use of cavatappi artificial muscles in many applications due to their simplicity as well as their low cost, light weight, flexibility, efficiency, and strain energy recovery properties, among other benefits.

For more information, contact Northern Arizona University Communications at This email address is being protected from spambots. You need JavaScript enabled to view it.; 928-523-2282.

This article first appeared in the August, 2021 issue of Motion Design Magazine.