Engine innovations enable portable muscle power in assistive devices

A team of engineers has developed a feather-light fluidic motor to power soft robots in assistive devices.

The distinguishing feature of the new engine is its ability to generate a lot of force on its own, without the need for an external power source.

According to researchers at North Carolina State University, their engine works on the principle of fluid dynamics. The new engine works by directing oil in and out of a chamber in a soft robot.

High suction fluid motor

Soft robots powered by fluid motors, such as hydraulic or pneumatic systems, can mimic muscle behavior in ways that rigid robots cannot. This makes them very attractive for assistive devices aimed at increasing the mobility of upper and lower limbs.

However, traditional liquid-powered motors are typically connected to external power sources such as large air compressors, which significantly limits their versatility.

According to the researchers, previous attempts to construct liquid-powered engines that were not dependent on external power sources did not provide sufficient force, further limiting their practical application.

“Our work here addresses both of these challenges. Our fluidic engine is not tethered to an external source but can still generate up to 580 newtons of force,” Hao Su, an assistant professor of mechanical and aerospace engineering at the university and an author of the study, said in a statement.

The researchers’ fluidic engine includes a pump powered by a high-torque, battery-powered motor. The resulting pressure allows the artificial muscle to generate significant force.

This solution uses a two-piece design. First, a direct drive system with a motor, gear pump, and hydraulic artificial muscle (HAM) creates a compact, lightweight, valveless configuration. Second, a fluid motor with a high-torque motor and custom gear pump generates high pressure to drive the HAM, providing high forces.

During concept testing, scientists evaluated the new engine’s ability to generate force and its efficiency in converting electrical energy into liquid energy.

Efficient soft robotics

Testing has shown that compared to traditional designs that are tethered to stationary sources or have limited force, the new design is portable (3.5 lbs) and withstands high force (580 N), which is critical for compact, lightweight, and human force applications in community settings.

Experimental results show that the device generates pressures up to 0.75 MPa at 15 percent peak efficiency, driving the McKibben muscle with a force of 580 N and a contraction ratio of 21 percent.

The team says that by combining hydraulic and electric control, this approach provides high power density, which is key to reducing the weight of supporting and flight equipment.

“We found that we were able to generate unprecedented force for a self-propelled engine while keeping the mass of the thruster low,” said Antonio Di Lallo, a postdoctoral researcher at the university and the study’s first author.

The researchers say future studies will explore controlling two soft actuators antagonistically, potentially mimicking artificial muscles. The proof-of-concept wearables demonstrate the system’s potential for free-form deployment in lower and upper limb assistance.

Details of the team’s research were published in the journal Advanced intelligent systems.