This Backpack Lightens Its Own Load

This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.

Backpackers are all too familiar with the uncomfortable burden of a heavy bag, but scientists are exploring ways to lighten the load. In a recent study, group in China unveiled a backpack prototype that nearly eliminates the vertical inertial forces of the load inside. Experiments show that the bag’s design significantly reduces the amount of energy required by the user to carry it.

If you place an object in a bag, there’s no way to alter the weight of that object—but there is another factor at play that makes the weight more difficult to carry. As a person takes a step, the load inside their backpack often shifts up and down, pushing against the interior of the backpack with extra force, which can make the bag feel heavier than it actually is.

Yanhe Zhu is the vice director of the State Key Laboratory of Robotics and Systems at the Harbin Institute of Technology in China, who was interested in findings ways to counteract these vertical movements of the load.

“A backpack capable of counteracting vertical forces addresses a real pain point for many people who carry heavy loads during commuting, hiking, or running,” says Zhu. “A product that can reduce this burden while enhancing comfort and flexibility would likely be very appealing.”

Designing a New Kind of Suspension Backpack

Several different suspension backpacks that counteract the vertical movement of loads within them have been developed, but these have motors that require energy input. Zhu and his colleagues developed one that requires almost no energy input, which they call a quasi-zero stiffness and controlled damping backpack.

Inside the backpack, the load is balanced by two sets of symmetrical constant-force mechanisms, primarily composed of springs and rotating rods. To prevent the load from colliding with the outer edges of the backpack—and thus adding extra inertial forces for the wearer—a motor adjusts an electromagnetic dampener as needed.

As the load approaches the inner walls of the backpack, the dampener will adjust just enough to counteract the weight shift, stopping the load from colliding with the outer shell of the backpack. Energy from the dampening device is then fed back into the motor.

“As a result, only the microcontroller needs to be powered to control the [device’s transistors], while no additional electrical energy is required for the motor,” says Zhu, noting that this approach is significantly more energy-efficient than other designs that require power to actively drive the motor.

A machine learning algorithm helps guide the system, helping it learn how to counteract the inertial forces of the load as the user walks with the backpack on.

In experiments, the researchers had volunteers carry a regular backpack and their new prototype while on a treadmill, comparing the volunteers’ energy expenditure as they wore each item and walked at different speeds.

The results, published 14 November in IEEE Robotics and Automation Letters, show that the new design can reduce energy expenditure more than 11 percent for users, compared to an ordinary backpack.

Tests also show that, inside the prototype backpack, the load stays nearly stationary in relation to the ground. For example, at fast walking speeds, the backpack offered an average reduction of accelerative vertical forces exceeding 85 percent, compared with an ordinary backpack.

“Additionally, when the user’s back bends, the system dynamically adjusts the load’s movement to prevent it from colliding with the end of the sliding rail,” says Zhu.

He says he believes that this technology has significant commercial potential, and is interested in exploring ways to bring it to market.

“Our next steps will involve integrating intelligent algorithms to enable the suspension backpack to adapt to a broader range of movement patterns, such as jumping,” says Zhu, adding that he and his colleagues would also like to explore energy recovery while using the motor in power-generation mode, to regulate the load’s motion.