Design and Investigation of a Suspended Backpack with Wide-Range Variable Stiffness Suspension for Reducing Energetic Cost

Suspended backpacks have been acknowledged for their advantages in load carriage, leading to the development of various designs aimed at enhancing their performance. However, current suspended backpacks typically possess fixed stiffness or limited adjustability, thereby limiting their adaptability to different load carriage tasks, such as varying walking speeds and load masses. This article introduced a suspended backpack design capable of modulating its stiffness over a wide range while maintaining a lightweight profile. The variable stiffness suspension (VSS) was integrated into the load frame of the suspended backpack and utilized a motor to adjust the stiffness by generating spring-like force based on the relative displacement between the load and the body. Experimental validation was conducted to assess the stiffness modulation of the suspended backpack. The VSS enabled the stiffness modulation of the suspended backpack ranging from 424 to 2182 N/m, which corresponded to the desired stiffness range for a 10-25 kg load at walking speeds for 3.5-6 km/h. Moreover, the mechanics of the carriers were analyzed to evaluate the impact of the suspended backpack on the individuals. Results showed that the designed VSS suspended backpack could reduce peak push-off force by 20.71% under the high working condition and energetic cost by 30.39% under the midworking condition. However, a tradeoff exists between minimizing the peak accelerative load force and energetic cost. The proposed design holds the potential for enhancing performance across various load carriage tasks, including human-in-the-loop energetic optimization.