Development of a novel elastic load-carrying device: Design, modeling and analysis

Carrying load manually is a highly strenuous task and costs additional energy during walking. The forward velocity and vertical displacement of the body center of mass (COM) changes along with the inverted pendulum-like motion. Thus the interaction between the load and carrier varies as well. The interaction between load and carrier has a big influence on the comfort and energetics of the carrier. In this paper, we present the design of a novel carrying device where the load is connected to the frame with springs arranged in the fore-aft direction. This design is capable of changing the interaction pattern of load-carrier system. A simple mass-spring-damper model is proposed to characterize the motion of load and carrier in the forward direction. The motion pattern of the load can be predicted with the model, and it differs according to the selection of the stiffness of spring and load weight. Experimental method is presented to determine damping coefficient in the interaction model. The effect of stiffness of springs on gait kinetics is also analyzed with the model and examined with experiments. The stiffness selection is suggested to be able to make the natural frequency of the mass-spring-damper model lower than the walking frequency. In this case the interaction force can be reduced. The result also reveals that the “touchdown” impact during walking can be weakened significantly with proper stiffness selection.