This study focuses on how the inertia force of a backpack induced by human walking can be compensated by active load modulation through a Second Spine, a device that provides an alternate pathway to transfer loads from the shoulder to the pelvis. Human walking induces periodic vertical acceleration of the upper body. A backpack worn on the upper body undergoes this same acceleration. Inertia force is induced by this acceleration and the human body has to sustain this motion and provide necessary energy.

Based on this knowledge and our previous studies on a passive Second Spine, we present studies on a motorized Second Spine that can actively modulate the vertical motion of a backpack such that the inertia forces can be reduced. This is realized by real-time sensing and actuation so that the backpack is kept inertially fixed. The performance of such a device was evaluated on an instrumented test-bed using an Instron machine, showing results in good agreement with simulation. It was shown that the backpack motion can be made nearly stationary with respect to the ground by active modulation using motors and the inertia force is reduced.

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