Lower extremity exoskeleton as lift assist device

United States workplace injury data demonstrates that in 2005 overexertion caused more than 270 000 cases of lower back disorders (LBD) severe enough to cause absenteeism. This amounts to more than one case reported for every ten warehouse manual material handlers in one year. Manual material handling remains a physically demanding task and existing assist devices have found limited success. Extensive research has been performed on workplace back loading, and several biomechanical models have been developed to study the issue. We propose a lower extremity exoskeleton device which adds a passive extensor moment (restoring moment) about the hips and acting on the upper torso when a wearer is in non-neutral bending and squatting postures, thus reducing forces on the lower back by (1) decreasing the required extensor muscle force, and (2) transmitting forces directly to the ground via the exoskeleton structure.;The maximum useful moment profile (providing the greatest restoring moment, yet comfortable for the wearer) was determined via iterative adjustments and oral interviews with six subjects. Video sequences were recorded of normal speed sagittal squat lifting a 44.5 N (10 lb) and a 133.5 N (30 lb) package with retro-flective markers. Marker locations were tracked, and forces were computed for static and dynamic cases. Surface electromyography (EMG) was performed on 6 subjects to measure muscle activation in the static squat posture: supporting 44.5 N (10 lb) and 133.5 N (30 lb) packages.;Biomechanical model calculations based on marker tracking data suggested that the device significantly reduces maximum erector spinae muscle tension and spine compressive forces when lifting 133.5 N (30 lb) and 44.5 N (10 lb) packages. Static EMG analysis with 133.5 N (30 lb) and 44.5 N (10 lb) packages showed that with the moment restoring exoskeleton, subjects also demonstrated a significant reduction in muscle activity, confirming results found using the biomechanical model. Dynamic EMG testing with 133.5 N (30 lb) and 44.5 N (10 lb) packages showed statistically significant reduction in average back muscle activation over the course of the lift.;The lower extremity exoskeleton effectively reduces low back forces during squat lifting. These results correlate to similar studies of the low back and of other lift assist devices. This exoskeleton device includes features not available on other devices including real-time adjustability of moment profile, ability to reduce moments in squat position, and eliminating high contact stress in the lower extremities by connecting directly with the ground.