The effect of control strategies for an active back-support exoskeleton on spine loading and kinematics during lifting

Abstract

With mechanical loading as the main risk factor for LBP, exoskeletons (EXO) are designed to reduce the load on the back by taking over part of the moment normally generated by back muscles. The present study investigated the effect of an active exoskeleton, controlled using three different control modes (INCLINATION, EMG & HYBRID), on spinal compression forces during lifting with various techniques. Ten healthy male subjects lifted a 15kg box, with three lifting techniques (free, squat & stoop), each of which was performed four times, once without EXO and once each with the three different control modes. Using inverse dynamics, we calculated L5/S1 joint moments. Subsequently, we estimated spine forces using an EMG-assisted trunk model. Peak compression forces substantially decreased by 17.8% when wearing the EXO compared to NO EXO. However, this reduction was partly, by about one third, attributable to a reduction of 25% in peak lifting speed when wearing the EXO. While subtle differences in back load patterns were seen between the three control modes, no differences in peak compression forces were found. In part, this may be related to limitations in the torque generating capacity of the EXO. Therefore, with the current limitations of the motors it was impossible to determine which of the control modes was best. Despite these limitations, the EXO still reduced both peak and cumulative compression forces by about 18%. The effect of control strategies for an active back-support exoskeleton on spine loading and kinematics during lifting Manuscript Click here to view linked References

Evaluation of an acceleration-based assistive strategy to control a back-support exoskeleton for manual material handling

“…The net L5S1 moment generated by subjects was significantly lower when wearing the exoskeleton for all the assistance modes, with reductions of up to 17%, in line with Koopman et al (2019c). The peak reductions observed were similar to those obtained when the PLAD passive device was tested (Frost et al, 2009), and greater than those with Laevo, a commercially available passive exoskeleton for which a similar study was conducted (Koopman et al, 2019a).…”

“…To validate this new strategy, its effectiveness was experimentally evaluated in terms of spine kinematics, muscle activation, lumbar extensor moment, and compression reductions and variations in the task execution relative to the condition without the exoskeleton. Additionally, to study its effects in greater detail, the acceleration-based strategy was tested against existing strategies for comparison (Toxiri et al, 2018;Koopman et al, 2019c).…”

Applicability of an Active Back-Support Exoskeleton to Carrying Activities

“…EMG data were normalized to maximum voluntary contractions (MVC) (McGill, 1991). Overall, lumbar extensor activity (averaged IL and LL muscle activity, right and left side) was computed prior to performing deep-back muscles analysis as in Koopman et al (2019).…”

Design and preliminary evaluation of a flexible exoskeleton to assist with lifting

“…In practice, people adopt a wide range of postures in daily life, and postures with smaller torso angles will have lower torques needed to support the torso. Additionally, torques of up to 50 Nm are provided by passive structures in the back (Dolan et al, 1994;Bazrgari et al, 2007;Olson et al, 2009;Koopman et al, 2019b), and this will reduce the torque needed by an exoskeleton unless the wearer is extremely flexible (Dolan and Adams, 1993a). Thus, it may be beneficial in most circumstances for a back exoskeleton to provide smaller torques than those in Figure 1.…”