Using parallel elasticity in back-support exoskeletons: a study on energy consumption during industrial lifting tasks

Abstract

The potential areas of application for exoskeletons are expanding as technological advances are made in their realization. Among the technological challenges still unsolved, actuator design affects many important properties of the resulting device, such as weight and user comfort. We consider here the case of an active exoskeleton designed to assist the lower back during lifting tasks. In previous studies, a parallel-elastic actuator was shown to improve torque control bandwidth over a "traditional" stiff actuator in generating the required torque profiles, by enabling lower-inertia designs. This paper reports our results on energy consumption showing that an appropriately designed parallel spring also substantially reduces the electrical energy consumption (by well over 50% in the proposed case), enabling exoskeleton designs with reduced weight and improved power autonomy.

Biomechanical Analysis of Stoop and Free-Style Squat Lifting and Lowering with a Generic Back-Support Exoskeleton Model

“…It is important to minimize these relative movements between the exoskeleton and the user, while small misalignments can be taken into account. To pursue this approach, additional kinematic structures, for example, joints, sliders, or elastic elements, are added to the existing exoskeleton solutions [ 28 , 30 ]. Hence, detailed hysteresis modeling of the passive exoskeleton support is neglected in the present analysis approach, which has a notable biomechanical effect in existing passive solutions [ 28 , 30 , 50 ].…”

“…To pursue this approach, additional kinematic structures, for example, joints, sliders, or elastic elements, are added to the existing exoskeleton solutions [ 28 , 30 ]. Hence, detailed hysteresis modeling of the passive exoskeleton support is neglected in the present analysis approach, which has a notable biomechanical effect in existing passive solutions [ 28 , 30 , 50 ]. As a further limitation of the present analysis, only one subject’s motions were investigated, and no individual spine movements were captured, which would be possible with more motion markers for an individual understanding of the spine loading [ 51 ].…”

“…The actuator torque elements are described in Table 1 as two interaction moments (exo-hip segment <> exo-thigh segment). Three support modes with different torque characteristics were defined and considered in the analysis to mimic the characteristics of the main categories of the existing BSEs as hip-support exoskeletons: a weak and a strong passive mode (WPM, SPM, respectively), and an active support mode (AM) [ 28 , 29 , 30 ]. Furthermore, an idealized fourth support mode, coined the optimal support mode (OM), was considered as the baseline.…”

“…Both peak and cumulative loads are affected by back support exoskeletons (BSEs) and should be investigated to understand hazards and prevent mechanical muscle, bone, tendon, and cartilage damage. Furthermore, to successfully implement BSEs, it is highly important to understand how they biomechanically can assist, e.g., as existing systems have different support intensities within various BSEs [ 28 , 29 , 30 ], whilst considering the effect of lifting techniques [ 31 ], handling weights, and application-given boundary conditions. However, there are further working conditions related to MSDs for which existing commercial solutions might not be applicable.…”

A Review of Exoskeletons Considering Nurses

“…Exoskeletons re-distribute the forces exerted on the body to avoid the risk of musculoskeletal injuries. Some of them re-distribute the load on the back of the user towards the legs to avoid low-back pain [48,52,70]. An exoskeleton [54] designed for nurses to assist patients during transfer tasks was made to distribute through the frame to the user's body the weight generated when the patient grips the frame, as seen in the Figure 2 below.…”