A Low-Back Exoskeleton can Reduce the Erector Spinae Muscles Activity During Freestyle Symmetrical Load Lifting Tasks

Abstract

Low-back wearable robots are emerging tools to provide support to operators during handling of goods and repetitive operations. In this paper, we present and validate a novel control strategy for an active pelvis orthosis, that operates intuitively and effectively to assist workers during lifting operations. The proposed control strategy has a hierarchical architecture: the first layer, the intentiondetection, is deputed to the online detection of the onset of the lifting movement; the second layer, the assistive strategy, computes the reference torque profile to assist the movement, after the onset of the lifting movement is detected; the third layer, the low-level control layer, aims at setting the current to drive the actuators. The control strategy grounds on the sensor signals acquired by the robotic device and does not need additional sensors to detect the event. The system was tested on a pool of five healthy subjects requested to perform repetitive lifting movements: first, the subject was requested to lower the trunk, grasp the box, lift it up and place it on a table; second, the subject was requested to grasp the object from the table, lower it down, place it on the floor and get up without the load. The tasks were executed with the exoskeleton controlled in transparent and assistive modes. Results show that the assistive action allows to perform the lifting movement faster. Surface electromyography of low-back muscles show a reduction of the Lumbar Erector Spinae activity in the assistive mode compared to the transparent mode: a 16% reduction is observed when extending the trunk while holding the weight and a 33% reduction resulted when extending the trunk without holding the load.

Towards methodology and metrics for assessing lumbar exoskeletons in industrial applications

“…In state-of-the-art experiments, the lifting trials have been designed to replicate a scenario of repetitive load lifting, similar to the one presented in [13]. In our previous studies, we used the APO, a powered robotic hip exoskeleton, designed to assist the hip flexion-extension movement [13]- [16]. Recruited subjects were asked to repetitively perform lifting and lowering of a 5-kg box between two locations at different heights.…”

“…Electromyography (EMG) analysis can be used to investigate superficial muscular activity. Regardless of the application, EMG analysis is a common practice in exoskeleton assessment [13], [17], [21]- [24]. Indeed, thanks to the measurement of EMG signals, the effects of using an exoskeleton on specific muscular groups can be investigated.…”

“…In this paper, we present an overview of the methodologies used in previous experiments carried out with healthy participants performing repetitive lifting tasks with an active lower-limb exoskeleton [13]- [16]. Moreover, we propose a set of suitable metrics that can be used to evaluate and compare lumbar exoskeletons.…”

“…Table I and Table II provide an overview of the methods and metrics from studies carried out with exoskeletons assisting the load lifting task. Reported examples include studies with active [13], [17], [18] and passive [19], [20] exoskeletons.…”

Classification of Lifting Techniques for Application of A Robotic Hip Exoskeleton

“…To fully exploit the potential advantages of active exoskeletons, control systems must be able to detect the onset of the lifting movement and generate task-appropriate assistance profiles on a dynamic, as-needed basis. To fulfill this aim, in our previous studies, we developed a real-time rule-based algorithm to detect the onset of the lifting movement, and we successfully validated the algorithm with an active hip exoskeleton [ 25 , 26 ].…”