OCCUPATIONAL APPLICATIONS Many new occupational back-support exoskeletons have been developed in the past few years both as research prototypes and as commercial products. These devices are intended to reduce the risk of lower-back pain and injury for workers in various possible application sectors, including assembly in automotive and aerospace, logistics, construction, healthcare, and agriculture. This article describes the technologies adopted for back-support exoskeletons and discusses their advantages and drawbacks. Such an overview is intended to promote a common understanding and to encourage discussion among different stakeholders such as developers, ergonomics practitioners, customers, and workers. TECHNICAL ABSTRACT Background: The large prevalence and risk of occupational lower-back pain and injury associated with manual material handling activities has raised interest in novel technical solutions. Wearable back-support exoskeletons promise to improve ergonomics by reducing the loading on the lumbar spine. Purpose: Since many new prototypes and products are being developed, this article presents an up-to-date overview of the different technologies. By discussing the corresponding advantages and drawbacks, the objective is to promote awareness and communication among developers, ergonomics practitioners, customers, and factory workers. Methods: The state-of-the-art is presented with a focus on three technological aspects: (i) the actuators generating assistive forces/torques, with a main distinction between passive and active devices; (ii) the structures and physical attachments that transfer those forces/torques to the user, with structures being soft, rigid, or a combination of the two; and (iii) the control strategies employed (i.e., how devices adjust assistive forces/torques to accommodate different activities and parameters). Discussion: The choice of actuation technology may determine the applicability of a device to different scenarios. Passive exoskeletons appear more suitable for tasks requiring relatively light assistance and little dynamic movements. By contrast, heavier and more dynamic tasks will justify the use of more complex active exoskeletons. While on-board battery power is increasingly present on active exoskeletons, the tradeoff between power autonomy and additional battery mass will probably depend on the specific application. Most back-support exoskeletons are implemented using rigid articulated structures, which tend to be heavy and bulky, but generate more appropriate patterns of forces. Fewer soft exoskeletons have been developed to date, although they could be integrated with or worn underneath standard working attire and offer greater user comfort. The adoption of any given device will ultimately depend on several factors, including user acceptance and the costs and benefits associated with specific applications.

Active exoskeletons are potentially more effective and versatile than passive ones, but designing them poses a number of additional challenges. An important open challenge in the field is associated to the assistive strategy, by which the actuation forces are modulated to the user’s needs during the physical activity. This paper addresses this challenge on an active exoskeleton prototype aimed at reducing compressive low-back loads, associated to risk of musculoskeletal injury during manual material handling (i.e., repeatedly lifting objects). An analysis of the biomechanics of the physical task reveals two key factors that determine low-back loads. For each factor, a suitable control strategy for the exoskeleton is implemented. The first strategy is based on user posture and modulates the assistance to support the wearer’s own upper body. The second one adapts to the mass of the lifted object and is a practical implementation of electromyographic control. A third strategy is devised as a generalized combination of the first two. With these strategies, the proposed exoskeleton can quickly adjust to different task conditions (which makes it versatile compared to using multiple, task-specific, devices) as well as to individual preference (which promotes user acceptance). Additionally, the presented implementation is potentially applicable to more powerful exoskeletons, capable of generating larger forces. The different strategies are implemented on the exoskeleton and tested on 11 participants in an experiment reproducing the lifting task. The resulting data highlights that the strategies modulate the assistance as intended by design, i.e., they effectively adjust the commanded assistive torque during operation based on user posture and external mass. The experiment also provides evidence of significant reduction in muscular activity at the lumbar spine (around 30%) associated to using the exoskeleton. The reduction is well in line with previous literature and may be associated to lower risk of injury.

A torque-controlled back-support exoskeleton to assist manual handling is presented. Its objective is to provide a significant portion of the forces necessary to carry out the physical task, thereby reducing the compressive loads on the lumbar spine and the associated risk of injury. The design rationale for a parallel-elastic actuator (PEA) is proposed to match the asymmetrical torque requirements associated with the target task. The parallel spring relaxes the maximum motor torque requirements, with substantial effects on the resulting torque-control performance. A formal analysis and experimental evaluation is presented with the goal of documenting the improvement in performance. To this end, the proposed PEA is compared with a more traditional configuration without the parallel spring. The formal analysis and experimental results highlight the importance of the motor inertia reflected through the gearbox and illustrate the improvements in the proposed measures of torque-control performance.

Manual material handling is one of the most frequent operations in industrial manufacturing processes. To avoid undesirable spinal loads, workers are often required to use external aid devices. This paper presents the analysis and design concept of a wearable assistive device for reducing the spinal loads during lifting tasks. A simplified model is used to compare the effects of two possible configurations for the device: the application of a force (a) parallel and (b) perpendicular to the spine. The model suggests that the perpendicular configuration (b) is preferable to (a). A subsequent numerical analysis suggests that the assistive device reduces substantially the spinal compression. This paper also discusses the design of a hardware prototype, that allows the operator to move mostly unhindered while performing lifting tasks. In particular the leg and torso movements on the sagittal plane are covered by the 90% and 60% respectively, while the movements on the frontal plane are fully covered.

Occupational exoskeletons are becoming a concrete solution to mitigate work-related musculoskeletal disorders associated with manual material handling activities. The rationale behind this study is to search for common ground for exoskeleton evaluators to engage in dialogue with corporate Health & Safety professionals while integrating exoskeletons with their workers. This study suggests an innovative interpretation of the effect of a lower-back assistive exoskeleton and related performances that are built on the benefit delivered through reduced activation of the erector spinae musculature. We introduce the concept of “equivalent weight” as the weight perceived by the wearer, and use this to explore the apparent reduced effort needed when assisted by the exoskeleton. Therefore, thanks to this assistance, the muscles experience a lower load. The results of the experimental testing on 12 subjects suggest a beneficial effect for the back that corresponds to an apparent reduction of the lifted weight by a factor of $37.5\%$ (the perceived weight of the handled objects is reduced by over a third). Finally, this analytical method introduces an innovative approach to quantify the ergonomic benefit introduced by the exoskeletons’ assistance. This aims to assess the ergonomic risk to support the adoption of exoskeletons in the workplace.