Shoulder Exoskeleton Research Articles

A Systematic Review of Occupational Shoulder Exoskeletons for Industrial Use: Mechanism Design, Actuators, Control, and Evaluation Aspects

Prolonged awkward arm postures and repetitive tasks in industrial environments can easily lead to worker injuries. The occupational shoulder exoskeleton is a promising solution to reducing the incidence of work-related musculoskeletal disorders, especially in the shoulder. In general, the device has to be compatible with the human shoulder, which is one of the most complex joints, thus posing significant challenges in existing efforts to design occupational shoulder exoskeletons. The purpose of this paper is to present a comprehensive review of exoskeletons designed to support human shoulders and arms in industrial applications. Recent developments and advancements in mechanism design, actuators, and control aspects are discussed in detail. A brief overview of the evaluation (i.e., participants, task design, objective, and subjective assessment) is also reported, and the experiment protocol to assess performance is summarized. Finally, existing challenges and possible future research directions for occupational shoulder exoskeletons are provided.

A modified human shoulder model considering the migration of the humeral head from the scapular glenoid fossa for the design of shoulder exoskeletons

The wearable upper limb exoskeletons designed using the traditional shoulder model have a serious issue related to joint axis misalignment with the human shoulder. The misalignment is primarily due to the limited degrees of freedom model assumed for the shoulder. The glenohumeral joint in the conventional upper limb model is considered a single spherical joint, which, when considering the human anatomy, neglects the humeral head translation from the glenoid fossa of the scapula. This shoulder model cannot be used for designing the wearable upper limb exoskeletons, which can damage the shoulder joint due to interactive forces generated from the human-exoskeleton joint misalignment. This paper presents a modified, anatomically similar, human upper limb model where the single spherical joint of the glenohumeral joint is modified into two spherical joints connected by a prismatic joint. The kinematic and dynamic model of the proposed shoulder model is explained in detail. The elbow reachable space for this model has been calculated and compared with that of the existing models, and it is found to be closer to the actual workspace. The proposed model is simulated with a conventional exoskeleton attachment to show the effect of misalignment during humeral head translation and the benefits of using the proposed model in the design of the shoulder exoskeleton. An exoskeleton test bench that uses the modified shoulder model is also presented.

The effect of a passive shoulder exoskeleton on a sensorimotor task when performed above and at shoulder height

The effect of a passive shoulder exoskeleton on a sensorimotor task when performed above and at shoulder height

Skilled Workers’ Perspectives on Utilizing a Passive Shoulder Exoskeleton in Construction

This field study explores construction workers’ perceptions of using a passive shoulder exoskeleton to better understand how to improve its adoption in construction. We provided forty-one construction workers with an exoskeleton to perform their regular work activities for two days. Workers’ feedback of the tool was collected at the end of each day. Two-thirds indicated they would likely or very likely use an exoskeleton if their employer provided it. Participants felt exoskeletons were helpful for specific overhead tasks, such as installing upper tracks, framing and drywalling bulkheads, taping and mudding ceilings, and installing light fixtures. To improve their adoption within the construction industry, exoskeletons should be designed to be compatible with harnesses and toolbelts, be close-fitting to allow working in tight spaces, be easily adjustable (for fit and level of support), be rugged and easy to clean, and should not encumber workers in performing their tasks.

Characterization of Human Shoulder Joint Stiffness Across 3D Arm Postures and Its Sex Differences.

Understanding the characteristics of shoulder joint stiffness can offer insights into how the shoulder joint contributes to arm stability and assists in various arm postures and movements. This study aims to characterize posture-dependent shoulder stiffness in a three-dimensional (3D) space and investigate its potential sex differences. A multi-degree-of-freedom, parallel-actuated shoulder exoskeleton robot was used' to perturb the participant's shoulder joint and measure the resulting torque responses while participants relaxed their shoulder muscles. The group average results of 40 healthy individuals (20 males and 20 females) revealed that arm postures significantly affect shoulder stiffness, particularly in postures involving shoulder flexion/extension and horizontal flexion/extension. Shoulder stiffness consistently increased as the shoulder flexion angle decreased and the shoulder horizontal flexion/extension approached the limit of its range of motion. The comparative group results between males and females indicated that shoulder stiffness in males was greater than that in females across all 15 arm postures measured in this study. Even after normalizing the data by subject body mass, the female group showed significantly lower stiffness than the male group in 12 out of the 15 arm postures. The results highlight that 3D arm postures and sex significantly affect shoulder stiffness even under relaxed muscles. This study provides valuable foundations for future studies aimed at characterizing shoulder stiffness in the context of active muscles and dynamic movement tasks, evaluating changes in shoulder stiffness following neuromuscular injuries, and formulating rehabilitative training protocols for individuals suffering from shoulder problems.

A Pilot Study Evaluation of a Passive Shoulder Exoskeleton for a Drilling-fastening Task

Exoskeletons have been considered as a method to mitigate Work-related Musculoskeletal Disorders (WMSDs) in industry. However, it is still unclear how they affect work performance and processes that have accuracy and precision requirements (e.g., drilling, riveting, welding). In this study, the effect of a passive shoulder exoskeleton on a drilling-fastening task performance (the flushness and tilt angle of the fastener) and user perceptions (discomfort, fatigue, and workload) was examined. Participants ( n = 13) performed a drilling-fastening task with the exoskeleton present and absent. Results support that the exoskeleton did not influence the quality of the drilling task, perceived fatigue, or perceived workload. There were mixed results on perceived discomfort, with participants feeling less discomfort, similar discomfort, and greater discomfort based on the body location. This study provides added context for industry decision-making on using passive shoulder-support exoskeletons as a method to mitigate WMSDs.

Design and Evaluation of a Novel Passive Shoulder Exoskeleton Based on a Variable Stiffness Mechanism Torque Generator for Industrial Applications

Design and Evaluation of a Novel Passive Shoulder Exoskeleton Based on a Variable Stiffness Mechanism Torque Generator for Industrial Applications

Mechanical design and kinematic performance of an anthropomorphic shoulder rehabilitation exoskeleton

Shoulder rehabilitation exoskeleton is a mechanical device to assist stroke patients in rehabilitation training, remodeling patients' neurological function by strengthening the muscles and promoting the recovery of shoulder function. At present, there are problems such as insufficient degree of freedom (DOF), insufficient overall range of motion (ROM), presence of passive joints, lack of the support of scapulohumeral rhythm (SHR), and poor kinematic synergy with the shoulder. This paper designs a 5-DOF shoulder rehabilitation exoskeleton based on the anatomical structure of the human shoulder and its motion characteristics, takes the 2-DOF shoulder girdle mechanism and the 3-DOF ball and socket mechanism as the main body taking into account the ergonomic factors in design, which ensures the synergistic motion with the patient's shoulder and provides the patient with a wide ROM. After setting up the drive and control system, this paper completes the prototype of the exoskeleton, furthermore, this paper describes the range of motion and kinematic synergy test. ROM tests and kinematic synergy experiments are conducted to evaluate the kinematic performance of this shoulder exoskeleton. The experimental results indicate that the shoulder exoskeleton prototype offers a high level of kinematic synergy with the wearer throughout a broad ROM.

Human-Exoskeleton Coupling Simulation for Lifting Tasks with Shoulder, Spine, and Knee-Joint Powered Exoskeletons.

In this study, we introduce a two-dimensional (2D) human skeletal model coupled with knee, spine, and shoulder exoskeletons. The primary purpose of this model is to predict the optimal lifting motion and provide torque support from the exoskeleton through the utilization of inverse dynamics optimization. The kinematics and dynamics of the human model are expressed using the Denavit-Hartenberg (DH) representation. The lifting optimization formulation integrates the electromechanical dynamics of the DC motors in the exoskeletons of the knee, spine, and shoulder. The design variables for this study include human joint angle profiles and exoskeleton motor current profiles. The optimization objective is to minimize the squared normalized human joint torques, subject to physical and task-specific lifting constraints. We solve this optimization problem using the gradient-based optimizer SNOPT. Our results include a comparison of predicted human joint angle profiles, joint torque profiles, and ground reaction force (GRF) profiles between lifting tasks with and without exoskeleton assistance. We also explore various combinations of exoskeletons for the knee, spine, and shoulder. By resolving the lifting optimization problems, we designed the optimal torques for the exoskeletons located at the knee, spine, and shoulder. It was found that the support from the exoskeletons substantially lowers the torque levels in human joints. Additionally, we conducted experiments only on the knee exoskeleton. Experimental data indicated that using the knee exoskeleton decreases the muscle activation peaks by 35.00%, 10.03%, 22.12%, 30.14%, 16.77%, and 25.71% for muscles of the erector spinae, latissimus dorsi, vastus medialis, vastus lateralis, rectus femoris, and biceps femoris, respectively.

A Lightweight Shoulder Exoskeleton With a Series Elastic Actuator for Assisting Overhead Work

A Lightweight Shoulder Exoskeleton With a Series Elastic Actuator for Assisting Overhead Work

A Novel Approach to Simulating Realistic Exoskeleton Behavior in Response to Human Motion

Simulation models are a valuable tool for exoskeleton development, especially for system optimization and evaluation. It allows an assessment of the performance and effectiveness of exoskeletons even at an early stage of their development without physical realization. Due to the closed physical interaction between the exoskeleton and the user, accurate modeling of the human–exoskeleton interaction in defined scenarios is essential for exoskeleton simulations. This paper presents a novel approach to simulate exoskeleton motion in response to human motion and the interaction forces at the physical interfaces between the human and the exoskeleton. Our approach uses a multibody model of a shoulder exoskeleton in MATLAB R2021b and imports human motion via virtual markers from a digital human model to simulate human–exoskeleton interaction. To validate the human-motion-based approach, simulated exoskeleton motion and interaction forces are compared with experimental data from a previous lab study. The results demonstrate the feasibility of our approach to simulate human–exoskeleton interaction based on human motion. In addition, the approach is used to optimize the support profile of an exoskeleton, indicating its potential to assist exoskeleton development prior to physical prototyping.

Using a shoulder exoskeleton in slaughterhouse work: Expectations, experiences, and feasibility

BackgroundWork in the slaughterhouse industry increase the risk of shoulder disorders due to high occupational mechanical exposures. Assistive devices, such as exoskeletons, have been developed to reduce the mechanical exposures, but few studies have investigated exoskeleton's feasibility, when used in a workplace setting. ObjectivesThe objective was to explore managers' and workers' expectations and experiences related to using a shoulder exoskeleton, and to evaluate its feasibility compared to an existing assistive device (a ‘lifting glove’) at a Danish slaughterhouse. ParticipantsThe participants included 26 production line workers and their managers at a packaging department at a large slaughterhouse facility. MethodsIn a 5-month field study, data on worker's expectations and experiences of using a shoulder exoskeleton, was compared to a lifting glove and to working without any assistive device. Data was collected using semi-structured interviews, questionnaires, and on-site observations. ResultsExpectations were that shoulder exoskeletons would reduce the mechanical exposure and strain in workers. Some managers also expected that workers could handle more weight/produce more and that the need for job rotation could be reduced. Workers reported the exoskeleton to ‘straighten the body’, and reduced strain, but e others experienced no perceived support or found donning and doffing too time consuming. ConclusionWe found different expectations as to what the shoulder exoskeleton should achieve. This could influence the evaluation of the feasibility of using a shoulder exoskeleton in slaughterhouse work. To facilitate the feasibility of exoskeletons it is important to explicate different expectations and to allow for individual tailoring in its implementation.

A Novel Passive Occupational Shoulder Exoskeleton With Adjustable Peak Assistive Torque Angle For Overhead Tasks.

Overhead tasks are a primary inducement to work-related musculoskeletal disorders. Aiming to reduce shoulder physical loads, passive shoulder exoskeletons are increasingly prevalent in the industry due to their lightweight, affordability, and effectiveness. However, they can only handle specific tasks and struggle to balance compactness with a sufficient range of motion effectively. We proposed a novel passive occupational shoulder exoskeleton designed to handle various overhead tasks at different arm elevation angles, ensuring sufficient ROM while maintaining compactness. By formulating kinematic models and simulations, an ergonomic shoulder structure was developed. Then, we presented a torque generator equipped with an adjustable peak assistive torque angle to switch between low and high assistance phases through a passive clutch mechanism. Ten healthy participants were recruited to validate its functionality by performing the screwing task. Measured range of motion results demonstrated that the exoskeleton can ensure a sufficient ROM in both sagittal (164°) and horizontal (158°) flexion/extension movements. The experimental results of the screwing task showed that the exoskeleton could reduce muscle activation (up to 49.6%), perceived effort and frustration, and provide an improved user experience (scored 79.7 out of 100). These results indicate that the proposed exoskeleton can guarantee natural movements and provide efficient assistance during overhead work, and thus have the potential to reduce the risk of musculoskeletal disorders. The proposed exoskeleton provides insights into multi-task adaptability and efficient assistance, highlighting the potential for expanding the application of exoskeletons.

A Novel Passive Shoulder Exoskeleton Using Link Chains and Magnetic Spring Joints.

Work-related musculoskeletal disorders represent a major occupational disability issue, and 53.4% of these disorders occur in the back or shoulders. Various types of passive shoulder exoskeletons have been introduced to support the weight of the upper arm and work tools during overhead work, thereby preventing injuries and improving the work environment. The general passive shoulder exoskeleton is constructed with rigid links and joints to implement shoulder rotation, but there exists a challenge to align with the flexible joint movements of the human shoulder. Also, a force-generating part using mechanical springs require additional mechanical components to generate torque similar to the shoulder joint, resulting in increased overall volume and inertia to the upper arm. In this study, we propose a new type of passive shoulder exoskeleton that uses magnetic spring joint and link chain. The redundant degrees of freedom in the link chains enables to follow the shoulder joint movement in the horizontal direction, and the magnetic spring joint generates torque without additional parts in a compact form. Conventional exoskeletons experience a loss in the assisting torque when the center of shoulder rotation changed during arm elevation. Our exoskeleton minimizes the torque loss by customizing the installation height and initial angle of the magnetic spring joint. The performances of the proposed exoskeleton were verified by an electromyographic evaluation of shoulder-related muscles in overhead work and box lifting task.

Adaptation of hand exoskeletons for occupational augmentation: A literature review

Limited research has been conducted on hand exoskeletons for an augmentative role. Hand and wrist exoskeletons for therapeutic purposes, however, are widely researched featuring existing technologies which can be adapted for occupational augmentation. This paper presents a literature review of upper-body exoskeleton systems researched within the past five years with a focus on the systematic comparison of augmentative or occupational design compared to other roles. Several important aspects of exoskeleton development for augmentation are identified and evaluated within this review. This includes actuation methods, which determine workspace and scalability, human-robot-interaction, thus ensuring affinity with the wearer, and use of modelling, design optimisation or generative design methods to arrive at effective solutions. This paper systematically reviews 108 upper limb exoskeleton systems and compares their design in three main aspects: The optimisation of their design, their physical features, and the data published to evaluate their effectiveness. Design optimisation in the exoskeleton field faces challenges in parameter choice, lack of integrated personalisation, complex models, computation time, and limited access to effective optimisation techniques. Although there are no perfect combinations of design features, observable trends suggest certain choices are more viable and efficient. The wide range of contemporary hand exoskeleton systems indicates both potential for diverse form factors and a need for further development to converge on a concise solution like that of shoulder exoskeletons.

Design of a wearable shoulder exoskeleton robot with dual-purpose gravity compensation and a compliant misalignment compensation mechanism.

This paper presents the design and validation of a wearable shoulder exoskeleton robot intended to serve as a platform for assistive controllers that can mitigate the risk of musculoskeletal disorders seen in workers. The design features a four-bar mechanism that moves the exoskeleton's center of mass from the upper shoulders to the user's torso, dual-purpose gravity compensation mechanism located inside the four-bar's linkages that supports the full gravitational loading from the exoskeleton with partial user's arm weight compensation, and a novel 6 degree-of-freedom (DoF) compliant misalignment compensation mechanism located between the end effector and the user's arm to allow shoulder translation while maintaining control of the arm's direction. Simulations show the four-bar design lowers the center of mass by cm and the kinematic chain can follow the motion of common upper arm trajectories. Experimental tests show the gravity compensation mechanism compensates gravitational loading within Nm over the range of shoulder motion and the misalignment compensation mechanism has the desired 6 DoF stiffness characteristics and range of motion to adjust for shoulder center translation. Finally, a workspace admittance controller was implemented and evaluated showing the system is capable of accurately reproducing simulated impedance behavior with transparent low-impedance human operation.

Design and Control of a Novel Active Shoulder Exoskeleton for Overhead Work Assistance

Design and Control of a Novel Active Shoulder Exoskeleton for Overhead Work Assistance

Experimental Study of Fully Passive, Fully Active, and Active-Passive Upper-Limb Exoskeleton Efficiency: An Assessment of Lifting Tasks.

Recently, robotic exoskeletons are gaining attention for assisting industrial workers. The exoskeleton power source ranges from fully passive (FP) to fully active (FA), or a mixture of both. The objective of this experimental study was to assess the efficiency of a new active-passive (AP) shoulder exoskeleton using statistical analyses of 11 quantitative measures from surface electromyography (sEMG) and kinematic data and a user survey for weight lifting tasks. Two groups of females and males lifted heavy kettlebells, while a shoulder exoskeleton helped them in modes of fully passive (FP), fully active (FA), and active-passive (AP). The AP exoskeleton outperformed the FP and FA exoskeletons because the participants could hold the weighted object for nearly twice as long before fatigue occurred. Future developments should concentrate on developing sex-specific controllers as well as on better-fitting wearable devices for women.

The Influence of Circular Physical Human–Machine Interfaces of Three Shoulder Exoskeletons on Tissue Oxygenation

Occupational shoulder exoskeletons need to provide meaningful torques to achieve the desired support, thereby high pressures can occur within the physical human–machine interface (pHMI) of exoskeletons that may lead to discomfort, pain, or soft tissue injuries. This pilot study investigates the effects of occurring circumferential pressures within the pHMI in three different shoulder exoskeletons on the tissue oxygenation underneath the interfaces in resting position and dynamic use of the exoskeletons in 12 healthy subjects using near-infrared spectroscopy. Similar to standard Vascular Occlusion Tests, the tissue oxygen decreases while wearing the exoskeletons at rest (−2.1 (1.4) %/min). Dynamic use of the exoskeleton enhances the decrease in tissue oxygen (−7.3 (4.1) %/min) significantly and leads to greater resaturation after reopening the interface compared to resting position. This can be a sign of restricted blood supply to the upper extremity while wearing the exoskeleton. The shape and width of the circular interfaces showed no effect on the tissue oxygenation during use. Tissue oxygenation can be established as an additional safety criterion of exoskeletal pHMIs. The design of pHMI of shoulder exoskeletons should be reconsidered, e.g., in terms of open structures or the elasticity of closure straps to avoid occlusion effects.

Effects of a passive shoulder exoskeleton on muscle activity among Danish slaughterhouse workers

AimTo evaluate the effect of a shoulder exoskeleton on muscle activity and to compare the effect with a lifting glove among slaughterhouse workers in occupational settings. Materials and methodsWe conducted a crossover study of 26 workers measured during two work days with and without the use of a passive shoulder exoskeleton and a lifting glove at a Danish slaughterhouse. Electromyography sensors were placed bilateral on 5 shoulder muscles. The 10th, 50th, and 90th percentiles of muscle activity normalized by maximal voluntary contractions were measured and analyzed using mixed effect models. ResultsFor the 50th percentiles of the agonist muscles, the exoskeleton reduced muscle activity bilaterally for deltoid anterior with up to 29.47%, deltoid middle with 10.22%, and upper trapezius with 22.21%. The lifting glove only reduced muscle activity for right deltoid anterior (36.59%) and upper trapezius (7.11%), but generally increased left muscle activity with up to 15.58%. DiscussionThe exoskeleton showed larger reductions in muscle activity compared to the lifting glove.