A Wearable Multi-Modal Digital Upper Limb Assessment System for Automatic Musculoskeletal Risk Evaluation.

Continuous ergonomic risk assessment of the human body is critical to avoid various musculoskeletal disorders (MSDs) for people involved in physical jobs. This paper presents a digital upper limb assessment (DULA) system that automatically performs rapid upper limb assessment (RULA) in real-time for the timely intervention and prevention of MSDs. While existing approaches require human resources for computing the RULA score, which is highly subjective and untimely, the proposed DULA achieves automatic and objective assessment of musculoskeletal risks using a wireless sensor band embedded with multi-modal sensors. The system continuously tracks and records upper limb movements and muscle activation levels and automatically generates musculoskeletal risk levels. Moreover, it stores the data in a cloud database for in-depth analysis by a healthcare expert. Limb movements and muscle fatigue levels can also be visually seen using any tablet/computer in real-time. In the paper, algorithms of robust limb motion detection are developed, and an explanation of the system is provided along with the presentation of preliminary results, which validate the effectiveness of the new technology.

Investigation of a Simple Viscoelastic Model for a PVC-Gel Actuator under Combined Mechanical and Electrical Loading.

PVC gels are gaining more attention in the applications of soft actuators. While their characteristics have been extensively studied experimentally, precise models that predict the deformation due to imposed mechanical and electrical forces are not yet available. In this work, a viscoelastic model based on a combination of a Maxwell and a Kelvin-Voigt model is developed to describe the responsive deformation of the actuator. The model parameters are tuned using data obtained from a unique experimental setup. The PVC gel used in the actuator is made from PVC and dibutyl adipate (DBA) together with a tetrahydrofuran (THF) solvent. A full factorial test campaign with four and three levels for the mechanical and electrical forces, respectively, are considered. The results showed that some of the viscoelastic response could be captured by the model to some extent but, furthermore, the stiffness behavior of the PVC gel seemed to be load-type-dependent, meaning that the PVC-gel material changed stiffness due to the magnitude of the electrical force applied and this change was not equal to a similar change in mechanical force.

The impact of interdisciplinarity and user involvement on the design and usability of an assistive upper limb exoskeleton - a case study on the EXOTIC.

This study describes an interdisciplinary approach to develop a 5 degrees of freedom assistive upper limb exoskeleton (ULE) for users with severe to complete functional tetraplegia. Four different application levels were identified for the ULE ranging from basic technical application to interaction with users, interaction with caregivers and interaction with the society, each level posing requirements for the design and functionality of the ULE. These requirements were addressed through an interdisciplinary collaboration involving users, clinicians and researchers within social sciences and humanities, mechanical engineering, control engineering media technology and biomedical engineering. The results showed that the developed ULE, the EXOTIC, had a high level of usability, safety and adoptability. Further, the results showed that several topics are important to explicitly address in relation to the facilitation of interdisciplinary collaboration including, defining a common language, a joint visualization of the end goal and a physical frame for the collaboration, such as a shared laboratory. The study underlined the importance of interdisciplinarity and we believe that future collaboration amongst interdisciplinary researchers and centres, also at an international level, can strongly facilitate the usefulness and adoption of assistive exoskeletons and similar technologies.

User Based Development and Test of the EXOTIC Exoskeleton: Empowering Individuals with Tetraplegia Using a Compact, Versatile, 5-DoF Upper Limb Exoskeleton Controlled through Intelligent Semi-Automated Shared Tongue Control.

This paper presents the EXOTIC- a novel assistive upper limb exoskeleton for individuals with complete functional tetraplegia that provides an unprecedented level of versatility and control. The current literature on exoskeletons mainly focuses on the basic technical aspects of exoskeleton design and control while the context in which these exoskeletons should function is less or not prioritized even though it poses important technical requirements. We considered all sources of design requirements, from the basic technical functions to the real-world practical application. The EXOTIC features: (1) a compact, safe, wheelchair-mountable, easy to don and doff exoskeleton capable of facilitating multiple highly desired activities of daily living for individuals with tetraplegia; (2) a semi-automated computer vision guidance system that can be enabled by the user when relevant; (3) a tongue control interface allowing for full, volitional, and continuous control over all possible motions of the exoskeleton. The EXOTIC was tested on ten able-bodied individuals and three users with tetraplegia caused by spinal cord injury. During the tests the EXOTIC succeeded in fully assisting tasks such as drinking and picking up snacks, even for users with complete functional tetraplegia and the need for a ventilator. The users confirmed the usability of the EXOTIC.

Hysteresis modeling and compensation of a rotary series elastic actuator with nonlinear stiffness.

Series elastic actuators (SEAs) have widely been adapted in robots where safe human-robot interaction is required for accurate and robust force control. Recent research on the SEAs has shown that the SEA with a user-defined variable stiffness possesses several advantages over the constant stiffness SEA, such as large force range and bandwidth while keeping low output impedance and high force fidelity. However, a limitation of this type of SEA is that an obvious hysteresis effect exists and the associated torque curves are nonlinear and vary with amplitudes. Conventional mathematical hysteresis models are usually developed with some kind of black-box modeling, and the model parameters are adjusted through parameter identification methods. It is challenging to tune the model parameters to match the experimental data well among inputs with different amplitudes, let alone the inverse model of the hysteresis, which is necessary to compensate the hysteresis effect in control. In this paper, a rotary SEA (rSEA) with nonlinear stiffness is proposed. A concept called "virtual deformation" is introduced to mathematically transform the nonlinear curve into a polyline hysteresis model. This eases torque estimation with respect to the deformation of the rSEA. A hysteresis compensation torque controller is implemented for precise torque control. A prototype of the rSEA was fabricated, and the experimental results verified modeling accuracy of the proposed model. Our results showed that, with the new model, the computation cost was greatly reduced while keeping the modeling accuracy almost the same compared with the nonlinear backlash model.

Design and optimization of a hip disarticulation prosthesis using the remote center of motion mechanism.

BACKGROUND: Hip disarticulation prostheses (HDPs) are not routinely seen in clinical practice, and traditional hip prostheses rotate around an axis at the front side of the pelvic socket. OBJECTIVE: This study proposes a mechanism to restore the rotation center to the acetabulum of the amputated side and uses comparative experiments with traditional HDP to verify the validity of the novel design. METHODS: A double parallelogram design of HDP based on a remote center of motion (RCM) mechanism was presented in this paper. Optimization was achieved by a genetic algorithm with the maximal integral size and minimal driving force of the mechanism. RESULTS: The prototype was developed by final optimal results and tested by a hip disarticulated amputee. Testing results revealed that the RCM-HDP improved the range of motion of the hip prosthesis by 78%. The maximal flexion of the assorted prosthetic knee was closer to the sound side than a traditional HDP by 15%. CONCLUSION: The proposed RCM-HDP promoted the kinematic performance and symmetry of the hip prosthesis compared to the traditional design.

A comparative study of motion detection with FMG and sEMG methods for assistive applications.

INTRODUCTION: While surface-electromyography (sEMG) has been widely used in limb motion detection for the control of exoskeleton, there is an increasing interest to use forcemyography (FMG) method to detect motion. In this paper, we review the applications of two types of motion detection methods. Their performances were experimentally compared in day-to-day classification of forearm motions. The objective is to select a detection method suitable for motion assistance on a daily basis. METHODS: Comparisons of motion detection with FMG and sEMG were carried out considering classification accuracy (CA), repeatability and training scheme. For both methods, classification of motions was achieved through feed-forward neural network. Repeatability was evaluated on the basis of change in CA between days and also training schemes. RESULTS: The experiments shows that day-to-day CA with FMG can reach 84.9%, compared with a CA of 77.8% with sEMG, when the classifiers were trained only on the first day. Moreover, the CA with FMG can reach to 86.5%, comparable to CA of 84.1% with sEMG, if classifiers were trained daily. CONCLUSIONS: Results suggest that data recorded from FMG is more repeatable in day-to-day testing and therefore FMG-based methods can be more useful than sEMG-based methods for motion detection in applications where exoskeletons are used as needed on a daily basis.

Effective Multi-Mode Grasping Assistance Control of a Soft Hand Exoskeleton Using Force Myography.

Human intention detection is fundamental to the control of robotic devices in order to assist humans according to their needs. This paper presents a novel approach for detecting hand motion intention, i.e., rest, open, close, and grasp, and grasping force estimation using force myography (FMG). The output is further used to control a soft hand exoskeleton called an SEM Glove. In this method, two sensor bands constructed using force sensing resistor (FSR) sensors are utilized to detect hand motion states and muscle activities. Upon placing both bands on an arm, the sensors can measure normal forces caused by muscle contraction/relaxation. Afterwards, the sensor data is processed, and hand motions are identified through a threshold-based classification method. The developed method has been tested on human subjects for object-grasping tasks. The results show that the developed method can detect hand motions accurately and to provide assistance w.r.t to the task requirement.

Mechanical Design and Kinematic Modeling of a Cable-Driven Arm Exoskeleton Incorporating Inaccurate Human Limb Anthropomorphic Parameters.

Compared with conventional exoskeletons with rigid links, cable-driven upper-limb exoskeletons are light weight and have simple structures. However, cable-driven exoskeletons rely heavily on the human skeletal system for support. Kinematic modeling and control thus becomes very challenging due to inaccurate anthropomorphic parameters and flexible attachments. In this paper, the mechanical design of a cable-driven arm rehabilitation exoskeleton is proposed to accommodate human limbs of different sizes and shapes. A novel arm cuff able to adapt to the contours of human upper limbs is designed. This has given rise to an exoskeleton which reduces the uncertainties caused by instabilities between the exoskeleton and the human arm. A kinematic model of the exoskeleton is further developed by considering the inaccuracies of human-arm skeleton kinematics and attachment errors of the exoskeleton. A parameter identification method is used to improve the accuracy of the kinematic model. The developed kinematic model is finally tested with a primary experiment with an exoskeleton prototype.

Validation of subject-specific musculoskeletal models using the anatomical reachable 3-D workspace.

A novel metric for the validation of musculoskeletal models is proposed, the reachable 3-D workspace (RWS). This new metric was used to compare a generic model scaled in a standard manner to a more subject-specific model. An experimental protocol for assessing the RWS was performed by ten participants for four distinct hand-payload cases. In addition, isometric individual strength measurements were collected for 12 different directions. The strength of subject-specific musculoskeletal models was then computed using the following assumptions: (1) standard routines including the length-mass-fat (LMF) scaling law; (2) the isometric strengths of the muscle elements were optimized to the individual strength measurements using joint strength factors (JSF). The RWS of each participant was subsequently estimated from each of the scaling approaches, LMF and JSF, for the four load cases. The experimental RWS showed that the volume and shape decreased with increasing hand-payload for every participant. The lateral and frontal far-from-torso aspects of the RWS were reduced the most. These trends were reproduced by both strength scaling approaches, but the LMF-scaled models were not able to track the overall RWS volume decrease with increasing payload, since they proved to be weaker than the participants. On the other hand, the optimised JSF subject-specific models performed better on the prediction of the RWS for all payload cases across participants. The RWS can potentially be further used as a subject-specific musculoskeletal model validation, enabling quantification of the volume and shape differences between experimentally and model-predicted RWSs.

The reachable 3-D workspace volume is a measure of payload and body-mass-index: A quasi-static kinetic assessment.

An experimental protocol with five tasks is proposed for a low-cost empirical assessment of the reachable 3-D workspace (RWS), including both close-to-torso and far-from-torso regions. Ten participants repeated the protocol for four distinct hand payloads. The RWS expressed as a point cloud and its non-convex alpha-shape were obtained for each case. Moreover, individual strength surrogates for glenohumeral flexion and abduction, and elbow flexion were collected using a dynamometer. The RWS volume was statistically modelled using payload, body-mass-index and the strength surrogates as predictors. For increasing payload, a significant (r = -0.736,p < 0.001) decrease in RWS volume was found for distinct payload cases across all subjects. The only significant predictors found for the RWS volume were normalized payload (F = 73.740,p < 0.001) and body-mass-index (F = 11.008,p = 0.003). No significant interactions were found. The consequent regression model (F(2,27) = 41.11, p < 0.001, Radj2 = 0.7345) explained around 73% of the variation in the data. The RWS volume is a function of payload and body-mass-index.

Design of a biologically inspired lower limb exoskeleton for human gait rehabilitation.

This paper proposes a novel bionic model of the human leg according to the theory of physiology. Based on this model, we present a biologically inspired 3-degree of freedom (DOF) lower limb exoskeleton for human gait rehabilitation, showing that the lower limb exoskeleton is fully compatible with the human knee joint. The exoskeleton has a hybrid serial-parallel kinematic structure consisting of a 1-DOF hip joint module and a 2-DOF knee joint module in the sagittal plane. A planar 2-DOF parallel mechanism is introduced in the design to fully accommodate the motion of the human knee joint, which features not only rotation but also relative sliding. Therefore, the design is consistent with the requirements of bionics. The forward and inverse kinematic analysis is studied and the workspace of the exoskeleton is analyzed. The structural parameters are optimized to obtain a larger workspace. The results using MATLAB-ADAMS co-simulation are shown in this paper to demonstrate the feasibility of our design. A prototype of the exoskeleton is also developed and an experiment performed to verify the kinematic analysis. Compared with existing lower limb exoskeletons, the designed mechanism has a large workspace, while allowing knee joint rotation and small amount of sliding.