Design Of Exoskeleton Research Articles

Analysis and Preliminary Design of a Passive Upper Limb Exoskeleton

This article reports the analysis and preliminary design of a passive, wearable, upper limb exoskeleton to support workers in industrial environments in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The system primary purpose is to compensate for gravity loads acting on the human upper limb. The proposed exoskeleton is based on 6 Degrees-of-Freedom (DoFs) kinematics with 5-DoFs for the shoulder joint (two displacements plus three rotations) and 1-DoF for the elbow. Gravity compensation is implemented with passive elastic elements to minimize weight and reduce cost. A detailed analytical tool is developed to support the designer in the preliminary design stage, investigating the exoskeleton kinetic-static behaviour and deriving optimal design parameters for the springs over the human arm workspace. By defining specific functional requirements (i.e., the user’s features and simulated movements), computationally efficient optimization studies may be carried out to determine the optimal coefficients and positions of the springs, thus, maximizing the accuracy of the gravity balancing. Two different solutions for the arrangement of the elastic elements are investigated, and obtained results are validated with a commercial multi-body tool for some relevant movements of the user’s arm.

Design, development and model analysis of lower extremity Exo-skeleton.

Over the past few years the growth and development of exo-skeleton has dramatically raised with the development of precise control elements and actuation systems. Many exo-skeleton systems have been designed, developed and tested for performance optimization. In the recent years, the significance of exo-skeleton in medical fields have got increased and are used in providing therapy and rehabilitation to the patients. With this development there comes the importance for analysis and control of the exo-skeleton for precise functioning and to avoid malfunction of the system in the later part. Dynamic analysis of limb joints is essential to better facilitate a deeper understanding of the exo-skeleton limb during various environmental conditions like varied loading. The dynamic model so developed will assist in choosing an apt actuation system based on the torque requirement of the model.This paper focusses on the analysis of a 2DOF lower limb active control exo-skeleton system and makes a torque calculation for actuator selection for the lower limb to provide rehabilitation to the patients as wearable walking aid. The work also makes a trajectory planning for the lower limb to move in sequence for making a walking cycle with angular limitations to avoid damage to the user's limbs. The motion analysis for the developed lower limb Exoskeleton as per the analysis is 52.055 Nm at hip joint 11.677 Nm at knee joint.

A Discussion on the Conceptual Design of Multifunctional Exoskeletons for Sustainable Regeneration of Buildings in Urban Areas

The design and erection of new buildings and structures are today driven by strict requirements in terms of sustainability and circular economy, but they represent only a minor part of the built heritage. Hence, it is clear that the maintenance and upgrading of existing buildings play a key role in the achievement of the objectives identified in many developed countries, so that the regeneration of buildings represents the core of many real-world projects. Regenerating existing buildings requires the achievement of modern reuse requirements, the modulation of structural and energy performance, but primarily the fulfilment of many objectives associated with extrinsic (urban planning) and intrinsic (architectural, structural and technological) features. In the present paper, a discussion on the role and potentialities of exoskeletons is reported with the objective of supporting decision makers in resolving the issues associated with the need to improve the overall performance of existing buildings in urban areas. In particular, relevant aspects associated with the conceptual design of multifunctional exoskeletons are reviewed in order to chart a rational course to perform multiscale and interdisciplinary design methodologies.

Design and Evaluation of a Knee Flexion Assistance Exoskeleton for People with Transtibial Amputation.

People with below-knee amputation walk with asymmetric gaits that over time can lead to further musculoskeletal disorders and decreased quality of life. While prosthesis technology is improving, prosthetic ankles may be fundamentally limited in their ability to restore healthy walking patterns because they do not assist the residual knee joint. The knee on the residual limb has muscular deficits due to the loss of the gastrocnemius, a biarticular muscle that crosses both the ankle and knee. Here we present the design, development, and preliminary evaluation of a robotic knee exoskeleton for people with transtibial amputation. The device is intended to restore gastrocnemius-like flexion moments to the knee on the residual limb. The exoskeleton uses a custom offboard actuation and control system to allow for a simple and lightweight design with high torque capabilities. A preliminary walking experiment with one person with transtibial amputation was conducted. The exoskeleton provided a range of knee flexion torque profiles and had an RMS tracking error of 1.9 Nm across four assistance conditions. This device will be used in future studies to explore the effects of providing knee flexion assistance to people with transtibial amputation during walking. Long term, findings from studies with this exoskeleton could motivate future assistive device designs that improve walking mechanics and quality of life for people with limb loss.

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.

Design of Spiral-Cable Forearm Exoskeleton to Assist Supination for Hemiparetic Stroke Subjects.

We present the development of a cable-based passive forearm exoskeleton that is designed to assist supination for hemiparetic stroke survivors. Our device uniquely provides torque sufficient for counteracting spasticity within a below-elbow apparatus. The mechanism consists of a spiral single-tendon routing embedded in a rigid forearm brace and terminated at the hand and upper-forearm. A spool with an internal releasable-ratchet mechanism allows the user to manually retract the tendon and rotate the hand to counteract involuntary pronation synergies due to stroke. We characterize the mechanism with benchtop testing and five healthy subjects, and perform a preliminary assessment of the exoskeleton with a single chronic stroke subject having minimal supination ability. The mechanism can be integrated into an existing active hand-opening orthosis to enable supination support during grasping tasks, and also allows for a future actuated supination strategy.

Design and feasibility of the T-GRIP thumb exoskeleton to support the lateral pinch grasp of spinal cord injury patients.

Improving the impaired hand function of spinal cord injury patients with a robotic exoskeleton can highly impact their self-management, and ultimately their quality of life. In this paper the design and evaluation of a new, lightweight (50 gram) robotic thumb exoskeleton, called TGRIP, was presented that supports the lateral pinch grasp. The mechanism consists of a linear actuator that was mounted to the dorsal side of the hand, and a force transmission mechanism that flexes the thumb towards the side of the index finger. The thumb movement was controlled through contralateral wrist rotation. Experimental results from an evaluation with three spinal cord injury patients showed that the achieved grip force (~ 7N) was higher and the overall performance during the Grasp and Release Test was better with the T-GRIP than without device. The device shows great potential for improving the hand function of patients with cervical spinal cord injury by actuating only a single degree of freedom.

Harnessing Energy of a Treadmill for Push-Off Assistance During Walking: a Proof of Concept study.

Various approaches in ankle exoskeleton design and control have recently been proposed and implemented, but few have been able to produce devices suitable for rehabilitation in clinical environment. In a recent in-silico study, we proposed a novel device: Ankle Exoskeleton using Treadmill Actuation for Push-off assistance (AN-EXTRA-Push). Using a brake and an elastic tendon, it harnesses energy of a moving treadmill during stance phase, then releases it during push-off to aid with plantarflexion torque generation. Simulation studies suggest inherent synchrony between the body's own efforts and ANEXTRA-Push assistance, allowing for intuitive use and simple control of the device. In this contribution we describe a mock-up device and the findings of a proof of concept study. Kinematics, ground reaction forces, interaction forces and EMG signals were measured for one subject walking with AN-EXTRA-Push with different levels of assistance. Using AN-EXTRA-Push did not result in substantial changes in the subject's kinematics and the activity of ankle plantarflexor muscles was successfully reduced. Preliminary results suggest that the concept is promising and appear to confirm the conclusions drawn from our previous simulation study.

Cooperativity Model for Improving the Walking-Assistance Efficiency of the Exoskeleton.

(1) Background: To enhance the walking-assistance efficiencies of exoskeletons, this paper proposed the biomechanical-based cooperativity model based on a passive exoskeleton prototype to fill the technical gap in exoskeleton design regarding the torque transmission law between humans and exoskeletons. (2) Methods: The cooperativity model was used to solve the key system parameters based on the minimum average dispersion degree, in which the average dispersion degree algorithm based on the joint angle was designed and applied. (3) Results: The influence of the cooperativity model on the exoskeleton was indicated by comparing the walking-assistance efficiencies of the exoskeletons with the same structure but with different elastic parameters of the energy storage components, in which the exoskeleton based on the cooperativity design exhibited the highest walking-assistance performance. The walking-assistance efficiency of the exoskeleton with the optimal parameter combinations was also tested by comparing the respiratory metabolisms with and without the exoskeleton, in which the exoskeleton provided the average walking-assistance efficiency of 14.45% for more than 80% of the subjects. (4) Conclusions: The effects of the cooperativity model on exoskeletons were proven, but the accuracy and efficiency of the model still have room for improvement, especially the accuracy of the offset principle.

The Effects of Unpowered Soft Exoskeletons on Preferred Gait Features and Resonant Walking

Resonant walking with preferred gait features is a self-optimized consequence of long-term human locomotion. Minimal energy expenditure can be achieved in this resonant condition. This unpowered multi-joint soft exoskeleton is designed to test whether: (1) there is an obvious improvement in preferred speed and other gait features; (2) resonant walking still exists with exoskeleton assistance. Healthy participants (N = 7) were asked to perform the following trials: (1) walking at 1.25 m/s without assistance (normal condition); (2) walking at 1.25 m/s with assistance (general condition); (3) walking at preferred speed with assistance (preferred condition); (4) walking at the speed in trial (3) without assistance (comparison condition). Participants walked at the preferred frequency and ±10% of it. An average 21% increase in preferred speed was observed. The U-shaped oxygen consumption and lower limb muscle activity curve with the minimum at preferred frequency indicated that the resonant condition existed under the preferred condition. Average metabolic reductions of 4.53% and 7.65% were found in the preferred condition compared to the general and comparison condition, respectively. These results demonstrate that the resonant condition in assisted walking could benefit energy expenditure and provide a new perspective for exoskeleton design and evaluation.

Enhancing force controllability by mechanics in exoskeleton design

This paper presents an exoskeleton concept based on low-size and low-cost electromagnetic motors which allows to improve force controllability and reduce costs at the same time. The idea comes from the theoretical analysis of a simple interaction control model which suggests that lowering the motor inertia leads to improved performance robustness. In particular, we show that a lower motor inertia reduces the sensitivity to the wearer impedance which is usually characterized by high uncertainties. In order to reduce the motor size, this paper proposes to lower the motor torque requirements and considers a parallelogram-based architecture with mechanical gravity compensation. A two degree of freedom prototype is realized to implement the concept and to experimentally validate our hypotheses, showing coherence with theoretical expectations and paving the way for a new generation of affordable forced-controlled exoskeletons.

Design and analysis of a lightweight lower extremity exoskeleton with novel compliant ankle joints.

The exoskeleton for lower limb rehabilitation is an uprising field of robot technology. However, since it is difficult to achieve all the optimal design values at the same time, each lower extremity exoskeleton has its own focus. This study aims to develop a modular lightweight lower extremity exoskeleton (MOLLEE) with novel compliant ankle joints, and evaluate the movement performance through kinematics analysis. The overall structure of the exoskeleton was proposed and the adjustable frames, active joint modules, and compliant ankle joints were designed. The forward and inverse kinematics models were established based on the geometric method. The theoretical models were validated by numerical simulations in ADAMS, and the kinematic performance was demonstrated through walking experiments. The proposed lower extremity offers six degrees of freedom (DoF). The exoskeleton frame was designed adjustable to fit wearers with a height between 1.55m and 1.80m, and waist width from 37cm to 45cm. The joint modules can provide maximum torque at 107Nm for adequate knee and hip joint motion forces. The compliant ankle can bear large flexible deformation, and the relationship between its angular deformation and the contact force can be fitted with a quadratic polynomial function. The kinematics models were established and verified through numerical simulations, and the walking experiments in different action states have shown the expected kinematic characteristics of the designed exoskeleton. The proposed MOLLEE exoskeleton is adjustable, modular, and compliant. The designed adjustable frame and compliant ankle can ensure comfort and safety for different wearers. In addition, the kinematics characteristics of the exoskeleton can meet the needs of daily rehabilitation activities.

Effect of External Damping on Ankle Motion During the Swing Phase of Walking

Manipulation of human ankle dynamics during walking is essential for a smooth gait cycle. Ankle exoskeletons have generally proven positive for rehabilitation and restoration purposes. With the focus on prolonged use of such exoskeletons, there is a need to study the effect of exoskeletons’ residual dynamics on gait adaptation. Understanding such inadvertent interaction can help future intervention paradigm decisions and exoskeleton design. The current work investigates the effect of residual damping on the ankle joint during the swing phase of walking, typically the non-targeted phase of a rehabilitation paradigm. A gait adaptation study was conducted using a cable-driven ankle exoskeleton that applied external damping, both positive and negative, on nine healthy individuals. The interventions resulted in varied perturbed ankle kinematics during the swing phase showing significant reduction and amplification of ankle motion due to the applied positive and negative damping, respectively. The current study demonstrates that healthy individuals can alter their ankle impedance during the swing phase of walking without limiting the overall gait performance.

NESM-γ: An Upper-Limb Exoskeleton With Compliant Actuators for Clinical Deployment

This letter describes the design and characterization of an upper-limb exoskeleton for post-stroke rehabilitation. The platform interacts with the shoulder and elbow of the user through four active joints, driven by series elastic actuators (SEAs) with custom springs to achieve compactness and ease of maintenance. The exoskeleton adopts a passive kinematic chain for aligning the user's and robot joints’ rotation axes, and a quick flipping mechanism to enable dual-side use. The pole-placement method based on the dynamic model of the SEA was used to design the low-level controller, to guarantee torque control precision and stability. The joint load due to the robot's gravity is counteracted by using a feed-forward gravity compensation algorithm. Experimental characterization demonstrates the torque control bandwidth up to 10 Hz and highly transparent behavior of the joints (namely, close to null parasitic impedance) at least up to 2 Hz, showing suitability for rehabilitation purposes.

Design and Electromechanical Performance Evaluation of a Powered Parallel-Elastic Ankle Exoskeleton

The widespread adoption of powered lower-limb exoskeletons for augmenting mobility requires energy-efficient actuation to provide meaningful assistance over relevant walking durations. We designed, modeled, and validated an ankle exoskeleton design with a parallel elastic element in the form of a carbon fiber leaf spring that stored and returned energy in parallel to a cable-drive ankle joint during stance phase. We assessed the impact of the parallel elastic element on the performance of the untethered robotic ankle exoskeleton at walking speeds of 0.75–1.25 m/s using a previously validated-controller, and a controller designed specifically to maximize the spring's benefit. The spring selected for our adult cohort had a stiffness of 97.2 Nm/rad, engaged best at 0-degrees ankle dorsiflexion, and produced 10–15 Nm peak assistive torque at all walking speeds. When tracking the previously validated exoskeleton controller, peak motor current was reduced by 14–20% and integrated current was reduced by 16–19% for parallel-elastic design vs. without spring engagement; this translated to 15–26% more assisted steps for the same battery capacity. When utilizing the controller designed to take advantage of the parallel spring torque, the number of assisted steps for the same battery capacity increased 46–76% compared to the no spring configuration depending on walking speed. Seeking to facilitate real-world adoption, this powered parallel elastic ankle exoskeleton design holds potential to significantly extend powered walking duration, and improve battery and motor life of operation by reducing peak and mean motor current requirements.

Hand Rehabilitation Devices: A Comprehensive Systematic Review.

A cerebrovascular accident, or a stroke, can cause significant neurological damage, inflicting the patient with loss of motor function in their hands. Standard rehabilitation therapy for the hand increases demands on clinics, creating an avenue for powered hand rehabilitation devices. Hand rehabilitation devices (HRDs) are devices designed to provide the hand with passive, active, and active-assisted rehabilitation therapy; however, HRDs do not have any standards in terms of development or design. Although the categorization of an injury’s severity can guide a patient into seeking proper assistance, rehabilitation devices do not have a set standard to provide a solution from the beginning to the end stages of recovery. In this paper, HRDs are defined and compared by their mechanical designs, actuation mechanisms, control systems, and therapeutic strategies. Furthermore, devices with conducted clinical trials are used to determine the future development of HRDs. After evaluating the abilities of 35 devices, it is inferred that standard characteristics for HRDs should include an exoskeleton design, the incorporation of challenge-based and coaching therapeutic strategies, and the implementation of surface electromyogram signals (sEMG) based control.

Optimal Design and Command Filtered Backstepping Control of Exoskeleton With Series Elastic Actuator

Abstract The lower limb exoskeleton can improve mobility and safety during rehabilitation for human. However, most current exoskeleton systems are not capable of providing variable joint stiffness in response to changing external demands. In this paper, a knee exoskeleton based on the series elastic actuator (SEA) is designed for safe human-computer interaction. The structural dimensions of the exoskeleton actuation mechanism were optimized based on gait biomechanics to ensure stability and compactness. While maintaining the mechanism range of motion (ROM), this optimization ensures that less peak force is required during the gait cycle. However, the insertion of series elastic actuators inevitably brings new challenges for high precision control of the exoskeleton, such as the problems of modeling errors, compliance, friction, and external disturbances in the exoskeleton joint. To achieve high precision control of the exoskeleton, an extended disturbance observer (EDO) based command filtered backstepping control (CFBC) of the knee exoskeleton is developed. The effective observation of friction, external disturbances, and modeling errors in the system is obtained by the EDO. Compared with conventional backstepping control, the CFBC can not only solve the “explosion of complexity” problem through a command filter but also reduce filter errors by an error compensation mechanism. Based on the Lyapunov stability, all signals in the closed-loop system are semiglobal uniformly ultimately bounded. Finally, comparison simulation results demonstrate the effectiveness of the proposed control approach.

Design and Validation of a Torque-Controllable Series Elastic Actuator-Based Hip Exoskeleton for Dynamic Locomotion

Abstract Series elastic actuators (SEAs) are increasingly popular in wearable robotics due to their high fidelity closed-loop torque control capability. Therefore, it has become increasingly important to characterize its performance when used in dynamic environments. However, the conventional design approach does not fully capture the complexity of the entire exoskeleton system. These limitations stem from identifying design criteria with inadequate biomechanics data, utilizing an off-the-shelf user interface, and applying a benchtop-based proportional-integral-derivative control for actual low-level torque tracking. While this approach shows decent actuator performance, it does not consider human factors such as the dynamic back-driving nature of human-exoskeleton systems as well as soft human tissue dampening during the load transfer. Using holistic design guidelines to improve the SEA-based exoskeleton performance during dynamic locomotion, our final system has an overall mass of 4.8 kg (SEA mass of 1.1 kg) and can provide a peak joint torque of 108 Nm with a maximum velocity of 5.2 rad/s. Additionally, we present a user state-based feedforward controller to further improve the low-level torque tracking for diverse walking conditions. Our study results provide future exoskeleton designers with a foundation to further improve SEA-based exoskeleton’s torque tracking response for maximizing human-exoskeleton performance during dynamic locomotion.

A Framework for Determining the Performance and Requirements of Cable-Driven Mobile Lower Limb Rehabilitation Exoskeletons.

The global increase in the number of stroke patients and limited accessibility to rehabilitation has promoted an increase in the design and development of mobile exoskeletons. Robot-assisted mobile rehabilitation is rapidly emerging as a viable tool as it could provide intensive repetitive movement training and timely standardized delivery of therapy as compared to conventional manual therapy. However, the majority of existing lower limb exoskeletons continue to be heavy and induce unnecessary inertia and inertial vibration on the limb. Cable-driven exoskeletons can overcome these issues with the provision of remote actuation. However, the number of cables and routing can be selected in various ways posing a challenge to designers regarding the optimal design configuration. In this work, a simulation-based generalized framework for modelling and assessment of cable-driven mobile exoskeleton is proposed. The framework can be implemented to identify a ‘suitable’ configuration from several potential ones or to identify the optimal routing parameters for a given configuration. For a proof of concept, four conceptual configurations of cable-driven exoskeletons (one with a spring) were developed in a manner where both positive and negative moments could be generated for each joint (antagonistic configuration). The models were analyzed using the proposed framework and a decision metric table has been developed based on the models’ performance and requirements. The weight of the metrics can be adjusted depending on the preferences and specified constraints. The maximum score is assigned to the configuration with minimum requirement or error, maximum performance, and vice versa. The metric table indicated that the 4-cable configuration is a promising design option for a lower limb rehabilitation exoskeleton based on tracking performance, model requirements, and component forces exerted on the limb.

Flexible lower limb exoskeleton systems: A review

As an emerging exoskeleton robot technology, flexible lower limb exoskeleton (FLLE) integrates flexible drive and wearable mechanism, effectively solving many problems of traditional rigid lower limb exoskeleton (RLLE) such as higher quality, poorer compliance and relatively poor portability, and has become one of the important development directions in the field of active rehabilitation. This review focused on the development and innovation process in the field of FLLE in the past decade. Related literature published from 2010 to 2021 were searched in EI, IEEE Xplore, PubMed and Web of Science databases. Seventy target research articles were further screened and sorted through inclusion and exclusion criteria. FLLE is classified according to different driving modes, and the advantages and disadvantages of passive flexible lower limb exoskeletons and active flexible lower limb exoskeletons are comprehensively summarized. At present, FLLE's research is mainly based on cable drive, bionic pneumatic muscles followed and matured, and new exoskeleton designs based on smart material innovations also trend to diversify. In the future, the development direction of FLLE will be lightweight and drive compliance, and the multi-mode sensory feedback control theory, motion intention recognition theory and human-machine interaction theory will be combined to reduce the metabolic energy consumption of walking.