Since the 1960s, research into the medical applications of wearable robots has been fueled by a growing need for assistive technologies that can help individuals impacted by musculoskeletal disorders such as sarcopenia independently manage common activities of daily living while maintaining their natural physical capacities. While contemporary research has demonstrated promising developments, the usefulness of exoskeletons in everyday settings remains limited due to design factors that include the limited practicality of existing battery technologies, the need for actuators exhibiting a high output torque-to-weight ratio, a need for modular designs that are minimally disruptive to wearers, and the need for control systems that can actively work in sync with a user. To explore potential solutions to some of these limiting factors, a novel ankle exoskeleton prototype supporting ankle plantarflexion during gait was developed under a design approach that seeks to optimize actuator performance. The actuation system featured in this prototype consists of a custom dual-action linear actuator that can provide mechanical assistance to both ankles via a single BLDC motor and an underlying Bowden cable system. The metric ball screw and BLDC motor implemented in the linear actuator were selectively chosen to minimize the motor torque and current required to assist wearers impacted by a degree of muscle weakness under an assistance-as-needed design paradigm. The prototype additionally features an array of force sensing resistors for tracking gait progression and exploring potential user-based control strategies for synchronizing the exoskeleton actuator with a wearer's gait. Performance analysis for this prototype was conducted with the goal of quantifying the exoskeleton's force output, actuator settling time, and the control system's ability to track gait and identify key events in the gait cycle. The preliminary findings of this experimental analysis support the viability of the actuator's dual-action concept and gait progression tracking system as a starting ground for future developments that build on a similar design optimization approach. / Master of Science / Healthy aging and good physical health are characterized in part by one's ability to self-manage a core set of daily living tasks, one of the most prominent of which is gait. Relative to existing assistive technologies such as wheelchairs, exoskeletons provide the unique benefit of providing active mechanical support while encouraging users to rely on their natural physical capabilities. While recent technological developments in the field of wearable robots show promise, the viability of exoskeletons in an everyday setting remains constrained in part by three underlying design factors: the limited practicality of existing battery technologies, a need for actuators that can satisfactorily balance a high force output with weight, and a need for control strategies that can properly synchronize wearable robots with users. The ankle exoskeleton prototype introduced in this thesis is a portable, energetically autonomous wearable device that supports ankle plantarflexion during the push-off stages of the gait cycle. The design for this prototype seeks to optimize actuator performance and features a novel dual-action linear actuator that provides walking support to both ankles using a single DC motor. The exoskeleton additionally features an array of contact sensors that track the user's progression throughout the gait cycle and allow for the examination of potential control strategies for synchronizing the actuator with the wearer's gait. Performance analysis conducted for this prototype quantifies the exoskeleton's force output, approximates the actuator's settling time between steps, and assesses the control system's ability to track gait and synchronize with a wearer. The findings from these performance evaluation experiments support the viability of the actuator's dual-action concept and gait progression tracker as a foundation for future developments that build on a similar design optimization approach.

A novel hip exoskeleton with six degrees of freedom (DoF) was developed, and multiple prototypes of this product were created in this thesis. The device was an upper level of the 12-DoF lower-body exoskeleton project, which was known as the Orthotic Lower-body Locomotion Exoskeleton (OLL-E). The hip exoskeleton had three motions per leg, which were roll, yaw, and pitch. Currently, the sufferers of hemiplegia and paraplegia can be addressed by using a wheelchair or operating an exoskeleton with aids for balancing. The motivation of the exoskeleton project was to allow paraplegic patients to walk without using aids such as a walker or crutches. In mechanical design, the hip exoskeleton was developed to mimic the behavior of a healthy person closely. The hip exoskeleton will be fully powered by a custom linear actuator for each joint. To date, there are no exoskeleton products that are designed to have all of the hip joints powered. Thus, packaging of actuators was also involved in the mechanical design of the hip exoskeleton. As a result, the output torque and speed for the roll joint and yaw joint were calculated. Each hip joint was structurally designed with properly selected bearings, encoder, and hard stops. Their range of motions met desired requirements. In addition, a backpack assembly was designed for mounting the hardware, such as cooling pumps, radiators, and batteries. In the verification part, finite element analysis (FEA) was conducted to show the robustness of the structural design. For fit testing, three wearable prototypes were produced to verify design choices. As a result, the weight of the current hip exoskeleton was measured as 32.1 kg. / Master of Science / Currently, patients who suffer from paraplegia are commonly treated with wheelchairs. However, the drawbacks of using wheelchairs introduced new medical challenges. One of the medical issues is the decrease in bone density. To address these medical problems and increase the quality of life of patients, lower-body exoskeletons are produced to assist with walking. To date, most of the current exoskeleton products require aids for balancing patients’ walking, and they don’t have fully actuated joints at the hip. As for the hip exoskeleton introduced in this thesis, all of the hip joints will be powered. Also, this device was the upper design of the Orthotic Lower-body Locomotion Exoskeleton (OLL-E), which aimed to create a self-balancing exoskeleton with total 12 of lower-body joints powered. The final goal of OLL-E is to assist the patient to walk at normal human speed without using aids. This thesis discusses the process of designing a hip exoskeleton, which starts from requirements development to modeling and prototype tests. The conservative calculations and assumptions made in this paper guided the structural design of the hip exoskeleton. The robustness of the structures was ensured with rigorous finite element analysis. In the end, wearable prototypes were produced to examine the fitting tests. Overall, this design of the hip exoskeleton provided critical references for the future development of the OLL-E.

Embedded systems for humanoid robots are required to be reliable, low in cost, scalable and robust. Most of the applications related to humanoid robots require efficient force control of Series Elastic Actuators (SEA). These control loops often introduce precise timing requirements due to the safety critical nature of the underlying hardware. Also the motor controller needs to run fast and interface with several sensors. The commercially available motor controllers generally do not satisfy all the requirements of speed, reliability, ease of use and small size. This work presents a custom motor controller, which can be used for real time force control of SEA on humanoid robots and exoskeletons. Emphasis has been laid on designing a system which is scalable, easy to use and robust. The hardware and software architecture for control has been presented along with the results obtained on a novel Series Elastic Actuator based humanoid robot THOR. / Master of Science / Humanoid robots can be used in several applications such as disaster management, replacing manual work in hazardous environments, helping human beings in navigation and day to day activities, etc. This increase in interests in humanoid robotics and related research in exoskeletons has led to the need of reliable embedded systems which is used to control the machines. These embedded systems are often required to be low in cost, scalable and robust. The specification required from the electronics and the embedded systems vary based on the robot’s capabilities. Also, there is a gap between the requirements of humanoid robots in research and in industrial setting. This work focuses on bridging the gap by proposing a solution which is semi-custom, low in cost, reliable and scalable. The work has been shown to perform as expected on the stat-of-art humanoid robot THOR which was built at Virginia Tech. Using the proposed design technique can not only deliver good performance but can also act as a quick prototyping tool for other robotics projects related to humanoid robotics and exoskeletons.

This thesis explores the field of hand exoskeleton robotic systems with slip detection and its applications. It presents the design and control of the intelligent sensing and force- feedback exoskeleton robotic (iSAFER) glove to create a system capable of intelligent object grasping initiated by detection of the user’s intentions through motion amplification. Using a combination of sensory feedback streams from the glove, the system has the ability to identify and prevent object slippage, as well as adapting grip geometry to the object properties. The slip detection algorithm provides updated inputs to the force controller to prevent an object from being dropped, while only requiring minimal input from a user who may have varying degrees of functionality in their injured hand. This thesis proposes the use of a high dynamic range, low cost conductive elastomer sensor coupled with a negative force derivative trigger that can be leveraged in order to create a controller that can intelligently respond to slip conditions through state machine architecture, and improve the grasping robustness of the exoskeleton. The mechanical and electrical improvements to the previous design, the sensing and force- feedback exoskeleton robotic (SAFER) glove, are described while details of the controller design and the proposed assistive and rehabilitative applications are explained. Experimental results confirming the validity of the proposed system are also presented. In closing, this thesis concludes with topics for future exploration. / Master of Science / Exoskeletons are robotic systems that have rigid external covering, such as links, joints, and/or soft artificial tendons or muscles, for the desired body part to provide support and/or protection. These are typically used to enhance power and strength, provide rehabilitation and assistance, and teleoperate other robots from a distance. While the US Army developed exoskeletons for strengthening purposes, another potential purpose of exoskeletons, which is serving medical needs, such as rehabilitation, attracted a lot of attention. Among numerous illnesses and injuries that may lead to impaired hand functionality, the U.S. Department of Health and Human Services estimated that approximately 470,000 people survive strokes every year in the United States and require continuous rehabilitation to recover their motor functions. Though medical professionals believe that the intensity and duration of rehabilitation is the key for maximizing the rate of recovery, it is often limited due to many reasons, such as cost or difficulty in attending rehabilitation sessions. To augment the availability and quality of rehabilitation, the study of exoskeletons has earned popularity. Beyond the capability of providing simple movements, such as passive rehabilitation, many scientists researched to provide active rehabilitation, which involves active participation from the patients. Furthermore, detecting the patient’s intention to activate the rehabilitation glove became a topic of interest, and many types of sensors were utilized in research. This thesis explores the design and control of the intelligent sensing and force- feedback exoskeleton robotic (iSAFER) glove, which detects the user’s intentions to activate the system through motion amplification. The iSAFER glove performs soft initial grasp until the fingers touch an object. After the object is gently grabbed and lifted, the grasp is autonomously adjusted through slip detection until there is no more slip. To facilitate this idea, a low cost force sensor was created and leveraged to improve the grasping control of the exoskeleton. The mechanical and electrical improvements to the previous design, the sensing and force-feedback exoskeleton robotic (SAFER) glove, are described while details of the controller design and the proposed assistive and rehabilitative applications are explained. Experimental results confirming the validity of the proposed system are also presented. In closing, this thesis concludes with topics for future exploration.

This thesis details several modifications to the mechanical design of the Orthotic Lower Limb Exoskeleton (OLL-E) that improve upon the functionality and manufacturability of parts and their assemblies. The changes made to these parts maintain or improve the factor of safety against yield and fatigue failure as compared to the original designs. Design changes are verified by FEA simulations and hand calculations. The changes included in this thesis also allowed parts that were previously difficult or impossible to manufacture using traditional methods to be made in house or outsourced to another machine shop. In addition to the mechanical design changes, this thesis also details the design and implementation of a six axis force-torque sensor built into the foot of OLL-E. The purpose of this sensor is to provide feedback to the central control system and allow OLL-E to be self-balancing. This foot sensor design is calibrated and initial results are discussed and shown to be favorable. / Master of Science / Recent developments in the fields of robotics and exoskeleton design have increased their feasibility for use in medical rehabilitation and mobility enhancement for persons with limited mobility. The Orthotic Lower Limb Exoskeleton (OLL-E) is an exoskeleton specifically designed for enhancing mobility by allowing users with lower limb disabilities such as spinal cord injuries or paraplegia to walk. The research detailed in this thesis explains the design and manufacturing processes used to make OLL-E as well as providing design details for a force sensor built into the exoskeleton foot. Before manufacturing could take place some parts needed to be redesigned and this thesis provides insight into the reasons for these changes. After the manufacturing and design process was completed the OLL-E was assembled and the project can now move forward with physical testing.

Work-related musculoskeletal disorders (WMSDs) cost US industries billions annually and reduce quality of life for those afflicted. Passive exoskeletons (EXOs) have emerged as a potential intervention to reduce worker exposures to WMSD risk factors. As EXO adoption is rising, EXO manufacturers are designing and producing new EXOs in accordance with growing demand. However, there are no standardized EXO evaluation protocols and EXO use recommendations, due in part to insufficient information on the reliability of EXO evaluation measures. The purpose of this thesis was to quantify the reliability of common EXO evaluation measures, using both traditional approaches a more advanced statistical approach (i.e., Generalizability Theory), while also identifying potential effects of EXO type, work task, and individual differences. This work used data from a recently completed EXO evaluation study, conducted in Virginia Tech's Occupational Ergonomics and Biomechanics Lab. Forty-two total participants completed simulated occupational tasks, in two separate experimental sessions on different days, while using an arm-support EXO (ASE) and a back-support EXO (BSE). Several outcome measures reached excellent within-session reliability within four trials for many tasks considered. Between-session reliability levels were lower than within-session levels, with outcome measures reaching moderate-to-good reliability for most tasks. Interindividual differences accounted for the largest proportion of variance for measurement reliability, followed by the experimental session. For all tasks, outcome measures reached excellent dependability levels, with many achieving excellent levels within five total trials. Inconsistencies observed in between-session reliability levels and dependability levels suggest that additional training and EXO familiarity may affect measurement reliability of outcome measures differently for some tasks, unique to each EXO type. These discrepancies emphasize the importance for additional research into this topic. Overall, the current findings indicate that many of the commonly used EXO evaluation measures are reliable and dependable within five trials and one experimental session, providing a potential foundation for standardized EXO assessment protocols. / Master of Science / Work-related musculoskeletal disorders (WMSDs) are a substantial economic burden and impair the quality of life for affected workers. Passive exoskeletons (EXOs), which use springs or elastic material to distribute the load placed on workers during manual labor, are a possible solution to reduce worker exposure to WMSD risk factors. EXO adoption is rising, but there are no standardized procedures to test the effectiveness of EXOs or standardized recommendations for EXO use. The purpose of this thesis was to determine the reliability of EXO evaluation measures commonly used in prior research, using both traditional reliability calculation methods alongside a more advanced method (i.e., Generalizability Theory). Data from a recently completed study were used, which were collected from 42 participants in two separate experimental sessions on two different days. Participants completed tasks intended to simulate manual work, using either an arm-support exoskeleton – which supported their upper arms during relevant tasks, or a back-support exoskeleton – which supported their lower back during relevant tasks. Many of the tasks and outcome measures reached excellent reliability within four repetitions in a single day. When examining reliability of evaluations across days, we found reliability levels were lower than levels obtained from a single day. All tasks and outcome measures reached excellent dependability levels, with many requiring only five trials to reach excellent levels. Reliability increased with the number of trials in an EXO evaluation experiment. Moreover, our results revealed that the EXO type being used and the biological sex of a participant both influence reliability, but individual participant differences had the greatest effect on measurement reliability. This research reveals possible experimental conditions required for reliable, efficient, and cost-effective EXO research, facilitating the development of a standardized EXO evaluation protocol.

In this study, structure-property relationships in the ironclad beetle (Zopherus nodulosus haldemani) exoskeleton are quantified to develop novel bio-inspired impact resistance technologies. The hierarchical structure of this exoskeleton was observed at various length scales for both the ironclad beetle pronotum and elytron. The exocuticle and endocuticle layers provide the bulk of the structural integrity and consist of chitiniber planes arranged in a Bouligand structure. The pronotum consists of a layered structure, while elytron consists of an extra layer with “tunnel-like” voids running along the anteroposterior axis along with smaller interconnecting “tunnel-like” voids in the lateral plane. Energy dispersive X-ray diffraction revealed the existence of minerals such as calcium carbonate, iron oxide, zinc oxide, and manganese oxide. We assert that the strength of this exoskeleton could be attributed to its overall thickness, the epicuticle layer thickness, the existence of various minerals embedded in the exoskeleton, and its structural hierarchy. The thickness of the exoskeleton correlates to a higher number of chitiniber planes to increase fracture toughness, while the increased thickness of the epicuticle prevents hydration of the chitiniber planes. In previous studies, the existence of minerals in the exoskeleton has been shown to create a tougher material compared to non-mineralized exoskeletons.

There is emerging evidence for the potential of occupational back-support exoskeletons (BSEs) to reduce physical demands, and thereby help control/prevent the risk of overexertion injuries associated with manual material handling. However, it is important to understand whether BSEs also introduce any unintended safety challenges. One potential risk associated with BSE use is increased risk of falls, since their extra weight, rigid structure, and external hip extension torque may increase demands on the postural control system. However, there is currently limited evidence on whether, and to what extent, BSE use alters postural stability and/or fall risk. The primary goal of this work was to understand the effects of exoskeleton use, and quantify the effects of exoskeleton design parameters, on balance and postural stability, with a focus on passive BSEs used for repetitive lifting work. A comprehensive evaluation of BSE use was performed under controlled laboratory conditions, focusing on three classes of human activity that form the basis of maintaining postural balance in diverse real-life scenarios: maintenance of a specified posture, voluntary movement, and reaction to an external perturbation. The first study demonstrated that during quiet bipedal stance, BSE use increased median frequency and velocity of the center of pressure in the anterior-posterior direction. In the second study on level walking, BSE use caused an increase in gait step width and gait variability, and decrease in the margin of stability. BSE use with high supportive torque led to adapted gait patterns in early-stance phase. Hip range of motion and peak hip flexion velocity also decreased, and participants exhibited different strategies to increase mechanical energy for propelling the leg in late-stance phase: these effects increased with increasing torque applied by the exoskeleton. In the final study, BSE use did not alter the maximal lean angle from which individuals could successfully execute single step balance recovery, following a forward loss of balance. However, several recovery responses were negatively affected by BSE use, including increased reaction time, impeded hip flexion, and reduced margin of stability in the high-torque condition. This is the first systematical investigation to quantify the effects of passive BSEs with multiple supportive torque levels on balance and postural stability. While exoskeleton effects on static balance were minimal, more substantial changes in gait spatiotemporal parameters, hip joint kinematics, and dynamic margins of stability were observed in the later studies. Our results indicate that postural stability deteriorated with exoskeleton use in dynamic conditions, and provide mechanistic insight into how stability is altered by different exoskeleton design factors such as added mass, restricted range of motion, and external hip extension torque. While our results are suggestive of increased fall risk, especially in the high-torque condition, fall risk in real life is moderated by a complex combination of individual and environmental conditions. Future work should consider more complex, realistic tasks and also include a more diverse sample that is studied under longer exposure durations, to further elucidate these findings. Our characterizations of a wide variety of postural responses as a function of exoskeleton torque settings are expected to contribute to improving both design and practice guidelines to facilitate the safe adoption of BSEs in the workplace. / Doctor of Philosophy / Occupational back-support exoskeletons (BSEs) – wearable mechanical systems designed to support, augment, and/or assist back extension – are expected to serve as an alternative workplace intervention to control and prevent overexertion injuries related to manual material handling tasks. While recent studies have shown the beneficial effects of BSE use in terms of physical load reduction on the low back, some concerns have also been raised on unexpected or unintended effects of exoskeletons. One potential risk associated with exoskeleton use is increased risk of falls, since a BSE's extra weight, rigid structure, and external hip extension torque are expected to place increased demands on the postural control system. Increase in fall risk is a critical safety concern, as occupational falls are a serious problem in terms of injuries, medical/industrial cost, and lost work time. However, there exists limited evidence on whether the use of a BSE alters postural stability and/or increases fall risk. Hence, the goal of our study was to quantify the effects of BSE use on postural stability in various conditions related to real-life scenarios, such as standing balance, walking stability and how one would respond to a loss of balance following an external perturbation. Our results showed that during quiet standing, BSE use slightly increased postural sway. In level walking tasks, BSE use had adverse effects on step length, step width, and dynamic stability. Furthermore, wearing a BSE with high supportive torque led to adapted gait patterns in early-stance phase, whereas participants showed different strategies to increase mechanical energy for propelling the leg in late-stance phase. In the final study investigating single step balance recovery following a forward loss of balance, we found that BSE use negatively affects balance recovery, mainly by impeding hip flexion. Thus, our work suggests that exoskeleton use can deteriorate balance and/or postural stability in situations of static standing, voluntary walking, and reacting to an external perturbation, thereby potentially leading to an increase in fall risk. These effects may be more pronounced among specific population sub-groups such as older workers, and may also affect individuals more severely under conditions of stress or fatigue. Hence, future studies must include more rigorous testing of BSE use using a variety of challenging and realistic scenarios, and also include more diverse population samples. The findings from this work are expected to contribute to improving design and practice guidelines to facilitate the safe adoption of BSEs in the workplace.

The need for mechanisms that assist human movements has been increasing due to the rising number of people that has some kind of movement disability. In this scenario, it is of great importance the development of control methods that assist the interface between a motor assistive device and its user. This work proposes a controller for an exoskeleton with one degree of freedom, using surface electromyography signals from the user as the input signal. An exoskeleton was adapted to serve as platform for the developed control method. To create an EMG-to-Angle model, a set of experiments were carried out with six subjects. The experiment consisted of a series of continuous and discrete elbow flexion and extension movements with different load levels. Using the experimental data, linear (ARIMAX) and non linear (Hammerstein-Wiener) system identification methods were evaluated to determine which is the best candidate for the estimation of the EMG-to-Angle model, based on its accuracy and ease of implementation. A new experiment wasconducted to develop a real-time controller, based on FIR model and tested in a real-timeapplication. Tests showed that the controller is capable of estimating the elbow joint angle with correlation above 70% and root-mean-square error below 25° when compared to the measured elbow joint angles. / A necessidade por mecanismos que auxiliam os movimentos do ser humano vem crescendo devido ao aumento do número de pessoas portadores de deficiências que afetam a capacidade motora. Nesse cenário, é de grande importância o desenvolvimento de métodos de controle que auxiliem a interface entre o dispositivo de assistência motora e o seu usuário. Esse trabalho propõe um controlador para um exoesqueleto com um grau de liberdade, usando sinais de eletromiografia de superfície do usuário como sinal de entrada. Um exoesqueleto foi adaptado para servir de plataforma para o método de controle desenvolvido. Para criar um modelo EMG-ângulo, um conjunto de experimentos foi conduzido com seis voluntários. O experimento consistiu em uma série de movimentos de flexo-extensão do cotovelo contínuos e discretos com diferentes níveis de carga. Utilizando os dados do experimento, métodos de identificação de sistemas linear (ARIMAX) e não linear (Hammerstein-Wiener) foram avaliados para determinar qual o melhor candidato para a estimação do modelo EMG-ângulo, baseado em sua acurácia e facilidade de implementação. Um novo experimento foi conduzido para desenvolver um controlador em tempo real, baseado no modelo FIR e testado em uma aplicação em tempo real. Testes indicaram que o controlador é capaz de estimar o ângulo da junta do cotovelo com valores de correlação acima de 70% e raiz do erro quadrático médio menor que 25º, quando comparados aos valores medidos de ângulo da junta do cotovelo.