The design of two passive back lift assist exoskeletons are presented in this thesis. The first exoskeleton uses carbon fiber as an energy storage medium while the second system utilizes a series system comprised of a gas spring and metal coil spring. The first exoskeleton was successfully tested long term in a warehouse environment and in laboratory experiments. From these tests and feedback from wearers several drawbacks to the design were discovered. Version two of the exoskeleton successfully addresses these concerns. / Master of Science / This document presents the designs of two lightweight passive exoskeletons. Exoskeletons are wearable devices that assist users in performing tasks that may be difficult or impossible without extra assistance. The exoskeletons developed and discussed in this thesis assist the wearer when bending or performing lifting tasks. As a user bends over or squats, energy is stored in the exoskeleton and is released when the user returns to standing. The first exoskeleton utilizes carbon fiber leaf springs to store the energy. It was successfully tested in a real-world warehouse setting and under laboratory conditions. Testing results and feedback from users led to modifications and new features which are included in the second version. The second exoskeleton uses a gas spring and coil spring in series for energy storage. It also incorporates a novel walking differential which allows users to seamlessly transition from walking to lifting.

Safety, quality, and production are critical factors that impact an enterprise organization’s success in industries where tasks are human-centered. One emerging area to help mitigate safety related concerns while enhancing quality and production is wearable technology. More specifically, studies have shown that wearable exoskeletons can prevent awkward posturing and excessive bending and reaching tasks. These are areas that can result in injuries and lost time for employees. While literature has shown that these devices can help prevent injuries and can assist employees with their job tasks, these devices are new, which can make critical stakeholders of an enterprise organization skeptical about adopting these devices. This dissertation studies the technology acceptance of the front-line workforce, human resources (HR), and subject matter experts (SMEs) within the industrial sector.

Loss of mobility and independence directly affects the quality of life of many vulnerable individuals. To address this, researchers have developed wearable walking assist exoskeletons to aid users with their daily activities. While this technology has advanced tremendously in the past decade, current exoskeletons cause discomfort and injuries to the user, leading to device rejection. This research intends to develop a kinematically compatible knee joint suitable for exoskeletons. The proposed knee design can be adapted to accommodate an offset and optimize force delivery. This is achieved by ensuring that the mechanical and biological joint rotation axes are aligned and that the moment arm varies throughout flexion. Model simulations and mechanical testing of fabricated prototypes were achieved to analyze and validate the design. The results confirm the kinematic compatibility of the design and that the moment arm could be varied throughout flexion to achieve optimal and effective moment transfer.

This paper presents the design of an underactuated lower body exoskeleton to assist with walking. It reduces the amount of bodyweight going through the user's leg by providing a supporting force to the user that is engaged and disengaged depending on the stage of the gait cycle the user is in. It is engaged when the leg is in stance, effectively pushing between the ball of the foot and the hips, and is disengaged during leg swing. This support force is provided by a linear actuator on each leg that consists of a compression spring, ball screw, and motor. It works by having the motor turn the ball screw, which moves a metal plate to either compress or decompress the spring. The actuator is designed to always be able to extend, to avoid limiting the user's motion. The spring is disengaged while the leg is in swing in order to reduce any impedance to the user's natural stride. The exoskeleton is also designed to minimize any range of motion limitations to reduce its restrictiveness. The exoskeleton was found to be able to provide 19 lbs (85 N) of support to the user per leg. / Master of Science / Exoskeletons are external devices worn to assist the user's natural movement or strength. This paper outlines the design of an exoskeleton that assists the user in walking by providing a supporting force on any leg that the user's weight is on. This effectively reduces the load on the user's legs, which could help reduce leg strain and fatigue. The exoskeleton releases this force when weight is removed from the leg to allow the user to easily swing their leg forward to step. The exoskeleton was designed to minimize limitations to the range of motion of the leg joints while walking, squatting, or sitting to ensure that the exoskeleton did not feel restricting or uncomfortable. Testing revealed that the exoskeleton was able to provide a supporting force of approximately 19 lbs (85 N) to the user per leg and met all the joint range of motion requirements to avoid restrictiveness.

We present and analyze two arm exoskeletons based on a pantograph linkage that allow for the support of 89~N (20~pounds) at the user's hand. Using a pantograph linkage allows for a constant force to be created at the hand in any orientation when a constant vertical force is supplied to the other side of the pantograph. We present several topologies and analyze them based on feasibility of manufacture and ability to provide a near vertical force to the pantograph linkage. Simulations are created using the best topologies and the resulting forces at the hand are reported. The mechanical design of an unpowered (passive) exoskeleton which uses a gas spring mechanism is presented. Additionally, simulations and block-CAD of a powered (active) exoskeleton which uses a motor for the supply of force are presented. The performance of the passive exoskeleton is qualitatively compared with simulations. / Master of Science / A wearable device or exoskeleton is presented which is designed to help a user support a weight of 20 pounds (89~N) at their hand. A pantograph linkage arm exoskeleton provides forces to the hand which are equal to the force provided to the linkage divided by the linkage's ratio. Providing a force to the linkage that is purely vertical will result in a purely vertical force at the hand. Layouts of the exoskeleton components which produce a near-vertical force for the linkage are explored. The more promising layouts are simulated and the forces are compared based on how vertical the forces are. The design of an unpowered exoskeleton is also presented, which uses a gas spring mechanism to provide force. Additionally, simulation results for the unpowered exoskeleton and the basic design and analysis of a powered exoskeleton are presented.

Lower extremity powered exoskeletons (LEPE) allow people with spinal cord injury (SCI) to perform activities of daily living, such as standing, walking, or stair and ramp ascent/descent. However, current LEPE walk slowly and require extensive use of forearm crutches to maintain user stability. Consequently, this limits LEPE time of use and overall system performance. While the biological ankle is known to be critical for energy efficiency, speed, and stability in able-bodied walking, current LEPE do not include biomimetic ankle designs and thus limit device performance. The objective of this thesis is to determine biomimetic ankle mechanics for a LEPE, thereby defining ankle design requirements that could reduce crutch loads and thus extend LEPE use. Virtual prototyping techniques were used to achieve this objective. Two 3D models of a real LEPE (ARKE, Bionik Laboratories) attached to a human musculoskeletal model were developed and validated. The first model (biomimetic model) was driven by 3D marker kinematics from 30 able-bodied participants walking at four realistically slow LEPE walking speeds. The second model (SCI model) was driven by 3D marker kinematics from five SCI participants walking in the ARKE LEPE with instrumented forearm crutches. Once the models were validated by comparing predicted to measured ground reaction forces (GRF) and centre of pressure (COP) trajectories, biomimetic LEPE ankle design requirements were determined. Ankle range of motion, quasi-stiffness, work, peak moment, and peak power were compared between human and human+ARKE models, across four gait phases and four slow walking speeds. The major findings were: the human+ARKE model had significantly different quasi-stiffness values across all four gait phases; quasi-stiffness increased with increasing speed; the human+ARKE model’s ankle always absorbed net-work, even at the fastest walking speed; quadratic regression was significantly more accurate than linear regression for modelling ankle quasi-stiffness. These results suggested that passive variable stiffness ankles incorporating quadratic elastic spring elements could achieve biomimetic ankle functions and thus potentially increase LEPE user walking speed, stability, and reduce overuse of crutches.

Aging is accompanied by a deterioration of physical abilities. For some this limits their mobility and thus their quality of life. Exoskeletons are a class of walking assist device that help reduce the effort required to walk. Currently, powered exoskeletons suffer from short battery life and thus limited usefulness. This thesis presents the design, fabrication, and testing of a novel unpowered ankle exoskeleton to assist normal walking over long distances. The design incorporates a Pneumatic Artificial Muscle (PAM) inflated and used as a passive air spring. To predict the behaviour of the PAM in this distinct application, a distinct dynamic model was developed to include the biaxial stress in the bladder as well as a polytropic gas assumption. Experimental testing was used to validate the model and indicated that the addition of the bladder stress enhanced the performance of the force prediction at low pressure but had negligible impact on the model at higher pressures. The experimental testing also showed that the temperature of the gas inside the PAM varies very slightly during passive elongation cycles, thus, validating an isothermal assumption. Once fabricated, the exoskeleton was tested in human walking trials. Electromyography results showed that the exoskeleton was able to reduced the muscular activation activation of the Soleus muscle, however the results also included a significant reduction in the angular range of motion of the ankle. This is thought to be attributed to an insufficient acclimatization period during the human testing. Furthermore, due to an improper fit of the exoskeleton, the clutch mechanism did not operate as designed, leading to a reduced range of motion of the ankle. The device demonstrated its ability to reduce the effort of the calf muscles during walking, however, further refinements of the device fitting and clutch mechanism are required.

Scoliosis is an abnormality of the spinal curvature that severely affects the musculoskeletal, respiratory, and nervous systems. Conventionally, it is treated using rigid spinal braces. These braces are static, rigid, and passive in nature, and they (largely) limit the mobility of the spine, resulting in other spinal complexities. Moreover, these braces do not have precise control over how much force is being applied by them. Over-exertion of force may deteriorate the spinal condition. This research presents a novel active soft brace that allows mobility to the spine while applying controlled corrective forces. The brace uses elastic bands to apply forces in the form of elastic resistance. These forces are regulated by varying the tensions in elastic bands using low-power, lightweight, twisted string actuators (TSAs). Use of TSAs and the elastic bands significantly reduces the weight and power consumption of the device. This results in higher comfortability and longer wear time. To realize the brace concept a finite element analysis was carried out. A FE model of the patient’s trunk was created and validated with in-vitro study from literature. The brace model was installed on the simulated trunk to evaluate in-brace correction in both sagittal and coronal planes. The brace was evaluated under various load cases by simulating the actuator action. The research also focused on the protype development which include the actuator and contact forces modeling of the active soft brace (ASB). The actuator modeling is required to translate the twisting of string in terms of contraction of the string’s length, whereas the contact force modeling helps in estimating the net resultant force exerted by the band on the body using single point pressure/force sensors. The actuators (TSAs) are modeled as helix geometry and numerical estimation was validated using a laser position sensor. The results showed that the model effectively tracked the position (contraction in length) with root mean square error (RMSE) of 1.7386 mm. The contact force is modeled using the belt and pulley contact model and validated by building a custom testbed. The actuator module is able to regulate the pressure in the range 0–6 Kpa, which is comparable to 0–8 Kpa pressure regulated in rigid braces. This makes it possible to verify and demonstrate the working principle of the proposed active soft brace. The use of stretch sensor to measure the stretch(tension) in the elastic bands is a crucial part of the brace. It is used as feedback to control the tension in the elastic bands using twisted string actuators. A few, fabric and silicon-based stretch sensors are analyzed to pick a suitable candidate for the active soft brace application. Two control modes were designed to control the amount of force being exerted by the brace. One using pressure sensors as feedback to keep the contact pressure at desired setpoint. Second mode using the stretch sensor to keep the tension in the bands at a desired setpoint. The active soft brace modules (TSA actuator, bands and stretch sensors, controller) were integrated and validated on the mannequin. This research concludes the preliminary part of conceptual design, construction, and validation of the demonstrator prototype, before going into the clinical trials. Clinical trials take longer duration to evaluate the effectiveness of the brace on real patients and were out of the scope of the project.

Low back pain is the number one cause of disability in the world. It is a well established problem in industry often caused by excessive repetition, awkward postures, and heavy lifting. Back support exoskeletons have increasingly been studied as a solution to this problem. In addition to evaluating exoskeletons, giving some focus to the various lifting styles themselves can also provide some insight into ameliorating this problem. Research evaluating warehouse workplace postures has found that workers switch between a variety of tasks and many different lifting styles, beyond the standard squat and stoop postures, on a daily basis. This dissertation is primarily a compilation of three papers. The first focuses on the VTLowe's exoskeleton and the kinematic differences found during Stoop, Squat, and Freestyle lifting. These lift styles were evaluated while the study participants lifted boxes weighing 0% or 20% of their body weight both With and Without the exoskeleton. Evaluating the kinematic results showed that wearing the exoskeleton resulted in a 1.5 degree increase in ankle dorsiflexion, a 2.6 degree decrease in knee flexion, and a 2.3 degree decrease in SHK angle. Subjects' shoulder, elbow, and wrist heights were slightly higher while wearing the exoskeleton, and they lifted slightly more slowly while wearing the exoskeleton. Subjects moved more quickly while bending down as compared to standing up, and with the 0% bodyweight box as compared to the 20% bodyweight box. The values for Freestyle lifts generally fell in between Squat and Stoop lift styles or were not significantly different from Squat. EMG data (analyzed in a different study) from the leg muscles had relationships with torso torque while the back and stomach muscles showed no significant relationships. Exoskeleton efficacy research has a strong focus on Stoop, Squat, and Freestyle lifting. However, asymmetric styles such as One Legged lifting and Kneeling were found to be frequently used lifting styles in a warehouse setting. The second paper in this dissertation focuses on variations of asymmetric lifts while lifting light objects including Split Legged, Heel Up, One Legged, Kneeling, Asymmetric Squat, Bent Over (a freestyle task) and Bend Walk (picking up bean bags from the ground while walking forward and maintaining a bent over posture). These lift styles can be found not only in industry, but in any individual's daily life such as when it comes to picking up a dropped pen or sorting toys in a bin on the floor. Evaluating Split Legged, Heel Up, and One Legged found that many of the significant differences in muscle activity are dependent on the lifting stance (whether the front foot is on the same side or opposite side as the hand used to pick up objects). Combining the results that same side lifts have greater muscle imbalance in the iliocostalis and overall back muscle activity is greater in Split Legged than in Heel Up or One Legged suggests that One Legged or Heel Up in an Opposite side stance are the best options in regards to minimizing back muscle activity. Although there is a trade-off with the biceps femoris for these lift styles, back injuries are far more prevalent and supporting the back takes priority over minimizing muscle activity in the legs. The analysis for Asymmetric Squat, Bend Walk, Bent Over, and Kneeling was divided into three portions: bending down, picking bags, and rising up. Relevant differences between the lift styles for these portions were seen in the biceps femoris, longissimus, and rectus abdominis, with Bend Walk generally being the most taxing activity. Overall, there were minimal differences while rising up from any of these postures with most changes seen in the biceps femoris. Rising Up also generally had a higher peak muscle activity compared to bending down or picking bags. The final paper in this dissertation evaluates the effect of a different back exoskeleton with the variety of lift styles studied in the second paper. It is important to see how exoskeleton use aids or harms many of the lift styles commonly used by industry workers. Lift side was once again a factor in the Split Legged, Heel Up, and One Legged tasks. Participants benefited more from the exoskeleton in same side lifts as opposed to opposite side. For Asymmetric Squat, Bend Walk, Bent Over, and Kneeling greater benefits were seen in the back and leg muscles while rising up as opposed to bending down. Focusing on the peak of the lift (taken at the peak of bending down for the more static postures) found that the exoskeleton had more significant differences for Split Legged, Heel Up, and One Legged compared to Asymmetric Squat, Bend Walk, Bent Over, and Kneeling. One highly important aspect in evaluating exoskeletons is determining the subject population that would most benefit from its use. Focusing on body mass, the longissimus saw decreased benefits as the body mass increased, with subjects under 75 kg benefiting the most from the exoskeleton, while the iliocostalis and biceps femoris typically saw the opposite effect when results were significant (i.e., heavier subjects benefited the most). / Doctor of Philosophy / Low back pain is the number one cause of disability in the world. It is a well established problem in industry often caused by excessive repetition, awkward postures, and heavy lifting. Back support exoskeletons have increasingly been studied as a solution to this problem. In addition to evaluating exoskeletons, giving some focus to the various lifting styles themselves can also provide some insight into ameliorating this problem. Research evaluating warehouse workplace postures has found that workers switch between a variety of tasks and many different lifting styles, beyond the standard squat and stoop postures, on a daily basis. This dissertation is primarily a compilation of three papers. The first focuses on the VTLowe's exoskeleton and the differences in how people move while wearing the exoskeleton during Stoop, Squat, and Freestyle lifting. These lift styles were evaluated while the study participants lifted boxes weighing 0% or 20% of their body weight both With and Without the exoskeleton. This resulted in small changes in the ankle, knee, and hip angles. Subjects' shoulder, elbow, and wrist heights were slightly higher while wearing the exoskeleton, and they lifted slightly more slowly while wearing the exoskeleton. Subjects moved more quickly while bending down as compared to standing up, and with the 0% bodyweight box as compared to the 20% bodyweight box. The values for Freestyle lifts generally fell in between Squat and Stoop lift styles or were not significantly different from Squat. Electromyography (muscle activity) data, analyzed in a different study, from the leg muscles had relationships with torso torque while the back and stomach muscles showed no significant relationships. Exoskeleton efficacy research has a strong focus on Stoop, Squat, and Freestyle lifting. However, asymmetric styles (i.e., where one side of the body is doing something different from the other side) such as One Legged lifting and Kneeling were found to be frequently used in a warehouse setting. The second paper in this dissertation focuses on variations of asymmetric lifts while lifting light objects including Split Legged, Heel Up, One Legged, Kneeling, Asymmetric Squat, Bent Over (a freestyle task) and Bend Walk (picking up bean bags from the ground while walking forward and maintaining a bent over posture). These lift styles can be found not only in industry, but in any individual's daily life such as when it comes to picking up a dropped pen or sorting toys in a bin on the floor. Evaluating Split Legged, Heel Up, and One Legged found many of the significant differences in muscle activity are dependent on the lifting stance (whether the front foot is on the same side or opposite side as the hand used to pick up objects). The results found that there were different imbalances between the sides of the body depending on the specific lift style examined. Overall, the muscle activity results suggest that One Legged or Heel Up in an Opposite side stance are the best options in regards to minimizing back muscle activity. While leg muscle activity does increase for these lift styles, back injuries are far more prevalent and supporting the back takes priority over minimizing muscle activity in the legs. The analysis for Asymmetric Squat, Bend Walk, Bent Over, and Kneeling was divided into three portions: bending down, picking bags, and rising up. Overall, Bend Walk was the most taxing of those activities. The final paper in this dissertation evaluates the effect of a second back exoskeleton with the variety of lift styles studied in the second paper. It is important to see how exoskeleton use aids or harms many of the lift styles commonly used by industry workers. Participants benefited more from the exoskeleton in same side lifts as opposed to opposite side. For Asymmetric Squat, Bend Walk, Bent Over, and Kneeling greater benefits were seen in the back and leg muscles while rising up as opposed to bending down. The exoskeleton helped Split Legged, Heel Up, and One Legged more than Asymmetric Squat, Bend Walk, Bent Over, and Kneeling. One highly important aspect in evaluating exoskeletons is determining the subject population that would most benefit from its use. One of the back muscles saw decreased benefits as the body mass increased, with subjects under 75 kg benefiting the most from the exoskeleton, while another back muscle and the legs typically saw the opposite effect.

Cerebral palsy is an occurrence in which the nerves and muscles if the body may function properly, but there is damage to the brain that causes it to transmit incorrect electrical impulses to the muscles including both too many and too few signals. Without the correct cohesive electrical impulses to balance the opposing muscles of a joint, normal everyday tasks that most of us take for granted become very difficult to learn and perform. As exoskeletons become more advanced and practical, their applications have a lot of room for growth. Cerebral Palsy is one portion of the medical field that can benefit from the development of exoskeletons. As demonstrated with modern rehabilitation techniques, the application of an exoskeleton has the possibility of making the learning process and performance of many tasks easier and faster for both the patient as well as the doctor working with them. However, in order to appropriately apply the technology to the need, many changes in both the controls and the actual physical design of current devices need to be addressed. An exoskeleton for the purpose of helping cerebral palsy patients learn to walk is not limited to one specific form depending on the complexity of the tasks it is desired to assist with. However, there are a couple needs of this type of exoskeleton that are absolutely necessary. The size of the exoskeleton must be designed around the size of a child and not an adult. If the individual is learning to walk from the very beginning, the controls of the device will need to initially be able to take complete control over the individual's limbs to exercise the motions of walking. With the nature of an exoskeleton controlling the limbs of a person instead of simply assisting with current movements, the physical attachments of the exoskeleton must be improved from current designs in order to make movements of the exoskeleton and the body more parallel. Other features such as different muscle sensing techniques may also improve performance, but are not required. An exoskeleton that can help cerebral palsy patients learn to walk can also be applied to many other rehabilitation needs. / Master of Science