The hip muscles account for a great percentage of the total human energy expenditure during walking and many wearable devices have been developed in assisting the hip joint to reduce the metabolic Cost Of Transport (COT) for walking. However, the effectiveness of assisting the hip in only one direction (either flexion or extension) or both directions has not been systematically studied and the underlying muscle mechanics and energetics affected by the assistance are not well understood. In this study, human-exoskeleton simulation based optimizations were performed to find optimized hip assistance torque profiles for (1) unidirectional flexion assistance, (2) unidirectional extension assistance, and (3) bidirectional flexion and extension assistance. Our results show that the bidirectional assistance is the most effective in reducing the COT of walking (22.7% reduction) followed by flexion (19.2%) and extension (11.7%). The flexion assistance resulted in more COT saving than the output of its net work by 35.9%, which indicates that the negative work done (42.2% of its positive counterpart) also played an important role in reducing the COT. The bidirectional assistance also reduced the activations of the hip extensors to a great extent and shifted the activation pattern of the hip flexor (ilipsoas). These results can provide valuable information for optimal hip actuation (timing and profiles) and help exoskeleton designers make informed decisions.

Soft robotics is projected to have a significant impact on healthcare, industry, and the military to deliver assistance in rehabilitation, daily living activities, repetitive motion tasks, and human performance augmentation. Many attempts have been made for application-specific robotic joints, robots, and exoskeletons using various actuator types, materials, and designs. The progress of creating soft robotic systems can be accelerated if a set of actuators with defined characteristics were developed, similar to conventional robotic actuators, which can be assembled to create desired systems including exoskeletons and end effectors. This work presents such an attempt by designing a modular corrugated diaphragm actuator that can apply linear displacement, force, and bending motion. This modular actuator approach allows for creating various robotic joints by arranging them into different configurations. Numerical simulation, fabrication, and testing were carried out to evaluate the displacement, force, and bending characteristics of the corrugated diaphragm actuator as a single unit and in multi-unit arrays to understand their applicability for different scenarios. Actuator arrays that are configured in a serial and parallel manner were investigated. The results will be presented in terms of using this modular actuator concept to create single and multi-DOF joints, which will demonstrate the versatility of this modular actuator approach.

We propose a novel online model-based motion planning algorithm for a family of rehabilitation exoskeletons to improve transparency in user-guided operation. In this study, we assume that the short-term human movement intention can be embedded in the time-delay dimensions of motion signals. The model-based estimation is employed to obtain the interaction load between the dynamical subsystems respectively controlled by the human and exoskeleton. The objective of the proposed motion planning algorithm is to reduce the interaction load, which leads to the establishment of a least-square optimization problem. A Support Vector Regression (SVR) model, driven by the time-delayed motion data, is implemented to solve the optimization problem by generating the acceleration of tracking reference. The motion planning algorithm based on SVR can be combined with a variety of trajectory tracking controllers. To ensure the efficiency of the algorithm for online applications, we also design the SVR model so that its properties can be calculated recursively based on latest data sets. The performance and characteristics of the motion planning algorithm are then observed and discussed through the control simulations of a wearable wrist exoskeleton designed for pathological tremor alleviation. The results show that while the planned tracking reference can approximate the synthetic human movement intention, the motion planning accuracy can be limited by system disturbances, and the delay of signals caused by digital filters.

To physically assist workers in reducing musculoskeletal strain or to develop motor skills for patients with neuromuscular disabilities, recent research has focused on Exoskeletons (Exos). Designing active Exos is challenging due to the complex human geometric structure, the human-Exoskeleton wrench interaction, the kinematic constraints, and the selection of power source characteristics. Because of the portable advantages of passive Exos, designing a passive shoulder mechanism has been studied here. The study concentrates on modeling a 3D multibody upper-limb human-Exoskeleton, developing a procedure of analyzing optimal assistive torque profiles, and optimizing the passive mechanism features for desired tasks. The optimization objective is minimizing the human joint torques. For simulating the complex closed-loop multibody dynamics, differential-algebraic equations (DAE)s of motion have been generated and solved. Three different tasks have been considered, which are common in industrial environments: object manipulation, over-head work, and static pointing. The resulting assistive Exoskeleton’s elevation joint torque profile could decrease the specific task’s human shoulder torque. Since the passive mechanism produces a specific torque for a given elevation angle, the Exoskeleton is not versatile or optimal for different dynamic tasks. We concluded that designing a passive Exoskeleton for a wide range of dynamic applications is impossible. We hypothesize that augmenting an actuator to the mechanism can provide the necessary adjustment torque and versatility for multiple tasks.

Myoelectric signals from the human motor control system can improve the real-time control and neural-machine interface of robotic leg prostheses and exoskeletons for different locomotor activities (e.g., walking, sitting down, stair ascent, and non-rhythmic movements). Here we review the latest advances in myoelectric control designs and propose future directions for research and innovation. We review the different wearable sensor technologies, actuators, signal processing, and pattern recognition algorithms used for myoelectric locomotor control and intent recognition, with an emphasis on the hierarchical architectures of volitional control systems. Common mechanisms within the control architecture include 1) open-loop proportional control with fixed gains, 2) active-reactive control, 3) joint mechanical impedance control, 4) manual-tuning torque control, 5) adaptive control with varying gains, and 6) closed-loop servo actuator control. Based on our review, we recommend that future research consider using musculoskeletal modeling and machine learning algorithms to map myoelectric signals from surface electromyography (EMG) to actuator joint torques, thereby improving the automation and efficiency of next-generation EMG controllers and neural interfaces for robotic leg prostheses and exoskeletons. We also propose an example model-based adaptive impedance EMG controller including muscle and multibody system dynamics. Ongoing advances in the engineering design of myoelectric control systems have implications for both locomotor assistance and rehabilitation.

Exoskeletons are poised to provide motion assistance to aid in rehabilitation and compensate for muscle weaknesses, augment human performance, and reduce repetitive stress injuries in healthcare, industry, and occupation settings, respectively. Soft actuator enabled systems are gaining widespread attention due to their mechanical simplicity, low weight, and compliance to the human body. Regardless of promises shown, the progress for these systems is slow due to a wide variety of actuator types and geometries, which complicate designs and model predictive performance to create application-specific systems. Learning from conventional hard robotic actuator approaches, this paper investigates a modular actuator concept that can be used for creating many exoskeletons and is easily customized for fitting different sized humans, joint types, and application scenarios. The preliminary investigation details the development of an elbow exoskeleton by implementing a modular corrugated diaphragm actuator arranged in a serial configuration. Numerical simulation and experimental evaluations were carried out to investigate the torque, load-bearing, and motion characteristics of the exoskeleton. Results confirmed the viability of the concept by showing that the exoskeleton can provide assistive motion to a forearm and hand of average weight. Additionally, the exoskeleton is able to apply continuous passive motion to an elbow joint, which can be used in rehabilitation settings.

In this paper, a customized optical force sensor is developed for an application with a cable-driven leg exoskeleton. Sensors are vital components of cable-driven, exoskeletal robotic systems, which require real-time and accurate measurement of cable tensions. While these systems’ accuracy is a consideration, the added weight, volume, and complexity of the system must is an essential part of widespread adoption for wearable applications. These sensors can also be costly, which is undesirable. An optical force sensor has the advantages of being lightweight, lower in manufacturing cost, and easy to incorporate within the exoskeleton architecture. We designed a sensor to accommodate the expected force profiles and magnitudes during gait while wearing the Cable-Driven Active Leg Exoskeleton (C-ALEX) during a walking task. We carried out four different calibration tests with dynamic loading of the sensors from 10N to 40N. Once a sensor calibration was established, the optical sensor’s performance was compared to a traditional load cell in validation tests. Both components were used in an assist-as-needed force controller in a walking task with a user, with the optical force sensor incorporated into the C-ALEX exoskeleton arms. Comparing the sensor responses to the command tension forces, the results show a root-mean-square error (RMSE) of 0.9595N ± 0.5360N.

Cable-driven exoskeletons add minimal inertia and restrictions to the user’s leg while still providing feedback and quantitative measures of the user’s performance. However, cable robots require at least n + 1 cables to control n degrees-of-freedom, i.e., they require more actuators than the leg’s degrees-of-freedom, challenging their widespread adoption as wearable technology. The state-of-the-art in this field aims to reduce the number of actuated motors. In this paper, we design and evaluate a “single motor-driven” leg exoskeleton prototype based on the Cable-driven Active Leg EXoskleton (C-ALEX). The prototype consists of four crank-spring mechanisms and a crankshaft designed using epicycle analysis. The epicycle analysis is performed using discrete Fourier transform (DFT) and sine curve fitting (SCF). While DFT suggests the maximum number of epicycles to imitate the target waveform, a large number of nested epicycles is challenging to design and manufacture for implementation. To validate the epicycle-guided design, we constructed a simple crankshaft model using one epicycle. Our proposed simplified model predicted and produced the joint angles calculated from the inverse and forward kinematics of a cable-driven leg exoskeleton with multiple motors. To our knowledge, this is the first multi-cable driven exoskeleton powered by a single actuator that is designed to provide continuous assistance to the user.

Design and evaluation of exoskeletons is often a time consuming and costly process that involves prototyping, human testing, and multiple design iterations. For active exoskeletons, the primary challenge is to detect the wearer’s movement intent and provide potent assistance, which often requires sophisticated control algorithms. The goal of this study is to integrate human musculoskeletal models with robot modeling and control for virtual human-in-the-loop evaluation of exoskeleton design and control. We present potential strategies for assisting various human motions such as squatting, lifting, walking, and running. Several exoskeleton designs (for back, upper extremity, and lower extremity) and their control methods are evaluated with an integrated human-in-the-loop simulation approach to study their functionalities and biomechanical effects on the wearer’ musculoskeletal system. We hope this simulation paradigm can be utilized for virtual design and evaluation of exoskeletons and pave the way to build or optimize exoskeletons.

Over the past decade, wearable robotics and exoskeletons have been gaining recognition in the field of medical, assistive and augmentative robotics and have led to numerous new innovative mechanisms and designs. Due to fast-paced research activities, the critical importance and performance of established mechanisms such as wrap spring clutch/brake, Wafer Disc Brakes have been overlooked or used ineffectively. This paper describes a practical design approach that will enable the designer to choose a mechanism based on the application of the device, which will promote overall growth in current technology. The Legged Anthropomorphic Robotic Rehabilitation Exoskeleton (LARRE) project used this approach to design, manufacture, and test the knee joint for ground-level walking. This paper provides the reasoning behind the selection of wrap spring clutch, its evaluation, and testing standards as the knee joint. A thorough literature review was conducted to understand the current state of the art. This project collected a rich set of biomechanical data to ensure that the mechanism will produce the right moments and range of motions during walking. To ensure that our mechanism meets the requirements, the mechanism was put through a wide range of stress tests. The paper establishes a methodology to choose a mechanism for an exoskeleton’s joint based on the desired requirements. The outcome of this paper is an analytical based design approach that can be used by other researchers to impart additional traits and weights, which will aid in the development of exoskeleton design.

This paper builds up on a recently developed novel planar inter-joint finger kinematic model for human hand configurations, which applies to the realization of a naturalistic human finger motion. The model is a function of the finger anthropomorphic data and is derived based on the geometry of a hand shape grasping a virtual cylindrical object. Unlike well-known inverse kinematics models, the inter-joint model is capable of describing the natural rotation configuration of the joints of a long finger independently by a single parameter, the radius of the cylindrical object. A novel inter-finger coordination model, based on the inter-joint model is proposed and experimentally tested. The preliminary results show that the model has the potential to simulate naturalistic human hand grasping motion. The merit of the proposed inter-finger coordination model is in its simplicity when used in hand-exoskeleton design assessment and naturalistic hand trajectory planning applications, among others. We would like to note that this paper is the first step towards exploring future simplified combined design-control strategies for the development and assessment of mechanical limbs for naturalistic movement.

This paper presents the design of an exoskeleton glove system for people who suffer from the brachial plexus injuries in an effort to restore their lost grasping functionality. The robotic system consists of an embedded controller and a portable glove system. The glove system consists of Linear Series Elastic Actuators (SEA), Rotary SEA and optimized finger linkages to provide motion to each finger and a coupled motion of the hand and the wrist. The design is based on various functionality requirements such as being lightweight and portable for activities of daily living, especially for grasping. The contact force at each fingertip and bending angle of each finger are measured for future implementation of intelligent control algorithms for autonomous grasping. To provide better flexibility and comfort for the users, abduction and adduction of each finger as well as flexion of the thumb were taken into consideration in the design. The glove system is adjustable for different hand sizes. The micro-controllers and batteries are integrated on the forearm in order to provide a completely portable design solution.

Efficient human-machine interface (HMI) for exoskeletons remains an active research topic, where sample methods have been proposed including using computer vision, EEG (electroencephalogram), and voice recognition. However, some of these methods lack sufficient accuracy, security, and portability. This paper proposes a HMI referred as integrated trigger-word configurable voice activation and speaker verification system (CVASV). The CVASV system is designed for embedded systems with limited computing power that can be applied to any exoskeleton platform. The CVASV system consists of two main sections, including an API based voice activation section and a deep learning based text-independent voice verification section. These two sections are combined into a system that allows the user to configure the activation trigger-word and verify the user’s command in real-time.

In this paper, we present a novel variable-stiffness joint for a walking assistance ankle exoskeleton. This design is adaptive to user needs in the sense that it can aid in different types of motion, i.e. walking, jogging and running, through different stiffness levels. We created a concept that utilizes multiple springs that could contort into different orientations in order to create a fully compliant ankle exoskeleton. The design provides a wide range of assistive torques without constant replacement of parts or springs for each type of activity. This design can be utilized by a wide range of people engaging in different types of activities. Those could be individuals with an active lifestyle or the elderly suffering from muscular atrophy.

With the duties and responsibilities of the military, they are on the cutting edge of R&D and the latest and greatest technologies. One significant problem effecting thousands of soldiers are injuries to the lower limbs, specifically the knees, as a result of high impact to the joints and muscles. Through the research of biomechanics and ergonomics during human locomotion of running, cause and effects fatigue, muscular activation during running, gait cycle force analysis, and biomimicry of kangaroos, we were able to identify lower limb exoskeletons as a viable solution to the problem. The purpose of this research was to develop a relatively inexpensive prototype of a passive lower limb exoskeleton to aid in injury mitigation and muscular efficiency for soldiers. The hypothesis was that a lower limb exoskeleton would reduce/mitigate injuries by reducing stride length and increases stride frequency to lower impact on the knees while running. The prototype was tested by one participant on a 2-mile course with two load variations tested while running. The key results were seen from the spring systems potential to increase average stride cadence/frequency by 6–14% and reduce impact on joints and muscles by increasing the number of steps and reducing high center of gravity oscillation by 13–27%. Furthermore, this study provides evidence and research that proves that a passive lower limb exoskeleton design, which increases stride frequency and reduces stride length, can mitigate injuries to the lower limbs when running with weight by reducing the impact forces on the knees and improving running economy.

In this paper, we present the design, modeling and, fabrication of a soft bending actuator that combines casting techniques and additive manufacturing. We performed tests to evaluate the bending actuator’s angular deflection and tip force. We demonstrated flexibility in the process by varying the bladder material. We also showed the actuator’s resilience to damage by cutting and puncturing the exoskeleton prior to operation. Finally, we integrated the bending actuator into a three-finger gripper configuration and performed a gripping test for four different objects with various weights and shapes. Results show that the curvature and force obtained in these actuators are comparable to other proposed bending actuators with a faster and more adaptable fabrication process. With these results we demonstrate that fast, effective, and versatile fabrication of soft robotic components can be attained by combining casting and additive manufacturing techniques.

This paper presents the design of a phase-based robust oscillator for wearable robots that assists the human performing periodic or repetitive tasks. The robustness of the phase oscillator controller is evaluated by finding bounds for perturbations that guaranteed the stability of the output. Then, the Lyapunov redesign method is applied to construct a robust controller using a bounding function which can handle the uncertainties such as noise and perturbations in the overall human-robot system. The robust controller produces a bounded control signal to modify the amplitude and frequency of the resulting second-order oscillator to modulate the stiffness and damping properties. In this paper, the focus is put on the wearable robot that assists human hip joint while performing periodic activities such as walking. The proposed approach is verified through a simple pendulum experiment. The results show that a better limit cycle can be obtained with Lyapunov redesigned phase oscillator which controls the radial spread of the steady state. Finally, the potential of the proposed approach for hip assistance in a healthy subject wearing HeSa (Hip Exoskeleton for Superior Assistance) during periodic activities are discussed.

The planar dual spring-loaded inverted pendulum (dual-SLIP) model is a well-established passive template of human walking on flat ground. This paper applies an actuated extension of the model to walking on inclines and declines to evaluate how well it captures the behavior observed in human slope walking. The motivation is to apply the template to improve control of humanoid robot walking and/or intent detection in exoskeleton-assisted walking. Gaits of the actuated planar dual-SLIP model are found via the solution of a constrained nonlinear optimization problem in ten parameters. The majority of those parameters define the actuation scheme that injects energy for incline walking and absorbs energy for decline walking to achieve periodic, nonconservative gaits. Solution gaits across the speed range of 1.0 to 1.6 m s and slope range of −10 to 10 degrees exhibit some of the characteristics of human walking, such as the effect of slope on stance duration, step frequency, and step length. Efforts to reduce the number of parameters optimized by enforcing relationships observed in the solution gaits proved unsuccessful, suggesting that future work must trade off model complexity with fidelity of representation of human behavior.

This study considers the development of an assist-as-need torque controller for an exoskeleton for stroke rehabilitation. Studies have shown that active patient participation improves the patient’s recovery from stroke. Assist-as-need control, providing the patient with the assistance they need to complete a task, is desirable, as the assistance can be varied to maximise patient participation. However, research is limited, and current methods cannot guarantee optimal assistance as non-zero assistive forces are still provided to subjects that are capable of completing the task unassisted. This study proposes a control system to vary and optimise the assistance for a subject based on their capabilities. A particle filter developed from previous research is used to estimate the subject’s voluntary effort. The assistive torque is determined from a target torque and the voluntary effort. The controller is shown to be effective, as zero assistance is provided to a subject capable of completing the task unassisted. Additionally, the assistance will increase if the subject fatigues. Using the estimate of the subject’s strength, the assistive torque can be accurately set to maximise a patient’s participation, and therefore, the assist-as-need controller can lead to improved therapeutic results.

With the goal of developing a spatial linkage exoskeleton for a shape-adaptive mobile robot, capable of navigating obstacle-laden environments through changes in geometry, initial research focused on the nature of axis transformations, and parameters affecting linkages, such as the Denavit-Hartenberg (DH) parameters. Building on this background, angulated linkages are developed such that a series of scissor pairs, two angulated linkages connected at their midpoints, forming a closed-loop. Using the DH parameters, the geometries are considered in the development of a planar model. A kinematic model is also developed to replicate the design in future work. A linkage was designed using SolidWorks, and then imported into MATLAB’s Simscape Multibody software where a visual, analytical model was developed. The nominal planar model acts as the basis of a spatial model. Using the spatial model, initial prototypes were built to verify the virtual model. A concept for an actuation mechanism is discussed, with a prototype built to identify any limitations. Through experimentation and analysis of the prototypes, areas for improvement in the design are identified. Future work is discussed to further mature the design and development of this solution.