Disturbance-Estimated Adaptive Backstepping Sliding Mode Control of a Pneumatic Muscles-Driven Ankle Rehabilitation Robot.

A rehabilitation robot plays an important role in relieving the therapists' burden and helping patients with ankle injuries to perform more accurate and effective rehabilitation training. However, a majority of current ankle rehabilitation robots are rigid and have drawbacks in terms of complex structure, poor flexibility and lack of safety. Taking advantages of pneumatic muscles' good flexibility and light weight, we developed a novel two degrees of freedom (2-DOF) parallel compliant ankle rehabilitation robot actuated by pneumatic muscles (PMs). To solve the PM's nonlinear characteristics during operation and to tackle the human-robot uncertainties in rehabilitation, an adaptive backstepping sliding mode control (ABS-SMC) method is proposed in this paper. The human-robot external disturbance can be estimated by an observer, who is then used to adjust the robot output to accommodate external changes. The system stability is guaranteed by the Lyapunov stability theorem. Experimental results on the compliant ankle rehabilitation robot show that the proposed ABS-SMC is able to estimate the external disturbance online and adjust the control output in real time during operation, resulting in a higher trajectory tracking accuracy and better response performance especially in dynamic conditions

A new fiber braided soft bending actuator for singer exoskeleton

This thesis presents a design, development and analysis of a novel bending-type pneumatic soft actuator as a drive source for a finger exoskeleton. Soft actuators are gaining momentum in robotic applications due to their simple structure, high compliance, high power-to-weight ratio and low production cost. Smaller and lighter soft actuator that can provide higher power transmission at lower operating air pressure will benefit finger actuation mechanism compared to motorized cable and pulley-driven finger rehabilitation devices. In this study, a soft actuator with new bending method is proposed. It is based on fibre reinforcement of two fibre braided angles of contraction and extension characteristics combined in a single-chamber cylindrical actuator. Another four design parameters identified that affect the bending motion and the actuating force were the air chamber diameter, position of fibre layer reinforcement, fibre reinforcement coverage angle, and silicone rubber materials. Geometrical and material parameters were varied in Finite Element Method (FEM) simulation for design optimization and some parameters were tested experimentally to validate the FEM models. The effects of fibre angles (contraction and extension) on the bending motion and force were analyzed. The optimized actuator can generate bending motion up to 131° bending angle and the end tip of the actuator can make contact with the other base tip at only 240 kPa given input pressure. Both displacement simulation and experimental testing results matched closely. Maximum bending force of 5.42 N was generated at 350 kPa. A wearable finger soft exoskeleton prototype with five optimized bending actuators was tested to drive finger flexion motion of eight healthy subjects with simulated paralysis conditions. The finger soft exoskeleton demonstrated the ability to provide gripping force of 3.61 ± 0.22 N, gained at 200 kPa given air pressure. The device can successfully provide assistance to weak fingers in gripping at least 240 g object. It shows potential in helping people with weakened finger muscle to be more independent in their finger rehabilitation exercise

Design of a shape memory alloy actuator for soft wearable robots

Soft robotics represents a paradigm shift in the design of conventional robots; while the latter are designed as monolithic structures, made of rigid materials and normally composed of several stiff joints, the design of soft robots is based on the use of deformable materials such as polymers, fluids or gels, resulting in a biomimetic design that replicates the behavior of organic tissues. The introduction of this design philosophy into the field of wearable robots has transformed them from rigid and cumbersome devices into something we could call exo-suits or exo-musculatures: motorized, lightweight and comfortable clothing-like devices. If one thinks of the ideal soft wearable robot (exoskeleton) as a piece of clothing in which the actuation system is fully integrated into its fabrics, we consider that that existing technologies currently used in the design of these devices do not fully satisfy this premise. Ultimately, these actuation systems are based on conventional technologies such as DC motors or pneumatic actuators, which due to their volume and weight, prevent a seamless integration into the structure of the soft exoskeleton. The aim of this thesis is, therefore, to design of an actuator that represents an alternative to the technologies currently used in the field of soft wearable robotics, after having determined the need for an actuator for soft exoskeletons that is compact, flexible and lightweight, while also being able to produce the force required to move the limbs of a human user. Since conventional actuation technologies do not allow the design of an actuator with the required characteristics, the proposed actuator design has been based on so-called emerging actuation technologies, more specifically, on shape memory alloys (SMA). The mechanical design of the actuator is based on the Bowden transmission system. The SMA wire used as the transducer of the actuator has been routed into a flexible sheath, which, in addition to being easily adaptable to the user's body, increases the actuation bandwidth by reducing the cooling time of the SMA element by 30 %. At its nominal operating regime, the actuator provides an output displacement of 24 mm and generates a force of 64 N. Along with the actuator, a thermomechanical model of its SMA transducer has been developed to simulate its complex behavior. The developed model is a useful tool in the design process of future SMA-based applications, accelerating development ix time and reducing costs. The model shows very few discrepancies with respect to the behavior of a real wire. In addition, the model simulates characteristic phenomena of these alloys such as thermal hysteresis, including internal hysteresis loops and returnpoint memory, the dependence between transformation temperatures and applied force, or the effects of latent heat of transformation on the wire heating and cooling processes. To control the actuator, the use of a non-linear control technique called four-term bilinear proportional-integral-derivative controller (BPID) is proposed. The BPID controller compensates the non-linear behavior of the actuator caused by the thermal hysteresis of the SMA. Compared to the operation of two other implemented controllers, the BPID controller offers a very stable and robust performance, minimizing steady-state errors and without the appearance of limit cycles or other effects associated with the control of these alloys. To demonstrate that the proposed actuator together with the BPID controller are a valid solution for implementing the actuation system of a soft exoskeleton, both developments have been integrated into a real soft hand exoskeleton, designed to provide force assistance to astronauts. In this case, in addition to using the BPID controller to control the position of the actuators, it has been applied to the control of the assistive force provided by the exoskeleton. Through a simple mechanical multiplication mechanism, the actuator generates a linear displacement of 54 mm and a force of 31 N, thus fulfilling the design requirements imposed by the application of the exoskeleton. Regarding the control of the device, the BPID controller is a valid control technique to control both the position and the force of a soft exoskeleton using an actuation system based on the actuator proposed in this thesis.La robótica flexible (soft robotics) ha supuesto un cambio de paradigma en el diseño de robots convencionales; mientras que estos consisten en estructuras monolíticas, hechas de materiales duros y normalmente compuestas de varias articulaciones rígidas, el diseño de los robots flexibles se basa en el uso de materiales deformables como polímeros, fluidos o geles, resultando en un diseño biomimético que replica el comportamiento de los tejidos orgánicos. La introducción de esta filosofía de diseño en el campo de los robots vestibles (wearable robots) ha hecho que estos pasen de ser dispositivos rígidos y pesados a ser algo que podríamos llamar exo-trajes o exo-musculaturas: prendas de vestir motorizadas, ligeras y cómodas. Si se piensa en el robot vestible (exoesqueleto) flexible ideal como una prenda de vestir en la que el sistema de actuación está totalmente integrado en sus tejidos, consideramos que las tecnologías existentes que se utilizan actualmente en el diseño de estos dispositivos no satisfacen plenamente esta premisa. En última instancia, estos sistemas de actuaci on se basan en tecnologías convencionales como los motores de corriente continua o los actuadores neumáticos, que debido a su volumen y peso, hacen imposible una integraci on completa en la estructura del exoesqueleto flexible. El objetivo de esta tesis es, por tanto, el diseño de un actuador que suponga una alternativa a las tecnologias actualmente utilizadas en el campo de los exoesqueletos flexibles, tras haber determinado la necesidad de un actuador para estos dispositivos que sea compacto, flexible y ligero, y que al mismo tiempo sea capaz de producir la fuerza necesaria para mover las extremidades de un usuario humano. Dado que las tecnologías de actuación convencionales no permiten diseñar un actuador de las características necesarias, se ha optado por basar el diseño del actuador propuesto en las llamadas tecnologías de actuación emergentes, en concreto, en las aleaciones con memoria de forma (SMA). El diseño mecánico del actuador está basado en el sistema de transmisión Bowden. El hilo de SMA usado como transductor del actuador se ha introducido en una funda flexible que, además de adaptarse facilmente al cuerpo del usuario, aumenta el ancho de banda de actuación al reducir un 30 % el tiempo de enfriamiento del elemento SMA. En su régimen nominal de operaci on, el actuador proporciona un desplazamiento de salida de 24 mm y genera una fuerza de 64 N. Además del actuador, se ha desarrollado un modelo termomecánico de su transductor SMA que permite simular su complejo comportamiento. El modelo desarrollado es una herramienta útil en el proceso de diseño de futuras aplicaciones basadas en SMA, acelerando el tiempo de desarrollo y reduciendo costes. El modelo muestra muy pocas discrepancias con respecto al comportamiento de un hilo real. Además, es capaz de simular fenómenos característicos de estas aleaciones como la histéresis térmica, incluyendo los bucles internos de histéresis y la memoria de puntos de retorno (return-point memory), la dependencia entre las temperaturas de transformacion y la fuerza aplicada, o los efectos del calor latente de transformación en el calentamiento y el enfriamiento del hilo. Para controlar el actuador, se propone el uso de una t ecnica de control no lineal llamada controlador proporcional-integral-derivativo bilineal de cuatro términos (BPID). El controlador BPID compensa el comportamiento no lineal del actuador causado por la histéresis térmica del SMA. Comparado con el funcionamiento de otros dos controladores implementados, el controlador BPID ofrece un rendimiento muy estable y robusto, minimizando el error de estado estacionario y sin la aparición de ciclos límite u otros efectos asociados al control de estas aleaciones. Para demostrar que el actuador propuesto junto con el controlador BPID son una soluci on válida para implementar el sistema de actuación de un exoesqueleto flexible, se han integrado ambos desarrollos en un exoesqueleto flexible de mano real, diseñado para proporcionar asistencia de fuerza a astronautas. En este caso, además de utilizar el controlador BPID para controlar la posición de los actuadores, se ha aplicado al control de la fuerza proporcionada por el exoesqueleto. Mediante un simple mecanismo de multiplicación mecánica, el actuador genera un desplazamiento lineal de 54 mm y una fuerza de 31 N, cumpliendo así con los requisitos de diseño impuestos por la aplicación del exoesqueleto. Respecto al control del dispositivo, el controlador BPID es una técnica de control válida para controlar tanto la posición como la fuerza de un exoesqueleto flexible que use un sistema de actuación basado en el actuador propuesto en esta tesis.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: Fabio Bonsignorio.- Secretario: Concepción Alicia Monje Micharet.- Vocal: Elena García Armad

A Review Study for Robotic Exoskeletons Rehabilitation Devices

Nowadays, robotic exoskeletons demonstrated great abilities to replace traditional rehabilitation processes for activating neural abilities performed by physiotherapists. The main aim of this review study is to determine a state-of-the-art robotic exoskeleton that can be used for the rehabilitation of the lower limb of people who have mobile disabilities as a result of stroke and musculoskeletal conditions. The study presented the anatomy of the lower limb and the biomechanics of human gait to explain the mechanism of the limb, which helps in constructing a robotic exoskeleton. A state-of-the-art review of more than 100 articles related to robotic exoskeletons and their constructions, functionality, and rehabilitation capabilities are accurately implemented. Moreover, the study included a review of upper limb rehabilitation that has been studied locally and successfully applied to patients who exhibited significant improvements. Results of recent studies herald an abundant future for robotic exoskeletons used in the rehabilitation of the lower extremity. Significant improvement in the mechanism and design, as well as the quality, were observed. Also, impressive results were obtained from the performance when used by patients. This study concludes that working and improving the robotic devices continuously in accordance with the cases are necessary to be treated with the best results and the lowest cost

Lower limb exoskeleton robot and its cooperative control: A review, trends, and challenges for future research

Effective control of an exoskeleton robot (ER) using a human-robot interface is crucial for assessing the robot's movements and the force they produce to generate efficient control signals. Interestingly, certain surveys were done to show off cutting-edge exoskeleton robots. The review papers that were previously published have not thoroughly examined the control strategy, which is a crucial component of automating exoskeleton systems. As a result, this review focuses on examining the most recent developments and problems associated with exoskeleton control systems, particularly during the last few years (2017–2022). In addition, the trends and challenges of cooperative control, particularly multi-information fusion, are discussed