In this article, two types of actuators are applied for a lower limb exoskeleton. They are DC motors with the harmonic drive and the pneumatic artificial muscles. This combination takes advantages of both the harmonic drive and the pneumatic artificial muscle. It provides both high accuracy position control and high ratio of strength and weight. The shortcomings of the two actuators are overcome by the hybrid actuation, for example, low control accuracy and modeling difficult of pneumatic artificial muscle, compactness, and structural flexibility of DC motors. The design and modeling processes are discussed to show the proposed exoskeleton can increase the strength of human lower limbs. Experiments and analysis of the exoskeleton are given to evaluate the effectiveness of the design and modeling.

The development of high-precision tasks, such as machining, needs a positioning device for the cutting tool with the smallest possible error. Multiple design factors need to be considered to ensure a mechatronic device successfully performs such tasks. One of these factors may be attributed to the control scheme, which is responsible for controlling the position of the machine. In view of the importance of designing a good control scheme for a robotic system, in this article, we propose a new extension of the robust integral sign of the error (RISE) for the positioning device a parallel kinematic machine (PKM). This extension consists in including a nominal feedforward term based on the inverse dynamic model of the robot and replacing the RISE fixed feedback gains with adaptive ones. The RISE part of the proposed controller ensures semiglobal asymptotic stability. Moreover, it can accommodate sufficiently smooth bounded disturbances. The feedforward part cancels the nonlinearities of the system, improving the tracking performance of the controller. The adaptive feedback gains produce corrective actions when an increase in the tracking errors is due to the contact forces that occur during the machining process. A Lyapunov-based stability analysis is conducted to prove the semiglobal asymptotic stability of the proposed control solution. To show its effectiveness, real-time experiments are performed for two case studies; the first one is on a free motion trajectory and the second on machining experiments under three different forward speeds on SPIDER4, a redundantly actuated PKM.

ResumenLos exoesqueletos mecánicos son robots acoplados a las extremidades del cuerpo humano enfocados en el incremento de su fuerza, velocidad y rendimiento principalmente. Las principales aplicaciones son en la milicia, en la industria y en la medicina. El exoesqueleto se puede utilizar para la rehabilitación de las extremidades cuando por causas de algún accidente o enfermedad se tiene una actividad muscular reducida o nula. En este artículo se presenta un exoesqueleto de dos grados de libertad para realizar ejercicios de rehabilitación para tobillo y rodilla. El diseño y fabricación del exoesqueleto está basado en la instrumentación de una ortesis del miembro inferior derecho. El Exoesqueleto utiliza sensores que estiman la fuerza producida por el humano y se encuentran incorporados en los actuadores de tipo SEA (Series Elastic Actuator) que se utilizan para amplificar la fuerza humana. Además mediante sensores se estima la posición y velocidad angular de las articulaciones, que se utilizan para controlar el movimiento de la pierna. En el artículo se presentan: un estudio del modelo dinámico del exoesqueleto y de los actuadores acoplados por medio del método de perturbaciones singulares, el diseño de un control basado en la suma de fuerzas generadas por el humano y el exoesqueleto, el diseño y fabricación del prototipo experimental y sus actuadores. Se realizaron simulaciones que muestran el buen desempeño del controlador propuesto. Los resultados experimentales muestran que existe una amplificación de la fuerza generada por el portador y amplificada por la mecánica del exoesqueleto, ofreciendo una disminución en el esfuerzo del usuario para mantenerse de pie y realizar ejercicios de flexión y extensión de las articulaciones. De manera que la amplificación de la fuerza puede aumentarse o disminuirse según se necesite, permitiendo al usuario una mejora evolutiva hasta llegar a la rehabilitación completa.AbstractExoskeletons are robots attached to the extremities of the human body focused on increasing their strength, speed and performance primarily. The applications are in the military, industry and medical. The exoskeleton can be used for the rehabilitation of limbs because of accident or illness that can cause little muscle activity or null. This article presents an exoskeleton of two degrees of freedom that is used to ankle and knee exercise rehabilitation. The design and manufacture of the exoskeleton is based on the instrumentation of a right lower limb orthoses. The exoskeleton contains sensors to estimate the force produced by a human and contains SEA actuators (Serial Elastics Actuators) that used to amplify the human force. Also contains sensors to estimate the position and angular velocity in joints. This paper presents in general: a study of the dynamic model of the exoskeleton and actuators coupled through the singular perturbation method, the design of a control based on the sum of forces generated by the human and the exoskeleton, and the design and manufacture of an experimental prototype. The simulation result shows that the sum of forces between the human and the exoskeleton is controlled to obtain a desired angular position of the joints (knee and ankle). Experimental results show that exist a human force amplification generated by the exoskeleton, providing a reduction in the patient's effort to remain standing and bending exercises. Then force amplification can be increased or decreased as needed in different workouts that will allow the user an evolutionary improvement to achieve a full rehabilitation