Ricardo Lopez

Design and control of hybrid actuation lower limb exoskeleton

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.

Altitude control improvement for a Quadrotor UAV using integral action in a sliding-mode controller

In this paper, a robust altitude control scheme is proposed for a mini-Quadrotor UAV system based on sliding mode controller with an integral action to eliminate the steady-state error induced by the boundary layer in order to achieve asymptotic convergence to the desired altitude with continuous control input. The proposed integral sliding mode controller is chosen to ensure the stability and robustness of overall dynamics during the altitude control at a desired height reference on the z-axis. Furthermore, we propose a Control Lyapunov Function (CLF) via Lyapunov theory in order to construct the robust stabilizing controller and demonstrate the stability of the z-dynamics of our system. A suitable sliding manifold is designed to achieve the control objective. At last, the theoretical results are supported by different simulation tests to verify the robustness and effectiveness of proposed robust control scheme in presence of bounded external disturbances.

Disturbance rejection for a Quadrotor aircraft through a robust control

This paper addresses the problem of designing and experimentally validating a nonlinear disturbance observer, focus on the attitude regulation control problem of a quad-rotor in presence of external disturbances. The proposed nonlinear observer scheme is based on the angular velocity measurements and the control inputs in order to compensate external disturbances. The stability analysis of the nonlinear observer scheme is proven via the use of Lyapunov theory. Finally, simulation and experimental results in a education platform are presented to show the effectiveness of the proposed nonlinear algorithm in presence of external disturbances.

A lower limb exoskeleton with hybrid actuation

In this paper, the lower limb exoskeleton uses a harmonic drive actuator and two pneumatic artificial muscles (PAMs). This hybrid actuation takes both advantages of harmonic drive and PAM. It provide high accuracy position control and compliant behavior. The disadvantages of each type of actuator are overcome. This exoskeleton is suitable for the strength augmentation of human lower limbs, such as the gait rehabilitation routine of hip and knee joints.

Simulation and robust trajectory-tracking for a Quadrotor UAV

In this article, a robust control algorithm using sliding modes is proposed for the efficient regulation on the trajectory tracking tasks, in the nonlinear, multivariable, quadrotor system model, that ensures the asymptotic convergence to a desired trajectory (reference signal - r(t)) in presence of all possible uncertainties and external disturbances. A smooth piecewise continuous function trajectory is proposed where the corresponding derivatives are bounded. Furthermore, we assume that the disturbances on the vehicle are bounded and the signal r(t) are available on line. The proposed algorithm employs a sliding surface based on the errors generated from the current state of the path in order to reach the desired reference r(t). The stability analysis of the closed-loop control system is proven via the use of Lyapunov theory. Finally, a numerical simulation of tracking a smooth trajectory is performed to demonstrate the validity and effectiveness of the proposed robust algorithm in presence of disturbances onto the vehicle.

Model and control of the ELLTIO with two degrees of freedom

Exoskeletons are robots attached for the extremities of the human body focused on increasing their strength, speed and performance primarily. The main applications are in the military, industry and medicine. The exoskeleton used in the rehabilitation of limbs because of accident or illness that cause little muscle activity or null. The ELLTIO (Exoskeleton for Lower Limb Training with Instrumented Orthoses) is an exoskeleton of two degrees of freedom for rehabilitation in ankle and knee. 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 are incorporated in the SEA actuators (Serial Elastics Actuators) to amplify the human force. Moreover contains sensors to estimate the angular position and velocity in joints to control the movement of the leg. The goal of this paper is the design of a PD control with gravity compensation based to dynamic model of experimental prototype. The prototype can be increased or decreased the human force as needed in different exercises, this will allow the user an evolutionary improvement to achieve a full rehabilitation as possible.

Real-time parameters identification for a quad-rotor mini-aircraft using adaptive control

In this article an adaptive controller is developed in order to estimate the inertia tensor, the mass and the wind parameters (considering wind as a parameter in the input) for the underactuated quad-rotor mini-aircraft. Experimental tests are performed in an educational platform. The proposed control scheme uses the parameter estimation issued from gradient type algorithm. Finally simulations and experimental results are included to illustrate the performance of the parameters identification for the quad-rotor helicopter.

Modeling and control of a lower limb exoskeleton with two degrees of freedom

The exoskeletons are bio-mechanisms used for amplification of strength, load heavy objects, increase speed and human resistance. for this reason the exoskeletons have many medical and military applications. The present paper concerns about construction and control of exoskeleton assisted by SEA (Series Elastic Actuators) having two degrees of freedom (knee and ankle). This exoskeleton offers a reduction in effort required by the user to reach and keep the stand up position as well as to performs some exercises like flexing the leg, etc.

Enhanced Robust Altitude Controller via Integral Sliding Modes Approach for a Quad-Rotor Aircraft: Simulations and Real-Time Results.

An enhanced robust altitude control scheme that indicates the improved performance than the typical sliding mode technique for a Quad-rotor aircraft vehicle is proposed in this article by including an integral action in the sliding mode control architecture in order to eliminate the steady-state error induced by the boundary layer and achieving asymptotic convergence to the desired altitude with continuous control input. The proposed integral sliding mode controller is chosen to ensure the stability and robustness of overall dynamics during the altitude control at a desired height reference on the z-axis. Furthermore, we propose a Control Lyapunov Function (CLF) via Lyapunov theory in order to construct the robust stabilizing controller and demonstrate the stability of the z-dynamics of our system. A suitable sliding manifold is designed to achieve the control objective. At last, the simulations and experimental studies are supported by different tests to demonstrate the robustness and effectiveness of the proposed enhanced robust altiutde control scheme subject to bounded external disturbances in outdoor environment.

Hybrid, discrete, non-linear, suboptimal force augmenting exoskeleton for the elbow joint

The design and implementation of a force augmenting exoskeleton for the elbow joint is presented in this paper. The force augmentation comes from electric motors as well as from pneumatic muscles that are the actuators of the device. This is the reason to say that the device is hybrid. Electric motors are more easily and precisely controlled than pneumatic muscles, however the last ones can move heavier weights. The autonomy of a device of this kind is reduced due to the energy expenditure of the two types of actuators employed. For this reason a suboptimal discrete nonlinear control was implemented which improves performance and lengthens considerably the operation time. A dynamical model of the device is also presented and a comparison between a PD+G and a suboptimal control is made. Simulation results are presented.