Hala Rifai

Lower-Limb Movement Assistance through Wearable Robots: State of the Art and Challenges

Recent technological advances made necessary the use of robots in various types of applications. Unlike traditional robot-like scenarios dedicated to industrial applications with repetitive tasks, the current focus of attention is on applications that require close human interactions. One of the main fields of such applications concerns assisting and rehabilitating of dependent/elderly persons. In this study, the state-of-the-art of the main research advances in lower-limbs human assistance is presented. This includes a review on research covering mainly lower-limb actuated exoskeletons. Some case studies related to full-limb exoskeletons are presented as well. Lower-limb movement restoration using functional electrical stimulation and treadmill-based rehabilitation devices is also investigated. In addition, the seamless integration of wearable robots in ambient intelligence spaces appears as one of the major challenges for ubiquitous environments and ambient assisted living. Some open issues related to this integration are discussed in this paper.

Nonlinear disturbance observer based sliding mode control of a human-driven knee joint orthosis

The present paper deals with the control of a knee joint orthosis intended to be used for rehabilitation and assistive purposes. A model, integrating human shank and orthosis, is presented. To reduce the influence of the uncertainties in muscular torque modeling on the system control, a nonlinear observer is proposed to estimate the muscular torque developed by the wearer. Additionally, a robust terminal sliding mode control approach combined with the nonlinear observer is presented. To illustrate the effectiveness of the proposed control method, a comparison with two control methods, basic sliding mode and sliding mode with nonlinear observer, are also given. The asymptotic stability of the presented approaches and observer convergence are proved by means of a Lyapunov analysis. Furthermore, the proof of advantage of the robust terminal sliding mode control method with the nonlinear observer (improving the tracking precision and reducing the required time for eliminating external disturbances) is proposed as well. The experiment results show that the robust terminal sliding mode control approach combined with the nonlinear observer has a significant advantage with respect to the position tracking and robustness regarding the modeling identification errors and external disturbances. This paper deals with the control of a knee joint exoskeleton for rehabilitation purposes.An observer is proposed to estimate the muscular torque developed by the wearer.A robust terminal sliding mode control method combined with the observer is presented.Asymptotic stability is proved by means of a Lyapunov analysis.Experiment tests were conducted with three subjects.

Adaptive control of a human-driven knee joint orthosis

The paper concerns the control of a lower limb orthosis acting on the knee joint level. Therefore, a model of the shank-orthosis system is given considering the human effort as an external torque acting on the system. A model reference adaptive control law is developed and applied to the orthosis in order to make the system (shank-orthosis) track a desired trajectory predefined by a rehabilitation doctor. The main advantage of this control law is the on-line parameters regulation allowing to ensure the best performance of the system. A Lyapunov-based analysis is performed to prove the input-to-state stability of the orthosis with respect to a bounded human torque. The performance of the system is then shown through some simulations.

A brief synthesis of QoS-QoE methodologies

This paper presents an overview of some existing techniques of Quality of Service QoS and Quality of Experience QoE. QoS stands for the quality of the network in terms of transporting data with a minimum of delay and packet loss and a maximum of bandwidth. The extremum values depend surely of the provided service. QoE defines the quality perceived by the user and is assessed at the terminal level. It can be computed through objective and subjective ways. A comparison of the two techniques as well as an improvement of the service by combining them are also addressed.

Haptic-based bilateral teleoperation of underactuated Unmanned Aerial Vehicles

Abstract The bilateral teleoperation of underactuated aerial vehicles is addressed. A force feedback joystick is used to remotely pilot the aircraft and reflect an image of the environment to the operator. This feedback is a virtual force, function of the distance to an obstacle or the rate of approaching it. It can be computed using the measurements of on-board sensors ( i.e. telemetric or optic flow). Input to State Stability of the teleoperation loop with respect to bounded or dissipative virtual environment forces is established based on Lyapunov analysis.

Bounded control of a flapping wing micro drone in three dimensions

This paper presents a bounded control of a flapping micro aerial vehicle (MAV) in three dimensions. First, a simplified model of the flapping MAV is presented aiming to test the control law. The averaging theory shows that for high frequency systems, only the mean aerodynamic forces and torques over a period affect the movement of the body. Therefore, a bounded nonlinear state feedback control, calculated using the averaged model, is applied to the time varying system in order to stabilize it at a desired position in hovering mode. The robustness of the control is tested with respect to the aerodynamic coefficient and to external disturbances.

Bounded control of an actuated lower limb orthosis

Wearable robots have defined a new horizon for elderly and disabled people, to regain control of their limbs, as well as for healthy people, to increase their abilities of hard missions execution. The present paper deals with the control of a lower limb orthosis applied at the knee joint level for rehabilitation purposes. A bounded control torque is developed in order to guarantee the asymptotic stability of the knee orthosis. The control law respects the physical constraints of the system. Moreover, it is robust with respect to external disturbances. The effectiveness of the control torque is tested in real-time using the EICOSI orthosis of the LISSI Lab.

EMG based approach for wearer-centered control of a knee joint actuated orthosis

This paper presents a new human-exoskeleton interaction approach to provide torque assistance of the lower limb movements upon wearers intention. The exoskeleton interacts with the wearer; the shank-foot orthosis system behaves as a second order dynamic system with gravity and elastic torque balance. The intention of the wearer is estimated by using a realistic musculoskeletal model of the muscles actuating the knee joint. The identification process concerns the inertial parameters of the shank-foot, the exoskeleton and the musculotendon parameters. Real-time experiments, conducted on a healthy subject during flexion and extension movements of the knee joint, have shown satisfactory results in terms of tracking error, intention detection and assistance torque generation. This approach guarantees asymptotic stability of the shank-foot-exoskeleton and adaptation to human-exoskeleton interaction. Moreover, the proposed control law is robust with respect to external disturbances.

Output feedback Control of an Actuated Lower Limb Orthosis with Bounded Input

Purpose – The purpose of this paper is the control of lower limb orthosis acting at the knee joint level for a passive rehabilitation purpose. Design/methodology/approach – A control law, based on a saturated proportional derivative controller, is proposed in order to drive the shank-foot-orthosis system along a desired trajectory. Findings – The proposed control law is tested in real time using the orthosis EICOSI of the LISSI-Laboratory. The experiments show that the proposed control law is capable of providing satisfactory trajectory tracking performance given only the knee joint angle measurement. Moreover, the control law is robust with respect to external disturbances. Originality/value – Robust control of an actuated lower limb orthosis.

Bounded control of an underactuated biomimetic aerial vehicle-Validation with robustness tests

Flapping wing Micro Aerial Vehicles (FMAVs) have recently emerged as a promising challenge lying on the progress of the avionics technologies. The present paper deals with the development of simple control laws for an embedded implementation on a biomimetic MAV, aiming to control its attitude and position. The control laws are bounded, taking into consideration the amplitude bounds of the control angles characterizing the flapping wings movement. In order to validate the control laws, a simplified model having a simple wing kinematic parametrization and considering only the main aerodynamic forces and torques is proposed. The stability of the controller is shown in simulations using a diptera insect model. The robustness of the proposed controller is emphasized through different robustness tests. They concern mainly, model and aerodynamic parameters errors, and aim to validate the considered simplifications in the model.