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This paper describes a developed verticalisation function integrated into a mobile transportation platform. The system is known as Gyrolift, a type of mobility-aided wheelchair based on a two-wheel auto-balanced personal transporter (PT). The system is equipped with a robotic module designed for helping users reach a standing position from a seated one. It also allows them to safely keep the standing posture to interact with the environment and have access to objects at a high level. The main contribution of this work resides in the design of verticalisation solution that ensures both the trajectory adapted to the user while respecting the constraint of the mobile platform. This solution is designed to not only keep the user in a standing posture but also to prevent instability of the PT. In order to justificate its feasibility, the proposed device as human-aid was evaluated in a series of simulations. Experimental tests were also conducted.

International audience; The aim of this study is to investigate the interaction characteristics between human upper extremity limb and mobility assistance device, in order to test the effects of different device designs on human arm movement. In this paper, the role of mobility-aid for the human arm was depicted by an ideal generalized spring force appended onto the human elbow joint. The main contribution of this work resides in the use of musculoskeletal modelling and predictive simulation to describe the interaction by exploiting the variables of the equivalent spring force during an elbow flexion movement. Results showed that the different variables of the spring force would result in a variety of levels of human muscle activation, where we can draw a conclusion that interaction characteristics affect the human arm movement. Besides, it is also available for recommending the most suitable force variables in terms of minimization of muscle activation.

In this paper, different techniques of analysis have been used to study the effects of perturbations generated from a robotic mobile platform called Isiskate. These disturbances were applied on two categories of people: post-CVA subjects suffering from cerebrovascular accident and healthy individuals. Our aim is to analyze some assessment tools to distinguish between different postural behaviors. In relevant works, very few studies have addressed the use of nonlinear time-series methods in diagnosis of post-CVA pathological postural behavior. Furthermore, our tools are based on parametric and non-parametric identification procedures, that can yield to an insight on how to improve the examination time. As part of our analysis, the tests were established with several levels of sinusoidal vibrations, along the anterior–posterior (A/P) and medial–lateral (M/L) planes. The mobile platform allowed us to record a set of coordinates that includes center of pressure (COP) as a function of time. First, we have quantified some linear parameters and spectral characteristics using power spectral density (PSD). Thereafter, we have deduced stochastic parameters using stabilogram diffusion analysis (SDA), which revealed some interesting invariants. Then transfer functions between the platform velocity and COP trajectory were evaluated. They were carried out at frequencies from 0.1 Hz to 3.3 Hz. Furthermore, we accomplished a comparison of models based on both parametric and nonparametric identification methods. The combination of the proposed techniques has provided us an understanding of human control process by establishing a behavior model and helped us to distinguish patients with postural disorders. This improves postural analysis and facilitates the diagnosis of pathologies related to equilibrium which serves in rehabilitation.

In this paper, we study the postural behaviour of two categories of people: Post-CVA subjects suffering from cerebrovascular accident syndromes and healthy individuals under several levels of anterior-posterior and medial-lateral sinusoidal disturbances (0.1-0.5 Hz). These perturbations were produced from an omnidirectional platform called Isiskate. Afterwards, we have quantified seventy postural parameters, they were combined of linear stabilometric parameters and non-linear time dependent stochastic parameters using stabilogram diffusion analysis and some spectral attributes using power spectral density. The aim of our analysis is to reduce data dimensionality using principal component analysis (PCA). Furthermore, we proposed a new PCA-related criterion named: criterion of contribution in order to evaluate the contribution of every variable in the resulted system structure, and thus to eliminate the redundant postural characteristics. Afterwards, we highlighted some interesting distinctive parameters. The selected parameters were used thereafter in comparison between the studied groups. Finally, we created a classification model using support vector machines to distinguish stroke patients. Our proposed techniques help in understanding the human postural dynamics and facilitate the diagnosis of pathologies related to equilibrium which can be used to improve the rehabilitation services.

This paper presents the design and implementation of IsiMove, a new dynamic posturography platform. It allows the evaluation of the static and dynamic balance of a human placed on a force plate. IsiMove is a robotic platform open kinematic with four degrees of freedom: anteroposterior tilt, mediolateral tilt, vertical rotation, and horizontal translation. It is capable of measuring the displacement of the center of pressure over time, with a resolution of 0.1 mm for each foot and support a human of about 120 kg. IsiMove can generate various types of balance perturbations based on parameters such as direction, amplitude, frequency and shape. In this paper, we will give a description of the mechanisms that constitute our platform. First, the technical specifications of the hardware and software architecture will be presented. Then, we will provide details related to extensive experimental evaluations of the platform in both static and dynamic condition as well as result of postural stability analysis with healthy subjects and stroke patients.

This paper presents the design and the implementation of a new platform for balance analysis. The designed platform called IsiSkate is an omnidirectional mobile robot. It is specially designed to reproduce the perturbation of a public transportation in a laboratory environment. It is equipped with force and inertial sensors intended for the evaluation of human posture for static and dynamic equilibrium analysis of a human subject standing on it. This platform is able to disturb the balance of a human weighing 120 kg with an acceleration of 3 m/s $^{2}$ , which is above the safe limit 1.9 m/s $^{2}$ in public transportation. The platform is capable of measuring in real time the displacement of the center of pressure independently for the left and right foot at baud rate of 100 Hz. With its integrated inertial sensor, the platform is also capable of estimating the displacement of center of mass of the human subject as well as the motion of the ankle, knee, and hip joint. In this paper, we give a description of the mechanism that constitutes the platform. Technical specifications of electrical and computer architecture are given. Some tests with a subject were carried out to assess the performance of this new platform. Some results from the stability analysis based on the model of an inverted pendulum are also presented in this paper.

This article describes the use of a robotic platform in the analysis of the posture. This platform is able to move while providing the position of the center of pressure (COP). Therefore, biomechanical data are calculated using the measurements provided by the sensors associated to the platform. These allow the estimation of joints stabilometric signals from the data and loads measured between the user and the platform. In our analysis, several levels of disturbance were tested to determine the level and type of disturbance compatible with the strategy adopted by the user. The experiments conducted have confirmed the usefulness of such platform in supporting therapists in their analysis. The features of the used platform enable the simulation of dynamic movements in transportation and it allows an omnidirectional movement on four axles. It is capable of supporting the weight of a human of about 120kg while applying maximum acceleration of \(2m/s^2\) along longitudinal or lateral directions. Some results on the design of the platform and the analysis will be exposed in this article.

A new approach to control an omnidirectional mobile manipulator is developed. The robot is considered to be an individual agent aimed at performing robotic tasks described in terms of a displacement and a force interaction with the environment. A reactive architecture and impedance control are used to ensure reliable task execution in response to environment stimuli. The mechanical structure of our holonomic mobile manipulator is built of two joint manipulators mounted on a holonomic vehicle. The vehicle is equipped with three driven axles with two spherical orthogonal wheels. Taking into account the dynamical interaction between the base and the manipulator, one can define the dynamics of the mobile manipulator and design a nonlinear controller using the input-state linearization method. The control structure of the robot is built in order to demonstrate the main capabilities regarding navigation and obstacle avoidance. Several simulations were conducted to prove the effectiveness of this approach.

This paper presents an application of the multi-agent system approach to mobile manipulators that cooperate to achieve displacement of heavy and large objects. Therefore, the task is distributed between agents, and each agent offers and negotiates its services that help in accomplishing the mission. The multi-agent system has been developed using the oRis platform. The main components of such a system include communication and negotiation protocols. Hence we present the behavior of robots, their interaction, and their behavior toward obstacles. Computer simulations are conducted in order to demonstrate the feasibility of the proposed approach.

This work presents a novel algorithm for the invertibility of switched nonlinear systems. An invertible switched system is one for which it is possible to reconstruct the entire unknown inputs and the associated evolving mode. In our approach, the dynamic of the inverse systems is given by means of a projection which decomposes the state space into two transverse foliations: one is tangent to the unknown inputs and the other is transverse. Illustrative examples and a missile application are given and discussed in this paper.

In this article we develop a new approach to control an omnidirectional mobile manipulator. This approach is based on a kinematic command structure and impedance control technique. First we define multiple control behaviors depending on the robot tasks. Two behaviors are considered here the synchronized one and the independent one. Each behavior mentioned above is described in terms of force and position models in order to allow each robot to regulate his corresponding behavior. In the case of synchronized situation, kinematic modelling is presented with particular emphasis on redundancy. We use the additional task concept to solve the control problem of these redundant holonomic systems by taking into account the external forces.

This paper deals with a new method to compute the left inverse for a class of dynamical systems. This method is based on a projection which decompose the state space into two transverse foliations: one is tangent to the unknown inputs and the other is transverse. Contrary to the traditional methods, our method enables us to write the inverse dynamic system under consideration. Within this work we highlight our propositions by examples.

International audience; This paper presents a new accelerometer based method for estimating the posture of a subject standing on a dynamic perturbation platform. The induced perturbation is used to study the control mechanisms as well as the balance requirements that regulate the upright standing. These perturbations are translated into different intensity levels of speed and acceleration along longitudinal and lateral directions of motion. In our method, the human posture is modeled by a tridimensional, three-segment inverted pendulum which simultaneously takes into account both the anterior–posterior and medio-lateral strategies of hip and ankle. Four tri-axial accelerometers are used her, one accelerometer is placed on the platform, and the other three are attached to a human subject. Based on the results, the joint angle estimated compare closely to measurements from magnetic encoders placed on an articulated arm joint. The results were also comparable to those found when using a high-end optical motion capture system coupled with advanced biomechanical simulation software. This paper presents the comparisons of our accelerometer-based method with encoder and optical marker based method of the estimated joint angles under different dynamics perturbations.

This paper is devoted to the problem of design a dynamic controller of switched linear systems. In the first part of this paper, we give some remarks about the influences of switching signal on the asymptotic stability of switched systems. We give a practical example to generate a large class of switching signals. The second part is devoted to the switched dynamic controller design, based on a common Lyapunov function approach. A sufficient condition are formulated as an LMI problem for the switched controller design under arbitrary switching. A stabilizing switched controller with regional pole placements is also formulated as a convex problem, an LMI approach is used to derive the switched dynamic controller with performance limitations.

In this paper, we give some sufficient geometrical conditions to analyse the observability of a class of hybrid systems: piecewise-smooth dynamical systems. For the subclass of piecewise linear systems, the analysis of the observability is refined. Indeed, thanks to the algebraic structure of this subclass, we improve one of these sufficient conditions by using the rank of a matrix associated to a piecewise linear system. This matrix takes into account all the observability matrices of the subsystems as well as the switch linear function. Throughout this paper we give examples to highlight our method.

International audience; In this article we develop a new approach to control an omnidirectional mobile manipulator. The robot is considered as an individual agent aimed to perform robotic tasks described in terms of displacement and force interaction with the environment. A reactive architecture and impedance control are used to ensure reliable task execution in response to environment stimuli. The mechanical structure of our holonomic mobile manipulator is built from two joint manipulator mounted on an holonomic vehicle. The vehicle is equipped using three motorized axles with two spherical orthogonal wheels. The dynamics of the mobile manipulator robot is defined tacking into account the dynamical interaction between the base and the manipulator. Then we design a nonlinear controller for the robot using input-state linearization method. The control structure of the robot is built in order to demonstrate the main capabilities in navigation and obstacle avoidance. Several simulations were conducted to prove the effectiveness of our concept.

International audience; In this article we develop a new approach to control an omnidirectional mobile manipulator. This approach is based on a layered command structure and impedance control technique. First we define multiple control behaviors depending on the robot tasks. Two behaviors are considered here the synchronized one and the independent one. Each behavior mentioned above is described in terms of force and position models in order to allow each robot to regulate his corresponding behavior. In the case of synchronized situation, kinematic modeling is presented with particular emphasis on redundancy. We use the additional task concept to solve the control problem of these redundant holonomic systems by taking into account the external forces.

In this paper we develop a new control law to steer an underactuated surface vessel along a predefined path at a constant forward speed controlled by the main thruster system. The methodology is based on the Serret–Frenet formulation to represent the ship kinematics in terms of path parameters, which allows for convenient definition of cross and along track error. Furthermore, our approach for path following overcomes the stringent initial condition constraints. This paper also addresses the path following with environmental disturbances induced by wave, wind, and ocean-current. The proposed controller is designed based on the Lyapunov direct method and backstepping technique. The closed loop path following errors is proven to be uniform ultimate bounded. Results are demonstrated by high fidelity simulation.

International audience; In this paper, we give sufficient conditions for the stability of a class of switched systems. Based on the symmetric part of the state space matrix and on the LaSalle's invariance principle, to ensure the asymptotic stability of switched linear systems, under a special class of switching signals. The proposed stability results are used to design observer of switched linear systems for which the discrete state is available. Examples are given to highlight our propositions.

International audience; In this paper, we focus on one of the central problem of observers design and control of general manipulation systems. The tasks performed by manipulators involve physical interaction with their environment. This naturally gives rise to interactive forces between each manipulator and the object. The mechanical compliance introduced by the cooperation between the manipulators and their interactions with load is complex. First, the control must be designed in this case in order to realize the object trajectory and/or external forces tracking. But, the controller action must respect and not violate at each moment the kinematic constraint of the manipulation system. Seconde and more importantly, the augmented manipulation system (the closed chain : manipulators-object) is nonlinear and complex system, then the observer design is very difficult, which motivate us to develop a new approach to design a multi models-based observer which we call hysteresis hybrid observer.

International audience; This brief addresses the problem of controlling the planar position and orientation of an autonomous underactuated surface vessel. Under realistic assumptions, we show, first, that there exists a natural change of coordinates that transforms the whole dynamical system into a cascade nonlinear system, and, second, the control problem of the resulting system can be reduced to the stabilization of a third-order chained form. A time-invariant discontinuous feedback law is derived to guarantee global uniform asymptotic stabilization of the system to the desired configuration. The construction of such a controller is based on the backstepping design approach. A simulation example is included to demonstrate the effectiveness of the suggested approach

International audience; In this paper, we deal with the observability of piecewise-affine hybrid systems. Our aim is to give sufficient conditions to observe the discrete and continuous states, in terms of algebraic and geometrical conditions. Firstly, we will give the algebraic conditions to observe the discrete state based on the switch function reconstruction for linear hybrid systems. Secondly, we will give a geometrical condition based on the transversality concept for nonlinear hybrid systems. Throughout this paper, we illustrate our propositions with examples and simulations.

This paper gives the sufficient and necessary conditions which guarantee the existence of a diffeomorphism which transforms the dynamic of a multi outputs nonlinear system without input into a linear dynamic up to a vector field which depends only on the outputs. The same diffeomorphism yields a diffeomorphism on the outputs. In this case we can design an observer which linearizes the error of the dynamical system under consideration.