N.-O. Negard

An FES-assisted gait training system for hemiplegic stroke patients based on inertial sensors

Abstract An inertial sensor mounted on the foot of the affected body side represents an alternative to traditional foot switches in Functional Electrical Stimulation (FES)-assisted gait rehabilitation systems. The inertial sensor consisting of 3 gyroscopes and 3 accelerometers can be utilised to detect gait phases which can be applied to synchronise the electrical stimulation with the gait. Additionally, the sensor can be applied to estimate orientation and 3 dimensional movement of the foot. Based on the estimated orientation and linear position several movement parameters can be defined. The most important are the foot clearance, which is defined as maximal distance between foot and ground, and the sagittal angle of the foot in relation to the ground at the time as the heel hits the ground. In this paper we describe a practical system for FES-assisted gait training based on inertial sensors where the electrical stimulation is triggered by the gait phase detection and the stimulation intensity is automatically tuned by feedback of movement parameters.

Online identification of the electrically stimulated quadriceps muscle group

In this paper, a new approach for estimating a nonlinear model of the electrically stimulated quadriceps muscle group under non-isometric conditions is investigated. In order to identify the muscle dynamics (stimulation pulse width-active knee moment relation) from discrete-time angle measurements only, a hybrid model structure is postulated for the shankquadriceps dynamics. The model consists of a relatively well known time-invariant passive component and an uncertain time-variant active component. Rigid body dynamics, described by the Equation of Motion (EoM). and passive joint properties form the time-invariant part. The actuator. i.e. the electrically stimulated muscle group, represents the uncertain time-varying section. A recursive algorithm is outlined for identifying online the stimulated quadriceps muscle group. The algorithm requires EoM and passive joint characteristics to be known a priori. The muscle dynamics represent the product of a continuous-time non linear activation dynamics and a nonlinear static contraction function described by a Normalised Radial Basis Function (NRBF) network which has knee-joint angle and angular velocity as input arguments. An Extended Kalman Filter (EKF) approach is chosen to estimate muscle dynamics parameters and to obtain full state estimates of the shank-quadriceps dynamics simultaneously.

Robust nonlinear control of single limb movement

Abstract The aim of this work was to design a robust nonlinear controller for the knee-joint angle by means of Functional Electrical Stimulation (FES). It is well known that a good mechanical model of the body segments can be obtained by first principles and simple pendulum tests, while it is hard to obtain a good model of the electrically elicited muscle contractions for control purposes due to time-variant and nonlinear properties of the muscles combined with limited measurements. For this reason the muscle activation dynamics are only modeled as a first order linear system. To describe how the muscle contraction depends on joint angle and velocity a simplified linear static function was introduced. Based on this model a nonlinear control design approach is performed applying the back-stepping methodology. This design approach is highly attractive as it can easily be extended to multivariable systems with many body segments and muscle groups, and it allows nonlinear muscle models to be incorporated into the control design. A simulation study of the controller is carried out using a physiologically based model of the neuro-musculoskeletal system as a substitution of the real plant. Robustness and performance of the designed controller, also with respect to the discrete-time implementation and an unmodeled time delay are discussed.

Regelung der Trittgeschwindigkeit beim Liegedreiradfahren von Querschnittgelähmten

Dieser Beitrag befasst sich mit dem Aufbau und der Regelung von Liegedreirädern für querschnittgelähmte Personen. Der Antrieb erfolgt dabei durch elektrische Stimulation der motorisch gelähmten Beinmuskulatur. Kommerziell erhältliche Dreiräder wurden speziell für diesen Zweck instrumentiert, um sie sowohl stationär in Form eines Ergometers als auch mobil für Freizeitzwecke verwenden zu können. Zur optimalen Regelung der Trittgeschwindigkeit wird in diesem Aufsatz ein neuer Ansatz vorgestellt. Ergebnisse mit querschnittgelähmten Probanden werden präsentiert.