A new and alternative method to measure the interaction force between the user and a lower-limb gait rehabilitation exoskeleton is presented. Instead of using a load cell to measure the resulting interaction force, we propose a distributed measure of the normal interaction pressure over the whole contact area between the user and the machine. To obtain this measurement, a soft silicone tactile sensor is inserted between the limb and commonly used connection cuffs. The advantage of this approach is that it allows for a distributed measure of the interaction pressure, which could be useful for rehabilitation therapy assessment purposes, or for control. Moreover, the proposed solution does not change the comfort of the interaction; can be applied to connection cuffs of different shapes and sizes; and can be manufactured at a low cost. Preliminary results during gait assistance tasks show that this approach can precisely detect changes in the pressure distribution during a gait cycle.

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(EN)This invention relates to a servo system for operating an exoskeleton adapted to encircle an object of interest and for supplying a force thereon. A servomotor is coupled to a power source and operates the position of the exoskeleton and thus the force exerted by the exoskeleton on the object of interest. A measuring unit measures a raw driving current signal I raw suplied by the power source to drive the servomotor. A low pass filter applies a low pass frequency filtering on the measured a filtered current signal I filtered. A processing unit determines an actuated current signal I actuated based on the servomotor setting parameters, where I actuated indicates the contribution to I raw from the servomotor when operating the position of the exoskeleton. The processing unit also determines a driving force current signal I force indication the force exerted by the exoskeleton on the object of interest, where I force is proportional to the difference between I filtered and I actuated.
(FR)La présente invention concerne un servosystème pour utiliser un exosquelette adapté pour encercler un objet d’intérêt et exercer une force dessus. Un servomoteur est couplé à une source d’énergie et modifie de la position de l’exosquelette, et ainsi de la force exercée par l’exosquelette sur l’objet d’intérêt. Une unité de mesure mesure un signal de courant d’excitation brut Iraw envoyé par la source d’énergie pour commander le servomoteur. Un filtre passe-bas applique un filtrage passe-bas de fréquence sur le signal de courant filtré mesuré l’filtered. Une unité de traitement détermine un signal de courant actionné l’actuated basé sur les paramètres de réglage du servomoteur, l’actuated indiquant la contribution à l’raw à partir du servomoteur lors de la modification de la position de l’exosquelette. L’unité de traitement détermine également un signal de courant de force motrice l’force indiquant la force exercée par l’exosquelette sur l’objet d’intérêt, l’force étant proportionnel à la différence entre l’iltered et l’actuated.

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To enable compliant training modes with a rehabilitation robot, an important prerequisite is that any undesired human-robot interaction forces caused by robot dynamics must be avoided, either by an appropriate mechanical design or by compensating control strategies. Our recently proposed control scheme of “Generalized Elasticities” employs potential fields to compensate for robot dynamics, including inertia, beyond what can be done using closed-loop force control. In this paper, we give a simple mechanical equivalent using the example of the gait rehabilitation robot Lokomat. The robot consists of an exoskeleton that is attached to a frame around the patient’s pelvis. This frame is suspended by a springloaded parallelogram structure. The mechanism allows vertical displacement while providing almost constant robot gravity compensation. However, inertia of the device when the patient’s pelvis moves up and down remains a source of large interaction forces, which are reflected in increased ground reaction forces. Here, we investigate an alternative suspension: To hide not only gravity, but also robot inertia during vertical pelvis motion, we suspend the robot frame by a stiff linear spring that allows the robot to oscillate vertically at an eigenfrequency close to the natural gait frequency. This mechanism reduces human-robot interaction forces, which is demonstrated in pilot experimental results.

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Walking impairments are a common sequela of neurological injury, severely affecting the quality of life of both adults and children. Gait therapy is the traditional approach to ameliorate the problem by re-training the nervous system and there have been some attempts to mechanize such approach. In this paper, we present a novel device to deliver gait therapy, which, in contrast to previous approaches, takes advantage of the concept of passive walkers and the natural dynamics of the lower extremity in order to deliver more “ecological” therapy. We also discuss the closed-loop control scheme, which enables safe and efficient operation of the device, and present the initial feasibility tests with unimpaired subjects.

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Most recent findings in robot-assisted therapy suggest that the therapy is more successful if the patient actively participates to the movement (“assistance-as-needed”). In the present contribution, we propose a novel approach for designing highly flexible protocols based on this concept. This approach uses adaptive oscillators: a mathematical primitive having the capacity to learn the high-level features of a quasi-sinusoidal signal (amplitude, frequency, offset). Using a simple inverse model, we demonstrate that this method permits to synchronize with the torque produced by the user, such that the effort associated with the movement production is shared between the user and the assistance device, without specifying any arbitrary reference trajectory. Simulation results also establish the method relevance for helping patients with movement disorders. Since our method is specifically designed for rhythmic movements, the final target is the assistance/rehabilitation of locomotory tasks. As an initial proof of concept, this paper focuses on a simpler movement, i.e. rhythmic oscillations of the forearm about the elbow.

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