Markus Grün

Observer Based Method for Joint Torque Estimation in Active Orthoses

Abstract This contribution presents a new approach of estimating the joint torques for an active orthosis. The new approach combines inverse dynamics and measured ground reaction forces. The joint torques can easily be computed from the ground reaction forces, but the measurement is usually flawed. An obsererver is employed to estimate the disturbance of the measurements and restore the original joint torques. A model of the human lower extremity is presented and additional seat forces are introduced to model the seat. Simulation results on the Sit-to-Stand movement illustrate the effectivity of the new approach.

Knee-ankle-foot orthosis with powered knee for support in the elderly

A prototype of a powered knee orthotic device was developed to determine whether fractional external torque and power support to the knee relieves the biomechanical loads and reduces the muscular demand for a subject performing sit-to-stand movements. With this demonstrator, consisting of the subsystems actuation, kinematics, sensors, and control, all relevant sensor data can be acquired and full control is maintained over actuator parameters. A series-elastic actuator based on a direct current motor provides up to 30 Nm torque to the knee via a hinge joint with an additional sliding degree of freedom. For reasons of feasibility under everyday conditions, user intention is monitored by employing a noninvasive, nonsticking muscle activity sensor to replace electromyographic sensors, which require skin preparation. Furthermore, foot plates with force sensors have been developed and included to derive ground reaction forces. The actual knee torque needed to provide the desired support is based on an inverse dynamics model using ground reaction forces signals and leg kinematics. A control algorithm including disturbance feed forward has been implemented. A demonstration experiment with two subjects showed that 23 % of moment support in fact leads to a similar reduction in activation of the main knee extensor muscle.

Seriell-Elastische Aktoren als Antrieb für aktive Orthesen / Serial-Elastic Actuators for Active Orthoses

Zusammenfassung Aktive Kniegelenkorthesen können eingesetzt werden, um älteren Menschen im Alltag ein selbstbestimmtes Leben im vertrauten Umfeld zu ermöglichen. Als Antrieb für solche Geräte erweisen sich seriell-elastische Antriebe (SEA) als vorteilhaft, da sie im engen Kontakt zum Menschen besser regelbar sind als direkt gekoppelte getriebeunterstützte DC-Motoren. Sie weisen darüber hinaus in vielen Fällen ein besseres Systemleistungsgewicht als fluidische Antriebe oder elektrodynamische Direktantriebe auf. Im Folgenden werden die Auswahl und Auslegung eines SEA für eine aktive Kniegelenkorthese, seine Regelung mit einem Zustandsregler sowie erste experimentelle Ergebnisse präsentiert und diese in den Stand der Technik eingeordnet. Summary Active knee orthoses can be used to allow the elderly comfortable everyday living in their familiar environment. To actuate these devices, serial-elastic actuators (SEA) prove to be advantageous as their controllability in close contact to the user is better when compared to directly coupled geared DC motors. SEA, in addition, usually provide a better overall system power-to-weight ratio than fluidic actuators or direct drive electrodynamic actuators. In the following, the selection and the dimensioning of an SEA for an active knee orthosis, its control strategy using a state-space controller, and first experimental results as well as their relation to the state of the art are presented.

Active Knee Orthosis for Supporting the Elderly

1 Dept. of Control Engineering and Mechatronics, TU Darmstadt, Darmstadt, Germany, mgruen@iat.tu-darmstadt.de 2 Measurement and Sensor Technology Lab., Institute for EMK, TU Darmstadt, Darmstadt, Germany 3 Microtechnology and Electromechanical Systems Lab., Institute for EMK, TU Darmstadt, Darmstadt, Germany 4 Dept. of Orthopedics, Trauma Surgery and Paraplegiology, Heidelberg University Clinics, Heidelberg, Germany

Power support by an active knee orthosis during sit to stand

An active knee orthosis has been developed for assisting elderly in challenging ADL-tasks like stair-climbing or sit-tostand (STS). In contrast to approaches of exo-skeletal devices, used in paraplegics without or with marginal motor function of the lower extremity, this orthosis aims to amplify joint moment in elderly with reduced muscle strength. Aim of this study was to test whether the user profits from the supportive function of this device. The support should be visible in reduced EMG-activation during STS when comparing to the situation without support.