Control of Adjustable Compliant Actuators

Adjustable compliance or variable stiffness actuators comprise an additional element to elastically decouple the actuator from the load and are increasingly applied to human-centered robotic systems. The advantages of such actuators are of paramount importance in rehabilitation robotics, where requirements demand safe interaction between the therapy system and the patient. Compliant actuator systems enable the minimization of large contact forces arising, for example, from muscular spasticity and have the ability to periodically store and release energy in cyclic movements. In order to overcome the loss of bandwidth introduced by the elastic element and to guarantee a higher range in force/torque generation, new actuator designs consider variable or nonlinear stiffness elements, respectively. These components cannot only be adapted to the walking speed or the patient condition, but also entail additional challenges for feedback control. This paper introduces a novel design method for an impedance-based controller that fulfills the control objectives and compares the performance and robustness to a classical cascaded control approach. The new procedure is developed using a non-standard positive-real Η2 controller design and is applied to a loop-shaping approach. Robust norm optimal controllers are designed with regard to the passivity of the actuator load-impedance transfer function and the servo control problem. Classical cascaded and positive-real Η2 controller designs are validated and compared in simulations and in a test bench using a passive elastic element of varying stiffness

Multi-Sensor Calibration of Low-Cost Magnetic, Angular Rate and Gravity Systems

We present a new calibration procedure for low-cost nine degrees-of-freedom (9DOF) magnetic, angular rate and gravity (MARG) sensor systems, which relies on a calibration cube, a reference table and a body sensor network (BSN). The 9DOF MARG sensor is part of our recently-developed “Integrated Posture and Activity Network by Medit Aachen” (IPANEMA) BSN. The advantage of this new approach is the use of the calibration cube, which allows for easy integration of two sensor nodes of the IPANEMA BSN. One 9DOF MARG sensor node is thereby used for calibration; the second 9DOF MARG sensor node is used for reference measurements. A novel algorithm uses these measurements to further improve the performance of the calibration procedure by processing arbitrarily-executed motions. In addition, the calibration routine can be used in an alignment procedure to minimize errors in the orientation between the 9DOF MARG sensor system and a motion capture inertial reference system. A two-stage experimental study is conducted to underline the performance of our calibration procedure. In both stages of the proposed calibration procedure, the BSN data, as well as reference tracking data are recorded. In the first stage, the mean values of all sensor outputs are determined as the absolute measurement offset to minimize integration errors in the derived movement model of the corresponding body segment. The second stage deals with the dynamic characteristics of the measurement system where the dynamic deviation of the sensor output compared to a reference system is Sensors 2015, 15 25920 corrected. In practical validation experiments, this procedure showed promising results with a maximum RMS error of 3.89°

Automatic control of the heart-lung machine

Die vorliegende Arbeit beschreibt die Entwicklung von Regelstrategien für die Automatisierung der Herz-Lungen-Maschine im kardiopulmonalen Bypass. Für den Entwurf einer Regelung der künstlichen Herz und Lungenfunktion wurden detaillierte Modelle entwickelt, welche die Strecke im Zustand des totalen kardiopulmonalen Bypasses beschreiben. Als technisches System wurde der extrakorporale Kreislauf, als physiologisches System das Gefäßsystem, das Organ Blut und der Blutgasaustausch in der künstlichen Lunge modelliert. Anhand dieser Modelle wurden nun Regler auf Robustheit bezüglich Nichtlinearitäten, variablen Totzeiten und Parameterunsicherheiten beim Patienten entworfen. Die entwickelten Blutgas- und hämodynamischen Regler wurden in Simulationen und in in-vitro-Experimenten an einem Kreislaufsimulator bzw. einer Blutgassimulationsstrecke getestet. Die Regler bewiesen Stabilität sowie eine hohe Güte im Hinblick auf physiologische Anforderungen und einen zukünftigen klinischen Einsatz