Modeling the Static Force of a Festo Pneumatic Muscle Actuator: A New Approach and a Comparison to Existing Models

Erratum published on 13 March 2018, see Actuators 2018, 7(1), 9. https://doi.org/10.3390/act7010009In this paper, a new approach for modeling the static force characteristic of Festo pneumatic muscle actuators (PMAs) will be presented. The model is physically motivated and therefore gives a deeper understanding of the Festo PMA. After introducing the new model, it will be validated through a comparison to a measured force map of a Festo DMSP-10-250 and a DMSP-20-300, respectively. It will be shown that the error between the new model and the measured data is below 4.4% for the DMSP-10-250 and below 2.35% for the DMSP-20-300. In addition, the quality of the presented model will be compared to the quality of existing models by comparing the maximum error. It can be seen that the newly introduced model is closer to the measured force characteristic of a Festo PMA than any existing model.BMWi, ZF4007503, Development of a PMA-driven Exoskeleton for the Upper Bod

A Novel Framework for a Systematic Integration of Pneumatic-Muscle-Actuator-Driven Joints into Robotic Systems Via a Torque Control Interface

In this paper, two different torque control approaches for PMA-driven (PMA = Pneumatic muscle actuator) revolute joints are presented and tested. In previous work controllers for PMA-driven robots are typically customized for the use on a specific robotic system. In contrast, the proposed controllers define a general control interface for every robot that is actuated by PMA-driven joints. It will be shown that controlling the torque of a PMA-driven joint enables the use of standard robotic motion control frameworks, because the torque represents the natural input of the robotic equation of motion. Therefore, both proposed torque control approaches are interconnecting PMAs and their challenging characteristics on the one hand and “conventional” motion control strategies for robots on the other hand. After a detailed discussion of two different torque control approaches, we show that a torque controller handles all characteristics and dynamics of a PMA-driven joint internally, which implies that only its bandwidth and its static torque characteristic must be taken into account for the design of the outer motion control loop. This feature simplifies the integration of PMA-driven joints in robotic systems enormously, as will be demonstrated by a design of a cascade-structured, flatness-based motion controller for an exemplary robot with one degree of freedom.BMWi, ZF4007503, Development of a PMA-driven Exoskeleton for the Upper Bod

Modeling and control of a fluidic muscle pair

Heutige stationäre wie mobile Roboter und Automatisierungsanlagen sind durch ihre noch zumeist starren Komponenten nicht für den Einsatz im unmittelbaren Bewegungsraum des Menschen geeignet. Da aber der Bereich der Servicerobotik immer mehr an Bedeutung gewinnt, müssen neue Aktuatoren für die gesteigerten Anforderungen an Nachgiebigkeit, Sicherheit und Robustheit nicht nur entwickelt, sondern auch modelliert und geregelt werden. Die vorliegende Arbeit beschäftigt sich mit der Modellbildung und Regelung eines antagonistischen Muskelpaares. Als Aktuator wird der fluidische Muskel der Firma Festo verwendet, da er einerseits über seine Membran inhärent elastisch und nachgiebig ist und andererseits über die fluidische Stellgröße Luftmasse seine Eigenschaften stufenlos eingestellt werden können. Einleitend werden einige für diese Arbeit wichtige Beziehungen des natürlichen Muskels dargestellt, seine biologischen Eigenschaften mathematisch beschrieben und der hier betrachtete fluidische Muskel als technisches Pendant seines biologischen Vorbildes vorgestellt. Nach der Beschreibung der Versuchaufbauten werden relevante Eigenschaften des technischen Muskelaktuators theoretisch besprochen und praktisch vermessen. In der anschließenden Modellbildung werden die zugrundeliegenden nichtlinearen Gleichungen entwickelt, ein lineares Modell am Arbeitspunkt abgeleitet und die fehlenden Parameter im Versuch identifiziert. Die daraufhin synthetisierten Regler werden dann sowohl am theoretischen Modell als auch am Versuchsstand verifiziert und abschließend auf ihre Praxistauglichkeit und Robustheit bei variierenden Lasten untersucht.Today's stationary or mobile robots and automation systems are not suitable for employment within the immediate operating space of people due to their mostly rigid components. Since the field of service robotics is becoming increasingly important, new actuators for the increased requirements for compliance, security, and robustness have to be developed but also modelled and controlled. The present thesis details the modelling and controlling of an antagonistic muscle pair. As an actuator, the fluidic muscle of Festo AG & Co. KG is used. On the one hand, its membrane is inherently elastic and compliant, and on the other hand, its properties can be continuously adjusted by the manipulated variable fluidic air mass. As introduction, features of the natural muscle significant to this work are reviewed, its biological properties mathematically described, and the fluidic muscle used in this work is presented as a technical counterpart of the biological model. After describing the experimental setups, relevant characteristics of the technical muscle actuator are theoretically discussed and actually measured. In the subsequent modelling, the underlying nonlinear equations are developed, a linear model at the operating point is derived, and lacking parameters identified experimentally. The resulting controllers are then synthesized, both in the theoretical model as well as on the test bench and finally validated regarding their practicality and robustness for varying loads

Erratum: Martens, M.; Boblan, I. Modeling the Static Force of a Festo Pneumatic Muscle Actuator: A New Approach and a Comparison to Existing Models. Actuators 2017, 6, 33

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