Browsing by Author "Pott, Andreas (PD Dr.-Ing)"

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    Model selection and parameter optimization for cable-driven parallel robots
    (Stuttgart : Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA, 2021) Miermeister, Philipp Reinhard; Pott, Andreas (PD Dr.-Ing)
    While various models, computation methods, and parameter identification schemes are proposed in the literature on CDPRs, a systematic analysis of the model selection process for CDPRs is missing. The answer to the question, which is the optimal model for a specific application, can only be provided by a concurrent consideration of the model structure together with its optimal parametrization. This must be done in the context of a distinct physical robot model which incorporates physical properties not present in the control model. This thesis investigates the effect of different modeling assumptions using a meta-model for the analysis of the position tracking accuracy and workspace. Focusing on safety critical real-time applications such as motion simulation with human-in-the loop control, constrained model complexity is essential for reliable and safe operation. The investigation starts with kinematics models that can be considered as minimal requirement for the operation of CDPRs and gradually increases model complexity to an elastostatic model which allows to deal with the inner tension state inherent to overconstrained CDPRs. Combining modeling and parameter optimization in the analysis together with a ground truth model allows to estimate the optimal performance which can be reached for a certain model class. This allows for an informed decision based on the estimated performance rating in context of the ground truth model. The experimental investigation and validation of the models is done on the Cable-Robot Simulator which was developed during this work. Results show the advantage of concurrent model building and optimization by comparing the prediction accuracy of optimized models of different complexity with the nominal model which is obtained by highly accurate laser-tracking measurements. With this approach the accuracy of a nominal model was improved from a mean position error of 39.8 mm and mean rotation error of 1.19 deg to a mean position error of 2.73 mm and rotation error of 0.11 deg for an optimal elastostatic model. Force predictions for the elastostatic model were improved from 2426 N for the nominal model to 582 N for the optimal model for a total force range of 9000 N. The main contribution to model accuracy is provided by an accurate estimate of the platform load and secondary by an accurate estimate of the system stiffness. Considering the CableRobot Simulator as highly representative for cable-driven parallel robots by means of architecture, scale, accuracy, and safety requirements, experimental results from this thesis should transfer well to other systems of this class.
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    Modelling and control of a cable-driven parallel robot : methods for vibration reduction and motion quality improvement
    (2019) Schenk, Christian; Pott, Andreas (PD Dr.-Ing)
    Seilroboter können aufgrund ihrer parallel Struktur und dem Aufbau ihrer Antriebsstränge hohe Beschleunigungen erreichen und besitzen einen großen Arbeitsraum. Beide Eigenschaften ermöglichen den Einsatz als Simulatoren. Durch die Verwendung als Simulator ergeben sich jedoch neue Herausforderungen und Aufgabenstellungen. Zu diesen zählen Robustheit, präzises Folgeverhalten von Positionen, Geschwindigkeiten und Beschleunigungen und eine schwingungsarme Betriebsart. Seile neigen aufgrund ihrer physikalischen Eigenschaften zu Schwingungen, die an die Platform weitergegeben werden und dadurch die Simulationsqualität negativ beeinflussen. Desweiteren können statische Reibung und aggressive Regelungsstrategien Impulse applizieren, die Schwingungen am Antriebsstrang provizieren. Diese Arbeit beschäftigt sich mit Methoden zur Reduzierung dieser Schwingungen und damit mit Maßnahmen zur Verbesserung der Folgeverhaltens. Die gewählten Methoden, diese liegen im Bereich der nichtlinearen robusten Regelung via Sliding-Mode Controllern, modellbasierter Vorsteuerung, Reibungskompensation, Zustandsbeobachtung mit Unscented Kalman-Filtern und Modellierung sowie Regler-Synthese basierend auf Port-Hamilton Modellierung. In Experimenten an zwei Seilrobotern mit paralleler Kinematik werden die vorgeschlagenen Reglerstrukturen und Modelle verifiziert und stellen deren Effizienz deutlich dar.