Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Increasing resource efficiency with an engineering decision support system for comparison of product design variants

2019 , Buchert, Tom , Ko, Nathanael , Graf, Roberta , Vollmer, Thomas , Alkhayat, Moritz , Brandenburg, Elisabeth , Stark, Rainer , Klocke, Fritz , Leistner, Philip , Schleifenbaum, Johannes Henrich

The development of sustainable and resource-efficient products requires consideration of multiple design targets concerning the whole product life cycle. Taking these factors into account leads to complex decision situations with conflicting targets and trade-offs. To support design engineers in these situations an Engineering Decision Support System (EDSS) has been developed. In this article, the overall concept of the EDSS is presented. Furthermore, one function of the EDSS to assist a systematic comparison of product variants is introduced in detail. It is based on combining an existing PLM solutions (in particular Siemens Teamcenter 11/Siemens NX9) and software for Life Cycle Assessment (GaBi 7). Beyond a proof of concept for information exchange between both systems a methodology is presented which enables design engineers to systematically assess and select multiple product variants based on their resource utilization. The approach is complemented with a comprehensive case study for different design options of a core slide. In the scope of this study, variations of geometry (solid vs. hollow design), materials (hot-working steel vs. nickel-based superalloy) and manufacturing processes (laser metal deposition vs. milling) were considered. Furthermore, a usability study of the decision support tool is shown.

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Robust Passivity and Passivity Relaxation for Impedance Control of Flexible-Joint Robots with Inner-Loop Torque Control

2018 , Haninger, Kevin , Tomizuka, Masayoshi

Passivity is a canonical condition for the safety of interactive systems, but practical limitations restrict its utility as a design tool. A system with a passive model can be unstable in high-stiffness environments, passivity is difficult to show with inner-loop controllers, and as it is a binary condition it provides limited design comparison insight; as a result, it is rarely used for inner-loop design. As passivity safety claims are limited by model accuracy, conditions for the passivity of a system with bounded-magnitude model uncertainty (robust passivity) are developed in this paper. Additionally, a condition for coupled environment-robot stability is developed using mixed passivity and small-gain condition, allowing rigorous relaxation of passivity at high frequencies for typical impedance-controlled systems. These approaches are used in the analysis of an impedance-controlled series-elastic actuated system with inner-loop torque control and also compared with traditional design tools (bandwidth ratio, sensitivity function, etc.). The approach is then validated experimentally, identifying model uncertainty bounds under various load conditions, and then using the measured uncertainty for controller synthesis. Robust passivity is then compared with nominal passivity in a validation experiment under manual excitation and impact.

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