Johannes Mathias

Developing Robust PSS Offerings

PSS are often used by multiple users as well as under varying conditions. These users do not know the PSS well and therefore are less likely to recognize problems or handle situations that could damage the product. Therefore design of robust product components for PSS is important.

Modellierung von Unsicherheit in der Produktentwicklung

Fur die erfolgreiche Entwicklung von Produkten sind typischerweise eine Vielzahl von Einflussfaktoren zu beruksichtigen. Aufgrund von Unsicherheiten, z.B. fehlenden Informationen oder schwankende Einflussgrosen im Produktlebenslauf, ist eine detaillierte Analyse jedoch haufig schwierig. In diesem Beitrag wird deswegen die Wahrscheinlichkeits- mit der Moglichkeitstheorie verglichen, um die Anwendbarkeit beider Theorien fur eine quantitative Analyse von Unsicherheiten im Rahmen der Produktentwicklung zu untersuchen. Am Beispiel eines Euler-Knickstabes werden die Einschrankungen einer statistischen Analyse sowie die Vorteile der Berechnung einer unscharfen, kritischen Knicklast aufgezeigt. Das Ziel ist eine geeignete Beschreibung relevanter Unsicherheiten als Grundlage fur die Entwicklung robuster Produkte. Die vorgestellten Betrachtungen sind Teilergebnisse des Sonderforschungsbereichs 805 „Beherrschung von Unsicherheit in lasttragenden Systemen des Maschinenbaus“ der Deutschen Forschungsgemeinschaft an der Technischen Universitat (TU) Darmstadt.

Uncertainties with Respect to Active Vibration Control

The content of this work is the presentation of the prototype of a new active suspension system with an active air spring. As being part of the Collaborative Research Unit SFB805 “Control of Uncertainties in Load-Carrying Structures in Mechanical Engineering”, founded by the Deutsche Forschungsgemeinschaft DFG, the presented active air suspension strut is the first result of the attempt to implement the following requirements to an active suspension system: Harshness and wear: Reduced coulomb friction, i.e. no dynamic seal. Plug and drive solution: Connected to the electrical power infrastructure of the vehicle. Vehicle and customer application by software and not by hardware adaption. These requirements were defined at the very beginning of the project to address uncertainties in the life cycle of the product and the market needs. The basic concept of the active air spring is the dynamic alteration of the so-called effective area. This effective area is the load carrying area A of a roller bellow and defined by A:=F/(p-pa). F denotes the resulting force of the strut, p the absolute gas pressure and pa the ambient pressure. The alteration of this effective area is realized by a mechanical power transmission, from a rotational movement to four radial translated piston segments. Due to the radial movement of the piston segments, the effective area A increases and so does finally the axial compression force F. The prototype presented in this paper serves as a demonstrator to proof the concept of the shiftable piston segments. This prototype is designed to gather information about the static and dynamic behavior of the roller bellows. Measurements show the feasibility of the concept and the interrelationship between the piston diameter and the resulting spring force.

An Assignment of Methods to Analyze Uncertainty in Different Stages of the Development Process

During its life cycle, each engineering product goes through different stages of planning, production and usage. Uncertainties occur in all of these phases. As defined, uncertainties in technical systems are present as far as product and process properties are not determined and deviations of these properties arise. They result either from imperfect information about output values of production processes (regarding product properties) or in terms of diverging uses of the products. Especially within the product development process, the occurring uncertainties have to be taken into account. During the early design stages, decisions that have a variously strong impact on the future product are made. Moreover, the knowledge about a future product is still low so that neither the expected processes nor the product’s properties are known. For this reason, well-known methods of probabilistic uncertainty analysis are not sufficient. They cannot be applied until the product is completely defined. A comprehensive uncertainly analysis in the product development process can be executed in an integrated process model with the Uncertainly Mode and Effects Analysis Methodology (UMEA) [1]. The underlying model of uncertainly is the basis for a comprehensive and consistent classification of uncertainly, a distinction comparable to concepts such as reliability, availability, error or risk. The model to analyze uncertainty has been exercised using the example of the product development process according to Pahl/Beitz [2]. It enables the assignment of suitable methods for the classification of uncertainty at different stages in the design process and thus different levels of abstraction. Based on this model, the quantitative methods of the probability theory are complemented by qualitative concepts such as risk analysis methods, for example, FailureMode and Effects Analysis (FMEA), Event Tree Analysis (ETA), or Hazard and Operability (HAZOP). The assignment of methods offers the possibility to analyze the classified uncertainties in the different phases of the product development process.Copyright