Modeling of reliability characteristics typically assumes that components and systems fail if a certain individual damage level is exceeded. Every (mechanical) system damage increases irreversibly due to employed loading and (mechanical) stress, respectively. The main issue of damage estimation is adequate determination of the actual state-of-damage. Several mathematical modeling approaches are known in the literature, focusing on the task of how loading effects damage progression (e.g., Wöhler, 1870) for wear processes. Those models are only valid for specific loading conditions, a priori assumptions, set points, etc. This contribution proposes a general model, covering adequately the deterioration of a set of comparable systems under comparable loading. The main goal of this contribution is to derive the loading-damage connection directly from observation without assuming any damage models at the outset. Moreover, the connection is not investigated in detail (e.g., to examine the changes in material, etc.) but only approximated with a probabilistic approach. The idea is subdivided into two phases: A problem-specific relation between loading applied (to a structure, which contributes to the stress) and failure is derived from simulation, where a probabilistic approach only assumes a distribution function. Subsequently, an adequate general model is set up to describe deterioration progression. The scheme will be shown through simulation-based results and can be used for estimation of the remaining useful life and predictive maintenance/control.
This contribution contains the conception, the components modeling, the realization, and first results for active disturbance decoupling including the experimentally checked ability of the concept for energy harvesting. The investigated mechanical structure consists mainly of a torsional spring. At one side of the spring the disturbances (time-dependent torques with varying frequencies) are driven by a position controlled hydraulic cylinder. The other side of the spring is locked and a force sensor is applied. Due to different torsion angles a torque between the left and right side of the torsion spring is induced. To eliminate or at least to reduce the torque in a passive system it is theoretically sufficient to adjust the stiffness of the spring situation-dependent, although this is practically not possible. For that reason an active disturbance control is presented here. The torque of the spring has to be controlled independently of the displacements at the right and left side. This sophisticated strategy is described in the following. In this contribution the concept and realization of a new active mechanism is realized by dividing the spring into two halves and inserting an electro-mechanical actuator. Hence, the active mechanism compensates the different torsion angles (resp. torques) by adjusting the rotor angle. The results of related test-rig experiments will be shown and the possibility to decouple the torques from each other, which can be interpreted as disturbances, is demonstrated. The strategy of active disturbance decoupling is based on the measured displacement of the hydraulic cylinder and the measured force. In chapter 2 the idea and conception of the test-rig is discussed and the realized solution is shown. The following chapter deals with the system model and especially with the idea of torque control. Furthermore the chosen disturbance profiles are shown and the effects of active decoupling are discussed. In the last chapter results of experimental tests for energy harvesting are given, showing principally the efficiency as well as the limits of todays technology.
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