In this contribution, an extension for the Proportional-integral-Observer (PIO) is presented. The observer can estimate unknown forces with impact character or e.g. friction forces acting on a system. Therefore, the observer does not use any information about the contact. The classical PIO is in the case of relevant measurement noise not able to achieve satisfactory performance. The new formulated observer design permits to estimate unknown input forces acting on a system while measurement noise is present. The main focus of the paper is a new extension of the PIO for general applications and an experimental improvement of the performance, given for the first time with this paper. The introduced extension is especially to improve the observer robustness to measurement noise. This is an issue of high practical importance due to the fact that the PIO-scheme works with high gains, getting sensitive to measurement noise. With the introduced extension, the sensitivity problem is attenuated. The estimation of impact forces acting on a fixed elastic beam is used as a principle example. The introduced method works generally and can be applied to different tasks for elastic structures.

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