Adjustable Impedance Elements for Product Validation in Compliant Environments

Validation of mechanical systems under dynamic loads requires the consideration of the system’s operation environment, since the boundary conditions have a major impact on the system’s behavior. For repeatable results, tests are conducted on test rigs to define, control and measure parameters. Systematic deviations occur inevitably, if the impedance of the real system is variable, but the test rig’s impedance is not.In this project, Adjustable Impedance Elements (AIEs) are researched as machine elements for test benches and guidelines on the examples of power tool and aircraft lightweight structures. In power tool testing the dynamic behaviour of the user’s hand is subjected to heterogeneity of users, different postures or changes in muscle tension during the application, which leads to different results. In a second case, the dynamic behaviour of aircraft cabin components, like galleys or lavatories are highly affected by different joint impedances, due to variable installation positions in the cabin. In both cases more realistic test results can be achieved by adjusting the stiffness and damping of the test environment with an AIE during test campaigns and systematic studies are possible to improve product design. The AIEs are machine elements that allow an independent adjustment of their mechanical stiffness and damping properties. So far, a variety of adjustable stiffness elements (ASEs) and adjustable damping elements (ADEs) have been investigated. But only little research addressed the combined application of adjustable stiffness and adjustable damping in AIEs. Different dimensions, operation ranges and measurement techniques complicate comparisons based on literature research.The project starts with an experimental investigation of different working principles for ASEs and ADEs as well as their static and dynamic characterization. The ASEs and ADEs are combined to AIE prototypes and then analyzed regarding their characteristic stiffness and damping behavior at high and low frequency bands. Based on the research a modular AIE design catalogue is developed, that covers different requirements, e.g. different frequency ranges and loads for the dimensioning as well as the selection process of suitable working principles. The catalogue supports scientists researching AIEs and scientists requiring specific AIEs for testing application.To demonstrate the potential of AIEs, two AIEs are chosen and investigated for tests of power tools and cabin interior. The two test set ups cover different ranges of requirements from low frequency band with high excitation forces and a high frequency band with low excitation forces. Thus, the two scenarios represent an application study on the modular AIE design catalogue. Guidelines for more realistic testing of power tools, including a wide range of user impedance variation, and aircraft lightweight structures, including different joint impedances, are derived to enable new knowledge for product development.

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