Automated Experimental Modal Analysis of Bladed Wheels with an Anthropomorphic Robotic Station
L. Bertini1 · P. Neri1 · C. Santus1 · A. Guglielmo
Abstract Experimental modal analysis is challenging when
the component has a highly three-dimensional shape, since
a great number of measurement points are needed with
accurate positioning. An anthropomorphic robotic station is
proposed to automate this analysis, specifically on bladed
wheels. This provides a reliable control of the spot location
and of the beam orientation of a Laser Doppler Vibrometer.
The modal frequencies were obtained along with the vibrational shapes and their spatial resolution was managed by
exploiting the programming flexibility of the robotic station.
The SAFE diagram was easily obtained by measuring a single point for each sector, and an extension of this diagram
was demonstrated for the splitter blade wheels. The use of
multiple measurement points, for each wheel sector, significantly improved the characterization of the modes having
the same number of nodal diameters, hence the same shape coordinate on the SAFE diagram.
This paper has presented an experimental set up to perform a
fully automated modal analysis of mechanical components.
This procedure was then applied to centrifugal compressor bladed wheels. An anthropomorphic robotic arm was
used to point a Laser Doppler Vibrometer sensor on selected
measurement locations to obtain fast and, more importantly,
accurate positioning and orientation, even for these highly
three-dimensional articles. The characteristics of the investigated bladed wheel types have been discussed and the
results of different tests presented and compared to FE
modelling. The tests with a single point for each blade characterize the modes sufficiently when only the number of
nodal diameters is required (as for the SAFE diagram) and
successful comparative results were obtained with respect
to the FE prediction. The particular feature of the splitter blade wheels was also analysed. By having one point
for each splitter blade, i.e. two points for each sector, an
extended SAFE diagram was newly proposed, where the
maximum number of nodal diameters follows the load input
either at the inner or at the outer wheel circle. Finally, by
measuring a certain number of points for each wheel sector,
the experimental modes were better described, providing an
improvement in the MAC matrix results and an increased
resolution of the vibrational shapes. This modal shape
enhanced representation could be exploited to expand the
SAFE diagram and provide a more sophisticated definition
for the modal-to-load shape matching.
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