DEPARTMENT OF MECHANICS AND APPLIED MATHEMATICS
PIANO HAMMER PARAMETERS MEASURING DEVICE
DESCRIPTION
A piano hammer is a rather complicated object. First, relationships of dynamic force versus hammer deformation show the significant influence of hysteresis, i.e. the loading and unloading of the hammer are not alike. Furthermore, the force-compression relationships of the hammer are essentially nonlinear, and the slope of the dynamic force-compression curve is strongly dependent on the hammer velocity. A model of the hammer that takes into account all the dynamical features of the hammer was derived in the paper:
A. Stulov, "Hysteretic model of the grand piano hammer felt", J. Acoust. Soc. Am. v. 97 (4), 2577- 2585, 1995.
According to this model the piano hammer possesses history-dependent properties or just, in other words, is made of the material with memory. In this case two additional hereditary parameters are involved to describe the hysteretic behaviour of the hammer.
To measure the nonlinear elastic and hereditary parameters of the hammer a device shown below was developed. This experimental arrangement gives a possibility to investigate the dynamical force-compression characteristics of piano hammer, and, using the hereditary (hysteretic) hammer model, to find the hammer parameters by numerical simulation of the dynamical experiments.
The device in conjunction with the hysteretic model of the piano hammer is a powerful instrument as for matching the piano hammers, as well as for their manufacturing. The numerical simulation using the hysteretic hammer model may significantly simplify the process of the manufacturing of piano hammers.
Actually, there are many parameters (e.g. the instantaneous hammer stiffness, the stiffness nonlinearity exponent, mass, radius of curvature, the hereditary parameters, and so on) that describe the properties of a hammer. The conditions of manufacturing piano hammers also vary on a large scale. By using this measuring device it is possible to find during manufacturing the dependencies of the hammer parameters on the technological conditions. Therefore the knowledge of these dependencies give a good practical hint to choose the best technological process for the hammers manufacturing. In this sense, the hysteretic hammer model is an irreplaceable model.
All the software and the measuring device has been designed and developed in the Department of Mechanics and Applied Mathematics of the Institute of Cybernetics at Tallinn University of Technology (Akadeemia tee 21, Tallinn, 12618, Estonia; http://www.ioc.ee/).
The device includes a piezoelectrical wide-band force sensor, and a infra-red sensor for registration of hammer deformation. The analogue signals from these two sensors are converted into two set of data by a digital signal processor ADSP-2181. This 8 channels, 12 bit signal processor is produced by ADIMIR Ltd (http://www.online.ee/~adimir/), and allows:
- to set up data communication speed from device sensors to computer,
- to present data in a scope mode or in an analyser (FFT) mode,
- to save data in a file,
- to print oscillograms and spectrograms.
CONTACT PERSON
Anatoli STULOV, Dr, senior researcher at IoC, email: stulov@ioc.ee, phone: +372 620 4164
PARTNERS
- ADIMIR Ltd http://www.online.ee/~adimir/
- Tallinn Piano Factory (mechanical part of the device), 41 Kungla street, Tallinn 10413, Estonia, email: hiis@online.ee
The financial support of the project was provided by Estonian Innovation Fund.