Laboratory for Dynamics of Machines and Structures 
The importance of harmonic versus random excitation for a human finger
 J. Slavič, L. Knez and M. Boltežar
International Journal of Mechanical Sciences, Vol. 131-132, p. 507-515, Oct 2017

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Abstract
In hand-held devices the vibration excitation is typically multi-harmonic (e.g., as a result of the eccentricity in rotating motors) on top of the random excitation. The excitation amplitude, excitation frequency and the push force typically vary with the application or the usage conditions. Typically, random excitation is used for finger or hand excitation. This paper investigates the importance of harmonic versus random excitation for a human index finger. Under different testing conditions the finger’s response was researched via the apparent mass. The harmonic excitation was studied using a sine sweep profile where the continuous wavelet transform was used for the extraction of the instantaneous apparent mass. The results show significant differences in the identified apparent mass for harmonic excitation when compared to random excitation (e.g., at frequencies close to 10 Hz the apparent mass was up to 3 times higher for a random excitation than for a harmonic excitation). As hand tools are frequently excited with a single or multiple harmonics, the identified differences should help in the process of designing safer hand tools.
Authors

Associate Professor

Janko Slavič, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  janko.slavic@fs.uni-lj.si
  +386 1 4771 226
jankoslavic     jankoslavic    
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Assistant

Luka Knez, PhD student

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  luka.knez@fs.uni-lj.si
  +386 1 4771 229
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Professor

Miha Boltežar, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  miha.boltezar@fs.uni-lj.si
  +386 1 4771 608
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