Identification of operating mode of a petrol chainsaw based on short-time parametrization and analysis of vibro-acoustic signals

Abstract

Petrol chainsaws during operation, regardless of the type of their drive and power, generate vibrations and noise that usually exceed the permissible values which are specified in standards and/or regulations. The values of vibration accelerations and emitted noise levels declared by the manufacturers are determined in standardized conditions and they may significantly differ from the values affecting operators. In order to determine the actual impact on operators of chainsaws under nominal operating conditions (in situ) one have to identify the percentages of the chainsaw's operating modes: Idle – ID, Full load – FL, Racing – RA. The article presents the methodology of identifying the operating modes of petrol chainsaws based on recorded vibroacoustic signals. Moreover, a method of identifying these states based on a tachometric signal has been proposed. Different approaches were considered to the identification of operating modes. Basic method is based on tracking of changes of the instantaneous values of vector sums of frequency-weighted values of RMS vibration accelerations – ahv and linear sound pressure levels – Lp. Advanced methods are based on short-time analysis and parametrization in frequency bands of the acoustic signal, as well as the time–frequency maps of vibration and acoustic signals. Discriminants of vibroacoustic signal were determined that allowed us to identify the operating mode of the chainsaw.