The wavelet transfer function of a human body–seat system

Abstract

In the analysis of vibration systems, classical transfer functions are used. Usually, it is the ratio of Fourier or Laplace transforms. The wavelet transfer function is proposed in this work. In this paper, the wavelets transfer function is the ratio of output and input wavelet transforms. It is considered as a distinctive correlation of the output and input system signals. The wavelet transform consists of coefficients, where the first is a scale and second time shift. To get input and output signals in the human body-seat system the dedicated test stand was made. The stand consists of a seat, moved by special shaker, which is used as a mechanical vibration device. The control program included in the source file is taken to imitate angular position of the engine. Motor shaft is connected with exciter's moving parts and stand base, which influences directly on the seat position. The disturbance signal usually simulates a horizontal road influence on a driver. It can be considered as a low-frequency signal. It is measured by accelerometers called inertial sensors, which are placed on the platform of the shaker. The output signal is measured by an accelerometer placed on a seat and on the human head. Both signals are recorded by the Inertia Studio software wireless in the real time. After the measurement, the signals are transformed into wavelet coefficients by using Matlab package functions. The transfer function and its visualization are presented in two dimensions scale-time. The scale is related to frequency (pseudo-frequency). By the transfer function it is possible to analyze the systems, evaluate safety, compare the systems, and many more.

Evaluation of vehicles’ active seat suspension system using wavelet analysis

“…The passive suspension system was investigated by using wavelet transfer function (WTF) in work. 6 The WTF calculated in this case showed that the examined seat suspension system may amplify vibrations in the widerfrequency range, exceeding resonance range for the same periods in time signal history. The essential feature, and in the same way, lack of passive systems, is observed when WTF is calculated for the driver's head.…”

“…The methodology and experiment procedure are introduced and presented in detail in Blazejewski et al, 6 where the passive seat suspension is considered. In this work, the same methodology and procedure are applied in the case of active suspension in order to compare both systems.…”

“…Therefore, it is still an important and huge challenge to develop active seat suspension systems, despite their higher price. 6 The parameters of such a system are fixed. It means that they are selected and compromise between the inequality of the road or terrain and driver comfort.…”

“…It has been examined previously. 6 The investigated seat suspension system, shown in Figure 1(a), consists of a shear guidance mechanism together with (like the passive one) a pneumatic spring and a hydraulic shock absorber. In addition, this active system is extended to control airflow, which is achieved by means of two proportional valves: inflating and exhausting, implemented in the pneumatic spring.…”

The Orthogonal Wavelets in the Frequency Domain Used for the Images Filtering

“…In contrast to the Fourier transforms, which localize the frequency, but do not give a temporal resolution of the process, and from the apparatus of delta functions, which localizes time instants, but does not have a frequency resolution, a WT that has a self-adjusting movable time-frequency window identifies both lowfrequency and high-frequency characteristics of the signal at different time intervals. The indicated universality of wavelet analysis leads to its widespread use in various fields of knowledge [6], [7]. Discrete WT is widely used in engineering and programming, and continuous WT -in scientific research.…”