抄録
Pulsed vibrations seen in forging and pile driving works have almost occupied the vibration problems concerning human sensation. Results derived by Reiher & Meister as shown in Fig. 1 are helpful for assessment of the puled vibrations. However, they have treated damped vibrations alone, although there are several other kinds of pulsed vibrations such as pulsed sinusoidal and built-up vibrations (Fig. 2). Sensation of the pulsed sinusoidal (PS) vibration of a certain constant level was matched to continuous (CS) vibration of variable level having the same frequency as the fundamental frequency of the PS vibration. Duration of PS vibration was changed between 6 and 0. 007 sec. The results of the matching experiments on the whole body and the hand for vertical or horizontal vibration are shown in Fig. 3, a, b and c. The ordinate indicates VAL_p-VAL_j (dB) and the abscissa the duration of the PS vibrations (t)(sec). VAL_p means vibration acceleration level (VAL) of the CS wave which has the same maximum amplitude and the same fundamental frequency as the PS vibration, and VAL_j means the VAL value of the CS vibration judged as the equal sensation with the PS vibration. These reults are approximated by three lines formulated as, VAL_p-VAL_j=7 log_<10> T_0/t, where T_0 is the critical time limit which was nearly 2 sec for 2-60 Hz, 0. 8 sec for 60-200 Hz and 0. 5 sec above 200 Hz. Then, the sensation of the damped or the built-up vibration was equalized to that of the PS vibration having the same fundamental frequency and the maximum p-p amplitude by changing the duration of the PS vibration every half period of its fundamental frequency. It was found that the damped vibration, regardless of decay processes, is equalized to one period of the PS vibration and that the built-up vibration is equalized to the PS vibration of the duration which corresponds to its duration just when the amplitude of the built-up vibration is smaller by 1. 5 dB from its maximum value. The matched duration of the PS vibration is defined as equivalent duration(Table 1). Thus, the vibration greatness sensation for the damped or the built-up vibration can be estimated from the equivalent PS vibration. On the other hand, the estimated values were compared with the observed values which were determined by the sensational comparison between the damped or the built-up vibration and the CS vibration having the same fundamental frequency. Both values are in good agreement as seen in Table 2. Evaluation methods for these three kinds of pulsed vibrations were eventually established.
