Nobuyuki Shibata

Determination of backrest inclination based on biodynamic response study for prevention of low back pain

Whole-body vibration experiments with subjects under vertical vibration were performed to examine and evaluate effects of backrest inclination on vibration transmitted through seats to the human body by using biodynamic response parameters represented by apparent mass (APMS) and vibration power absorption (VPA). The biodynamic response parameters of twelve male subjects, exposed to vertical random vibration at 0.8 m/s(2) r.m.s., were characterized under three different backrest support conditions, with the upper body supported against backrest inclined at angles of 0 degrees (vertical), 10 degrees, and 30 degrees with respect to the vertical axis. An increased backrest inclination angle resulted in reduction of the total power absorption calculated particularly the frequency range of 1-20 Hz. Normalized APMS magnitudes showed a principal resonance at about 5 Hz for each subject for a backrest supported vertically. A second resonant peak appeared at about 7.5 Hz in addition to the primary resonant peak for a backrest inclined at an angle of 10 degrees and then became much steeper for a backrest inclined at angle of 30 degrees. For a backrest inclined at an angle of 30 degrees, the resonant peak at 5 Hz was less apparent than in other backrest inclination postures. All subjects showed the second resonant peak at about 7.5 Hz in the double-normalized VPA for a backrest inclined at an angle of 30 degrees. According to the evaluation of vibration absorption behavior performed in this study, backrest inclination angle is preferable between 10 degrees and 30 degrees from the viewpoint of prevention of low back pain disorder.

Effect of shelf aging on vibration transmissibility of anti-vibration gloves

Anti-vibration gloves have been used in real workplaces to reduce vibration transmitted through hand-held power tools to the hand. Generally materials used for vibration attenuation in gloves are resilient materials composed of certain synthetic and/or composite polymers. The mechanical characteristics of the resilient materials used in anti-vibration gloves are prone to be influenced by environmental conditions such as temperature, humidity, and photo-irradiation, which cause material degradation and aging. This study focused on the influence of shelf aging on the vibration attenuation performance of air-packaged anti-vibration gloves following 2 yr of shelf aging. Effects of shelf aging on the vibration attenuation performance of anti-vibration gloves were examined according to the Japan industrial standard JIS T8114 test protocol. The findings indicate that shelf aging induces the reduction of vibration attenuation performance in air-packaged anti-vibration gloves.