Abstract

Exposure to hand-transmitted vibration (HTV) arising from operating hand-held power tools has been associated with various health consequences such as vascular, neurological and musculoskeletal disorders of the hand-arm system, which are collectively termed as hand-arm vibration syndrome (HAVS). In order to decrease the effects of HTV, substantial efforts have been made to protect the operator from the vibrating tools and decrease the vibration exposure. One of the convenient means to isolate the hand from the vibrating tool handle is the anti-vibration (AV) glove. These gloves are constructed from different isolation materials, which are capable of reducing the vibration transmitted to the hands. Vibration isolation performance of AV gloves has been widely evaluated based on measurements of vibration transmitted to the palm of the hand following the method recommended in ISO 10819 (2013). The standard does not require the measurement of transmitted vibration at the fingers side, and consider similar vibration isolation performance of the gloves at the palm and the fingers. The standard also does not address the effect of AV gloves on the hand grip strength, which can be a reason for not wearing these gloves by tool operators. This dissertation seeks to develop a finger adapter capable of measuring the transmitted vibration to fingers and assess the AV gloves based on the integrated performance of vibration isolation at palm and fingers as well as the grip strength preservation.
Three different finger adapters (a steel ring, a split ring and a Velcro adapter), each instrumented with a tri-axial accelerometer, were developed and assessed to measure the vibration transmitted to the index and the middle fingers. The assessment of the three adapters showed that the Velcro adapter exhibit relatively lower inter-subject variability and yields resonably good agreements with the data reported in a recent study that measured fingers vibration using laser vibrometer. The effectiveness of the Velcro finger adapters was further explored through their ability of generating repeatable and reproducible vibration measurements. Good repeatability was observed from the vibration transmissibility measured during three trials perfromed with bare hand fingers. In the reproducibility tests, the subjects were asked to remove and reinstall the finger adapters between the trials. The assessment results showed that the obtained vibration transmissibility measurements were reproducible within each subject.
In order to enhance the understanding of fingers vibration, an investigation was conducted through measurements of vibration transmissibility of four different vibration reducing (VR) gloves at the middle phalanges of index and middle fingers using two Velcro finger adapters. Four male subjects participated in the measurements, which were conducted under the standardized vibration spectrum and the spectra of three different hand tools. Vibration transmissibility of the gloves were also measured at the palm using the standardized palm adapter. The frequency response functions (FRFs) of gloves at the index and middle fingers were utilized to estimate the vibration transmissibility of the gloves under different tool spectra. Only two gloves would be considered as AV gloves, although these showed fingers vibration amplification. The FRF method of estimating fingers vibration responses resulted in reliable prediction of the perfromance for different tools.
Furthermore, 12 male subjects participated for assessment of integrated performance of 12 different VR gloves in terms of vibration transmission performance at the palm and fingers, as well as the effect of gloves on the grip strength preservation. The grip strength magnitude was measured using the cylindrical handle utilized in the vibration transmissibility measurements. The overall vibration transmissibility of the gloves at the fingers were obtained using the frequency weighting recommended in the standard and the reported fingers weighting. All the gloves attenuated fingers vibration in the 10–200 Hz frequency range, with exception of only two gloves. At greater frequencies (>200Hz), majority of the gloves amplified the middle finger transmitted vibration, while only a few gloves showed vibration amplification at the index finger. The effect of different frequency weightings on the vibration isolation performance of gloves at the fingers was only evident in the high frequency range (200–1250Hz). Only four gloves passed the standardized screening criteria despite their vibration amplification at the fingers. All the gloves resulted in reduced hand grip strength with only one exception.