M.S. (Master of Science)
Department of Mechanical Engineering
Exposure to power hand tool-generated vibrations may lead to several health disorders collectively known as hand-arm vibration (HAV) syndromes. Power hand tools are often used in overhead postures in the manufacturing and construction industries. However, HAV risks are examined in the front-of-body posture in the existing safety standards and guidelines. Therefore, it is important to understand the effects of overhead working posture on vibration transmissibility (VT) in the upper extremities (UEs) and the spine. Secondly, there is a rising trend of using occupational exoskeletons (Exos) in the manufacturing and construction industries, especially involving overhead work with power hand tools. However, the role of Exo in VT in the body has not been examined systematically. The primary aim of the present study was to create a laboratory study protocol to examine the combined effects of overhead work and the use of Exos on VT in the body. The extended random vibration spectrum (3 Hz – 1600 Hz) modified according to ISO 10819 (2013) was generated using an electromagnetic shaker. Same as ISO 10819 (2013), the coupling forces with live feedback were set at 30 N for the grip force and 50 N for the push force, respectively. Acceleration was assessed at the wrist, elbow, shoulder acromion on the right arm and at the C7, T10, and L3 levels of the spine using triaxial accelerometers. Acceleration was also assessed at the shaker handle and the right arm-supporting link of Exos. In addition to acceleration, activities from 9 muscles surrounding the shoulder area were examined using surface electromyography (EMG) to aid our understanding of related health effects. A high-throughput maximum voluntary contraction (MVC) protocol was developed for EMG data normalization. The present study employed a nested design with working posture as the level 1 factor (overhead and front-of-body postures), Exo condition as level 2 (Without Exo, Vest-type Exo, and Strap-type Exo), and vibration condition as level 3 (no vibration immediately followed by vibration turned on in one testing run). Three right-handed male subjects were recruited to validate the study protocol. Spectral analysis of the shaker acceleration data suggest that the shaker system can deliver random vibration more reliability above 7 Hz. Circular plastic adaptor bases for accelerometer placement on the skin could help to prevent excessive pressure over the skin and possible adverse effects. Descriptive results indicate that the acceleration level and VT decreased drastically along the arm and the spine based on the distance of the body parts from the shaker handle. Posture and Exo conditions had little effect on VT along the arm and the spine. The shoulder muscle activity was more significant in the overhead posture, especially for the anterior deltoid and upper trapezius. The effects of Exo and vibration conditions on muscle activities showed promising results as expected, though shouldn’t be over interpreted. There was a moderately higher peak push force for the overhead posture. There were a significantly higher peak grip force and a moderately higher peak push force with vibration turned on. These results suggest that HAV in the overhead posture may increase mechanical load in the body. Future studies with a larger sample size are needed to validate the findings of the present study.
Torkinejad Ziarati, Parisa, "Study Protocol to Analyze The Effects of Posture and Exoskeleton on Human Exposure to Hand-Transmitted Vibration" (2022). Graduate Research Theses & Dissertations. 7734.
Northern Illinois University
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